454 backfire (pops) in exhaust

[grewvin1]

1987 454 new points set dwell, timing,cap, rotor and plugs. Tried new coil. Get it up to 2200rpm under load and pops in exhaust no power. Timing light can see variance in light will float from 8 to 10 degrees.

 

[Scott Danforth]

its not the coil - it almost is never the coil

poping in the exhaust is most likely really late timing.

poping in the intake is advanced timing or running lean

are you sure you set the timing to 8 degrees BTDC and not 8 ATDC?

also, you may need to verify the outer ring of the damper hasnt moved. pick up a cylinder stop tool. rotate engine manual until #1 cylinder stops against tool and mark damper at 0 degree timing mark. rotate engine backwards until #1 cylinder stops again and mark the damper at 0 degree timing mark. directly between these two marks is TDC. if your balancer has not moved, this middle mark will be on the scribed line. if it has moved, buy a new damper.

 

[grewvin1]

Yes sure timing is 8deg. BTDC but light will fluctuate between 8 & 10 in a constant rate like a dead miss. Wondering if sticky valve or such?

 

[alldodge]

Double check your firing order 1,8,4,3,6,5,7,2 and if correct, do a compression test

 

[harleyman1975]

Agree check compression My initial thought is burned exhaust valve. or possible blown head gasket between cylinders cross firing.