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Trans HELP!

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3 replies to this topic

#1 Rpd783


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  • Year: 1993
  • Make: Pontiac
  • Model: Trans am
  • Engine: 5.7l lt1
  • Transmission: 4 speed auto

Posted 08 July 2012 - 03:54 AM

Help Please. Okay lets start with some specs. I have a 1993 trans am with the lt1 and auto trans. I believe it's the th400 but i'm not sure.The car has 197,000 miles on it and only gets driven once or twice a month unless my daily driver is broke down. The problem that I am having started with a hesitation when applying power from cruising speed to either merge with traffic or if I just plain needed to get out of the way in a hurry. I also noticed a hesitation in third gear while accelerating from a stop at normal (adult) speeds. To get the car to come out of this hesitation I have to feather the gas pedal and get the trans to shift to a lower gear (wich means a higher rpm) and then it accelerates fine. Last weekend I drve the car to walmart wich is about six miles from my house. On the ride there, I had the same symptoms I just described. On the ride home, The car would not get out of it's own way. The car would hesitate or was very slugish from stop up to cruising speed and felt very rough and almost like it wanted to stall out. Is this a transmission issue or an engine issue. I am most likely going to have the trans serviced because of the high mileage but I would like to know if this might be a bigger issue than that. PLEASE HELP!!! Thanks for looking and thanks for your time and help.

#2 GaryDoug


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Posted 08 July 2012 - 04:38 AM

I would start by checking the fuel pressure. You may have a weak fuel pump. I think it should be 41+ PSI when the ignition is ON just before starting.

1998 Trans Am - LS1/A4 - all stock - one owner - driven daily - Scan9495 author

#3 98firebird


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Posted 08 July 2012 - 06:21 AM

Doesn't sound like a trans issue. How long has that gas been in the tank? Try scanning the car for codes, if you can (even if the SES light is not illuminated). What codes does it show? After driving the car, check your catalytic converter under the car. Is it glowing red?
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#4 Injuneer


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  • Transmission: TH400 + GV O/D

Posted 08 July 2012 - 06:25 AM

The stock auto trans in a 93 is a 4L60 (non-electronic)..... pretty much a direct copy of the 700R4. That is a 4-speed O/D automatic. The TH400 is a 3-speed automatic without O/D.

Sounds more like the engine is experiencing misfires under heavy loads (low RPM in higher numerical gear). When is the last time it was tuned up? How old are the plugs and wires? Has the distributor ever been replaced? When were the O2 sensors changed? Have you scanned it for codes - easy to do on a 93 because all you need is a paperclip.

And as Gary points out, check the fuel pressure. Best way to check is at idle, with the vacuum compensation line off the fuel pressure regulator (FPR). Should be 43.5psi, with GM accepting anything from 41-47psi as OK. Reattach the vacuum line to the FPR, and fuel pressure should drop proportional to intake manifold vaccum - about an 8psi drop with a stock cam, less with a more aggressive cam. Than tape the pressure gauge to the outside of the windshield, take it out on the road and observe the fuel pressure under max engine load - over 5,000RPM/WOT. Should not drop below 40psi.



381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor



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