Inlet, crankcase and exhaust pressure testing!

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Inlet, crankcase and exhaust pressure testing!

Postby bigBADbenny » Sat Oct 10, 2020 4:52 pm

This post discusses fundamental procedures as regards engine health checks.

Engine health checks revolve around the Air, Fuel, Fire triangle and this FAQ covers many of the factors relating to AIR.

The faq is mostly specific to stock cars that are mostly emissions compliant, and use a MAF (mass airflow sensor) and a return-to-inlet PCV system (positve crank case ventilation)

Before proceding, check your MAF and engine air filter
is clean and that it, and the air filter, are properly seated in the airbox.

Other basic health checks are exhaust pressure test and crankcase pressure tests.

Vacuum and boost checks, inlet pressure testing part 1.

Firstly check your maf is clean and that it and your air filter are properly seated, airtight: viewtopic.php?f=6&t=36513&p=451943#p451943

The most basic version of an inlet pressure test.
This is an engine off test.

I want to say performing this check is reasonably simple to undertake, you can definitely do this at home with minimal tools.

You'll need:
A screwdriver or basic 1/4' drive socket set.
This is used to undo and tighten the clamps on your cars "S" pipe, aka SFB (short fat bit)...
Or whatever pipe joins your your airbox or maf housing outlet to the inlet pipe (from the front of the intake manifold to the turbo compressor inlet)

A bung, aka blanking plug.
This must be the same, or very slightly smaller external diameter when compared to your airbox, pod filter or maf housing *outlet* diameter.

For most stock Subarus the out side diameter of the plug will be around 80mm or 3", but check yours by diameter or circumference.

You can use various measuring methods, eg a piece of string, a ruler, calipers and then look in your recyling bin, jar stash, hardware shop or supermarket for suitable jar lids or pipe fittings, aka bungs.

The important point being able to tighten the usual inlet clamp with the bung *inside* of the SFB, the S pipe or the main inlet pipe *after* the filter/airbox/pod (without crimping the that pipe which would cause an air leak).

Your inlet tract is now sealed and you can pressure test it at 1-2psi max *regulated* pressurised air.

Your inlet is temporarily sealed for pressure testing from the bung in the inlet all the way to the exhaust valves, which will leak a little requiring you to maintain regulated pressure at 1-2psi maximum. Go over this pressure at your own risk of popping cam and crank seals.

You can add pressure using your breath (circular breathing required and yes I can) a bicycle floor pump, a 12v tyre inflator or a shop compressor. The more powerful your pressure source the more likely you’ll need a regulator, but an emergency 12v tyre compressor will struggle to keep up with the loss: keep an eye on its gauge and or your boost gauge.

You can add pressure:
at the bung itself,
the bpv pressure reference hose between the bpv and the intake manifold adding pressure to the intake manifold.
the bpv return hose, using another smaller bung in the return hose leading to the intake,
the brake booster hose: if the brake booster one way valve is *not* in the brake booster hose
the oil cap, if on a car with pcv valve *and* by closing off any vent to air catch can, *if any*.

Bear in mind a closed throttle can be a restriction between the inlet and the intake, so either open the throttle plate, (key on not running for dbw cars) or add air to both sides of your inlet tract.





Why though?
The air filter is (probably incorrect terminology but anyway) a restriction at the start of the inlet tract and creates a pressure reference against which the MAF (mass airflow sensor) is calibrated, and against which engine vacuum pulls.
The inlet pipe, PCV (positive crankcase ventilation) system and crankcase operate under engine vacuum.
The intercooler and intake manifold under engine vacuum and turbo pressure.
The fuel purge system operates under engine vacuum, and has returns to the inlet and intake manifold which are solenoid controlled.

The inlet tract essentially ends at the exhaust valves in the cylinders.

Over time with heat cycles and miles, the hoses, plenums, gaskets, seals and orings will harden, compress, loosen or crack and cause inlet tract leaks.
Any leaks in the entire inlet tract can cause drivability and reliablility issues because the calibration and operation of the engine management system is thrown out of whack.

You can find evidence of the fault:

In the drivability experience, bad mileage, rough idle, stalling.
ECU (engine contol unit) Learning Values eg Fuel Correction, Fuel Learning and knock related parameters FLKC (fine learning knock count), FBKC (feedback knock count) and Knock Sum.
ECU DTC's (diagnostic trouble codes, aka CEL codes aka check engine lights), typically P0171, system too lean or P0172, system too rich. Not suprisingly the diagnosis for the former is the same as the latter.
Misfire codes or cylinder roughness counts in logging. The FSM DTC diagnostics for P0304 include P0171.

To test for leaks, its possible to replace the engine air filter with a plug or bung that should seal the inlet tract all the way to the exhaust valves in the engine.
Generally the stock airbox is not a convenient place to seal off the inlet tract completely.
If you can, go for it as you'll also be testing if the airbox and maf sensor are sealed.
So disconnecting the next pipe in-line, the SFB, is the perfect approach to a quick inlet pressure test.

Back to the test!

Ok your SFB pipe now has a bung in it, temporarily for the test.
To make putting the bung in easier, undo the clamp closest to the inlet pipe and rotate the SFB upwards by 90' for easier access.

Find the smaller pipe (of two pipes) leading from the intake manifold to the BOV (blow off valve, back pressure valve etc), remove the pipe and blow into it, using your mouth and breath.

Thats going to be an issue for some home mechanics, but you wanted the very simplest approach.
Its also going to be not very ergonomic, bent over on the LHS engine bay, but it will make for a quick indication of the presence of a leak or leaks in the inlet tract, plus you'll more easily hear hissing and wheezing from any partial leaks.

There's four possible outcomes at this point:
You'll "pump up" the inlet tract with a few to half dozen or so breaths, until you'll need to take a short break before adding more air. The inlet tract will take a similar amount of time to decompress, eg it will return to atmosperic pressure slowly. This is good, but you may still need to escalate the test further.

The inlet tract will "pump up" but you hear wheezing, sighing and the inlet tract loses pressure quickly. You'll be escalating the test further for sure.

You're trying to inflate the inlet tract but there's simply no resistance to the air you're trying to introduce into the inlet tract at all. You have a huge leak and the inlet tract is not airtight. You'll need to locate the huge leak and blowing cigar or vape smoke into your test hose will help hugely for this fault, when performed in a draft free area. If you find and fix the huge leak, you'll still need to repeat the test to look for more inlet tract leaks.

You cannot blow any air into the test hose at all. This is an unlikely outcome, but is possible with non standard fuels like e85 or perhaps cars that have never had UEC treatment (upper engine cleaner). In this instance you'll need to clean the affected hose or replace it, and repeat the test.

Just bear in mind, finding one leak in the inlet tract may reveal another leak if you continue testing and thats a good thing. Depending on the age of your car some leaks may be deep down and really hard to find, we'll get to that in "escalating the test procedure further".

So depending on the outcome of the test, you'll have no apparent leaks in your inlet tract, as such your drivablilty issue may not be leak related, eg the
AIR leg of the combustion triangle: it might be related to:
FUEL: fuel pump, jet pump, fuel filter, fuel pump relay, regulator, control module dampers, lines, looms and plugs; or
FIRE: spark plags, coilpacks, battery, grounds, alternator, looms and plugs or:
a control system eg AF (air/fuel) and O2 (oxygen) sensors, the exhaust or catalyctic converters.

Escalate the test and add some extra things to the test kit:
You can go to the car parts shop and buy a hose butt connector (or find one at the self serve wreckers) and a piece of hose the same diameter.
Put that on the end of the bov reference hose so you can stand back and blow, or use an air mattress or bicycle pump, or your breath still.

Or a step up is to buy some rubber tyre valves, sealant and a step drill (or scissors) and inset it into your lid or can inlet plug.
Remove the tyre valve.

Apply a pressure source, eg breath, bike pump, smoker, tyre compressor, but keep it under 1psi. Eg regulated air.

Use soapy water, eg hair shampoo and dish detergent/water mix in a trigger spray bottle (or a smoke source) liberally.
Big leaks/no pressure in inlet: check your oil cap is tight, or use smoke in the pressurised air.

From there, if you have tmic, use a plug or blank plate at the turbo & throttlebody hose to inspect all the pipes under the rear of the inlet manifold.

One leak found will reveal the next, so don’t give up looking till you’re sure and your learning view is correct.

If you’re still experiencing hesitation, rough idle, you can blind test the front o2 sensor by unplugging it temporarily, endure the resultant CEL, and see if the hesitation/rough idle improves.

If it does, replace the sensor with the oem or denso equivalent part number.

Now imagine finding a mechanic to do all of the above...

And being able to afford it :shock:

The thing is turbo cars over 250k km are absolutely cooked in the cyl3 area.

I just did lower inlet manifold gasket, upper orings, breather pipe, injector seat & oring, Pcv and breather hoses, check pcv (ok), bov ref, fpr ref/mod, and stock tmic... all leaking :(

My inlet and Tb hose all good since redone 50k ago.

Blank plugs sizes.

Stock airbox outlet OD: 80.5mm
Kobe SFB big end OD: 88.5mm (for upgrade clamp)
Kobe SFB small end 82.5mm (for upgrade clamp)
Stock postfl tmic outlet: 79.5mm




Inlet pressure test part 2.

It will help to be able to id all the hoses.

Ziptie everything without a clamp.

Going clockwise around the engine bay:

Inlet to turbo (rots underneath), replace with silicone inlet.

Wastegate to compressor outlet, tee’d to boost control solenoid.

Turbo compressor outlet to intercooler gasket/s

Blow off valve gasket

Blow off valve vacuum reference hose

Blow off valve return hose to inlet

Intercooler to throttlebody hose (stock hose has a gasket that causes leaks that may vary according to boost/vacuum)

Fpr vacuum reference hose to lhs rear inlet manifold runner (backfire under boost)

Front of inlet manifold: left to right

Fuel purge solenoid/s: check the hose is not cracked before the solenoid and after it at the return to front of inlet manifold

MAP sensor

Boost control solenoid, from wastegate tee, return to inlet manifold.

Around the top of engine: head breather balance tube and head blow by and crank case breather returns to inlet pipe

Injector seats. Really difficult to spot these leaks on cyl3 under the turbo coolant tank.9

Cam position sensor o-ring: viewtopic.php?f=10&t=36503

Don’t forget that for this test supposed to block the inlet tract post maf.
Note that for this test the engine should not be running.

The idea is to pressurise the entire inlet tract at no more than 1psi, after the maf.

Usually if doing a high pressure test, you’d isolate eg inlet tract from the throttlebody to prevent blowing out your cam seals.

Eg isolate the inlet to compressor outlet and throttle-body entry to low pressure check the inlet tract and crank case using a low pressure test to 1psi.

Then the intercooler and piping can be tested separately using high or max boost pressure.

Stock intercoolers with plastic end tanks will seperate. Use parallel pliers or clamps to re-crimp the tabs.




Prefl GT’s are notorious for rough idle issues.

There’s sharpies uec fuel rail soak for that, linked here: viewtopic.php?f=17&t=36178
Or get your injectors replaced or serviced, eg cleaned & tested, new orings and seals.

However that’s really a great excuse to refresh every gasket, hose and oring in the general area, as IME, based on my 280k postfl GT, they’ll mostly all be compressed, hardened, cracked and leaking.

Another consideration I spotted over at LGT is that side feed generation engines (usdm at least) have an (adjustment?) screw in the middle of the fuel pulse damper which, again on side feed usdm LGT at least, is located on the fuel rail on each engine bank.

Apparently if this screw backs out it can also cause issues.
I’d imagine some Locktite or a dab of paint might trap the screw at the desired setting, probably all in, or a few turns out (conjecture see FSM or forums for more info.


Now my issues were only bad enough to cause negative fuel trims and the occasional iam drop during cruise, plus extra fuel use, black smoke on boost etc.

What was leaking?
Stock tmic, bov ref, head pcv & balance breather pipes, upper and lower inlet manifold gaskets, injector seat oring, and right now, cam sensor oring.

A bunch of basic stuff wasn’t leaking due to being replaced a year or two ago but also check or replace the inlet & throttlebody hose and all related returns, and check, clean or replace pcv :shock:

Now paying someone to do all this would have been completely prohibitive.

I have a bunch of mods for the car but there’s no point putting them on a half rooted car.

Whilst I could have just replaced a bunch of stuff during the modding procedure, I have to say I didn’t entirely understand the scope of what’s required on such a high k car.

Well I sure do now.
I’ll fix the leaking cam sensor oring, see how it goes, then write a big list for all the extras I’ll need to take it up a notch with the mods.
Last edited by bigBADbenny on Mon Jan 01, 2024 6:28 am, edited 33 times in total.
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Re: Inlet pressure testing, rough idle, bad economy, etc

Postby Gen5Miles » Fri Jul 30, 2021 12:20 pm

This is perfect, thanks. for a g4 but reguardless the list of things to look for is grat. going to crack the propane torch out i have my suspicions on where its coming from. we will see
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Re: Inlet pressure testing, rough idle, bad economy, etc

Postby bigBADbenny » Mon Aug 02, 2021 6:27 pm

I haven’t had the opportunity to test a GenV GT alas.

So many more opportunities for inlet leaks with the low mount turbo.
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Re: Inlet pressure testing, rough idle, bad economy, etc

Postby bigBADbenny » Wed Sep 08, 2021 6:01 am

The MAF and air filter, in relation to inlet pressure testing:

The maf sensor wires are at the bottom of the long tube extending from the sensor mount.
A second tube runs parallel with a small opening joining the two tubes…

Clean the maf wires indirectly through the adjacent hole with maf specific cleaner eg CRC brand, also clean the inlet air temperature sensor which is brown tip sensor in an exposed housing next to the maf tubes.

Let the solvent cleaner soak for a few minutes before giving it another indirect squirt, then gently shake out any remaining maf cleaner.

Take care to properly reseat the maf in the airbox, making sure the o-ring is properly seated. New o-rings are available online or from eg the dealership, I used a generic type with a little Teflon tape behind for a good seal.

Basically if the maf rises up in its mount when the screws are loosened, the oring is probably not seated, is potentially pinched.
A little twist can help seat it.

If the maf isn’t seated, pinched oring, or the air filter is loose in the airbox, that’s potentially equivalent to an inlet leak as regards proper maf operation.

