92firebirdRAY

ok, I'll start off by saying I have a 92 firebird 5.0 TBI. I have had many problems with my car, all starting around the time my fuel pump decided to crap out on me. i replaced that, no problem. Then I blew the heads on it. I was told it would ultimately be less expensive to just put a new engine in it than replacing the heads so I put in a brand new engine, same one, 5.0. The engine was brand spanking new, had 0 miles on it, so of course I had to baby it for the first 500 miles or so, and I did it no problem. then, out of no where, a strange thing began happening. no matter what i was doing with the car (in park, in drive, in reverse, in neutral, giving it gas, coasting, at idle, stopped, etc.) the tachometer would drop to zero, the car would violently jolt (only really when moving), a loud knock can sometimes be heard, then it will sometimes run fine for a while. but it had become so frequent that i had to put it in the shop. that shop told me it was the O2 sensor, replaced it, problem, knocking, bucking, whatever you want to call it, kept happening. took it to another shop, told me it was the distributor, so i replaced the cap and rotor, and the problem kept happening, i took it to a third place who had no idea what the problem was...this jolting sometimes causes the car to stall. it makes this car unable to drive. it is sitting in the lot of a fourth shop now and i am hoping i will get some answers this time. I had my uncle, who has been a mechanic for a very long time, look at everything. he says its getting exhaust out, getting enough fuel in, sparking etc. and he doesn't know what the problem is either... I NEED SERIOUS HELP. this is the car i rely on to get to work, to get to school, home and everywhere else in between. i appreciate anything you can tell me! Thank you in advance for all advice and help!!!

-Ray, disgruntled firebird owner

oramac91

iTrader: (5)

can u post the sound, can help u better that way,sound like it in the trans.

ASE doc

I'd like some clarification. What Im hearing is the car doesn't die, the tach drops out and the engine jolts, sometimes with a knock. Does it jolt once or repeatedly? Does this happen only after some driving or even when cold? Are there any stored codes in the ECM?

I can say that this problem will most likely be fuel or spark related. Fuel includes fuel management such as injector drive.

I would probably start with a visual inspection looking for loose grounds. The ECM grounds to the rear of the passenger side cylinder head. There may also be ground points at the rear of the driver's side head. Once you verify these grounds are good, run the engine through the conditions where this problem occurrs while monitoring spark with an inline spark tester. You may need to use an old plug wire to route the tester so that you can see it from the driver's seat. As the problem occurs watch to see if spark drops out with the tach. Then, use a testlight and some patience and see if power on the pink or red wire to the coil drops out as the problem occurs. My guess is it doesn't but need to be sure to eliminate a bad ign switch or connection. My guess is you have an intermittent short or poor connecton in the EST circuit. It's the four wires that run between the ignition control module and the ECM. One test for this would be to disconnect the timing connector in the tan/blk wire and drive the car. See if the problem doesn't go away in this state.

The engine can run in default timing mode without EST. However, once EST is activated, if signal is lost on the white "timing control" wire or if the EST bypass circuit is shorted to ground, the engine will die. If the break in signal is only momentary, the engine may only "jolt" but not die. If the problem doesn't occur with the EST bypassed, find the short to ground or open in the EST circuit.

Another possibility is a short to ground in the Tach circuit. The Tach connects to the coil though the white wire in the gray connector. There will be an inline connector somewhere close to the coil that seperates the Tach from the coil. Try disconnecting the Tach at this point and see if this doesn't prevent the problem occurring. If it does, you need to find the short in your tach circuit or have you cluster repaired.