ECMlink ECU Reset Temporarily Fixes Lean WOT

[90 TSI FWD]

BLUF: Car runs lean above 4.5K RPMs. Resetting the ECU fixes the issue, but it slowly returns after a couple pulls.

I’ve been chasing a lean issue in WOT for years and never completely figured it out. I rarely drive the car, and when I do, it’s to troubleshoot and not so much enjoy it. I can’t say for certain when it started, but I noticed it two years ago some months after I changed the turbo. For perspective, I’ve put 500 miles on the car in 2 years. It’s always ran, but had the WOT lean problem so I’ve stayed off the throttle unless I was troubleshooting.

I believe I falsely solved the problem every time I “fixed” something. I would have no lean WOT issue doing a pull after “fixing” or “changing” something: I rebuilt the AFPR, changed the fuel filters, cleaned and tested the injectors, redid the wiring at the pump, changed the alternator, fixed lots of wiring (nothing was necessarily wrong, but cleaned up prior amateur wiring thinking it may help)… but the problem always returned the next day I drove the car. I learned today while tuning that the problem actually temporarily resolves itself after I disconnect the battery and reset the ECU.

Today, I decided to just restart fresh with my SD table and idle settings. My tune was for my old 16g and adjusted for the FP green after I installed it. The table wasn’t very smooth, granted, I ran consistent 11.5s down the quarter, so it worked for me. But to take the tune out of the potential problem, I wanted to start from scratch. I got the idle dialed in. Adjusted the BISS, got my airflowperrev to .25, and adjusted my global and deadtimes, and got a cruise tune dialed in.

After my initial settings were done, I boosted in 2nd just to see if I had the problem. I didn’t. So I continued to do a 3rd gear pull, and it pulled hard. Problem solved. Might as well get my SD table squared away while I’m out. I made a global adjustment to get my AFRs lined up, then did a pull. I’m lean again. I go home, disconnect the battery, pull the pump out to see if any connections are loose. Nothing. I ziptie my gopro to my strut bar to record the AFPR gauge. I go for a drive and pull in 2nd gear to see if my fuel pressure goes up with boost… problem solved!... My gopro died, but I went to do another pull. Here comes the lean issue. I noticed it gets progressively worse in time. During my last ECU reset, the problem was there, but not nearly as bad, but it got worse on the second pull. Notice it’s the upper 4K RPMs where it starts to go lean.

Once my gopro is charged, I’ll record it again to see if my pump is unable to keep up with the demand. I’m not sold on it being the problem though, because I still had this issue with my last pump. I redid my rewire and tested the voltage at the pump. I also tested the AFPR rises with pressure using hand pump.

I’m now at a loss on what to do next. Could the ECU be bad? I’ll pull it out again for a picture, but I didn’t physically see anything leaking or bad. What could resetting the ECU (or battery) actually fix that makes my issue go away, but slowly come back? Where should I shift my focus to next?

1) Any boost, vac, or exhaust leaks? No
- Resurfaced exhaust manifold to fix exhaust leak to the turbo
- Fixed leak at FPR; set dedicated vacuum lines to the FPR, MAP, Boost gauge, and BOV

2) Verified mechanical timing? Yes

3) Verified base timing? Yes

4) Ignition system
- NGK BPR7ES gapped to .022 (fixed WOT break-up) - 700 miles
- NGK wires - 3800 miles

5) Motor health (Compression Test) - Not performed

6) Performed basic throttle body adjustments? Yes
- TPS adjusted
- ISC tested
- Biss adjusted

7) Compression ratio - Wiseco 8.3:1

8) Wiring and Sensors?
- Fixed poor wiring/connectors at alternator
- Fixed broken fuel pump bulkhead

9) Any DTC/CEL codes? No

10) Electrical system
- New (rebuilt) AutoZone 90A Alternator

11) Base fuel pressure and injector values
- New Walbro 525
- Rebuilt Fuelab AFPR and new filter
- Base Fuel Pressure: 38 psi
- 8AN Supply, stock return
- FIC 1600

12) Properly calibrated and configured wideband sensor? Yes
- AEM X-Series

13). Type of fuel
- E85, personally tested 85% ethanol at the pump

14). Watched ECMlink how-to videos?
- Probably all of them +YouTube more than once

 

[90 TSI FWD]

I may have posted this thread too soon.

It may or may not be coincidental that this happens when I reset the ECU. First test pulled fine without resetting the ECU, second was lean. See the video for my fuel pressure fluttering. Not sure where the problem lies, but I am now doubting the ECU reset has anything to do with it.

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Comparing previous video to testing the fuel pressure regulator with the car off

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[Justin DuBois]

Wow - Never tuned a turbo that does this: 2psi @3k, and max boost 20psi finally hits a 5K.
This must feel like riding in a sling shot!