Don’t overtighten the maf philips screws, they’ll eventually strip after a dozens of reinstalls if you’re ham fisted like me :P

If you have ecu logging, log maf volts (and maf g/s), if the maximum volts are capped at 4.06V the maf is faulty and must be replaced with a new oem maf.
Thanks to my tuner buddy Matt ThrottleHappy for this tip.

Also, if analysing logs in MLVHD, one can create a custom maf V parameter to enhance eg idle maf, this may reveal spikiness in the signal, just another trend to take note of and compare after maintenance or mods.

The air filter is another maintenance item, generally use an oem spec air filter, otherwise your maf scaling will change, requiring a tune tweak in some cases, eg a more free flowing filter. Avoid oiled filters as they can contaminate the maf.

When changing the filter be sure to peep the maf side of the airbox with a bright torch for dust traces from leaks around the air filter.

This can be caused by an incorrectly closed airbox, a worn out old airbox getting loose or some aftermarket filters.

I use stick on draft excluder foam on the fresh air snorkel side of the airbox to push the filter into the maf side of the airbox.

Back to inlet pressure testing: viewtopic.php?f=6&t=36513&p=448984#p448984
Last edited by bigBADbenny on Sat Oct 15, 2022 6:42 am, edited 4 times in total.
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Exhaust pressure and cats temp testing!

Postby bigBADbenny » Sat Sep 18, 2021 10:45 am

Exhaust pressure testing and cats temperature tests:

These test are very basic and non-intusive.
The primary targets to look at are between exhaust flanges and the welds at the base of where flanges meet pipes.

You can:

Spanner check: check all nuts n bolts, preferably soak loose items with penetrating fluid, spray off any excess and re-torque to factory spec (see FSM workshop manual)…

Look for black soot fallout at the dump, turbo & header flanges and gaskets…

Spray soapy water on cold starts to peep for bubbles…
Don’t let the zorst get too warm, wait between each test for it to cool down…
Ideally have an assistant key on and off the car for you as you move from exhaust join to join, front to back.
You'll need stands, ramps, a hoist or a pit to get under the car safely.


Stuff rags lightly in the exhaust tips and listen for whistling noise during idle…
Leaks may squeal like a kettle, if you get the test right.
You're not looking to block the exhaust entirely, as the car won't run at all or will potentially blow up, so go easy and use your common sense here.

Use a piece of hose, potentially with a solid section of pipe with a right angle at the end to NEAR (not in) your ear to hear puffing at the dump, turbo & header flanges and gaskets… This approach is popular at exhaust shops apparently.

You can use a gas match/stove lighter to observe the flame being blown around or out, near the leak, if any.

With the car idling, safely raised on a hoist, ramps or stands, wave a smoke source, eg incense, cigar, smouldering rag, dry ice, smoke machine, around any welds, joins or flanges: observing the smoke being blown around by the leaks.

Before making assumptions about exhaust catalyser CEL/DTC codes, and replacing exhaust cats, do an easy cats temp test.
Put simply, this is using an infra red temperated testing gun to measure the temperature of the cats whilst the car is running, idling.
If the cat is hotter at the exhaust exit side than the exhaust inlet side of the cat, the cat is likely to be functioning properly.
Here's a video from EricTheCarGuy that explains the test: https://www.youtube.com/watch?v=9VZ5K8n5jj0

back to inlet pressure testing: viewtopic.php?f=6&t=36513
Last edited by bigBADbenny on Fri Oct 14, 2022 11:26 am, edited 7 times in total.
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Re: Inlet pressure testing, rough idle, bad economy, etc

Postby bigBADbenny » Fri Sep 24, 2021 5:43 am

Choice of compressed air sources.

For testing intercoolers in isolation 18 psi is great.

Testing the inlet, intake & crankcase, keep pressure under 1psi so as to not blow cam or rear main seals.

A tiny compressor with no tank will struggle to add 1psi vs leakage from the exhaust valves, thus unregulated air from a compressor with a tank is the main danger to seals.
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Crankcase pressure test and failsafe!

Postby bigBADbenny » Wed Oct 06, 2021 8:28 am

Crankcase pressure test and failsafe.

This is an engine running test...

The test:


Tap a fitting into a spare oil cap*, run boost hose to a boost gauge.
Observe the needle or log behaviour, whilst idling and driving, negative or zero pressures are good during all running conditions.

Positive pressure requires immediate concern as regards the integrity of vacuum in the crankcase and related airways.
Failure to solve the issue, which can usually be diagnosed with an inlet pressure test, can lead to severe detonation and turbo damage.

*The hose can be connected to anywhere on the main crankcase, but care must be taken that the fitting or gland is attached in such a way that the end cannot fall or be sucked into the crankcase, if it were to become detached from the hose.
A spare oil cap is convenient, tapping the oil filler neck has been used for a more permanent install, and some have proposed a tee into the pcv hoses, although these are subject to pressure and flow.

Why monitor or test crankcase pressure?

At one extreme, crankcase pressure testing is the least intrusive approach to diagnosing failed compression, eg a less intrusive and more convenient alternative to an actual compression and leakdown test.

The difference being the tester can be left in place, can be connected to a pressure alarm, for instant notification that your engine is experiencing a major issue.

At the other extreme, crankcase pressure testing will reveal faults and inefficiencies related to the PCV (positive crankcase ventilation, blocked hoses, sticky or stuck PCV valve) system and any installed AOS/CC (air oil separator/catch can, incorrect routing schema, inefficient flow).

Diagnosing crank case pressure issues:


Oil and blowby leaks:
Clean the area and use an eBay UV dye and torch kit on sucessive drives to spot the source of the leak or fallout.

Blow-by leaks :
Inlet pressure test at under 1psi regulated air, on a stock PCV system the crankcase is connected to the inlet tract.
Use smoke and a bright led torch to backlight the smoke, or apply soapy water spray and look for bubbles, listen for hissing.

Stuck or sticky PCV valve:
Personally, I remove the valve, clean the ends, suck or blow into it from both ends, do this at your own risk lol.
Most solvents will clean the varnish off, otherwise they're affordable and commonly available.

Compression issues:
Will still be apparent after any of the above issues have been resolved...
In particular, positive crankcase pressure over 3krpm is a red flag and requires further diagnosis, eg reading spark plugs and compression and leakdown test.

Outlying issues:
A failure to the egr system, eg egr valve stuck open can cause some related mayhem. I'd expect a related DTC though (clarification required).

PCV vent tube:
Observe required maintenance when removing the gearbox from the engine, eg rear AOS reseal or upgrade, and replace the pcv tube oring if removing the sump.



What is the crank case on a flat four engine?

Basically its the void inside the engine between the insides of the pistons, the cylinder bores and case halves in which the crank rotates.

At the lower end of the assembly is the sump, which is where all the engine oil drains to, that's already passed through the rotating assembly.

Additionally, the valve covers drain to the sump, and as such may be considered part of the crank case.

At the upper end are:

The crankcase vent:
This is located on the rear upper centre of the crankcase and connects to the rearward breather balance ports on the heads: this is considered the crankcase balance pipes assy, and is crucial for managing oil surge in the heads under extreme cornering forces.
The FSM (workshop service manual) considers the balance pipes to be part of the PCV system.
The balance pipes are joined by the lower of two hard PCV crossover pipes (ej255).

The heads balance pipes:
Mentioned immediately above ^.
These connect exclusively to the crank case vent.

The heads breather ports:
The smaller diameter forward ports on each head, these are fed by an in-built on oem air oil separator/baffle assy inside each cam cover.
These are referred to as fresh air ports in the FSM.
These use the upper PCV crossover pipe which returns to the inlet, the larger pipe forward of the BOV return hose.

The PCV tube:
Aka the sump breather.
This pipe vents the sump to the 3-way tee that returns to the PCV valve and intake manifold (under cruise or engine vacuum) and the rearmost return on the inlet pipe before the turbo compressor (under boost when the PCV valve is closed).
On it's way up to the PCV 3-way tee, the PCV tube passes through the oem air oil separator thats located on the rear of the bank 1 case half.
This tube is the recipient of the primary vacuum generated by the engine, under cruise and boost.

PCV valve:
A spring loaded one-way valve that "points" away from the intake manifold.
Under boost, the PCV valve closes, is pushed shut, preventing boost from entering the crank case.
Under engine vacuum, eg cruise or idle the PCV is "sucked" open, and draws vacuum on the sump breather.

The PCV valve can fail open or closed and excessive blow-by gum orn varnish is usually the culprit and can affect even otherwise clean looking PCV valves.
I clean the ends of the valve and blow and suck on the valve to test it prior to cleaning, do this at your own risk.

The turbo oil drain hose:
This drains into the lower rear bank 1 head, presumably into one of the oil galleries that drain the cam covers.
Aftermarket turbo drain hoses are rarely worth the effort over stock items, alas, but if you're tempted, do yor research thoroughly.
They're generally not an effective bandaid for related issues eg those caused by excessive prankcase pressure.

The oil filler neck and cap:
A quick test for a worn, compressed or hardened oring under the oil cap is evidence of blowby under the cap around the oring.
The oil filler mount oring is a known oil leak/blowby point.

The dipstick tube and dipstick:
This originates in the sump but obviously terminates up top in the engine bay. A loose dipstick eg with a hardened, worn and compressed o-ring might be considered an inlet leak.

The cam position sensors:
These read the cams and thus poke into the cam cover voids, mentioned above.


So the crankcase on an ej may be considered a complex space with many penetrations, some designed to breath and others definitlely not!

The crankcase is linked to the inlet tract via the PCV system at the inlet (under boost) and the intake manifold (under engine vacuum).

In order to not generate too much crancase vacuum that would potentially negatively affect eg cylinder wiping with economy oriented engine oils, Subaru implemented so-called fresh air ports from the inlet to the forward heads breather ports, which allow for close to static crank case pressure in all running conditions, whilst drawing primary vacuum at the sump to assist oil return.

