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Lean LTFT!

L

Lumpo

New member
Ive been chasing this problem for about a month now and i cant figure out why my LTFT are pegging at 16.4 during cruise. What I did so far is a vacuum gauge test and its holding at about 20 in/hg so a vacuum leak is not my problem. Changed fuel filter, MAP and both O2 sensors with same problem with LTFT. At idle my LTFT hangs between 0.0 and -3.2 but anytime i give it any gas it jumps right to 16.4 and stays there until i let off the gas and at WOT it locks in at 14.8. I first discovered this problem when i saw i was getting KR at freeway speeds and when i checked for LTFT they were pegged at 16.4 and not moving. Ive had all my mods listed below for a good 6 months problem free and then this problem appeared. Im beginning to think that my PCM wasnt right from the beginning and it just took the temperature to rise for me to see my KR im getting now because all the mechanicals seem to check out fine.
When i first decided to buy a pcm all i wanted to do to the car was downpipe, CAI and a 3.5 so thats what i got it tuned for. My plans changed when my uncle gave me a set of headers and with that i dropped to a 3.4. Would adding these two things through my tune this far off? Any ideas would be great!
 


You need a MAF tune to start with. That should fix the problem right there.
 
Lumpo said:
i have a programmed pcm.
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Which is why you have the trims like you do. It's very hard to get trims in line without having a custome tune on the car. Ambient temps as little as 10 degrees difference will cause your trims to be off.
 
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TDCRacing said:
Which is why you have the trims like you do. It's very hard to get trims in line without having a custome tune on the car. Ambient temps as little as 10 degrees difference will cause your trims to be off.
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Again...
 
Im just trying to figure why i went from having 0 KR to having up to 5* of KR at freeway speeds when i changed nothing. When i started reading KR on my aeroforce i switched it to view LTFT and they were pegged at 16.4 and not moving. Now this could have been like this from the beginning since i never had a reason to scan LTFT since the car was running great but i definantly see a problem now. I have a guy nearby who is willing to tune my car but i find its hard to believe its the tune since the car was fine one day and KR the next.
 
Yeah, unless the tune is absolutely horrible, I don't see it just pegging the LTFTs like that. Bad MAF, maybe? How do your MAF frequencies look?
 
Ill have to take a look tomorrow where should they be? I have a Mac Mentor so im able to read alot of parameters i just dont know where they should be. So any help on what to check and where the numbers should be would be great.
 


The main things I would look for is nice linear scaling, and staying fairly constant during cruise. There are a few things that can screw up the MAF reading, contamination from over oiling a gauze filter (like your K&N) or removing the screen in the TB, for example. At times, they just go bad, as well.
 
I welded up my EGR the other day but at cruise my LTFT still seem high hanging at 10.1 which is a little better than 16.4. I did notice that all my KR is gone since my LTFT came down so im happy about that but still would like it to come down some more. Is it normal for an off the shelf tune to be like this with these high LTFT? Am I going to harm my car if i leave it be or do i have to do something about this?
 


so here is a question then....since temp can throw my trims off so much then should i have a bin file for every type of driving weather? say, one for every ten degree temp difference?
 
I personally keep a winter/summer bin.

But I had the 16.4 issue with no vac/exhaust leaks... and I sent it to a friend to hex edit the catalyst diag test it kept running. That fixed mine.
 
Well i decided to swap out my MAF with my dads car who also has 1998 GTP to see what would happen as suggested by another member. Well first my car only got half boost and my tranny started shifting really strange. Another thing is that it started running way rich going to about -20 where as my other MAF was hanging around 10.1. Whats the deal with this????
 
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