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Where did my power go??

B

Bandit1228

New member
I need some expert help and I figured that this would be the best place to get answers. My Pontiac dealer definitely does not rate as an expert.

I have a 99 GTP with 130k miles. When I was around 90k miles my car started to hesitate when I really punched the throttle. It didn't happen all of the time but enough to be somewhat annoying. My SES light started to come on occasionally and would stay on for several days before it turned off on it's own. After multiple trips to the dealer where they were more interested in selling me tires or replacing my belts instead of telling me what was causing the probelm, I have tried to replace parts that I thought may be causing the problem. The dealer's scan came back with codes P0300 and P0172. I don't remember which code shows the engine is running rich but I had already told the dealer, my MPG dropped from 29mpg to 19mpg. Now 40k miles later, I have gotten back up to 23mpg but the problem has got to the point that I'm nervous merging into highway traffic and I wouldn't dream of passing someone on the highway. I even have to get out of the fast lane when going up hill. (I know...I have a GTP and I'm getting out of the fast lane...It's embarrassing) I drive 100 miles round trip everyday to work and I either need to fix it or junk it. I can't take it any more!!!

Here is a quick break down of what I have replace already:
(3) ignition coils
(1) ingintion module
(1) catalytic converter
O2 sensor
all plugs
all wires
fuel filter (twice)
air filter (twice)
(2) belts
SC tensioner pulley
NO MODS

I don't remember where in the time frame it happened, but my SC tensioner pulley had fallen off so I was driving for a while without any SC. It either happened right before I started having trouble or right after it started acting up. Could this have caused a problem? Right now it seems that the hesitation happens whenever the SC Boost kicks in.:th_sick2:

Any help would be appreciated.
 


You addressed the P0300 code I would say with the tune up (plugs, wires, etc.) but the P0172 is the system rich code. That would point, in part, to a possible fueling issue. The more common point of failure that may affect your issue is the fuel pressure regulator. Take the vacuum line off going to the FPR and see if you have fuel present there, if so, it could indicate that the FPR is bad. The running rich certainly explains your mileage issues though. My next place I would have checked would be the O2 sensor, but you got that covered already.

Next thing I would do is check the fuel pressure. You have a schrader valve on the fuel rails (the thing that looks like a valve stem for a bike tire) and you can get a fuel pressure gauge and hook up to that and check your pressure. Should be around 40 - 45 psi if I remember correctly.

If its not then it could point to a fuel pump issue. But I suspect that its not going to be that as I would expect a lean condition from a fuel pump issue rather than a running rich issue.

It could also be an issue with one or more of the fuel injectors, but I have not see a lot of failures there. Running rich though is really the clue here cause I dont think that condition shows up very often as a result of other possible issues.

The only other thing I could think of that may cause that off the top of my head would be a faulty MAF sensor. If its not reading the air correctly then it could run rich as a result.

There are other things that could cause that hesitation feeling too, like possible drivetrain issues, but thats obviously not going to cause a rich condition so I think your issue is likely some component or sensor failure. Those two things, the runnning rich and hesitation are the symptoms to focus on.
 
does the motor dog out when you punch it or does it hesitate for a second and then go like nothing was ever wrong?
 
Thanks for the quick response.

I'll try to take a look at it again tonight to see about the vacuum line on the FPR. I don't have a fuel pressure guage so I'll have to try and get one.

Being that you mentioned the drivetrain, every once in a while when it hesitates, it sort of jolts like it just slammed into gear. It never seems to over revving like it's looking for the next gear though so I don;t know what it may be. Someone had mentioned to me that it might be the torque converter. Is this possible and what does it take to replace this?
 
Bio248 said:
does the motor dog out when you punch it or does it hesitate for a second and then go like nothing was ever wrong?
Click to expand...

It seems that it actually gets worse with the more gas I give it. I have to completey get off the gas and just barely touch the pedal to get it going.
 
do you think your torque converter is locking and not unlocking when you get into the throttle? does it surge when you push the pedal down farther?
 


