Lean issue upper rpm range under full load.

[JT-A4B7]

I have a 2006 2.0t B7 A4 6MT Quattro. Its currently on unitronic stage 2 Hpfp tune. Im having a lean issue occurring in the 5k-6k rpm range. This has been happening for a while and is the reason i did the hpfp upgrade. Stft will jump to 25% during the run and will go back close to 0% after 6k rpms. I dont see it happening in 1-2 gears, mainly in 3-4 gears. Looking at the fuel pressures, high and low pressures, when it leans out or when its near 0% is not different. The difference between the actual and the specified pressures are actually further off when it its running a near zero or rich stft. Im doing logging with obd11 and im not sure how to upload the logs yet. The car had the same issue on Unitronic stage 2 also. Lpfp and filter have been changed in the last year.

[JT-A4B7]

Another 3rd-4th gear pull. It didn't go lean in 4th this time.

[Jayz691]

Kinda hard to tell from these screenshots, but looks like your lpfp is really struggling. Hitting 85%, and low pressure dropping1-1.5bar below requested.

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[JT-A4B7]

I seen that too, but I didn't think it was affecting it because the duty % get worse as the rpms go up. But the fuel trim goes back to rich after around 6k. I did notice the stft starts to go lean just after the injector timing starts climbing to 7ms. Then when it hits 8ms and 9ms it maxes out at 25%. It's starts to go back to normal when the injector timing drops back to 6ms in the upper rpm range. I tried to load the screen shots in order but that didn't happen. I did another log with rpm, stft, and injection timing and the same pattern happened.

[JT-A4B7]

I can do more logs if that would help someone come up with some ideas.

[JT-A4B7]

Where are all the B7 wizards at. I took a screen recording of a 4th gear pull that would help alot but its too big to upload.

[Jay-Bee]

Your lpfp is probably dying out.

But i would try drilling out the HPFP brass feed line like many people do.

https://www.golfmkv.com/forums/index...to-5mm.382982/

(lol bamboo fitting)

[Jay-Bee]

[JT-A4B7]

You might be onto something here. I'll give it a shot this weekend sometime. Thanks for the input.

[JT-A4B7]

Well I did the drilling mod and my fuel pump duty percentage did drop about 5-8%. But the lean issue remains the same. I feel like there has to be a sensor problem or something. The car never even ran rich when I did the hpfp upgrade on just the stage 2 tune before I got the stage 2 hpfp tune. The only other thing I can think of would be the relief valve, but no where in the hardware requirements for the tunes does it say you need the rs4 relief valve.

[Jay-Bee]

What's your low presure pump duty cycle % at fully warm idle and at full throttle high rpm?

[Jayz691]

Its hard to read a bunch of screen shots too. Thats where vcds is better. Being able to put your logs into spreadsheet for, with excel. So much easier to look through and spot something off.

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[JT-A4B7]

Yeah the screen shots do make it difficult. Idle is around 55% and full throttle at 6700rpm is at 80%.

[JT-A4B7]

Also, my stft on a cold start is 25-27% at idle and causes misfires. All the fuel pressures at this time are identical to the requested. The two issues maybe or may not be connected.

[esandes]

Is the MAF dirty?

[Jayz691]

I see you lpfp duty cycle getting to like 87%, which is basically max, while the pressure drops about 1bar under requested. Don't think its the problem, cuz rail pressure stays good, but its not healthy. And can't just it at cold start idle, let it warm up then check. Should be under at or under 50%. Still would need a good vcds log or 2 to really see whats going wrong. For me to read it well anyway. Just seems like fuel is coming up short, or bad air/load reading. Seen recently in FB group, MAP sensor was cause of lean code. Not reading correct load for proper fuel trim. Idk, just a thought.

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[Jayz691]

Is the MAF dirty?

Looks fine, reading to 190ish g's in his graphs.

