Knocking 87
Burning Brakes
Joined: Jul 2002
Posts: 871
Likes: 0
From: Costa Mesa CA
Re: Knocking 87 (imavettegirl)
I have an '87 with some engine work. I took out the thermo (I live in CA. You might not wanna do that in other states). My car runs between 140F and 160F on the freeway at night. The 200F fan switch kicks on at that temp and off at 180F. Stock initial timing is at 6 degrees BTDC. I run 8 degrees. Knock sensor is new and the same O2 since '87, I think. Looks that way.
Even with all my porting it doesn't knock although I know for a fact it needs more F.P. I have the new reg but haven't installed as yet.
Just a little background but really, any good shop can scan and see why you are pinging. Lots can go wrong and not set a code. I have the EGR removed and the pipe blocked. Still no codes.
BIG JIM
Even with all my porting it doesn't knock although I know for a fact it needs more F.P. I have the new reg but haven't installed as yet.
Just a little background but really, any good shop can scan and see why you are pinging. Lots can go wrong and not set a code. I have the EGR removed and the pipe blocked. Still no codes.
BIG JIM
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Knocking 87 (imavettegirl)
Welcome to the Forum.
Indeed your mechanic is correct in that the ECM tests the knock sensor and so should detect a bad knock sensor; however it ain't foolproof.
Plug a portable scan tool into the ALDL connector and drive the car; when knock/ping occurs the ECM will pull as much timing it can to stop it, if it "hears" the knock. This will show up on the scanner as knock counts and degrees of knock retard (I've seen knock retart on my scanner but never heard ping or knock as the ECM pulls timing before my ear can detect it).
If your ECM isn't pulling timing or doesn't hear the knock, upgrade the ESC module (see my site) and replace the knock sensor, as described. Then recheck it with a scan tool hooked up while driving it.
You might also install a 160 deg theremostat & fan switch. I get emissions checked in OH where they use a dyno and sniffer and with this setup my L98 easily passes.
Also check the TPS voltage at idle; it should read around .6-.7 Vdc.
Indeed your mechanic is correct in that the ECM tests the knock sensor and so should detect a bad knock sensor; however it ain't foolproof.
Plug a portable scan tool into the ALDL connector and drive the car; when knock/ping occurs the ECM will pull as much timing it can to stop it, if it "hears" the knock. This will show up on the scanner as knock counts and degrees of knock retard (I've seen knock retart on my scanner but never heard ping or knock as the ECM pulls timing before my ear can detect it).
If your ECM isn't pulling timing or doesn't hear the knock, upgrade the ESC module (see my site) and replace the knock sensor, as described. Then recheck it with a scan tool hooked up while driving it.
You might also install a 160 deg theremostat & fan switch. I get emissions checked in OH where they use a dyno and sniffer and with this setup my L98 easily passes.
Also check the TPS voltage at idle; it should read around .6-.7 Vdc.
Burning Brakes
Joined: Feb 2000
Posts: 927
Likes: 0
From: Saginaw TX
Re: Knocking 87 (imavettegirl)
Welcome to the world of Corvette information....My 86 auto had the same problem. Changed everything but the ESC module with no improvement. I did find the catalytic converter was definitely not right and probably the precats. When I pulled the engine down it had a lot of carbon buildup in the cylinders. You might have your converter checked for flow. All other suggestions are good also. If you change the knock sensor, just be prepared cause it screws into the water jacket and it will leak (gush) coolant. Good Luck
Racer
Joined: Feb 2003
Posts: 415
Likes: 0
From: Joppa Md
Re: Knocking 87 (mash557)
When I pulled the engine down it had a lot of carbon buildup in the cylinders. You might have your converter checked for flow.
Carbon buildup on your valves will make your engine ping. :thumbs:
