Inlet tract leaks, rough idle, bad economy, smoke on boost..

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Inlet tract leaks, rough idle, bad economy, smoke on boost..

Postby bigBADbenny » Sun Sep 27, 2020 12:09 pm

Inlet tract leaks.

The stock Gen4 turbo pcv system has inbuilt air oil seperators at the rocker cover breathers and sump vent.
The former returns to the turbo inlet pipe, the latter to the pcv or inlet pipe.

The other hoses, from the rear ports on the heads and the crank case vent are tee’d together forming the heads/crank case balance pipes.

So if you have air leaks from any of the orings or gaskets on the engine and heads, the pcv system won’t work as efficiently.

There will be less vacuum in the inlet, which affects maf scaling and thus fuel trims.
The car will run richer, potentially fouling the exhaust sensors.

My guess is reduced flow of blow by evacuation from the cranks case allows more oil to condensate in the pcv system and inlet, eventually blocking the pcv, which in turn pressurises the crank case, making the leaking seals leak more and also reducing the scavenging effect of pulling oil from the turbo drain.

The effect of the reduced turbo oil drain is probably to cook the chra bearings, blowing the turbo.

Its a downward spiral that starts with leaks around the inlet tract, and that ends with a blown turbo or engine.

In the meantime the owner puts up with reduced performance, economy and a smelly engine.

Additionally, anyone experiencing these issues risks contaminating the engine loom as sensors can become soaked with hot oil.

Due to the watertight design of the loom and its plugs, oil contamination can spread throughout the loom all the way to other sensors and the ECU.
The oil contamination reduces the resistance and flexibility of the wiring, and all these problems can cause massive issues to the engine’s proper operation. I wrote a post on this issue here: viewtopic.php?f=10&t=36481

The solution begins with health checking the car, logging, learning view and inlet pressure testing at 1psi with smoke or bubbles.

After that an educated decision can be made as to whether the perishable items can be replaced with the inlet manifold in place but loosened or fully removed to access eg the injectors.

At this point it’s a good idea to consider upgrades, some are essential eg the throttle body hose (AVO or Kobe), turbo inlet pipe and other mods that improved reliability and or headroom.

Also: if the inlet manifold is coming off: doing the coolant crossover pipe orings, tgv deletes, airpump deletes, phenolic spacers, injectors, rails fuel hoses and fuel pressure regulator etc all present the perfect opportunity.

Depending on what’s being changed a tune may be required, and that will be so much more successful on a properly health checked engine.

The difference even on a stock or stock tuned car is simply incredible, even just one failed oring at eg a cam sensor, as I found out recently.


https://www.blingstrom.com/diy-project/ ... e-manifold

This is for lhd foz but the process is similar for Liberty 2.0t and 2.5t.

N/a cars are roughly similar but with way less stuff in the way.

When to take action?

Well I’ve seen these issues on my car as early as 150k km (oil filler oring).
From there it simply gets progressively worse, until I had to do everything bar removing the inlet manifold completely for rectification.
And that step would have been way more efficient time wise at 285k km than doing it with the manifold lifted, as I still need to do all the injector seals, crossover pipe and knock sensor.

One tip worth mentioning for early prefl GT’s that have rough idle is Sharpies UEC fuel rail soak trick described here:
viewtopic.php?f=17&t=36178

Its worth a try on any car, but another approach is to use Subaru fuel additive or UEC in the fuel tank as described in my tune faq post, link in my signature. Or on a high milage car to remove the inlet manifold, get the injectors cleaned and flow tested and new seals.
Last edited by bigBADbenny on Mon Sep 28, 2020 8:43 pm, edited 1 time in total.
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bigBADbenny
 
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Re: Inlet tract leaks, rough idle, bad economy, smoke on boo

Postby JAWolf » Mon Sep 28, 2020 3:01 pm

Thank for these in depth run downs of these issues. Makes sense the cause and effect side of things. Good info to have around!
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Re: Inlet tract leaks, rough idle, bad economy, smoke on boo

Postby bigBADbenny » Mon Sep 28, 2020 3:09 pm

Ah yes, if I could do it all again with what I know now! :P

So I’m dealing with a stuffed battery right now, but since I replaced those cam sensor o’rings, and cyl3 injector seat seal, plus a month or two of finding and fixing half a dozen leaks elsewhere, the car runs like an absolute champ!

The learning view has positive corrections in idle range and the map sensor reads zero as +0.2psi.
Meaning the car had these “deep” leaks when it was last tuned 3+ years ago.

So basically the car had some of these issues when I bought it quite thrashed by the previous owner, and service abused by the dealership at 150k km.

I’m simply staggered and disbelieving that most dealerships, mechanics and tuners have little to no idea of these basic pitfalls and stumbling blocks and could give very few cares about fixing them properly.

Basically I’m so confident of the air tightness of the inlet tract, I want to do the Hg test in the FSM!

So my car seems new to me, it’s running better than it ever has since I bought the thing :good:
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bigBADbenny
 
Posts: 10420
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Re: Inlet tract leaks, rough idle, bad economy, smoke on boo

Postby bigBADbenny » Tue Sep 29, 2020 8:53 am

btssm my07 gtb ezgif.com-optimize tiny.gif
btssm my07 gtb ezgif.com-optimize tiny.gif (194.37 KiB) Viewed 4565 times


Here's all the Learning Views I've made just this year to track the progress of of my inlet leak issues.

Once the last major leak was fixed (drivers side cam position sensor oring) the Fuel Learning in Idle range acually goes positive, indicating that the car had the leak over 3 years ago when it was last tuned.

BtSsm_LV_20200925_1840.png
BtSsm_LV_20200925_1840.png (50.7 KiB) Viewed 4565 times


Here's the latest LV ^
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bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
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Real name: Ben Richards
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