Lean Fuel Trim Problem

[MCP]

So I normally like to solve these types of things on my own, but this problem has been around too long without any resolve and any helpful advice would be much appreciated. I rebuilt my engine from the bottom up starting early last year, and then decided to do the trans too. The car was originally bought an awe stage 3, and the reason I started the rebuild was because what originally was a light ticking from the lifters turned into a monstrous chugging after a pull. A few lifters with holes, shaved camshaft lobes, bent rods, and smoked piston rings later the engine was rebuilt with new seals, bearings, ect. Changes to modifications were as follows: 85mm CAI, RS4 y-pipe, rebuilt K04s(New CHRAS), ER Intercoolers, APR bipipe (the lobes where bolts go through shaved), RS4 throttle body, RS4 intake manifold, RS4 fuel rail, 550cc Bosch injectors, 2.0 coil conversion, and a base tune from Daz. The rebuild was finished in late August. First problem was the car was only misfiring terribly. Turned out to be bad ICMS(hence the 2.0 conversion). Then it was firing on only 5 cylinders , which turned out to be a bad coil conversion harness. Then again the car was firing on only 5 cylinders and that turned out to be a bad fuel injector adapter. After fixing that, around octoberish, the only fault codes I had left were for a bad 02 sensor. So I bought some used 02 sensors to replace mine. At this point when I was checking fuel trims they were pretty lean with slight disparities between the banks, and also the 02 sensors would set off the open circuit intermittent fault codes, so I just decided to buy them new and hopefully that'd get rid of the problem. Surprise surprise it didn't.

The fuel trims are as follows under normal driving(some of it on the freeway)

Adaption(Idle) bank 1 sensor 1: -3.4%
Adaption(partial) bank 1 sensor 1: 25%
Adaption(Idle) bank 2 sensor 1: -3.8%
Adaption(partial) bank 2 sensor 1: 21.1%

And here are the fault codes

Friday,26,February,2016,

4 Faults Found

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 -
16689 - Cylinder 5
P0305 - 35-00 - Misfire Detected
17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 35-00 - System too Lean
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 35-00 - System too Lean


Under REALLY babied driving the fuel trims are as follows


Adaption(Idle) Bank 1 Sensor 1: -5.3%
Adaption(Partial) Bank 1 Sensor 1: 17.2%
Adaption(Idle) Bank 2 Sensor 1: -4.9%
Adaption(Partial) Bank 2 Sensor 1: 9.4%

(note the disparities between the two banks)

Some other things I have noticed are; when I have VCDS open and am checking fuel trims real time, they seem to go very lean when there is a bit more load, but sometimes it is very random and under normal load on the freeway itd shoot up to 25% on both banks, also when getting off the freeway and putting it in neutral it has trouble finding its idle rpm and will bounce around for a bit dipping mostly down until it settles down back at idle after a few seconds, and when braking slightly harder than normal in neutral the rpms dip a decent amount. Other than that the car idles and purrs beautifully and isnt making any weird noises. Hope this helps get me some help on pinpointing exactly what the problem could be. Thanks for any future input.

[vavJETTAw36]

Have you checked for vacuum leaks? Compression test?


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[rguil]

I dont think it is a vaccum leak, if it was a vaccum leak your idle adaptation values would be off, not partial adaptation values. I would look into your fuel delivery system. You said you got new injectors, Are they configured properly to your file? Clogged fuel filter? Bad fuel pump? What kind of FPR do you have and is that properly configured to your file? Daz might think you have a 5 bar when you have a 4bar or something weird.

[vavJETTAw36]

I read on Ross tech that positive long term trims out of spec (+10%) can be indicative of a faulty MAF.


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[S4gasm aka LOTR]

You're still on the base tune with Daz? You should consult him on this as well, have you done that?
What fuel pump are you using?
And as mentioned, could be a boost leak.

[erykv1]

I'm on a base tune as well... experiencing rich conditions (opposite of you) bank 1 and bank 2. I will also get an occasional overboost code even though the map is limited to 10psi. Apparently its normal until I get some revisions.

