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Stumping all the 3800 guys...

8

88FieroGTS

New member
So, to start I have an '88 Fiero, with an L67 (Stock motor) in it.

For the first week or two, mileage was roughly 20-22MPG (Should be seeing 25+ more or less with HWY conditions)
As of the last two weeks, my mileage dropped from 20-22, to 16, to 12MPG.

My LTFT's (Long term fuel trims) have been steading steady when I cruise around -10.9.
They've hit a max of -16.4 (On an unprogrammed ECM) and up to -23 (On a programmed ECM, VATS, DTC codes removed, that's it.)

We've covered 99% of the basics, nobody that does these swaps for a living, can pin point WHY this is happening.
I've taken it to two shops and not even they know.

So, I figured I'd turn to the GPF Community, it may not be a Grand Prix, but it's an L67.

Here are known numbers:

Fuel pressure:
48psi KOEO
40-42psi KOER
50psi KOER, Vacuum disabled.

-Can not smell fuel in the vacuum line.
-No fuel in the oil.

Vacuum is about 17-19psi
(MAP sensor on my Actron is showing around 10inHg at idle, but goes up greatly as I accelerate.)
TPS voltage shows .58v on my Aeroforce (Which died, two weeks of owning it.)
TPS voltage shows .40v on my Actron scanner
TPS Value goes 0-100 smoothly.

IAT * is ~100*
ECT is functioning normally.
O2 sensor is functioning normally.
Fuel pump is brand new, no issues with the pump.

I've tried two different MAF sensors, replaced the o2 sensor, No CAT on the car (Pre-Cat o2 sensor only, Post-cat is neutraled out at .450mv)

I removed the fuel rail and injectors to see if any were peeing with KOEO full pressurized rail. Nada.

Have a MAP sensor on the way.

ANYONE have a clue? LOL.
 


This would help:

1999 Grand Prix GTP Motor/Trans
1999 Stock GTP ECU
2001-2003 ECU (Flashed to read as a '99 GTP, just with some DTC codes removed.)
 
It's not a tune at all. Just a stock ECM that has had DTC's removed, no tables were messed with.
I don't know anyone around here that does tuning on the 3800's. So... Mail is all I got.
 
who DR'ed the pcm for ya in the first place? or did you just buy the pcm like that?

for under 300 you can buy your own tuner and learn to tune.

hows it running other then the high neg numbers?
 


It runs great, and a man from Canada did it, he's very well known in our (Fiero) community for his swaps.
I've been asked to send his PCM to another gentleman who is willing to work his magic on it.

I have to replace the hot water tank in my house... So $300-400 on software won't happen. Especially after a $250 Aeroforce gauge quit after two weeks, and that I need to get a Wideband o2 now, to see if Commanded AFR is actually 14.7, and it's not seeing something else.

It does run better without the high Neg numbers, It was doing so-so Yesterday (Around -8.6 or so at cruise) but it's back up to the high points again.
 
try un hooking your evap from the tb. ( cap the port on the TB) that may have something to do with it. re set the pcm/fuel trims ( un hook battery for 30 minutes) then put some miles on it and a few restarts and see where your lifts end up.

tank of gas gets low ltft's can change vs a full tank. evap is a line to the gas tank.
 


It's a stock L67, Obviously swapped.. If I had to have the ECM programmed to have VATs and such removed.
Hooked up the Programmed 01-03 ECM just now, @ idle my LTFT is -10.9...
 
He's done quite a few of these and hasn't heard back with any problem like this.
The whole situation is just weird, nobody knows. Hence why I turned here..
 
was the pcm done by overkill? hes member here pretty active too.


i just did a top swap pretty much, (car came sc'ed, so its a bottom swap) i set all my files back to stock but the timing, right now my lifts are -10.3 at idle, but -7 and lower while driving, lock in at 0.0 if i get into the gas.

the lifts are fix able, but you need a tuner and a scan to know what to change and how much.
 


I think you need to get some maf tuning. my car went rich all of a sudden for no apparent reason, and some maf adjustments fixed it.
 
My timing is 22* at idle, 27* Idle in Drive, I haven't seen it really get over 30* timing.
I do scan, just can't tune/don't have the pockets for it right now.

No, wasn't done by Overkill. His name is FieroFlyer from Pennocks Fiero Forum.
 
you got guys up there, you just dont know it yet lol im not kidding. you may have to drive a hour or two but theres guys in mass that tune.
 
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