Subaru implemented this arrangement with a Bernoulli effect arrangement in the inlet and multiple restrictors in the PCV pipes system to proportion the flow of blow-by gasses across various pressure gradients and differentials in the inlet tract and PCV system.

Big thanks to Yowie et al, for getting to the restrictor sizing info which he helpful documented over on the AOS/CC discussion and discovery thread.

So... So what?

If theres a fault related to crankcase pressure, the pcv system can go haywire, soaking the inlet tract with oil, pressurising the crankcase, leading to a blown turbo or detonated engine.

The stock crank case and pcv system works beautifully on a normally driven stock car.
Eg on a healthy car at 100kkm, the blow-by oil captured in the inlet tract may amount to a smear in the inlet pipe and a drip in the throttlebody hose.

Extreme track duty, non-standard fuels and pcv system and crankcase vacuum leaks can all play havoc with this carefully balanced system, as can an ineffecient or ill-considered AOS/CC system.

The symptoms are many and not necessarily related to engine oil useage between services if any, so what are the symptoms of an issue?

Inlet tract inundated by oil:
Look at the base of the inlet manifold runners where they meet the injector risers, aka TGV's.
Are the bases wet with oil, or do they look like theyre covered in black dust?
If so its a sure sign of an inlet tract leak or pcv system leak or issue.

Smoking turbo on boost:
Excessive crankcase pressure pushing oil past the turbo journal or ball bearings and into the dump pipe.
It might be just a worn out CHRA due to other factors, but its best to look for underlying issues prior (eg CCP/PCV testing)

Excessive oil in the inlet pipe before the compressor inducer, see above ^.

Blow-by fallout and or oil leaks:
At penetrations around the crankcase: again, an oil leak and or black dusty or wet blow-by fallout around any of the aforementioned penetrations.

The pcv tube from the sump:
There’s an oring where the sump meets the block, and potential issues related to the oem pcv tube rear oil separator.
Clarification needed re upgrade & maintenance thereof if eg separating the gearbox for other maintenance.

But.. I still don’t get it!

Pcv system:

If an engines crank case was sealed with no effective breathers, it would generate positive crankcase pressure until the dipstick, cam or rear main seals blew out.

Thus a working pcv system opens the crankcase to the inlet tract.

The pressure reference point is the air filter at the start of the inlet tract.

The pressure differentials and gradients generated by the intake manifold and inlet pipes become the primary crankcase vacuum sources under cruise and load respectively.

Vacuum leaks in the inlet tract, crankcase,heads, pcv system ruin this schema and major oil control and blow-by issues occur.



The oil control issues can independently affect:

AFR, fuel and knock learning values by introducing excessive oil into the inlet tract, increasing detonation under load.

Turbo oil drain back to the sump.

See turbo failure modes.



TBC...
Last edited by bigBADbenny on Sat Oct 09, 2021 7:55 am, edited 12 times in total.
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Re: Inlet, crankcase and exhaust pressure testing!

Postby bigBADbenny » Fri Oct 08, 2021 9:56 am

Turbo failure modes, boost sanity check

Restricted turbo oil supply:

This is mainly specific to engines with avcs vvt cam advance.

The avcs oil control solenoids that vary the amount of oil going to the avcs cam pulleys, in turn actuating the cam advance, are generally supplied with oil from the heads.

On turbo engines with avcs, the right side head, bank1, also supplies the turbocharger centre rotating housing (chra) with oil for cooling and journal or ball bearing lubrication.

In the avcs oil feed lines at the heads supply end the union screws, aka banjo bolts, contain filters made from fine stainless steel mesh with a black plastic frame. The banjo bolts containing filters have a raised dimple or nubbin/nipple on top of the bolt head to identify them.

The filters are also considered by Subaru to be baffles or dampers for the avcs oil control to help the system achieve and maintain sync.

The filters are quite small and can be clogged with soot or varnish, causing avcs to loose sync or induce turbo oil starvation.

Therefore don’t top off oil and skip oil changes (like I did).
Top off oil, using your dipstick of course, and definitely stick to 5kkm oil change intervals.

There’s way more considerations related to avcs issues however bear in mind P0011 (cam pos over advanced bank1 DTC is a *red flag* for impending turbo failure due to a clogged avcs banjo bolt filter on the bank1 head.



Restricted turbo oil drain:

Whilst stock turbos are coolant cooled, this is primarily for protecting the CHRA (Centre Housing Rotating Assembly) after engine shutdown.
When the engine is running, engine oil cools and provides lubrication to the CHRA.
Oil pressure is fed to the CHRA at close to engine oil pressure (for a journal bearing turbo) but the flow is also dependent on the drain being unresricted.

If vacuum in the crankcase is compromised by a vacuum leak, or pressure in the crank case is allowed to build eg from a stuck pcv or inefficient aos/cc, the oil fed to the turbo CHRA will either stall and overheat (conjecture) in the CHRA or seek another point to escape, usually past the bearings.
Or the turbine shaft overheats and stretches along its axis, potentially crashing the compressor or turbine into the respective housings.

