I am have a 77 302 and its kinda missfireing? It is not bad, it does it all the time, (not constant so I know its not a valve) it does it at random and depending on my rpm's. It sounds like a small pop, and if I rev it up it gets louder but not as often.I have a small exhaust leak, but it is not big enough to cause my problem.... I bought the truck in september and it sat for 2 months befor I drove her home, I started her up and had to adjust the timing because it was way off and I had a 4 hr drive to my house. So I got her running good (set timing by ear) and drove her up, made it half way and found out the gas guage was stuck and I ran out of gas (sat in the cold for hours trying to figure out what was wrong... Put some gas in the carb and vvrroom... Got home ok. Week after that I replaced the spark plugs and wires, also the cap and rotor. It ran fine untill one day I started her up and she started missfireing really bad, I found out that I had a bad EGR valve, so I took it off and blocked it off and she ran much beter but still not the same. I wanted to do an upgrade and (stupidly) did not fix my problem befor I put in a Power+Plus Intake without EGR, I useto have EGR would I have to adjust anything to make up for it or will I just get bad emitions?and Edelbrock 600cfm carb, I got her running as best as a beguiner could, and tryed fixing smaller things like the E-break and steering stuff while I didnt want to mess with the engine because I was geting frusterated.... I again started on working with it, got a vacuum guage and everything needed, and got her running almost perfect, set the mixture perfect timed the engine with a light got it set perfect, and then when I went to take out the spark plugs to see what they looked like one of my plug wires broke! I was ****** so I grabbed an old wire and put it on so I could still start the engine to work on it. my #6 cylender was black with carbon'y suit like stuff and all of my others looked the same. So I am thinking that is the cylender that is missfireing, I am again going to replace the plugs and wires with better ones, and replace me cap and rotor again and this time I am going with brass, last time I did not know the difference so I just put the same aluminum one on that it had. I was almost going to replace the distibutor, but I ran out of money and have to wait untill I get payed next. Does anyone know what this problem could be? Does anyone else out there have a 77 302 that has had this problem or hasnt had this problem?

 

When you save enough for a compression tester, get one with the hose as opposed to the type you just hold in the spark plug hole. That way, if you do find one cylinder is down on compression, you can take the schraeder valve out of it and adapt it to your air compressor to do a leakage test to find out where the compression is going. Just did the same thing with a truck I bought for parts. Wasn't running but I could tell by the way it turned over that one cylinder didn't have compression. Thought it was probably a burnt valve. Wasn't too worried about it as I didn't buy it for the engine anyway. After figuring out which cylinder was bad I pulled off that valve cover and found a bent pushrod that wasn't opening the intake valve. Cheap fix! Turns out the parts truck is in better shape than my driver and with some TLC it will be.