popping exhaust

[87burb4x4]

My exhaust pops if I barely hit the gas and release it. Doesn't do it if I get into the throttle a little heavy. Truck has short tube headers singled into a cherry bomb muffler. 350 tbi is 100% stock and was rebuilt about 20k miles ago. I know valve issues can cause this but any other causes?

[bd]

Unburned fuel is entering the exhaust.  Might be running very slightly rich or the air injection system may not be responding properly.

[87burb4x4]

Ok, sounds reasonable. I do smell gas pretty heavily at times. This engine is becoming a nightmare. One thing after another. It was supposedly a crate engine from GM. Some people tell me it has a dead miss, but I don't feel/hear it. I have rebuilt the TBI, changed the EGR, vacuum line to EGR, and the EGR solenoid and I still get a code 32 which is EGR Circuit Fault. I posted about the truck running very sluggish a week or so ago. Timing was the main problem. Got it timed and it ran awesome. But my excitement got the best of me and now I realize it's still not 100%. It will now run 70 down the highway and hold it's own, but still a little weak getting there. And the exhaust sounds horrible, aside from the small leak that I cannot find. If it weren't my only vehicle at the moment, I would pull the engine and go through everything. But as it is, I need to go through every other option that I can to keep me from temporarily losing my only vehicle

[bd]

This site hosts a full set of GM factory manuals covering your truck that was graciously scanned and provided by one of our members, hatzie:

1987 Fuel, Drivability and Emissions Manual - a tremendous reference for troubleshooting the TBI system

1987 Service Manual

1987 Wiring Manual

1987 Unit Repair Manual

Clean fuel and fuel pressure (plugged filters) may be the greatest nemesis for TBI.  Generally, they are fairly trouble free and responsive.

Use the Drivability and Emissions manual to walk through code 32 diagnosis.  If you have a DVM check TPS function for a smooth voltage transition and base voltage setting - they have a tendency to be electrically noisy.  Verify MAP voltages - they can fall out of calibration w/o setting a code.  You can also check the injectors for fuel dribble, CTS calibration and air management valve function.

Still, it sounds like you already have most of the important kinks worked out... no?

[87burb4x4]

As far as I know, I've done everything I can do externally. I haven't checked the MAP sensor but the TPS is new. While changing the EGR stuff out, I found that someone had plugged the vacuum hose with a BB, thought that was for sure my problem. It did have a stopped up converter on it up until about a month ago. There was a good bit of carbon build up in the old EGR ports and the ports on the intake. You think the intake and heads could be gunked up from the stopped up converter and EGR not functioning for some time? If I go through the trouble of taking the intake and heads off, I have access to a good set of Vortec heads cheap. But I am not sure about what all is involved in swapping to Vortec other than having to change intakes

[roundhouse]

I doubt its the heads

You may want to install a wide band O2 sensor and gauge so you can see what's really happening with the engine

[78BIG-TEN]

pop is when rpm going up or when coming down

[87burb4x4]

Pop is when coming down. But only in park and at an idle. It has never popped when decelerating while coming to a stop sign etc, even if I downshift