Bugly87

1987 corvette coupe. My corvette has what sounds like a octane knock..it is different then other knocks that I have heard as in that it is more of a squeaky chirpy knock. It gets worse as you accelerate. No knock at idle. Plugs, cap, wires, and rotor were changed last week. I always Use Premium fuel and have used Chevron Techron in the past. The knock seems to be audible more on the drivers side of the engine. Is this a combustion knock..and what else can I do to try to correct this issue. The car runs fine otherwise.

Thanks again for any suggestions

Kevin

ladystoy69

exhaust leak? if it were a true knock your ecm would be retarding that timing and you should be able to tell that in its running(power output) or lack of.

Cliff Harris

Tighten the exhaust manifold bolts, especially the ones on #7 and #8... ;-)

John A. Marker

Tighten the exhaust manifold bolts.

Cap'n Rich

Squeaky chirpy knock? Check the belt tensioner pulley.

aklim

Check the scanner for knock counts on a scanner.

Dump oil and put the thickest crap you can find in it. If the knocking goes away, you might have an engine issue.

383vett

Check the timing.

bob guzzy

The belt tensioner on my car was banging against the stop causing a racket it was so bad it was retarding the timing.

Check to see how close the stop is and stick something between the stop and the arm see if your knock go's away. amazon had a new tensioner for under 40 bucks.

Bugly87

Thanks for all of the replies. I checked the exhaust lots and 5 of 6 were loose on the drivers side. I was able to tighten them by hand..got them nice and tight and no more chirpy knock. Thanks for the help..now on to my hot start problem. Will the CTS always throw a code when bad? My next thing to check

Kevin

DinoBob

INSANE. I happened across this and the chirpiness caught my attention. I have had what I thought was a manifold gasket leak since I got the '86. Only heard it under hard acceleration. I figured I would handle it come winter. After reading this I ran out and pulled the torque wrench and clawfoot sockets out of the drawer. Sure enough, my #7 and 8 bolts were so loose I could not even get ratcheting action on the click wrench. I got them snugged down to 20# and will be heading out for a test drive shortly. The Forum Saves!

DinoBob

Yeah, the exhaust noise = gone. Super job guys. Thank you!

Cliff Harris

Mine only made the noise under load. I really heard it going up a hill. My Corvette club had a dyno day so I figured that's the perfect place to put the car under load and check out the noise. The owner found the noise with a piece of rubber hose. One of the bolts on #7 was sticking out about 3/8". I don't know if it could have fallen out, but I think that was close... The bolts on #8 were loose also. I thought it was weird that it was only the rear cylinders on both sides. All the other bolts were tight.

bob guzzy

Years ago big block chryslers used to do the same thing it was common to find bolts missing or finger tight, on the 383 and 440's