2002 Impala, NO POWER

[IsaacHayes]

My friend has a 2002 Impala, 3400 and it is slower than a turtle.

He took it to autozone to have them scan it and they said no codes would show up if there isn't a check engine light. I don't know if their code reader can't read stored codes or they didn't know what they were talking about, but there was no codes basically.

Would a slipping transmission not leave a code? I thought ODBII would show up? It doesn't sound like it's reving up high, it sounds normal, just does not pull.

3rd gear on the highway moves, and if you floor it and it goes into 2nd, it actually slows down.

I'm thinking it's either the transmission, or an EXTREMELY clogged fuel filter. The motor sounds fine, just no power/pull. He doesn't have a tach and the car is quiet so it's kind of hard to tell. He does always run it with less than 1/8th of a tank of gas....

Any other ideas? When he moves into his new place with a garage I'm gonna change his fuel filter... He drives like a grandma, so I don't think it could be his transmission unless he is just very unlucky.

[Bowtie70SS]

Bad Gas? If you got ahold of some bad gas then the PCM will revert to the low octane timing table...no power. Also could be a bad fuel filter or dirty Mass Air Flow sensor (especially if he has a K&N air filter).

Dave

[sharkey]

i had an issue like this on a 2001 chevy venture. after overhouling the transmission, the engine stumbled when you step into it, had poor fuel economy and generaly had no power. worst part it was intermittent. aftyer chasing it for a couple months on and off it ended up being a bad mass air flow sensor, the filliment in it was "loose".

i would however see if you can find another one to test with to make sure as they are around $500 new.

[JMo60]

yeah i would think mass air flow right away as well.. those autozone scanners are generic and only pick up a handfull of stuff.. if you have access to a tech 2 that might really help

[Niteflight]

Could be a bad cat as well, if its a slipping tranny/torque converter there would generally be a code, the check engine light would come and go by itself and there should be a stored code.

[IsaacHayes]

Thanks guys! I was just about to bump the thread.

Tomorrow I'm going to change his fuel filter as suspected. I will take a look at the MAF too. It's gradually gotten worse so I'm thinking it's the fuel filter. He continues to not fill his tank up and only puts $5 tops worth of gas at a time!! He wont do that anymore he says once it's fixed!!

If that still doesn't work then I'll see if I cant find someone with a better scanner.

QUESTION: If you disconnect the MAF, will the engine make more power than if the MAF was faulty and giving really whack readings? (easy way to check it?) :P

[Niteflight]

If you disconnect the maf it will use pre programmed maf tables via pcm, so yes if there is a problem with the maf and you disconnect it, it should work better. BUT DON'T go flooring it a lot with the maf disconnected its unsafe, can pop a piston.

[IsaacHayes]

Right. Got ya. I figured it would default to something since RSM supercharger guys disconnect the MAFs and the cars have some power (but do pop pistons LOL). Thanks.

[onefastV6]

If you disconnect the maf it will use pre programmed maf tables via pcm, so yes if there is a problem with the maf and you disconnect it, it should work better. BUT DON'T go flooring it a lot with the maf disconnected its unsafe, can pop a piston.

Actually it runs rather rich with the MAF unplugged. When doing VE table changes they recommend scanning in SD mode, which I have done many times and have went WOT with no negative effects. Just remember with the MAF unplugged the tranny will shift at full line pressure.

[IsaacHayes]

He told me today it's running a little better than the other day when it was super cold. This leads me to think it's defiantly a fuel starvation issue.

The trans shifts at full line pressure? That's odd, I guess the 4t6*E's are no longer vacuum modulated, and determines load off of the MAF? I'd think it'd go by the MAP for that.... _shrug_ But I guess the MAF is more accurate to determine power being made....

[sharkey]

it shifts with a combination of maf tps and map

[tractorman]

Don't overlook something obvious like a plugged air filter.

If you unbolt the exhaust and let it hang, you can drive the car and see if it runs better. It WILL if the cat is plugged.

[IsaacHayes]

tractorman, I'll check all the little things like that. Maybe a squirrel crawled up there and died? haha. But yeah. And I'm also going to pull the front plugs and look at them to see how the motor has been running. I wont suspect the exhaust until I check out the other things cause it's likely a fuel filter the way he never fills up the tank...

[Niteflight]

Are the shift points not defined with the pcm? either by speed or rpm?

[IsaacHayes]

Nightflight: yes the shift points are, both by speed and RPM. We are talking about line pressure (how much force on the clutches). When the throttle is not open much, the PCM lowers the pressure so the shift is smoother. When the throttle is wide open, it raises the pressure so the shift is fast and firm so the clutches don't burn up.