Huge Power drop "TUNER INPUT NEEDED"

Stangt00

New Member
Oct 6, 2003
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Brought the car back to get the idle tweaked, and FINALLY saw on the dyno what I was feeling during every day driving.

There was a huge DROP in power and Tq, then it came back up, with the A/F pegging out lean. After trying to tweak the current tune, the tuner started from scratch. Impressively enough, the car picked up 12-20 Tq low-mid range, and 10 peak, 7-9hp low-mid range, but lost 1 peak. No biggie. Looked great and no more drop could be seen on the dyno. So I drove it home with no noticeable problems (just cruising at highway speed, not accelerating alot like on the streets).

Now, driving around town, I still notice a loss of power intermittently, but not as much as before. The tuner checked the coolant temp (held steady), Fuel pressure was good, Maf was good, TPS was good, nothing out of the ordinary could be seen while it was doing this on the dyno. He assumed it was something in the tune, but this is basically the same tune he has used on MANY cars before, modified slightly for my setup of coarse. As I said, he did a fresh retune from scratch and it went away on the dyno, but showed itself later on that night on the street.

Since there were no trouble codes, and nothing could be seen that would have caused it to lean out intermittently like it was, could there be a problem with the computer itself not following the instructions of the tune? Are there ANY suggestions that some of you may have to offer? The tuner is 2 hours away, and costs me $40 in gas and tolls each time I have to go there. Thank you so much for any tips you may have.
 
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I took my car to a dyno tuner also and when i got it back more things were wrong with the car then when i took it like lack of power and the little power i had only went to like 3700 rpm i called back and he said he would fixe it for another 400 dollars i said no way. so i took it to the dealeship and they re flashed the computer with the newst ford promgram for the mustang gt and it runs better than ever didn't increase hp really but it brang it all back to stock and that felt great so maybe you just want to bite the bullit and cut your loss i kno it sucks but id rather have my stock hp over lower numbers
 
My numbers are not lower by any means. I dont hink I said that anywhere. Also, the tuner NEVER CHARGED me another cent for the retuning. Thats just the way he does buisness. FYI, Baseline with stock settings on the PCM netted 284 RWHP and 292 RWT. The tuning is not the problem. I dont think it is anyway. It makes no sense as to why it would pull strong and hard on the dyno, but intermittently go lean while normal driving. Thats the question I am looking for an answer to. As I said in maybe too many words above, this was the first time they actually saw it on the dyno.
 
did the tuner datalog the fuel pressure I know Tim at T&Js had a fun time tuning mine , he said the fuel pump could give just as much trouble as anything on the car , thats why im saving for an 03 cobra pump and tank now . just an idea to run by your tuner .
 
I will ask him if he data logged the fuel pressure. I know he was looking at it during the runs where he could see it lean out.

*EDIT* Meaning, he was checking the fuel pressure when the A/F was pegging on the dyno. The same time the power drop occurred.
 
Thing is, he said the fuel pressure was normal during the whole run. The A/F was leaning out on the screen from the dyno. It has a bar that runs across the bottom that shows when it's lean or rich. Also, my car smells REAL rich at idle. I guess thats what having no cats does though.