3.4L backfiring through intake

I could really use some advice on this.

I am working on my daughters 1995 Firebird with 3.4L engine. The problem is backfiring through the intake manifold. It is a loud popping sound. I took the car to a car repair clinic for diagnosis. After examination, I was told the valves may be stuck. I replaced the heads with rebuilt ones. The engine still behaved the same. I replaced the timing gears and chain. The engine still behaved the same.

I also replaced the plugs, wires, all three ignition coils. No improvement. But, when you disconnect each spark plug wire one at a time, the backfiring ceases when #5 plug is disconnected. And, I am on my third set of sparkplugs...all are getting gas fouled.

My AutoXRay EZ-Read 2000 (just bought it) says "Vehicle Not Responding" when I try it. So, I haven't seen any trouble codes.

I would appreciate any ideas. I am thinking of checking the camshaft, but I don't really feel that is the problem. Could an injector be bad?

Thanks,
Alton

you said camshaft, is just about the only thing left to check push rods to thats all I can think of right now.

The pushrods appeared fine when I was re-assembling. Any other ideas would be appreciated.

I now know the problem with the reader is due to the wrong cable being used. I am going to order one Monday.

Thanks,
Alton

when you say back fireing through the intake can you explane that more

It is a loud popping sound that can also be felt when you put your hand on the air intake. Not violent like when the timing is off. It only sounds off when you rev the engine or try to accelerate while driving.
Thanks,
Alton

oddly enough i had a bad fuel pump, (long story, more than just pump) and the same problem was happening because i adjusted the timing because i thought that was the problem, just throwing that out there to see if that might help, sorry do'nt have nothing definite.
Jake

Well, I replaced the timing chain and gears. That should have it mechanically timed. But, there is no distributor to turn on this model. So, I wonder if something else is causing the computer to have the engine out of time.
Thanks,
Alton

oooh, i forgot about that? is it throwing any codes, map maybe? or esc? I'm kinda lost, sorry.
Jake

I hope to find out about the colds in a few days. Had to order a special cable because it is a mid '95 GM car.
Thanks,
Alton

well if it's obd II it will automatically change your timing to what the computer wants it to be... that's why it could be violent when you accelerate

I could really use some advice on this.

I am working on my daughters 1995 Firebird with 3.4L engine. The problem is backfiring through the intake manifold. It is a loud popping sound. I took the car to a car repair clinic for diagnosis. After examination, I was told the valves may be stuck. I replaced the heads with rebuilt ones. The engine still behaved the same. I replaced the timing gears and chain. The engine still behaved the same.


Thanks,
Alton


Did you ever get this problem fixed and if so, what was the solution?

papasmith, please don't resurect old threads. If you have a question pretaining to a topic in an old thread, then simply start a new thread, state your problem, and then the link to the old thread. Thanks.