fuel trims

[LGHTNG02GT]

so i developed a problem with my car and i have not been able to figure it out myself and nothing has been helpful from other sites so i figured i'd try my luck with the SVTP Gods.

the car: 2002 GT with a 1998 lincoln mark VIII motor swap. cobra upper/lower intake, imrc deletes and some other minor things (shorty headers, 03 cobra maf, 24lb injectors)

what it does: it is most prominent at idle. it will be rough and my vacuum will drop off slightly (normally -20in/hg is good but i will pull like -17~ish or so when it starts acting up) on my sct, my fuel trims are way out of wack from one side to the next. short terms are like .98 for one side and the other will be way up to like 1.25. the only code i pull is a P1152. my O2 sensors are new (motorcraft replacements so they are OEM pieces) so i fugure that isnt the issue. my fuel pressure hold steadyr at 40psi so i dont believe its a delivery problem.

so what could cause this ??? it seems to come on at random times because every once in a while it will sit right at -20 and idle just fine (it doesnt happen often but sometimes it will) i'm assuming its something to do with the passenger side bank but i'm comming short on ideas of what to look for.

any help?!?!

thanks guys!

:beer:

 

[01yellercobra]

When it acts up is after doing anything specific? Like after a WOT run or after sitting in traffic for a long time? Do you know anyone with a MAF you can try? That's where I'd start looking.

 

[LGHTNG02GT]

the fuel trims are always mis-matched that badly. it isnt noticeable when you are driving but at idle you can tell because it idles rough and i'm pulling in a low vacuum reading.

 

[Savn4Mods]

Vacuum leak maybe? That might explain the low vacuum at idle and possibly the fuel trim compensation on that one bank.

 

[LGHTNG02GT]

Vacuum leak maybe? That might explain the low vacuum at idle and possibly the fuel trim compensation on that one bank.

thats exactly what i thought and where i started out looking. i deleted my EGR because i figured that may have had something to do with it but that didnt work. its weird because every once in a while it will run perfect and i have the right vacuum reading on my gauge which lead me to believe it was something electronic screwing me up. if it was mechanical, i would get a low reading 100% of the time.

 

[01yellercobra]

Did you have the EGR turned off in the tune when you deleted it? If not it will cause some issues.

 

[LGHTNG02GT]

Did you have the EGR turned off in the tune when you deleted it? If not it will cause some issues.

yes sir i did. this one really has me stuck on what my issue is. i really dont think its an exhaust leak, i cant hear/pin-point one before my upstream O2's. as far as a vacuum leak goes, i'm relatively sure i dont have any at all because as i mentioned before sometimes i can pull in -20in/hg and everything is good...now as i keep driving it, it gets worse and now its to the point where it reads low 9 times out of every 10 i come to a stop and the engine is at idle. i made sure to clean my IAC and my MAF as well right as soon as i started having this problem and nothing changed with it. the only thing i can see is maybe a leaking injector or something ??? but i would think that would cause a lean code but i could be wrong.

 

[SVT99Stang]

Can you post a datalog? It would be very helpful for us to see exactly what is going on.

 

[LGHTNG02GT]

Can you post a datalog? It would be very helpful for us to see exactly what is going on.

i can. i will actually have to get one.right off hand i can tell you STFT's are way out. drivers side bank will hold steady from .97-1.00. the passenger side will bounce around from 1.05 and find a resting place up at 1.25. the long terms are closer in numbers but still apart. usually hold around 1.03 and 1.15 area on those.

am i right in my thinking that an exhaust leak would cause a lean code and not a rich code like i have?

 

[Alscobra]

Just a thought. Are you holding the brake pedal down when it starts cutting up? Also you can't always go by vacuum. A slight missfire will cause vacuum readings to go crazy. LTFT is an average over time and it doesn't sound like it's too far out of range. If it was pegged out either direction I would say maybe vacuum. Are you using a scantool or just a tuner?

 

[LGHTNG02GT]

Just a thought. Are you holding the brake pedal down when it starts cutting up? Also you can't always go by vacuum. A slight missfire will cause vacuum readings to go crazy. LTFT is an average over time and it doesn't sound like it's too far out of range. If it was pegged out either direction I would say maybe vacuum. Are you using a scantool or just a tuner?

no, no brakes. it will read low, just sitting there running at idle. i never paid close attention but i dont believe when i push on the breaks it gets any better or worse but i see where you're going with this. i will have to double check that then too. right away i had some misfire issues but since i got new plugs and swapped over to some 04 Cobra COPs, that problem seemed to have went away.

and to get all the readings, i'm using my datalogger on my SCT XCal3

 

[guitar maestro]

i can. i will actually have to get one.right off hand i can tell you STFT's are way out. drivers side bank will hold steady from .97-1.00. the passenger side will bounce around from 1.05 and find a resting place up at 1.25. the long terms are closer in numbers but still apart. usually hold around 1.03 and 1.15 area on those.

am i right in my thinking that an exhaust leak would cause a lean code and not a rich code like i have?

Yup an exhaust leak should cause a lean code because the O2 sensor only detects excess oxygen not fuel. If you insist on using the O2s as a guide to solve this issue, you can but you hhave to be absolutely sure that you have no exhaust leaks--otherwise it renders the closed-loop fueling all out of whack. A much better solution is to use a wideband O2 but again you need to be certain of no exhaust leaks.

Here's what I would do to get a better view of what's going on. Reset the car's pcm to clear to the fuel trims. Then datalog to see what the STFTs are doing before the LTFTs have a chance to move part of those corrections into the KAM. This will let you get a better view of the total and true amount of fueling correction by looking at solely the STFTs and not having to worry about the corrections stored in the LTFTs.