'96 Voyger 3.3L engine backfire badly

The 3.3L engine was rebuilt and ran for two days perfectly then quit. It can be restarted but backfires badly. Obvious things were already checked by the rebuilder: cp/cs sensors, fuel delivery, injectors, flexplate, coil pack, sparkplugs, wire harness, timing chain, etc). Engine was torn down and rebuilt with a new crankshaft. It ran again for couple of days perfectly and then started backfiring exactly in the same way as before. It will crack and run very roughly at very low rpm, backfiring into the intake. Engine rebuilder is stumped. :frown: He claims he checked and rechecked all connections, looking for pinched wires, back connections, but cannot see anything wrong with them.

Any ideas what he could check?

Thanks.

Try a new engine control module. It sounds like the ECM has gone bad and is not sending the proper signals to the engine. If he has checked everything else that is all that is left to go bad.

Welcome to AF!!

That is what he thought after the first time the engine ran when the rebuilt was first done. He could not figure what to do next. I took it to dealer who messed with it, but also gave up saying all electronics checked out and there it some "other problem" with the enfgine. The rebuilder took it from the dealer, put back whatever the dealer left undone and the car fired right and ran for two days before developing the same backfire. So ECM was fine. Now it has exactly the same symphomps. So I doubt the ECM is bad. Those things seem quite roubust.