Questions and Answers
Two Dead Holes
Q. My daughter got the 454 in her 1 ton Chevy rebuilt less than 50,000 miles ago. She has run Valvoline semisynthetic in it since the build. Runs rough. Lousy gas mileage. #3 and 8 produce no change when you pull the wire off the plug.
Replaced plugs, wires, distributor cap and rotor. No Change.
Swapped carbonators. No Change.
Took rocker covers off and observed as far as I could tell that all valves move the same amount.
Did compression check. All holes 100 pounds +- 3 pounds.
Checked wires had correct firing order. They are correct.
Put vacuum gauge on intake manifold. Smooth -- no fluttering.????????????????????????????????????
KirkA. 100 pounds of compression is kind of low in a rebuilt 454. I would expect to see about, at least, 160 to 180 pounds of compression. Perhaps your compression gauge is off? Readings like this would make me diagnose the engine as weak.
The first two things I would check are the fuel mixture and Exhaust Gas Recirculation (EGR) valve. If there were valve problems, it would show up in the compression test and on the vacuum gauge. I would take it to a shop that has a four-gas emission analyzer and make sure the fuel mixture is correct. I would also try blocking off the EGR valve temporarily and see if that makes a difference. Although the EGR would tend to suppress the whole engine, I have seen it effect individual cylinders.
