I have a 94 maro 3.4 manual trans that had a spun rod bearing when I got it. Found a rebuilt 3.4 engine to replace it with that had only 30k miles on it. I put it in and it ran for about 2000 miles and just locked up. Removed the engine and took it apart, found the crankshaft was broken in half. Bought an engine from a junkyard that the guy said was ran and tested before it was pulled. Put it in and it would start but would only stay running if it was kept at 2000 RPMs or higher. But it would spit and sputter and backfire and smelled like it was running REALLY rich. It was also knocking, come to find out the flywheel bolts where never tightened. We then bought a whole car, it is a 1995 3.4 automatic that had 2000 miles on a fresh engine rebuild and drove that car for about 15 miles just fooling around with it before we pulled the engine to put into the original car. We only bought it for the engine, never had any intention of putting that car on the road, but it ran perfectly. Drove both cars into my shop and pulled both engines, and swapped in the good engine. Got everything hooked up and the same thing as before, it spit and sputtered and backfired(no knock, flywheel bolts got tightened this time) and it wont stay running unless its kept above 2000 RPMs. and has the same rich fuel smell. I used as many parts from the good running car as I could. The only thing I could not use was the exhaust manifolds, the originals from the car had the air tube on it where as the donor car did not have the tube. Any ideas? I dont know if this problem is what caused the crank to break in the first replacement engine or if that was cause by driver error(my oldest son). The factory original engine ran perfectly except for the rod knock, and so did the first replacement engine, is there an electrical component that could have failed that would not throw a code but cause the car to run so poorly? Removed all of the older gas from the tank and filled it with fresh 93 octane with some fuel additives. Checked the plug wires and made sure they are ran correctly. HELP!!!!

 

do you have a scanner that will work on a 94, can be a challange to get one to work correctly. check all wiring and check again. most times you will find something hooked up wrong.

 

I do have a scanner for the older cars, but never tried to hook it up since the engine light is not on. I did go back and check the connections and everything was tight, I didnt check the wires going into each of the plug ends. I have three of everything for the engines(intakes, blocks, switches, etc) but is it possible that the ECM/ECU is bad, and if so, how would I test that? It has to be something with that car, because I know the engine is good and ran perfect in the other car.

 

I would check all the vacuum lines and triple check the connections. We had a car in the shop that would not run under 2000 rpms, following a clutch job, and after testing major ground connections and verifying the alternator was putting out a charging voltage, we double checked the plugs/ connectors and the the connector for the clutch switch was just tight enough to let the car run but not very well. Sounds stupid but once we plugged it back in all the way the car ran perfect. Go over everything again it has to be an electrical connection or a vacuum line or something

 

Thanks guys, sounds like I need to check the wiring and connections again.

 

did you use the computer from the good running car?

 

Tried the new computer, and it allowed the car to run at idle so i could do some testing. Saw and heard the coil arcing, replaced the plug wires and it was still arcing and running bad. Replaced the coil pack with one from one of the many engines for this car and I noticed that 2 of the coils where not in the same place on the pack. Installed the replacement pack and the car ran perfectly. Surprising amounts of power outta that V6 engine. Put about 400 miles on it and it blew a head gasket, I dont think I was meant to have this car running, ever! Thanks to all that offered tips.