I never had a problem with a torque converter so I'm not sure how it would feel if it was going bad. Usually when the car starts to hesitate, if I press harder on the gas, it feels like the entire car is rumbling. I normally need to get off the gas and ease into it again to be able to accelerate. Especially at highway speed. If I stay on the gas with the car is hesitating and running real rough, usually the SES light will blink approx. 6 times and then stay lit for a few days.
 
hm, the blinking SES is a misfire for sure. a ton of fuel being dumped into the cylinders would cause a misfire as well as the rich code, so im thinking you are starting to figure it out.

im thinking this is a fueling issue.
 
Well it's been a long time coming but I have finally had some time and some extra cash to pick up a few things. I picked up a scanner and fuel pressure tester recently and this is what I have come up with.
I keep getting the codes for misfire and running rich. I cleared them out only for them to reappear.
Yesterday I changed the plugs and wires again. When I removed the plugs, they all had a pretty strong odor of gas on them. I don't remember if that's normal or not. This still didn't help the situation of the car hesitating when I nail the gas.
Today I hooked up the fuel pressure tester. With the ignition turned to ON, I was getting a reading of 43 psi. I tried this a few times and I kept getting the same reading of 43 psi. Then I started the car to see what the reading was when the car is running. Now the guage needle is vibrating between 78 psi and 84 psi. I shut the car off, drained the fuel in the tester and tried again. As soon as I start the engine, the pressure goes right up to 78 psi and 84 psi. I tried to rev the engine a few times to see if it would come down but it stayed with the high readings. The car rightnow was cold since it sat overnight so it is idling a little higher but if I understand correctly from what others have said on this forum is that the pressure should ALWAYS be between 40 and 50 psi.
Does anyone know what would be causing this high pressure and hopefully be causing this entire headache?
 
that fuel pressure is high as crap. is your regulator gone? if you pull off the vacuum line from the regulator when the car is running does fuel spit out? if so you need a new one.
 
I just checked the fuel pressure regulator and there was no sign of fuel when I pulled off the vacuum line. I did hear the vaccum when I pulled it off and covered it with my finger and there a good amount of suction. When I put the line back on, I don't hear any other signs of an air leak from the vacuum line.
 


hmm..cause an o2 sensor would cause it to run lean. what are your LTFTs when youre driving? are they really negative?
 
I see what you were talking about. When I first started my car I was getting a reading of -6.8. After about 2 minutes and giving it a little gas, the reading fluctuated in the range between -6.8 and -21.8. The STFT first started at 0 and then went between 0 and -50.
 
LTFT = long term fuel trim

the short term i really dont pay a ton of attention to (STFT). if they are really negative then you are running rich. they should stay somewhere around 0 to be tuned correctly. some people even run a little lean (low positives) as the car runs better.

so you are definately running rich. what are your injector pulse widths (IPW)? i just wonder if it is possible that an injector is stuck open. are the misfires on one cylinder only, or is it random?
 
How would I find out what my IPWs are? The misfire code I usually would get was 0300 which I think is a general misfire. One of the last times I checked the code it was 0303 which I think is for cylinder #3.

Is there a way to check to see if an injector is stuck open?
 


scan for misfires. there should be a parameter that you can watch where the misfire is according to the cylinder. if it is mainly on one cylinder then try to switch that injector to another cylinder and see if it does anything (misfires on the cylinder you put it into).

there is also a parameter to see what your IPW is. low 20s are static (open all the time) for stock injectors.
 
I'll have to try moving the injector during the week or next weekend when I have some time.
I'll also try to look into the manual for my scanner to see if can see what my IPW is, otherwise I'll have to ask around to see if any friends have a fancier scanner I can borrow.
Thanks for the quick responses.
 
I haven't had a chance yet to swap around the injectors yet but I did just try removing the vacuum line from the regulator while the car was running and nothing changed on the fuel pressure. I was still getting the same reading in the area of 80psi. Would this alone be a sign that it's the regulator?
 
its possible. i have never replaced one so i am unsure whether they are expensive or not. i dont know why i am the only person answering in this thread either. :p
 
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