Join Date: Mar 2002
Location: Austin, TX, USA
Re: no idea what is wrong
The popping could be a lean condition or it could be an ignition timing problem. I can imagine a degraded spark at high engine speeds due to a bad coil, bad reluctor, module etc. Ignition problems often show their ugly head on a loaded motor that otherwise would run fine.
I can also imagine a vacuum leak causing this. Does this car have a MAF? If so, is the MAF mounted on the throttle body or is there a length of ducting between the MAF and the throttle body? Look in those places for a leak.
Does the car loose power when it pops? Could a bad diverter valve be pumping air into the cat or exhaust manifolds at high engine speeds? If so, it could explain exhaust backfire at least. Also, it probably would lead to a very hot cat / O2 sensor.
Did you experience the backfire on the dyno?
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI