Thread: Power loss / slight stumble @ WOT

Hello everyone,

This is my first post and I'm skipping the intro post. I have read posts here for sometime and I must say, you guys are great.

Now down to business...

I have a 1996 Pontiac Grand Prix SE 3.1L with 108k miles and the car runs great except for one BIG issue. Everytime I floor it it reaches the RPM as it should but it goes no where like it is in neutral. At times it will pick up somewhat but it also has a few misfires and seems to be running rich due to the smell of the exhaust.

Now, the problems were worse off a week ago but I had repaired some issues with good results. Basically I have more then 1 issue and I believe I fixed it all except for the one problem that remains as described above.

It would start rough, idle rough for 3-10 seconds then idle high (1.5-3k rpm). If the car sat for a few hours the drive was fine except for the WOT power loss and misfire. Once the car warmed up and was driven for some time, it would begin to stumble a lower throttle positions. At this point when I shut the car off it would refuse to start again and if it did start up the idle was very rough like a Harley Davidson idle and then die. I would have to let the car sit for 2-3 hours before it would start again and the cycle repeats.

I pulled codes (can't remember the numbers) but they were MAF signal too high, TPS signal too low and random misfires. No other codes so far.

I replaced the TPS, cleaned the MAF (it was very dirty), changed the plugs and wires, new oil filter and gas filter, new PCV valve and hoses, flushed the coolant system, new catalytic convertor (oem) and seafoamed the gas tank/oil/ and intake. Flushed the oil and added quality synthetic oil with synthetic Lucas treatment 40/60 ratio. Cleaned the battery terminals very well and put in new battery.

The gas tank is 1 year old so I doubt there is junk in the fuel system. No fuel coming from the FPR.

Since the repairs, the rough start still exists but not as bad and it restarts consistantly with out dying. The idle is normal (around 800rpm) and general performance has improved.

The car is a great car and has operated very well for 13 years going strong. The opposite of a lemon for sure. But this extreme power loss and stumble at 75%-100% throttle is really bugging me.

I suspect a bad fuel pump but not sure.

Any advice and/or input would be greatly appreciated.

Thanks in advance,

Wilford

BTW, the issue at hand seemed to come on more gradual then sudden.

The pump sounds healthy as I can here it every time I turn the key and it doesn't make an suspicious noises. It is the same general buzz noise everytime. Though I guess that may not mean much.

Ah HAAA Fixed it, but with a little work!

As it turns out, it was the Fuel Filter. Damn mechanics charged me for a new one + labor but never put it in. The symptoms were screaming bad fuel filter yet I kept ignoring that since I 'thought' I had a new one. Glad I looked.

But, the filter was sooo old the bolts rusted shut. I tried everything to get it loose. WD40, tapped it, vice grips..ect. Ends up I had to cut it out and patch the line. The patch worked like a charm.

I used high pressure rubber fuel line wrapped over a steel line that threaded into my filter, wrapped the line over the remaining fuel line, used gasket seal resistant to fuel in between the rubber and steel and used 8 strong screw clamps. The rubber line was also reinforced with tin wrap. Only 1/16" where the 2 steel lines meet is where the weakest point is. That was wrapped well and clamped very tight.

No leaks after hours of driving. But I still plan to replace the fuel line from the filter to the FPR.

Go figure...I guess it is smart to check over a mechanics work. I should've and it would have saved me time and money.

Oh well, problem fixed!