Exhaust Popping Sound?

I have a 87 Bronco EFI 302 with aftermarket exhaust on (no cat with a glasspack) and whenever I fire it up and let it idle it makes a popping sound out the muffler. A buddy of mine thinks its the o2 sensor in the y-pipe. Any ideas?

You may have a miss in the engine, and the glasspack just makes it more noticeable. Check the plugs and wires. etc.

I did they all good.

Does it pop after its warmed up? or just when you first start it? cus if it only does it when its cold, you may have a small leak, and then when the engine and exhaust warm up, the pipe will expand and cloes the leak.

Assuming you don't have a miss due a bad plug or wire, two other things come to mind. The first is a vacuum leak, second is a cylinder with low compression, either due to worn rings or a bad valve. You can quickly check this with the paper/dollar bill method on the exhaust pipe. Place a sheet of paper or a dollar bill over the end of the pipe with the engine running. If the paper lays flat, no problems. If it jumps or sucks into the pipe, you have an engine problem. In the old days of glasspacks, we would run the motor really hard, like 120 mph or at the red line for a good while, to get the glasspacks red hot. Then, shoot a cold stream of water thru the exhaust. This would melt or destroy most of the glass beads inside the glasspack, resulting in a louder but smoother sound. Just be sure the engine is turned off if you try this, so you don't suck up any water into the motor by accident.

Thanks man I'll give that a try.

is it a light poping sound? like right after you rev and its winding back down? if so i have not herd of any good dual exahaust that did not do that. mine does it also when i downshift and i think it sounds awsome!

oh yeah, i have a transplanted 351wEFI and dual flowmaster 40's