Impala Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
I have a 2005 3.8 liter impala with 250K miles. If I keep the car under 3 grand it seems to run fine. It gets 27.8 mpg driving to and from work. Although the hire the RPM's it acts like a clogged fuel filter. And at full throttle it will not accelerate it bucks and chugs and just won't go. Just like it has a clogged fuel filter. Things I have done to try and fix the problem. First a new fuel filter. No luck. 2nd a new converter. Still no luck. Fuel pump key on engine off over forty pounds of pressure. Same when it is running. If you rev it up the fuel pressure jumps above fifty psi. When you shut it off pressure holds so i am assuming the Fuel pressure regulator is good. This meets the specs for the pump. I have inspected the MAF sensor. No damage seen and the scan tool data looks good and smooth. When I put the pedal to the floor the scan tool goes nuts. It goes from closed loop to open loop, best i can tell all sensors start jumping around with their readings even the fuel injectors pulse width gets erratic. But if you let up to say 98 percent throttle all of the readings calm down and the car starts to accelerate all though it is slow to reach speed the more you let out of it the faster it picks up speed. I hate guessing as it seems to cost a hundred buck every time i do. So if you have any ideas please let me hear them. Thanks in advance.
 

·
Registered
Joined
·
2,922 Posts
I have a 2005 3.8 liter impala with 250K miles.
<snip>
And at full throttle it will not accelerate it bucks and chugs and just won't go. Just like it has a clogged fuel filter.
<snip>
When I put the pedal to the floor the scan tool goes nuts.
I'm thinking bad throttle position sensor (TPS). According to the schematic, it's a potentiometer. I suspect the wiper inside is making a bad connection when you go WOT. The signal from the pot will be erratic when the wiper hits the bad spot. Think static on an AM radio. That may explain why "the scan tool goes nuts".

Looking at my manual, it makes no mention of needing to do any sort of re-learn when it's replaced. So it's simply a bolt-on replacement. It should be easy.

For confirmation, I would put a voltmeter on pin B of the connector of the suspected bad TPS, and watch the voltage change as you move the throttle up and down. Then see what happens at WOT. If the voltmeter won't settle down, that would be my confirmation.

An old analog meter might be easier for this app, since the needle should move steadily with the moving throttle, until you hit the bad spot.

With a digital meter, you'll need to move the throttle to a position and hold it steady while the meter settles. Then move it to another spot and see the voltage settle again at a new value. At the bad spot, I would expect the reading to keep changing, to never settle.

In my driveway, I'd probably put a scope on pin B just so I can see the noise waveform, but that's not really necessary.

HTH,

Doug

.
 

·
Registered
Joined
·
257 Posts
Unplug the maf sensor and start the car with it unpluged. Drive the car and go wot, if the problem is gone it's the maf. ECM has a strategy to run with maf unpluged.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #5
Of all the sensors the tps is the only one that dose not go nuts. It reads 100% at Wide open and looks smooth from idle to wide open according to my scan tool. But I will try anything once. Thanks for the reply.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #7
I have been meaning to post this for a couple of days now. I found the problem. What are the odds. Plastic bag over the air filter. I have been a mechanic for more years than I can count. This is a new one. I tried to post a pic of the air filter and bag. but I can't get it to upload. Let's just say the air filter was being sucked into the engine. Hope this helps someone in the future.
 
1 - 7 of 7 Posts
Top