Turbo Overspeed

Another turbo failure mode is turbine shaft overspeed, this is usually boost leak related, or a fault with wastegate control.

In the case of a boost leak, it may appear that the engine is hitting acceptable boost, but since the boost is leaking downstream, the ecu may push the turbo well outside of its acceptable operating range in order to hit the expected level of boost.

The turbine continues to rotate beyond the acceptable specification and the compressor or tubine breaks up due to excessive vibration or rotational inertia.
To failsafe this failure mode, some modern turbos have the option of a shaft speed sensor, which can be logged and failsafed.
Otherwise, try an inlet pressure test, or pressure test the intercooler and piping in isolation from the inlet tract.

How NOT to diagnose boost issues:

I have seen owners trying to diagnose boost issues, usually not enough boost, by disconnecting boost control hoses to the boost control solenoid, so that the turbo no longer has any boost control :shock:

A very important aspect of this is that ECU's, tunes, do have boost limiting features to self protect the engine, and an engine making less than expected boost should be checked for CEL/DTC codes and preferably be checked as regards the Learning Values: DAM/IAM, FBKC, FLKC, Knock Sum, Fuel Learning.

How TO: Safe sanity check for boost control issues:

Using unrestricted boost control to diagnose boost issues is extremely detrimental, and a far safer approach is to
revert the turbo to mechanical wastgate control at wastgate pressure.

This test is acheived by running a new section of boost hose (no restrictor pills or bleeds just a plain section of hose) between the boost reference outlet on the compressor cover to the boost reference port of the wastgate.

This will revert the turbo to wastgate spring pressure, and if all is well, a reasonably gentle third gear pull will net the wastegate spring pressure correlating as the same manifold relative pressure (corrected), or the same boost pressure on a mechanical boost gauge.

Eg the stock wastegate is usually 7psi, and a gentle pull should reach 7psi boost.

If a harsher launch eg in a lower gear is made, you may see evidence of boost creep, especially with stock internal wastegate turbos.

Test wastegate spring pressure, wastegate opening
This is an easy test for external wastegates…

Grab regulated shop air, set it to your wastegate spring pressure eg 7psi max etc, pull the end of the hose that leads to the wastegate pressure reference port.

Use your regulated air source via a schraeder mattress adapter or air trigger gun to gently appply pressure to the wastegate.
The wastegate arm should open at spring pressure.
Personally I use a bicycle floor pump with a gauge and pointy adapter to do this test.

If the wastegate doesn’t open, spray the diaphragm body (the circular cylinder) with soapy water to see if air is leaking from the rear of the housing where the actuator arm exits: torn diaphragm.

If the wastegate passes that test, but doesn’t open, the wastegate flapper arm might be stuck shut or internally obstructed.

Boost control solenoid: DTC blind test

There’s diagnostic trouble codes related to the boost control solenoid (BCS, EBCS).
Use the FSM workshop manual DTC diagnostics…

If for example your DTC is P0245, “this indicates that circuit is being driven low, the 2x bcs control wires are shorted together at some point.
Clear the code (reset ecu) unplug the bcs harness plug, and run the engine.
You should now get another code to inicate the bcs is high, open circuit.
If P0245 remains, the short is in the harness, if not, new code, the short is in the bcs itself.”

Thanks Sean Regan aka Sick Chips for this tip.

Is my Boost control solenoid even working?

Pull the hose leading to your wastegate pressure port.

Do the revert to mechanical wastegate pressure tip above, do not use unrestricted boost.

Use a butt joiner to extend the hose to wastegate all the way into the cabin and go for a drive.

You might hear and feel intake manifold air pressure when the ecu calls for wastegate control.

Thanks to Manuel Olabaza for this tip.

Be sure to reinstate your stock bcs boost tee and restrictor properly after the test, the restrictor goes to the compressor side of the tee.

Make and share datalogs as part of the boost diagnostic process.

Your tuner can advise on the specific parameters to log, but here’s a basic list in this faq:

viewtopic.php?f=6&t=36932&p=452065#p452065






How to test for boost leaks in the inlet tract:


See inlet pressure testing.
Just a reminder, this is safely achieved at under 1psi using a regulated air source, if you need to test the intercooler and piping at higher psi, its a great idea to test this tract in isolation from the intake manifold, inlet and crankcase as the latter two areas are designed to be run only under engine vacuum, as are the dipstick, cam and rear main seals.
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Re: Inlet, crankcase and exhaust pressure testing!

Postby bigBADbenny » Fri Nov 18, 2022 4:41 am

Boost control issues: under-boost and over-boost.

