1986 Chevy Corvette engine knocking

RICK.BASS

MEMBER
1986 CHEVROLET CORVETTE
V8
2WD
AUTOMATIC
90,000 MILES

I have purchased an 86 corvette to restore so the car is new to me. It has platinum spark plugs that I'm not sure should be in it, it has all new cap rotor and coil. I live in Salt Lake City an elevation of 4,500 feet. I have set the timing at factory specs 6 degrees BTC and I get engine knock when accelerating and when the car is under even a small load. I set the timeing to 8 BTC and still knocks, I set the timing to 10 BTC and still knocks but runs like crazy. I generally have set the timing of my cars starting at facrory specs and adding 1 degree for every thousand feet above sea level. So I would normally set my Vette at 6 + 4.5 a totlal of 10.5 BTC. Not sure if I have a bad Knock sensor or the wrong plugs etc. I get a little less knock at the 6 BTC setting but the better performance at 10 BTC. Can you lend a hand on what I might do to correct the engine knock?

1 Reply

ERNEST CLARK

MECHANIC
1,730 POSTS

I'm assuming you have the 5.7 TPI motor. (Big difference) If so, check your MAP and Mass Air Flow sensors.

You can also have a malfunctioning knock sensor. If the sound you are hearing is indeed a "Knock", then your sensor should retard the timing.

Also, if your engine is knocking, then advancing the timing is the ABSOLUTE wrong thing to do. You will quickly blow a hole in the piston, break a ring, valve or even spin a rod bearing.

Are you using high-octane fuel? If not, try that. If it works, then you probably have excessive carbon build up in the combustion chambers. And also try using plugs that are manufacturer recommended.

If you need to to drive your vehicle now, then manually retard the timing until you locate your problem.