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[JT-A4B7]

I have a fuel filter coming later this week that I'm going to throw at it. Doubt it will work but can't hurt. I just seen apr had a inline lpfp kit that they use for the stage 3 and up stuff. I dont see why I couldn't put one behind the fuel filter and only run it when I plan on driving hard. You would think the fuel filter would regulate the pressure. They have a Hobbs switch that could turn it on at a certain boost level. Instead of having to deal with that controller issue. Not sure if this would cause a CEL or limp mode.

[esandes]

What condition is your air filter in? In the ram air hose there's a fine screen near the grille. Check that too. I removed my screen long ago.

[JT-A4B7]

A little update. Replaced cam follower, lpfp controller, and fuel filter and there has been no change.

[KingKostas]

A little update. Replaced cam follower, lpfp controller, and fuel filter and there has been no change.

depending on how bad ur follower was, damage may have been done to the intake camshaft even a few mm will cause issues, also if it was like my car (damaged lobe) but also depending on the yr(mine is an 07), the ecu may need updating. While getting tuned was hitting fuel cuts until the realization it needed an update then worked fine.


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[JT-A4B7]

I got the car with about 120k miles on it. So I'm not sure of maintenance before my ownership. But for the time I've owned the car,the cam follower gets changed every 10k miles. I've changed it 3 times so far and it always looks good. The cam lobe isn't perfect but doesn't look too bad. I thought about changing the cam but im making sure all other possibilities are looked at first. I am just confused why there was absolutely no difference in fuel trim numbers before and after the hofp upgrade. Even with regular stage 2 tuning. And I thought that when you tuned your car that it is rewriting the whole ecu, so there wouldn't be a need to update anything. The tune would be the update in a sense.

[KingKostas]

I got the car with about 120k miles on it. So I'm not sure of maintenance before my ownership. But for the time I've owned the car,the cam follower gets changed every 10k miles. I've changed it 3 times so far and it always looks good. The cam lobe isn't perfect but doesn't look too bad. I thought about changing the cam but im making sure all other possibilities are looked at first. I am just confused why there was absolutely no difference in fuel trim numbers before and after the hofp upgrade. Even with regular stage 2 tuning. And I thought that when you tuned your car that it is rewriting the whole ecu, so there wouldn't be a need to update anything. The tune would be the update in a sense.

the lobe off a few mm can cause issues, u cant tell by the eye u would have to measure it to be exactly sure. all ik is once i replaced mine and made sure my ecu was up to date, my fueling issues went away


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[JT-A4B7]

I'll try to do some measurements on the lobe lift when I can. I have another used cam to compare it took. I'll also see if I can see the cam numbers on it to see what revision it is.

[Jayz691]

I'll try to do some measurements on the lobe lift when I can. I have another used cam to compare it took. I'll also see if I can see the cam numbers on it to see what revision it is.

If its an 07-08 it should have the newer, 2 piece lobe. Heres a pic of what it should measure. Sometimes it hard to read when I post it. Its 42.5mm across, from flat spot to peak. 5.25mm lift.Screenshot_20200220-055338.jpg

Edit: Does anyone know why pics degrade when posting??
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[CoalCo]

Did you ever resolve this? I'm having the exact same issue and have replaced the lpfp, module, and fuel filter with no luck. Lpfp is still hitting 94% duty cycle and car is leaning out and sometimes falling in it's face at high rpm

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[Jayz691]

Did you ever resolve this? I'm having the exact same issue and have replaced the lpfp, module, and fuel filter with no luck. Lpfp is still hitting 94% duty cycle and car is leaning out and sometimes falling in it's face at high rpm

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Do you have and 07-08? If so, check the hpfp inlet hose for damage inside, can clog the fuel inlet. What your low side look like when on it, req vs actual.?

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[CoalCo]

Do you have and 07-08? If so, check the hpfp inlet hose for damage inside, can clog the fuel inlet. What your low side look like when on it, req vs actual.?

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I have an 06. Replaced lpfp, fuel filter, lpfp module, hpfp, and fuel rail pressure relief valve all in the last two weeks hunting it down. Still having the issue. Cam follow has no damage and was just replaced 500 miles ago. Can't remember exact numbers but requested pressure on low pressure system is way over the actual when under load.

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