Fuel Trim> 25% (Lean)

[Pantera950]

Hello,
So i've got an issue that been killing me for some time. Fuel Trims at idle are beetween 18-28%, and decreasing to 8-10% on load, sounds like classic vaccuum leak.
A4 , Engine 2.OT, Code: CPMB FlexiFuel
Car drives pretty fine, no stalling, no rpm jump, oil doesnt smell like fuel, no CEL, starts fine after night or fuel fill(cold, warm)

What i done so far:
Timing done, includes both camshaft, crank sensors , phase position sits at 0.3%
Changed PCV to OEM , LTFT was 18 before change, after change 25, so even worse, but now when removing oil cap engine stalls a bit so i guess it's working fine, no suction from pcv test place
N80 - changed
Smoke intake test 3x times - used oil tube place/also direct from air intake box - no leak
Did full decarbonization with intake manifold removal
HPFP seems to work fine gets to 8k mpa after 3-4mins
Reseted Fuel Trims - goes in like 5mins.
Air filter - replaced
MAF - looks fine 2-3.5g at idle.
Sparks - replaced

What i havnt done:
O2 sensor replace , i dont have any indication that is faulty, no code etc. Maybe someone could share their broadband o2 sensor graphs from obdeleven, or vcds Mine sits 0.97-1 lambda, and i guess 1.5v, but since it's broadband voltage does show anything i guess
I didn't replace injectors - maybe its clogged? But no stalling, fuel pressure is fine, no misfires detected.
Fuel filter?

Any reccomendations is appreciated.

[Smac770]

When you talk about the long term fuel trim, are you saying the idle one is really high, or the mix one is really high when idling? There's two separate long term fuel trim values.

"HPFP seems to work fine gets to 8k mpa after 3-4mins", no idea what that means. The CPM engine has both a high pressure rail pressure sensor and a low pressure line pressure sensor. The low pressure line should be 5-6 bar normally, the pressure relief valve on the fuel filter will kick in if it gets to 8 bar. The high pressure rail should instantly get to 40 bar on engine start. During a cold start 1200 idle, it'll be 50-60 bar. But normal idle, should be right at or just below 40 bar. WOT is 150 bar.

CPM has a 5th injector, in the intake manifold, for E85 cold start, but is not used otherwise. Are you running E85 or normal gas?

I'd have to vote for injectors. That's what it was for me. Though my long term idle was always fine, and my long term mix didn't change much with load. But yeah, they get clogged and don't delivery as much fuel per pulse as they should so the pulse duration (what the fuel trim actually changes) is extended (+trim). I never had any engine performance issues, just the reduced mpg by a similar % as the long term mix fuel trim had increased.

[Pantera950]

When you talk about the long term fuel trim, are you saying the idle one is really high, or the mix one is really high when idling? There's two separate long term fuel trim values.

"HPFP seems to work fine gets to 8k mpa after 3-4mins", no idea what that means. The CPM engine has both a high pressure rail pressure sensor and a low pressure line pressure sensor. The low pressure line should be 5-6 bar normally, the pressure relief valve on the fuel filter will kick in if it gets to 8 bar. The high pressure rail should instantly get to 40 bar on engine start. During a cold start 1200 idle, it'll be 50-60 bar. But normal idle, should be right at or just below 40 bar. WOT is 150 bar.

CPM has a 5th injector, in the intake manifold, for E85 cold start, but is not used otherwise. Are you running E85 or normal gas?

I'd have to vote for injectors. That's what it was for me. Though my long term idle was always fine, and my long term mix didn't change much with load. But yeah, they get clogged and don't delivery as much fuel per pulse as they should so the pulse duration (what the fuel trim actually changes) is extended (+trim). I never had any engine performance issues, just the reduced mpg by a similar % as the long term mix fuel trim had increased.

Hello, thanks for reply.
What i meant that fuel pressure is intact , at normal.idle it is 40bar
When warm engine is shut off and ignition on i check how fuel pressure line goes up. I saw information that if hpfp works fine fuel pressure should go up 2-3x time more from normal.
For fuel i run normal 95, never use E85

I'm talking Long term adaption mixture, i added photo maybe it shows better what i mean.
I wont be diggin into issue since no any codes, but fuel consumption is quite huge right now and i believe lean is not good for engine.

[Smac770]

On mine, the "engine off heat soak fuel pressure" goes to 170 bar before the 10 minute inactivity timeout cuts off the comms. So I would consider 80 bar to be low (if that's all it is getting to). But your engine might not be getting as hot as mine; my shortest drive "out and back" is nearly 30 minutes. If it was failing to retain pressure, that's going to be HPFP, or injectors. But as your fuel trim is lean, not rich, your injectors would seem more likely to be clogged than leaking. So maybe more likely to be the HPFP. Or could be 80 bar is simply fine for your situation.

27.3% on mix while idling, yeah, HPFP or injectors. Odd case would be the pressure sensor is actually misreading. But there's no means to test any of those three components short of part swap and see how/if things change.

[WHT13AR]

Sort of a question:

Leaky injector, would O2 call to lean mixture seeing excessive fuel?

Check plugs. If you have 3 that are light tan or white (lean) and one black or wet, thats the leaky cylinder.

[Theiceman]

my question....what's the problem !?



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[Pantera950]

Problem is a LEAN condition on a car. Sometimes you can feel that performance is not as good as should be.
Anyway i'm looking at injector now. What is the part code i should look for ? I found few

06H 906 036 P/06H 906 036 G or
06H 906 036 N

Thinking that p/g/n just release years ?

[Smac770]

J > N is for CPM engine
E> G > P > S > AB > AE are for CAE engine

[SNice]

I just rebuilt my CPMB engine and replaced the injectors in the process.
The injectors that came off were:
Vw branded (Bosch) - 06H 906 036J /0261500087

The ones I replaced them with are:
Bosch 62823 0261500164


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[featherman]

Fuel filter clogged? Just a thought.


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[Pantera950]

Thx for clarification.