Serious Engine Touble, Help Needed

[HzEmall]

I need to pick some people's brains.

I recently bought a 91 Buick Roadmaster with the TBI 305 in it.

When I bought it, once it warmed up it would stall when slowing down at a light sometimes. I replaced the Throttle Position sensor, then the AIC (air intake control) valve and finally the EGR and it fixed it.

I then did a full tune up on it and replaced the plugs, wires, fuel filter, air filter, o2 Sensor and the oil sender (gauge is screwy).



Then a few weeks ago it starting "popping" bad.......kind of a back fire but from under the hood, not the exhaust and it sound like it's "popping". I did some checking and it pointed towards the MAP sensor, so I replaced it. I also was going to replace the ESC (electronics spark control) module but they didn't have the right one in stock, but I had unplugged it and then put it back in. It fixed the problem. Now two days ago the "popping" has come back.

The popping only does it in 3 and 4th gear (700r) and in third gear it only does it if I exceed 2000rpm or when the engine is under load (slight inclines etc). It only does it when it warms up and it does NOT do it in park (can rev the motor right up and nothing happens)

The other day I was coming up a really big hill and it was guttless as all can be but the problem didn't appear back until a day or so after that.

I have a ESC module coming for it. Someone said it could be a fuel pump, but I don't know how to test that. I was also told it could be a loose timing chain, but I would think that it would do that in any gear and all the time.

Thoughts ?

Thanks for any help you can give with this.

[HILROD]

You can check the fuel pressure with a gauge. If it's like the tbi pickups you'll need an adapter that goes inline in the pressure fuel line. Does it show any other codes? If it has a lot of miles the timing chain will be loose. Just about all older smallblocks have a plastic upper timing gear that will let timing flutuate or will fail without much warning.

[Serpa69]

I did not see a cap and rotor in your tune up parts. The exact same thing happend to me. I changed the cap and rotor completely fixed the problem

[David Pozzi]

Is it actually popping back into the air cleaner? Or is it just missing?
Missing is probably ignition related like a bad ignition coil or pickup coil.

Popping into the intake under load can be due to retarded ignition. Check the mechanical advance, it likes to freeze up due to corrosion.

My motorhome had the ign timing retarded by over 20 degrees and would pop under load. Someone set the timing without disconnecting the brown lead that puts the computer in base timing mode.
David