Lean Code/Weird fuel trims
 

So I put the car back to stock in order to sell it. It popped a P0174 code, and so I went to investigate. This has been a long running issue with the car, but thought it was solved. It has an aftermarket header that I have long suspected to be the culprit, which I found a crack in at one point but had it fixed.

The behavior it's exhibiting now - LTFT is extremely high, 20-22% but only under no or very little throttle. Any throttle and LTFT goes to 0. STFT are within 1-2% under all conditions. I checked under the car, and lo and behold I found a nut missing from the header that I guess I didn't torque properly at some point. I fixed that problem, and assume that is the cause. I pulled the positive battery cable for about an hour under the assumption that it would reset the fuel trims.

There's no obvious sign of misfire or knock, the car doesn't appear to be pulling timing. My next thing to do is just to put the stock header back on.

I guess I have two questions:
1. Is it possible that the fuel trims didn't reset and that the LTFT will come down over time?

2. Am I barking up the wrong tree chasing after the header? I don't really hear any signs of an exhaust leak, but I'm close to positive there's no vacuum leak because I was extremely careful when assembling the intake.

the high LTFT at idle and going to near 0 with any throttle sounds like either an exhaust or vacuum leak. How are the header gaskets- what gaskets did you use? Make sure there's no leak in the PCV or brake booster lines. If you have a catch can, check that.

But it sounds like a header gasket issue to me.

as above guy said If the LTFT is high positive at low rpm and ok at higher rpm and the afr is ok at higher rpm.


then its most likely an exhaust leak gaskets crack or leak at front 02 sensor itself

Yeah... that's my thought process too. I guess I will put the stock header on tonight and see if that fixes the problem.

Use new gaskets, re-used ones almost always leak

You didn't use new header gaskets did you? Get the Grimmspeed gaskets, they are cheaper and better than OEM

I did when I installed the header the first time (grimmspeed gaskets), but now I don't know if there's additionally an issue with the header itself. If the header works fine and it's the gaskets I'd rather use it, but at this point not sure there's any point.

Installed the stock header with brand new gaskets last night.

No change :bonk: long term fuel trim is still ~19% at idle or coast, and drop to zero with even the slightest bit of throttle.

I did try leaving the positive cable off overnight to reset things, not sure if that actually works or not. I'm considering re-flashing the ECU. I guess I may have to spend the evening rigging up a smoke machine to double check for vacuum leaks...

is the trim LTFT +19 or -19 ?


at idle is the measured AFR about 14.7 ? and steady at around 14.7 or is it moving around considerable like to 12 then 15 for example

i have the same lean issue except my car is stock besides oft stage 1 tune, my ltft is way high

could someone look at my data log and possibly help me figure out whats wrong?

https://drive.google.com/open?id=0B1...3J3SFdMbk5KWHM

So, I'm here to eat crow. You know how I said I was almost positive there were no vacuum leaks?

I gave up and tore the top end apart again... wrong size hose clamp on the evap solenoid, the hose slid right off. I guess that's what arrogance gets you. Once I fixed that... fuel trim is down to about +4% at idle. Not perfect, but I can live with that for sure.

What fuel are you running? Your AFRs are very high - I would flash back to stock mapping until you know what's going on.

Also, I know you said "stock," but I just want to make sure...you haven't changed your intake system at all, have you? Your MAF voltage isn't responding as aggressively as I would expect during your higher RPM runs.

It's hard to tell from such a small log and only revving up to the 3000's, but that car is running lean, I wouldn't go WOT with that. Fuel pump pressure logs would help. But without a CEL, I can't say for sure but this looks like a fuel system issue. Either one of the fuel pumps or an injector. What other symptoms are you getting?

I found your other thread about this issue. You're throwing lean and direct injector codes. You also had some plastic stuck in your throttle body. I wonder how plastic got in your intake. I'd start by tearing down the entire intake and checking out how that happened. Normally with a fuel issue, you swap injectors from one bank to the other and see if the problem follows. But on this car I don't know how difficult that is