Please help. I have a 1976 Silverado with a 1968 Chevy 427.
The previous owner reported that the engine had been refurbished with a mild cam, high compression heads, Holley 750 cfm Double Pumper, and HEI ignition.
The truck doesn't get driven very often, but the last few times that it was used drivability got progressively worse.
I mistakingly concentrated on the carburetor since my exhaust exhibited symptoms of an overly rich mixture. I was able to get the idle smooth but suffered from the effects of too lean a mixture.
I moved to checking the ignition system and found the spark at the plugs to be visually weak, just barely noticeable. During these cranking evolutions I used another vehicle's battery in parallel with the truck to keep voltage up.
The battery (Duralast Gold,less than six months old), at rest, reads 12.5 to 12.7 volts. While cranking, voltage drops to 11 volts. The voltage at the distributor feed reads 10.5 volts during cranking.
Coil checks done: .7 to 1.O ohms (tach terminal to battery terminal on distributor cap);
tach to distributor center terminal infinite ohms; ground terminal to distributor center terminal (coil in cap) 12.5 k ohms, (coil removed from cap) 8.7 k ohms. This coil is relatively new, one year or less.
New pick up coil and ignition module.
No. 1 TDC verified with a compression gauge and physically checked with a screw driver through spark plug opening.
All plug wires checked with shortest wire reading 6k ohms and longest at 9.1 k ohms. Spark plugs, R43XLS, are gapped at .045 inches.
Start circuit wires checked, grounds cleaned, and suspect power wires under the hood repaired.
On subsequent try with another vehicle's battery in parallel, a couple of distributor adjustments, disengaging the truck's battery lead to distributor primary and running a jumper from assist vehicle to distributor battery terminal (maintaining 12.5 volts during cranking) I was able find a spot that gave a nice bright spark pattern from no. 1 plug that was out of it bore and against a ground point.
I installed the plug and tried again to no avail. Pulled no. 1 and 3, set against ground points and tried again for sparks with none present. Can anyone suggest where I'm going wrong or what I'm over looking. Any help will be most appreciated.
The previous owner reported that the engine had been refurbished with a mild cam, high compression heads, Holley 750 cfm Double Pumper, and HEI ignition.
The truck doesn't get driven very often, but the last few times that it was used drivability got progressively worse.
I mistakingly concentrated on the carburetor since my exhaust exhibited symptoms of an overly rich mixture. I was able to get the idle smooth but suffered from the effects of too lean a mixture.
I moved to checking the ignition system and found the spark at the plugs to be visually weak, just barely noticeable. During these cranking evolutions I used another vehicle's battery in parallel with the truck to keep voltage up.
The battery (Duralast Gold,less than six months old), at rest, reads 12.5 to 12.7 volts. While cranking, voltage drops to 11 volts. The voltage at the distributor feed reads 10.5 volts during cranking.
Coil checks done: .7 to 1.O ohms (tach terminal to battery terminal on distributor cap);
tach to distributor center terminal infinite ohms; ground terminal to distributor center terminal (coil in cap) 12.5 k ohms, (coil removed from cap) 8.7 k ohms. This coil is relatively new, one year or less.
New pick up coil and ignition module.
No. 1 TDC verified with a compression gauge and physically checked with a screw driver through spark plug opening.
All plug wires checked with shortest wire reading 6k ohms and longest at 9.1 k ohms. Spark plugs, R43XLS, are gapped at .045 inches.
Start circuit wires checked, grounds cleaned, and suspect power wires under the hood repaired.
On subsequent try with another vehicle's battery in parallel, a couple of distributor adjustments, disengaging the truck's battery lead to distributor primary and running a jumper from assist vehicle to distributor battery terminal (maintaining 12.5 volts during cranking) I was able find a spot that gave a nice bright spark pattern from no. 1 plug that was out of it bore and against a ground point.
I installed the plug and tried again to no avail. Pulled no. 1 and 3, set against ground points and tried again for sparks with none present. Can anyone suggest where I'm going wrong or what I'm over looking. Any help will be most appreciated.