Persistant knock on acceleration - no codes
Thread Starter
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Persistant knock on acceleration - no codes
My stock 86 knocks at near WOT or WOT. ECM is not throwing codes. I'm running 93 octane fuel. I have the base timing set at 4 deg BTC (at 6 it knocks worse). When I run 87 octane the knock is much worse. Any ideas folks?
ESC and knock sensor are not new. But I'm not getting any codes.
ESC and knock sensor are not new. But I'm not getting any codes.
Le Mans Master
Joined: May 2000
Posts: 5,159
Likes: 1
From: Indiana
Re: Persistant knock on acceleration - no codes (Mike263)
Believe it or not, my cat plugged and for some reason, caused a ping in my L98. Also, the TB coolant bypass seemed to have helped. It used to occasionally ping even with Sunoco 94 but now I can run 92 and maybe even less with no pinging if I leave the base timing at 6 degrees. I'd drop your catback and have a look in there.
Randy
Randy
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Persistant knock on acceleration - no codes (Mike263)
Had similar problem on my '86 (it drove me nuts), pinging during wot and under load (going up hill). I could hear the ping and the tech running the dyno refussed to continue because the car was pingning so bad. I bought an AutoXray to trouble shoot the problem, (I also had no codes). I checked to make sure system was operating properly. Knock sensor, ESC, all passed, trouble shooting book said replace ignition module, which I did, but still had knock, next was ECM, still had knock according to AutoXray, but I could not hear it any longer so I took car to a Corvette repair shop, they tested the car on the rack and test drive and said my car was not pinging and ran fine. I then called AutoXray to see if something was wrong with their equipment, the answer I got was that the AutoXray does not interface very well with 84-86 ECM's. I think replacing the ECM is what cured my car and at less than $90.00 at Kragen it was a bargin.
Burning Brakes
Joined: Feb 2000
Posts: 958
Likes: 1
From: SF Bay area, CA USA
Re: Persistant knock on acceleration - no codes (Mike263)
Check to see if your EGR valve is stuck open. I would also agree with the post that mentioned a clogged cat possibly being the cause.
Burning Brakes
Joined: Feb 2000
Posts: 927
Likes: 0
From: Saginaw TX
Re: Persistant knock on acceleration - no codes (Mike263)
I had the same problem and have replaced knock sensor, tps, ecm, coolant temp sensor, set timing correctly, checked wiring to ESC and even with 92 octane would still ping on hard acceleration. It had always had a rattle under the car at idle. Car is currently undergoing major mtce and I had the front Y and cat separated at the exhaust shop and the catalyst bricks in the cat were loose. I'm betting that this is what was causing the problem, but I also have a new EGR valve so may not ever know for sure, but I aim to get it fixed. Good Luck on yours.
