Powerless Trans Am

Tiny
CAR TOM
  • MEMBER
  • 1985 PONTIAC TRANS AM
  • V8
  • 2WD
  • AUTOMATIC
  • 184 MILES
Hello; I have a question regarding my 1985 Pontiac trans am with the 5.0 h.O. 'F' motor.I have been scratching my head bald with this for the last month. The vehicle is stock except for an Accel coil, wires and bosch plugs, it has over 180,000 miles I assume since I bought the car two years ago. The problem that I have encountered is that as of a month ago, while driving the car all of a sudden lost power. The motor runs fine at idle, no tapping no backfiring nothing at all. But when I step on the gas the car just feels as if its suffocating, backfiring, and slows down the more that I give it gas. When I was on the local road, I gave it gas so as to reach the towns 30 mph, as I did that the car bogged down and it felt as if someone had attached a bungee cord to my rear bumper, just as if you would flood the motor, but once I backed off the gas pedal the car returned to a good idle and ran on its own power at 10 mph without any problems. When I popped the hood and pulled the gas cable the car again backfired and you could see the air intake collapse under suction.I was forced to drive home with my 4-ways at 20 mph just slightly tapping the gas pedal so as not to stall. I also noticed that when I left the car in my garage foe that month and restarted the car ran fine even when I reved the motor high, but once I had the car run for 25 minutes and reved the motor again it began to backfire and sputter. Any help would be greatly appreciated; Thank you
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Thursday, May 5th, 2011 AT 5:26 AM

9 Replies

Tiny
JDL
  • EXPERT
Do you have a feedback carb on this, or is it fuel injected? Check for applicable mil codes. You can check those yourself.
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Thursday, May 5th, 2011 AT 1:38 PM
Tiny
CAR TOM
  • MEMBER
P.S. The pontiac is a fuel injected and no check engine codes at all.
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Thursday, May 5th, 2011 AT 5:18 PM
Tiny
JDL
  • EXPERT
Use a gage and check fuel pressure. Are you TBI or port fuel injected? With TBI you can see the injector spray pattern, and the fuel pressure is about 10 psi. With port fuel injection, the pressure is higher. Port fuel injection usually has a schrader valve where you check fuel pressure. Tbi doesn't, you have to tee into the supply line. Make sure, no pressure on line if you take anything loose.

You should have at least got a code 12? Can you communicate with computer at all? Some of the national brand autostores used to loan out a fuel pressure gage. How long since a tune-up?
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Thursday, May 5th, 2011 AT 5:48 PM
Tiny
CAR TOM
  • MEMBER
The car has the port fuel injection with 8 individual injectors, the computer is pre-odb1 I havent yet grounded the diagnostic ports for a code since no check engine light came on. About 250 miles ago I changed the oil and the fuel filter, as far as a last tune up.I purchased the car two years ago from a guy who had the car registered and inspected last in 2006. So I assume he did nothing with the car that time, but when I tested the car two years ago it ran fine as it did last year. The only issue was the tps which I set to specs using an ohm reader.
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Friday, May 6th, 2011 AT 5:18 AM
Tiny
JDL
  • EXPERT
With it in park or neutral, does it rev ok? I'd still check fuel pressure, when you get the chance.
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Friday, May 6th, 2011 AT 4:03 PM
Tiny
CAR TOM
  • MEMBER
No matter if its in park, once its warmed up and you hit the throttle it just sputters and backfires. Iam wondering if its anything to do with the distributor or possibly the distributor mounted module.
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Saturday, May 7th, 2011 AT 4:58 AM
Tiny
JDL
  • EXPERT
I'd want to check fuel pressure.

If there is no spark advance, it will run like a dog.
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Saturday, May 7th, 2011 AT 2:35 PM
Tiny
CAR TOM
  • MEMBER
I changed the rotor and the distributor cap and drove it for a test drive of 3 miles and ran fine, no suffocating or backfiring, maybe it was only the cap, will try to pull the plugs out, but noticed that the rear ones are a hell to get to. Thanks
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Friday, May 13th, 2011 AT 5:46 AM
Tiny
JDL
  • EXPERT
Sounds like you got it going your way, good job. Some engines, the plugs are easier to get at from underneath, your decision. You'd have to safely raise and support the vehicle.
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Monday, May 16th, 2011 AT 3:05 PM

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