[MCP]

I have consulted him and he said he is not sure what it could be (Im guessing he doesnt want to recommend me buying parts and then them not being the actual problem so it is understandable). I do not think it is a compression problem as the heads were just rebuilt then resurfaced and the valves lapped. There might be a slight vacuum leak but I HIGHLY doubt that it is causing all these problems at Partial throttle. Fuel filter is brand new (I broke the line when replacing it and got a new rubber hose to replace it). I am hoping that Daz configured them properly to my file. The FPR I am using is the stock RS4 one(I think it is 4 fpr, and I told Daz about it either way). I dont think it is the MAf that is faulty because I ran with it unplugged and it did the same lean running conditions as before. I did do a boost leak test a while back(also I thought if it is a boost leak it will set off a positive deviation fault code?) The only unknown is my fuel pump, as the previous owner never told me anything about it and I never bothered to check.

[S4gasm aka LOTR]

If you're sure there's no boost leaks, then you need to fix those misfires, the lean issue might resolve itself once you fix the misfires. You need to look good and hard into your coil conversion, it's possibly a grounding issue.

[MCP]

Hmm, not a bad idea, I might just go back to the regular coils since i do have some good icms lying around and see if the problem persists. Still open to other suggestions too. Thanks for all of the input thus far.

[MCP]

Also forgot to ask, is it the misfires that could be causing the lean fuel trims, or is it the lean fuel trims causing the misfires?

[Royal769sr]

That.
If it misfire due to bad spark, fuel would be rich (unburnt)

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[Royal769sr]

Check maf, plugs, coils. What fuel?

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[Tjtalan]

If the car does not go rich with the maf unplugged I would look at the fuel system.

[phila_dot]

That.
If it misfire due to bad spark, fuel would be rich (unburnt)

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No, the O2 sensors only register the unburnt oxygen not fuel, so misfires read lean.

However, fuel trims will stop learning if the misfires are that severe for this exact reason.

Your trims point towards a MAF error and away from a vacuum leak or injector error.

[Royal769sr]

No, the O2 sensors only register the unburnt oxygen not fuel, so misfires read lean.

However, fuel trims will stop learning if the misfires are that severe for this exact reason.

Your trims point towards a MAF error and away from a vacuum leak or injector error.

Woops. That makes sense. . O2. Thanks philla

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[MCP]

Mhm, but why the disparities between the two banks? At one point the difference between the two banks was a whopping 12%. Also under any extra load the trims hit hyper lean, say for example on the freeway going around 75mph, if I press the throttle just a bit it will max out the lean condition for the fuel trims immediately.

- - - Updated - - -

In theory if it was the MAF I could just disconnect it and see if the problem persists correct?

[Tjtalan]

If it was a maf issue, when unplugged you would never get lean faults. Go over the fuel system, pressure test and volume test. The volume test is probably more important in this case.

[MCP]

So I took a quick look around the engine bay and in the back noticed some oil around there, looking around more closely I found that the POS stock spider house has oil all over it indicating that it could have cracks and therefore letting unmetered air in the engine. So I wanted to see if it was affecting the trims that much so I disconnected the MAF and did some mild/semi aggresive driving to see how the fuel trims respond. Trims were as follows

Adaption(Idle) bank 1 sensor 1: 0.2%
Adaption(partial) bank 1 sensor 1: 18.8%
Adaption(Idle) bank 2 sensor 1: 0.3%
Adaption(partial) bank 2 sensor 1: 11.2%

So the car is not running as lean, but its still there, and the thing that has been bothering me forever, the inconsistencies between the two banks, is still present.
Since a misfire was detected on cylinders 4,5,6, I am thinking that there could be possibly a bad ground for the conversion harness on that side causing that so I am going to get to fixing that asap and see how and if that helps. Is there a possibility my fuel pump is on its way out and is very weak? Any additional insight is appreciated.

[prizmatik]

3 months since the last post! Have you learned anything that may help end this discussion?

[MikeyB3]

have you checked O2 sensors?

[cjt671]

Crazy man, I had a really similar problem with mine, cam ate a hole in a lifter, replaced cams and lifters, got the car running good, started to misfire and fuel trims were out of wack, then got the lean codes. Turned out to be a bad maf for me. Replaced maf car ran good again, but then right after I started getting an intermittent egt fault so I replaced those too.

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[cjt671]

Its been running fine since then.

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[rguil]

Crazy man, I had a really similar problem with mine, cam ate a hole in a lifter, replaced cams and lifters, got the car running good, started to misfire and fuel trims were out of wack, then got the lean codes. Turned out to be a bad maf for me. Replaced maf car ran good again, but then right after I started getting an intermittent egt fault so I replaced those too.

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Yep, it sounds like a audi... lol