Question about 1985 Pontiac Firebird

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The car is slugish at takeoff.

I have an 85 Pontiac Trans Am. I have done virtually every test and replaced everything possible that was faulty that I can think of on the car. The vacuum tests out good. It seems as though the engine runs ok once you get it off an idle. It is much worse when the car is cold. I'm not sure what else to try. Any suggestions??? Thank you very much for your help!!!

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  • cdsampo Jun 20, 2009

    It is a manual transmission.



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Have you done an exhaust back pressure check? The brief description of your symptoms could be a clogged catalytic converter....which might be worse when cold than warm. If you've got any reason to believe the catalytic converter has been damaged (incorrect fuel or additives, physical damage/crushing, excessive heat, etc) I'd definitley eliminate it as a potential cause. It's tricky to check exhaust back pressure....but here's some ideas that might confirm or deny.

1. Is there a hissing or whistle from the tail pipe at idle? might indicate an obstructed exhaust causing a hiss or whistle from gases trying to force around/through the obstruction

2. Does the car initially fire up fine but start to loose a few RPM within a few seconds of idling? possibly indicating back pressure build up starting to hurt engine performance.

3. The best method is probably to disconect the exhaust from the engine and use a leaf blower or similar to blow a large volume of air through the exhaust....the problem then is determining how much back pressure is "normal", but generally the back pressure or resistance to air flow through an exhaust should be low - a few psi differential at most.

4. The most accurate method would be to set the engine up with one cylinder exhaust valve fully open, pull that spark plug, plumb in a differential pressure guage and compressed air source and put air into the cylinder. The pressure guage should indicate how much back pressue it is present in the exhaust system. The pressure differential will rise with the pressure and volume of air supplied to the cylinder, but if it's possible to build up more than 1-2 psi in a cylinder with the exhaust valve open, the most likely cuase is obstructed exhaust. The most common cause of obstructed exhaust (after physical crush damage) is a clogged catalytic converter.

Posted on Jul 06, 2009

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What type of transmission is it?

Posted on Jun 20, 2009


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Where is the location of my starter relay ********* fuse on a 2003 Chrysler Sebring sedan


The starter relay is located in the Power Distribution Center (PDC) in the engine compartment. Refer to the PDC label for relay identification and location.

Remove the starter relay from the PDC as described to perform the following tests:
  1. A relay in the de-energized position should have continuity between terminals 87A and 30, and no continuity between terminals 87 and 30. If OK, go to Step 2. If not OK, replace the faulty relay.
  2. Resistance between terminals 85 and 86 (electromagnet) should be 75 ±5 ohms . If OK, go to Step 3. If not OK, replace the faulty relay.
  3. Connect a battery B+ lead to terminals 86 and a ground lead to terminal 85 to energize the relay. The relay should click. Also test for continuity between terminals 30 and 87, and no continuity between terminals 87A and 30. If OK, refer to Relay Circuit Test procedure. If not OK, replace the faulty relay.
  1. The relay common feed terminal cavity (30) is connected to battery voltage and should be hot at all times. If OK, go to Step 2. If not OK, repair the open circuit to the PDC fuse as required.
  2. The relay normally closed terminal (87A) is connected to terminal 30 in the de-energized position, but is not used for this application. Go to Step 3.
  3. The relay normally open terminal (87) is connected to the common feed terminal (30) in the energized position. This terminal supplies battery voltage to the starter solenoid field coils. There should be continuity between the cavity for relay terminal 87 and the starter solenoid terminal at all times. If OK, go to Step 4. If not OK, repair the open circuit to the starter solenoid as required.
  4. The coil battery terminal (86) is connected to the electromagnet in the relay. It is energized when the ignition switch is held in the Start position and the clutch pedal is depressed (manual trans). Check for battery voltage at the cavity for relay terminal 86 with the ignition switch in the Start position and the clutch pedal is depressed (manual trans), and no voltage when the ignition switch is released to the ON position. If OK, go to Step 5. If not OK, check for an open or short circuit to the ignition switch and repair, if required. If the circuit to the ignition switch is OK, see the Ignition Switch Test procedure.
  5. The coil ground terminal (85) is connected to the electromagnet in the relay. It is grounded through the transmission range sensor only when the gearshift selector lever is in the Park or Neutral positions. Check for continuity to ground at the cavity for relay terminal 85. If not OK with an automatic transmission, check for an open or short circuit to the transmission range sensor and repair. It is grounded by the PCM if the conditions are right to start the car. For automatic trans. cars the PCM must see Park Neutral switch and near zero engine rpm. For manual trans. cars the PCM only needs to see near zero engine rpm. To diagnose the Park Neutral switch of the trans range sensor refer to the transaxle section for more information. Check for continuity to ground while the ignition switch is in the start position. If not OK and the vehicle has an automatic trans. verify Park Neutral switch operation. If that checks OK check for continuity between PCM and the terminal 85. Repair open circuit as required. If OK, the PCM may be defective

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First thing, try to extract a trouble code. Autozone will do this for you.

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