Rough Idle & Engine Shaking under load like AC

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Re: Rough Idle & Engine Shaking under load like AC

Postby ilib11 » Mon Aug 30, 2021 8:53 pm

Thank you, subyroo !
I visited Subievolution earlier with this idle issues, they did their investigation and unfortunately did not find any leaks or any other troubles.
Will try your suggestion boxerservice.
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Mon Aug 30, 2021 9:31 pm

I have a diy guide if you’re keen to save funds.
Here: viewtopic.php?f=6&t=36513

The simplest approach is to find an 80mm jar lid or similar object.

Pull the S pipe post maf and clock it upward on the inlet at 90’.

Insert the bung (lid) and do up the clamps.

Pull the vacuum reference hose from the bov.

Blow into it, pump up the inlet tract.

After say 30 seconds, is there any resistance?

If you let go of the hose does the inlet tract exhale?

You can watch your boost on Romraider, see how long it takes to leak down from say 1psi.

If you’re using air compressor do use regulated air under 1psi to preserve engine seals.

If you’re unable to maintain pressure in the inlet tract, you have a leak.

I simply do not have time or funds for misdiagnosis, so I diy.
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Mon Aug 30, 2021 9:49 pm

Warmup. Next time please log more warm idle ;)

Best viewed on a decent size screen but check out tgv in sync with ac.


ilib11 idle warmup.png
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Mon Aug 30, 2021 9:54 pm

Idle delta warm.
ilib11 ide delta.png
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Mon Aug 30, 2021 9:58 pm

I’ll post the other graphs tomorrow :)

With your diagnosis, or anyone’s… we’re going to assume absolutely nothing.

You need to prosecute health checks with extreme prejudice towards identifying issues.

Just hope is isn’t some weird outlying issue lol.

Like some I’ve had :P
Last edited by bigBADbenny on Tue Aug 31, 2021 6:57 am, edited 1 time in total.
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Re: Rough Idle & Engine Shaking under load like AC

Postby ilib11 » Mon Aug 30, 2021 10:16 pm

Thanks heaps!
I'll study the test leak procedure and try to implement.

Re TGV synched with AC signal - TGV signal variation is 0.02 v, I would say it is not a real change or a real TGV command, looks like a noise change or a ground voltage fluctuation associated with AC clutch current.

With best regards,
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Tue Aug 31, 2021 6:41 am

Yes indeed, well done :good:

Are you using MLV yet?
The free version is very useful…

The paid version is simply amazing, once you want to move past the basics.
I’m fairly new to MLVHD, just scratching the surface really.

I used the free version for years before upgrading.
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Tue Aug 31, 2021 6:51 am

As regards the inlet pressure test, I still use the most basic method as it’s so quick.
My pressure device otherwise is an oem tyre compressor.

Its noisy when running so makes listening for leaks difficult.
Bubbles is easy if you can see them.

Discuss static vs dynamic leaks in the context of inlet pressure testing.

Either way, blocking the inlet pipe post maf, on a stock car, you’re inflating the inlet, tmic, intake manifold, any cylinder with an open intake valve, and the crankcase. Some air will escape the exhaust valves, but leak down is fairly slow regardless, ime.

To that end, there’s even a spec using a vacuum gauge or similar in the FSM.
Its inches of mercury over time iirc.
I’ll have to dig that up for context.
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Re: Rough Idle & Engine Shaking under load like AC

Postby ilib11 » Tue Aug 31, 2021 8:52 pm

Thank you for detailed test procedure!
I'll try carbcleaner + romraider option this weekend and see how it goes, will post the results.
Then will go to Bannings for plugs etc or buy something like this https://www.aliexpress.com/item/1005002332294297.html for further experiments.

From what I can see from your latest graph, may be the ecu is playing with timing to get to target idle rpm after AC got on.

I have a vaccum gauge and the vaccum as per specs ( 20 mmHg vacuum).

I tried MegaLogViewer - without payment it is limited to 500 log rows. I consider to buy it later on if I succeed with a spare ECU and go for further tuning.
I currently use free version of LogView by DiselPower https://www.logview.net/features/

Kind regards, ilib11
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Wed Sep 01, 2021 7:26 am

Grouse!
I’ll try it out for fun ;)

Yeah I gotta peep the parts & FSM diagrams for the specifics on GenV GT inlet tract piping, its a rather different beast to a gen4.
As long as the inlet pipe comes out of the same spot before diving down to the turbo it should be possible.

