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No Acceleration issue

BooGTS

BooGTS

New member
I have a 2002 Pontiac Grand Prix GT. I have an issue with the car not accelerating. It will slowly go up to 4000rpm and stick. If I let off the gas completely, it will downshift, and then I can slowly go up to 4000 in the next gear, ect...

I am pulling a low voltage to MAF/VAF code. I have tried swapping out the fuel pump, MAF, TPS, and temp sensor with known good ones as well as whatever pressure sensor is located on the left side of the intake. Fuel filter was replaced. Any ideas?
 


check wires for abrasion, when my icm harness got chewed thanks to someone at a shop I got low voltage codes constantly as the wires bounced off different parts
 
It sounds like there's wires either broken or shorted out.But I am guessing that there is a bare spot somewhere in the harness for the maf sesnor. To find it you need to take the maf harness apart and trace each wire as far as u can to see if there are any bare spots. Don't give up wiring can be hell but it will pay off in the long run
 
Alrighty, ill try tracing the wires - I got 12v, 0v, 5v when I measured the outputs of the harness. I think this is normal - 12v in, 0v ground, and 5v computer feed?

UR LOSN said:
also....are you still running a CAT? how many miles on the car?
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Yes, have a cat. 90k. I was thinking it could be clogged - but would that throw a code?
 
Easiest way to see if it is the cat, jack the car up and look at it. When they go bad and clog, they get very hot. See if the metal has discolored in any way.
 


what we did at the dealership was unbolt them, and seperate the exhaust a couple inches, and see if the issue goes away
 
You could do that but if the cats been changed then the metal might not get super hot of its just starting to clog. But that sounds about right for the volts you were seeing on the maf wires. There should be one constant hot one ground and the pcm feed.
 
If the maf is the prob, unplug it and run the car, the car will run in a "fail safe mode" if this fixes, issue solved.... Sometimes isues like this are cosed by bad/corroded grounds, check all grounds and make sure you battery and Alt are working properly.... but sounds like a cloged cat to me, I think the dealerships have to replace it it is under a extended warranty cause they like to clog
 
BooGTS said:
yes, have a cat. 90k. I was thinking it could be clogged - but would that throw a code?
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of all the cars that have had bad cats...they have yet to throw a code.:th_wtf:

get under the car, like reptile said and see if the Cat is discolored at all. if you dont see anything, hit it with your hand...and listen to see if it sounds like it has marbles inside. if it does...cat is bad and inside is breaking down, if not...stuff could be just too compact.

if you have a friend with a welder.....I would cut the pipe about 3in in front of the cat...it will be LOUD!! but drive it and see if the car feels more there.. yes I know there is no backpressure....

OR.

you could go on instinct and pick up an aftermarket DP...and just eliminate, or add a high flow.

these are my thoughts.......sounds like it is being restricted..rather than a sensor.:th_scratchhead:
 


there is a mass air flow sensor right inside the throttle body, it just a little wire that over time will get grime, carbon and dirt build up on it you might want to clean it with crc cleaner. you need to be careful not to touch the wire, the cleaner evaporates. just blast that a couple of times. and let air dry
 
To everyone that gave suggestions in this thread, thanks! It was the cat. I bought a new one with 2.5" DP from ZZP. Little louder and faster (than stock). Most importantly, it gets out of its own way now! On to my suspension fixes...
 
BooGTS said:
To everyone that gave suggestions in this thread, thanks! It was the cat. I bought a new one with 2.5" DP from ZZP. Little louder and faster (than stock). Most importantly, it gets out of its own way now! On to my suspension fixes...
Click to expand...

good deal!!!
 
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