Passing Car Prob 93 Pont GP 3.1

[Stumppullerover]

3.1 engine, auto trans, 93 Pont Grand Prix Runs great usually. Spin tires taking off on dry pavement WOT. Shifts up OK but feels like falling off in power just before upshift. Cruise at 70 just fine. 28 to 32 miles per gallon depending on hills etc. going 70 to 85 mph. Worst highway mileage was 24 in real heavy wind. Try to pass a car WOT and speed will drop to 55 from 70 if held WOT. Back off to 1/2 throttle or little more and car will pull good back up to 70. Can do 95 if not WOT. Used to be able to do 115 no prob. No More. (I live in Montana if thats explains anything). Dogs at WOT when punched at cruising speed. Staying in Drive the whole time. Downshifts but will not GO. 186,000 miles. New plugs helped bottom end pull. New fuel filters did nothing. Code check on reader gives only 12. No other codes. If I was an old Granny there probally would not be prob. Any Clues?

[Cliff8928]

Is it a 4T60-E? I had noticed when we had a problem with my mom's fuel pump on her 96 GMC C1500 Pickup with the 4L60-E, it was not delivering the required volume for higher RPMS, and the engine would starve, however since it was at WOT, it would stay downshifted, and wouldn't get enough fuel and the speed would decrease just like yours is... (similar situation with a electronically controlled 4-Speed automatic)

I would first check the fuel filter..

Cliff Scott
89 BerettaGT
89 Volvo740

[robby1870]

In 93 its gotta be a 4T60E

[Cliff8928]

In 93 its gotta be a 4T60E

Show's how much I know about the Ws


Cliff Scott
89 BerettaGT
89 Volvo740

[Stumppullerover]

replaced filter with no result. Considering fuel starvation, I decided to invest in fuel pressure tester. Can get get one for $99 that is supposed to work on ALL vehicles. Tons of adapters etc. Thought better investment than paying garage for receipt to tell me same thing I can find out for myself. Got into a repair manual and see pressure regulator vacuum controlled. Correct fuel pressure high vacuum and WOT no vacuum and if "Stuck" not letting enough fuel to injectors? Maybe bypassing most of fuel back to tank at WOT instead of sending it down the pipe? Don't know how regulator works for bypassing fuel with out doing a dissection on one at this point. Pull throttle back and runs OK. Any way, I see, you need pressure tester to check the regulator and the pump. Ordering on internet, so will be next weekend before I try it out. I see pressure regulator $125 and pump $110 from one source. Trying to keep costs down. I hate to spend the money on tester but could use the tester for other rigs around here. Thanks for the input. Appreciated. Gave me a path to go down.

[Cliff8928]

Did you check the fuel pressure while driving the car? Even in my case, it said the correct (62 psi) pressure at idle and would rev fine when not moving..

Cliff Scott
89 BerettaGT
89 Volvo740

[Stumppullerover]

Have not got tester yet. Directions in repair manual say to check with engine off. Turn key on and check pressure. Then start engine. Pressure supposed to drop 3 to 10 lbs from non running to running. If drops more than 10 lbs fuel pump bad. Normal pressure 40 to 47 lbs. If pressure does not drop, you are supposed to apply vacuum to pressure regulator and if drops then fix the vacuum on car. If pressure does not drop after using external vacuum, the regulator is supposed to be bad. Next weekend will tell. Thanks.

[Cliff8928]

I would still test the fuel pressure when your symptoms are present..

Cliff Scott
89 BerettaGT
89 Volvo740

[RLJ]

A plugged catalytic converter will cause the same drivability issues you are having. (I speak from experience). Just a thought.

[Stumppullerover]

Will check that too. Thanks

[GPXSS]

Pressure testers are $40 or under from AutoZone / Pepboys... not sure why the one you are getting costs $99, Mine will work on All GM , Chrysler, and Nissan.. those are at least what I've used it on. Ford may need an adapter.

Sounds like you are having open loop fueling problems.. once you hit WOT the computer stops metering everything precisely and kinda goes wide open with the fuel.. so if everything is good up to 95% throttle.. then that extra 5% messes it up then thats the problem. The fix? well... lets see if we can get some ideas from other people.

[SappySE107]

The fuel pump is likely the problem, unless your injectors are leaking and causing the computer to cut fuel during normal driving (cut fuel compared to the stock programmed fuel tables, so this isn't something you would notice much just driving it). Your best bet on spending money for diagnosing is to get a scantool setup. I prefer a laptop and freescan, but that costs you a laptop and an ALDL connector for the laptop. Otherwise, i would find a cheap hand held model.

The point of that is to get the BLM and INT during driving conditions. If its just an issue of the fuel pump being too weak at WOT, then you should notice a lot of knock retard at WOT and the O2 sensor voltage wont be very good either for WOT.

The fuel pressure tester wont help you here. When my pump was shot and anything over 25% throttle was murder, the pressure tested fine. It was the flow that was crap. For issues at WOT, its hard to mimic that without a dyno and still read the pressure (probably will show something at WOT).

Ok, this is getting long. Fuel pump is still an idea, but it could be ignition side too. Wires any good? Coil packs could be it as well but id start at the wires.

[Stumppullerover]

Did not get fuel tester yet. BUT, I did cut off the catalytic converter and put in "test" pipe. Very much improved. Shifts out of passing gear at 85MPH and runs up to the computer limit of 115MPH Has not done that in year or so. Thanks to all of you for your input. Still going to check fuel pressure. Thanks.