I got onto the laptop last night but got lost just looking at the scatter graphs.
I’ll try get my act together today :P

Just measure the diameter of your airbox outlet: that’s the size of your blanking bung plug.

The inlet test assumes your maf is properly seated in its oring and the air filter is snug in the airbox.
The filter creates the pressure differential for the maf to read airflow accurately so it’s a precursor to the rest of the inlet tract.
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Wed Sep 01, 2021 9:16 pm

Do hit the books to get an idea of the info in the logs and graphs...

https://www.romraider.com/forum/viewtopic.php?t=1840

Whats interesting is that IAM jumps around yet theres little FKC and so much scattered FLKC that its difficult to get a bead on the trend.

However fuel learning is out of range at low load.

Here's the whole log compressed to see overall trends...


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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Wed Sep 01, 2021 9:32 pm

FKC filtered and long term fuel trim...

ilib11 driving scatter graph fkc & ltft .png
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Wed Sep 01, 2021 9:45 pm

FBKC over AFR and STFT x map x rpm

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Re: Rough Idle & Engine Shaking under load like AC

Postby ilib11 » Wed Sep 01, 2021 10:51 pm

bigBADbenny wrote:Whats interesting is that IAM jumps around yet theres little FKC and so much scattered FLKC that its difficult to get a bead on the trend.


As far as I understand:
I see the following - FKC is disabled as the AC is just turned on (See the Subaru's knock control strategy explained link you mentioned)
and this https://www.romraider.com/RomRaider/HowToUnderstandKnockControl says that FLKC aka Knock Learning is dynamic, i.e. contents are learned as you drive. The table is 3 dimensional and the FLKC parameter in data logs is just the value from this table, at the current RPM and load. So it is ok to have scattered FLKC - as the load and RPM changes constantly hence we got a fresh value from that 3D table each time.

I did not get yet how ECU makes that 3D table - if it is a result of a detected knock event? I am not sure I can have amount of knock counts in the log, I only found Knock Corrections. And at idle they are all zero.

Above idle , may be ECU thinks the engine knocks? Can a knock sensor be faulty but do not cause a check engine light?
The second post here https://www.romraider.com/forum/viewtopic.php?t=8509 says "FBKC is defined, and it is instantaneous knock compensation (not learned). The ECU is hearing knock and pulls timing (typically -2° per event to a max of -8°) as you see in the log and the total correction decays over a defined time period, about 10 seconds. "

It looks like there are two different patterns - idle/low load and the rest, plus a conditions when FKC is disabled by design.

Or another theory - if this ECU being a later model, listens knock sensor in idle too, then if a knock sensor is bad and takes AC clutch for a knock, then changes ignition timing any time AC is on? Too much assumptions but ....
Here is an idle log (log3). Purple is Ignition Total Timing, yellow is Throttle Opening Angle, white is AC on/off. Plus engine speed. Any time AC is on there're is an increase in the Ignition Total Timing.

log3_.png
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Re: Rough Idle & Engine Shaking under load like AC

Postby bigBADbenny » Wed Sep 01, 2021 11:46 pm

0EDBBB27-54FB-4F36-B850-1F11305434D5.png
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So this is the gross effect of inlet tract leaks…

Fuel corrections and learning will adjust in closed loop in order to maintain stoich.

Eg adding fuel when lean and reducing fuel when overly rich.

But they might indicate where a leak may be located…

The LTFT adjustments in the log are not particularly extreme.

Stft is trending to positive corrections.

Ignition timing will be adjusted in response to knock.

That particular log demonstrates little fkc, iam all over its middle range, and fbkc everywhere but low load.

Ime lots of fbkc isn’t particularly unusual, but unstable iam to me indicates a need to take action by looking at the basics.

We can further drill into the log info by using filters, eg acceleration, deceleration, rpm bands, stoich, lean and rich etc.

I’d consider turning off every parameter that’s not directly related to your diagnosis, and adding some others.

But keep your basic tuning parameters, there’s a list in my tune faq…
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