I noticed you have the "Anti-Lag" feature enabled in ECM Link - Does this do anything for you? I've never been able see any effect using that feature.

Your boost performance explains why you have your timing tables set up with aggressive timing down low, and then a jump from 8-16 and a flat 17deg above 3.5k - E85 is amazingly forgiving.

Your Fuel pressure should raise at the same rate as your boost, and it does climb, but the needle on that thing is vibrating lIke crazy - Is that really what the pressure is doing?

 

[90 TSI FWD]

Wow - Never tuned a turbo that does this: 2psi @3k, and max boost 20psi finally hits a 5K.
This must feel like riding in a sling shot!

I noticed you have the "Anti-Lag" feature enabled in ECM Link - Does this do anything for you? I've never been able see any effect using that feature.

Your boost performance explains why you have your timing tables set up with aggressive timing down low, and then a jump from 8-16 and a flat 17deg above 3.5k - E85 is amazingly forgiving.

Your Fuel pressure should raise at the same rate as your boost, and it does climb, but the needle on that thing is vibrating lake crazy - Is that really what the pressure is doing?

Yeah, this turbo is much laggier compared to the 16g, but it was a gift from my brother who actually gave me the car back in high school, so on it went. He wants me to get into the 10s, so that’s the goal. It pulls a lot more up top than the 16g for the lower boost level but doesn’t come alive til late as you can see. I plan to play around with the timing/fuel once my issue is fixed to see where I can gain some power down low.

I’ve actually never tested the antilag. I set it up according to some other video I found on YouTube. I want to try it out once I fix my problem.

Yes, that’s what the pressure is doing. On the occasional good pulls, it is steady. On the lean pulls, it shakes like the video. I have a couple other videos on my GoPro showing it more erratic. I’m currently brainstorming why the pressure would be acting this way. With the car off, the regulator raises fuel pressure with boost. With a load, it’s erratic, most of the time.

Injectors- wouldn’t it cause the car to run rich? FIC cleaned and flow tested them.

Pump- it’s new, and I know it’s getting the voltage. I don’t know how I could test if the pump is bad.

Regulator- I may need to take it apart and see if the diaphragm has any reason not to seat. Perhaps I may have changed the diaphragm, but maybe the actual housing is cracked or warped.. I’m leaning towards just getting a new one.

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[Justin DuBois]

Yeah, this turbo is much laggier compared to the 16g, but it was a gift from my brother who actually gave me the car back in high school, so on it went. He wants me to get into the 10s, so that’s the goal. It pulls a lot more up top than the 16g for the lower boost level but doesn’t come alive til late as you can see. I plan to play around with the timing/fuel once my issue is fixed to see where I can gain some power down low.

I’ve actually never tested the antilag. I set it up according to some other video I found on YouTube. I want to try it out once I fix my problem.

Yes, that’s what the pressure is doing. On the occasional good pulls, it is steady. On the lean pulls, it shakes like the video. I have a couple other videos on my GoPro showing it more erratic. I’m currently brainstorming why the pressure would be acting this way. With the car off, the regulator raises fuel pressure with boost. With a load, it’s erratic, most of the time.

Injectors- wouldn’t it cause the car to run rich? FIC cleaned and flow tested them.

Pump- it’s new, and I know it’s getting the voltage. I don’t know how I could test if the pump is bad.

Regulator- I may need to take it apart and see if the diaphragm has any reason not to seat. Perhaps I may have changed the diaphragm, but maybe the actual housing is cracked or warped.. I’m leaning towards just getting a new one.

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Its harder to get more fuel through an injector than not. Any pressure oscillation in the rail will push less per pulse than a steady stream, so the lean condition seems correlated to the "noise" in the rail pressure.

I'm wondering if this is a similar effect you see in household plumbing called water hammer. Looking at the moving parts in the regulator seems like the right place to look.

 

[90 TSI FWD]

I sent a message to Fuelab to get their input. I took the diaphragm out and found some some of buildup on one corner of the ball. I’m wondering if this could cause intermittent turbulent fuel flow as the fuel travels around the ball and through the outlet hole. I was able to scratch it off with a thumb tac but I can still feel some residue where the ball sits. There’s also small scratch marks in the housing, but not where the ball seats, so I’m not sure if that affects anything.

I changed this about a year and a half ago. Not sure how this happened. Maybe because I drive it so little and it built up.

I’ll wait to see what Fuelab says before I order a diaphragm, or regulator altogether.

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[90 TSI FWD]

I never closed the loop on this, but changing both fuel filters and the diaphragm fixed my issue. I will now make it a point to change my filters yearly, even if I put less than 500 miles on the car. Perhaps sitting so long allowed the filter to clog much sooner.

 

[CrackedDSM]

I am extremely envious of your idle with those HKS 264/272s. With these horrible BC272's my vacuum at idle is like, half of what yours is. Helps to look at a relatively similar setup though that actually idles and drives.