How NOT to diagnose boost issues:

I have seen owners trying to diagnose boost issues, usually not enough boost, by disconnecting boost control hoses to the boost control solenoid, so that the turbo no longer has any boost control :shock:

A very important aspect of this is that ECU's, tunes, do have boost limiting features to self protect the engine, and an engine making less than expected boost should be checked for CEL/DTC codes and preferably be checked as regards the Learning Values: DAM/IAM, FBKC, FLKC, Knock Sum, Fuel Learning.



How TO: Safe sanity check for boost control issues:

Ecu test mode, aka delivery mode aka diagnostic mode.

To enable test mode, find the two green plugs below the drivers side dash, or pull the carpet at the upper front of the passenger footwell towards the centre console, look for a pair of green plugs, with the engine off, plug them in.

Put the key to on, engine not running and the radiator fans will cycle on and off.
This mode cycles switches and accessories, including the boost control solenoid.

So the boost control solenoid should be able to be heard switching on and off, or use a mechanic stethoscope to confirm it’s switching.

If test mode was activated during an inlet pressure test, and the boost hose to the wastegate pressure reference port was detached, that hose would release air when the boost control solenoid was open, iirc that equates to 100% wastegate duty cycle.

Its also possible to view and or log this test using eg BtSSM, Romraider or FreeSSM.

Note that whilst one could inlet pressure test at over 1-2psi, in order to observe the wastegate opening and closing in test mode, it’s not advisable due to the likelihood of pressurising the crankcase leading to the possibility of blowing the cam, rear main or rear aos seals.


Revert to mechanical wastegate pressure:

Using unrestricted boost control to diagnose boost issues is extremely detrimental, and a far safer approach is to
revert the turbo to mechanical wastgate control at wastgate pressure.

Prior to performing this test, and in the instance of an overboost fault, it’s safer to first test at what pressure the wastegate opens, by applying regulated air pressure at your wastegates spring pressure, directly to the wastegate pressure reference port.

I use a bicycle floor pump with a built in gauge and a pointy air mattress adapter.

Eg most stock Subaru wastegates will open at 7-9 psi if operating properly.


This test is acheived by running a new section of boost hose (no restrictor pills or bleeds just a plain section of hose) between the boost reference outlet on the compressor cover to the boost reference port of the wastgate.

This will revert the turbo to wastgate spring pressure, and if all is well, a reasonably gentle third gear pull will net the wastegate spring pressure correlating as the same manifold relative pressure (corrected), or the same boost pressure on a mechanical boost gauge.

Eg the stock wastegate is usually 7psi, and a gentle pull should reach 7psi boost.

If a harsher launch eg in a lower gear is made, you may see evidence of boost creep, especially with stock internal wastegate turbos.

Test wastegate spring pressure, wastegate opening
This is an easy test for external wastegates…

Grab regulated shop air, set it to your wastegate spring pressure eg 7psi max etc, pull the end of the hose that leads to the wastegate pressure reference port.

Use your regulated air source via a schraeder mattress adapter or air trigger gun to gently appply pressure to the wastegate.
The wastegate arm should open at spring pressure.
Personally I use a bicycle floor pump with a gauge and pointy adapter to do this test.

If the wastegate doesn’t open, spray the diaphragm body (the circular cylinder) with soapy water to see if air is leaking from the rear of the housing where the actuator arm exits: torn diaphragm.

If the wastegate passes that test, but doesn’t open, the wastegate flapper arm might be stuck shut or internally obstructed.

Boost control solenoid: DTC blind test

There’s diagnostic trouble codes related to the boost control solenoid (BCS, EBCS).
Use the FSM workshop manual DTC diagnostics…

If for example your DTC is P0245, “this indicates that circuit is being driven low, the 2x bcs control wires are shorted together at some point.
Clear the code (reset ecu) unplug the bcs harness plug, and run the engine.
You should now get another code to inicate the bcs is high, open circuit.
If P0245 remains, the short is in the harness, if not, new code, the short is in the bcs itself.”

Thanks Sean Regan aka Sick Chips for this tip.

Is my Boost control solenoid even working?

Pull the hose leading to your wastegate pressure port.

Do the revert to mechanical wastegate pressure tip above, do not use unrestricted boost.

Use a butt joiner to extend the hose to wastegate all the way into the cabin and go for a drive.

You might hear and feel intake manifold air pressure when the ecu calls for wastegate control.

Thanks to Manuel Olabaza for this tip.

Be sure to reinstate your stock bcs boost tee and restrictor properly after the test, the restrictor goes to the compressor side of the tee.

Make and share datalogs as part of the boost diagnostic process.

Your tuner can advise on the specific parameters to log, but here’s a basic list in this faq:

viewtopic.php?f=6&t=36932&p=452065#p452065






How to test for boost leaks in the inlet tract:

See inlet pressure testing.
Just a reminder, this is safely achieved at under 1psi using a regulated air source, if you need to test the intercooler and piping at higher psi, its a great idea to test this tract in isolation from the intake manifold, inlet and crankcase as the latter two areas are designed to be run only under engine vacuum, as are the dipstick, cam and rear main seals.
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Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop


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