AFR dipping lean between from 3k-3700rpm, coupled with mild underboost

After recently setting up my standalone logging, I've learned that I'm consistently dipping lean (around 14 AFR at 16psi boost), then dropping back to 10.6ish. Attached is a log, however I have about 5 others that follow the exact same trend. I should note that the resolution isn't that great as I'm temporarily logging with a 4gig card. I'll have more precise logs with a few more parameters thrown in (open to suggestions) next week.

 

The question is, should I:

A) Assume it's caused by the tune and let my tuner fix the fueling in that zone

B) Assume it's a problem with the WB02 sensor (AEM UEGO has been rumored to have inconsistent readings)

C) Investigate possible mechanical issues

-Torn inlet?

-Minor boost leak?

-Weak fuel pump/clogged fuel filter?

 

If it sounds mechanical, I plan to do a boost leak test, as well as install my DW65c pump. I'd prefer to rule out options (A) and (B) until I know it's not a mechanical issue.

 

Thanks guys, I'm hoping this will fix my slight stutter during spool.

log0002.csv

Log the AF sensor #1 on your car and see what it reads and compare. If it's truly that lean, the AF sensor #1 will be able to maintain its reading.

Log the AF sensor #1 on your car and see what it reads and compare. If it's truly that lean, the AF sensor #1 will be able to maintain its reading.

 

I have logged A/F#1 in the past, and it dipped lean around the same range. I initially was under the impression that the sensor wasn't reading correctly, and wanted to verify with the more accurate WB02. I'll add that parameter back in once I get my 1gig SD card.

 

Also, my WB02 is located in the bell of the downpipe- could the turbulent flow be causing it to misread? Is it worth me relocating the WBO2 sensor downstream to the rear 02 bung?

I honestly don't have the answer to that question but I wouldn't worry about relocating until you can figure out for sure it's a sensor or sensor location problem. Just doublecheck by logging the AFR via the built in sensor and compare to see what you get.

Cobb pipes have always come with the WBO2 bung right in the bellmouth area. No issues here with two different Cobb pipes and two different sensor setups (AEM UEGO the first time and PLX now.)

 

Thanks.. Did you ever have any bad readings from the UEGO? I'm going to trust that the AFR readings are accurate and lean towards a mechanical/tune issue. The only knock in the logs is shift knock, so it's obviously not lean enough to cause det. That leaves either a boost leak or insufficient fueling.

 

IMO, if the pump was on its last leg I'd be running lean towards redline, but that's not the case. I guess it's possible that the pump isn't reacting fast enough to keep up with the turbo spool..

 

A torn inlet makes the most sense, since the leak would be pulled open at the moment of the max pressure differential, or mid spool. Since it's just the VF40, the turbo won't be pulling as hard in higher revs, so the leak can close up.

 

To sum it up, I'm going to fab a boost leak tester and check all of my vacuum lines. Any other thoughts/comments?

I think i had one logging run where the UEGO acted up, but otherwise no. I switched setups when I sold the last car because I wanted something more standalone that didn't require a gauge for power. That's the main reason I switched to the PLX, not a performance reason.

 

Good to know.. Thanks. I waited until I knew everything was hot before I took the last few logs, and they're all consistent. Heck, I may even add AF#1 today and log during lunch. Since I'm on limited on sampling rate, are there any parameters I have right now that I can pull out to get a little more resolution on the fueling?

Why not pull everything but engine speed and fueling if that's what you are looking for?

 

I'll do that and post the log after lunch. I may throw in knock count just to be sure I'm not knocking in that zone.

Eff.. I accidentally put A/F learning #1 instead of A/F sensor #1.. That's what I get for rushing. I did notice in log0004 that the issue is becoming more obvious and the AFR spiked to 15 before dropping back to 10ish. I fixed my config file to log the right parameter, so I'll post the next logs after work.

log0003.csv

log0004.csv

What's up with you not even coming close to target boost? Are you heatsoaked badly? No positive compensation dialed in for IAT?

What's up with you not even coming close to target boost? Are you heatsoaked badly? No positive compensation dialed in for IAT?

 

I was overboosting in 4th, so my tuner pulled some wastegate. I wasn't heatsoaked at all, so he either pulled too much, or I developed a leak. Where can you leak that would cause it to underboost and run lean?

You don't run lean from boost leaks. You run rich. You're losing air. But no, I was just commenting on the boost. Work on one thing at a time. Figure out if your WB is working or not first.

 

Remind me later to talk about the under/overboosting issue.

That makes perfect sense.. I just wasn't sure if there was a possibility of the two issues being related. So first: I'll log my front 02 vs. the wideband to see if they both dip lean. If so, I trust the readings and there's something causing me to run lean. Why would it only run lean at midrange, as opposed to higher revs?

No point theorizing until you verify the sensor is ok.

Well, I logged the front 02 vs. the WB02 and I'm getting the same #'s. My tuner shortened the open-to-closed loop fueling delay and it seemed to eliminate the lean condition, however I'm still running a little rich per the WB02. This could be due to a boost leak, so I'm in the process of building a boost leak tester to confirm/diagnose.

 

What do you think? I should have more accurate logs this evening, however I think this still shows what I'm looking for.

log0001.csv

Interesting that he would still keep that fueling delay. Many tuners just disable it all together.

Interesting that he would still keep that fueling delay. Many tuners just disable it all together.

 

told me that you can save mpg's by using it. I can attest to that, since I've been averaging around 23mpg's city at stage 2. What's the purpose of disabling it?

To prevent the lean dip that you see and also prevent possible knock. It seems like your tuner's on top of it though since there was no knock in your logs I believe?

This car has been relatively knock-free.. I'll get the occasional shift knock, and I've had some low-load knocks, but no timing pulled or anything under load. Now that my lean dip is fixed, I'm definitely running rich, and my boost doesn't seem to be holding very stable, even though I'm hitting target now.