2002 grand prix stumble

[thecrow1986]

when i get in the car hot or cold it doesn't make a difference. ill start driving and it doesn't make a difference if im going fast or slow. when i reach about 50 mph it kinda stumbles . not sure what this is. i have 222000 on it and had changed the plugs and wires and cat and fuel filter and had a fuel system cleaning done. the transmission was serviced last june. nothing has helped this go away. could it be injectors or something else like transmission?

[tblake]

It could be injectors, but I would check for a vacuum leak, then unplug the MAF sensor and start it to see if it still stumbles.

What brand plugs did you install?

[thecrow1986]

where should i check for vacuum leaks? i took the maf off and the throttle and cleaned it with the cleaning spray that is recomended but it didnt help. one thing that i have noticed that i was reminded of is sometimes when i start my car i hear like a kind of thunder from the rear of my car. could it be the fuel pump dieng out? this seems to happen more when the car has been running around

[thecrow1986]

ac delco iridium plugs and wires

[serge_saati]

When you press the gas, do you feel a lack of power compared as before? Like if the pedal is more easy to press. If you put gear in neutral or just release pedal, it makes a difference?

If not, I think it might be a lack of pressure in tire. Check pressure on all tire. Maybe a very small flat that you need to seal.

But no, it's not the plugs.

[rkvons]

Originally Posted by serge_saati

When you press the gas, do you feel a lack of power compared as before? Like if the pedal is more easy to press. If you put gear in neutral or just release pedal, it makes a difference?

If not, I think it might be a lack of pressure in tire. Check pressure on all tire. Maybe a very small flat that you need to seal.

But no, it's not the plugs.

I gotta say, I lost my way after getting to this reply...

[serge_saati]

Originally Posted by rkvons

I gotta say, I lost my way after getting to this reply...

One time I get a small air leak in my tire. So when I exceed 55mph, all the car stumbled. Not the engine, but all the car. When I changed the bad tire, problem was gone. I was able to go to 95mph (above the speed limit) w/o any problem.

But if the problem is on the engine, tests must be done to the engine. Like release the gas or put in neutral when it stumbles to see if it reduces. Cause the engine is unbalanced if a cylinder lack of power. Advanced test can be done on the engine.

[thecrow1986]

do you think maybe i might need a new fuel pump? sometimes i hear a rumble coming from the rear of the backseat when i first start the car

[serge_saati]

Maybe. Test the fuel pressure.

[thecrow1986]

im gona see about testing it today

[CrazyHorst]

I think with 222k changing the fuel pump is just a very good step in the right direction to keep you from walking home!! Sounds like you have crossed off some of the more common ignition and induction problems.

The other thing i would consider is the crank sensor...both fuel and ignition pulses are based on this signal -- known weak point of 3800s. And also another walk-home problem...so something good to change as a maintenance item.

[thecrow1986]

where should the pressure be at. i tested it the first time and it said 46. then i tested it again and it kept bouncing back and forth from 44 to 46

[serge_saati]

On this car with 3.8L, it should be between 48-55 psi (steady) when engine is off.
When engine is idling, it should be between 38-52 psi. It can fluctuate a little bit while running.

[grandprixgtx00]

If you drive the car with the gear position in "3" (turn OD off) does it still do it? I'm thinking more along the lines of a bad TCC. 50mph is about where it should be going into OD

[richtazz]

I agree with the TCC issue, 50 mph is right where the converter will lock. With the noise from the tank the fuel pump isn't out of the question, but a pump can be noisy and still work fine. The pressure readings are within spec as real world fuel pressure specs on these cars is more in the 42-48 range, regardless of what specs sheets say.