cplonner

When i bring the car up in the high rpms i can hear detonation.
Now i know things like lean fuel mixture, timing being off, hot plugs, can cause this.
I can hear it when the temp is at about 190-200. I had the timming set recently.
How do I figure out what is causeing it?

conv90

Year?
have you a scanner (datamaster or similar) to confirm the detonation?
-Beppe-

CFI-EFI

In NEUTRAL??? It shouldn't knock at all if it isn't under load. Usually an engine will be most prone to knock, ping, detonate, when it is lugged at lower rpms or in the mid range, under heavy loads, again, at WOT. Your ESC should prevent you from actually hearing the knock and retard the timing to stop the knock IT hears before you do. Are you sure what you are hearing is detonation?

RACE ON!!!

cplonner

Sorry I usually dont forget to put my year! 86'. I dont have a scanner but it sure sounds like detonation. Its was even doing it when i got it dynoed, you could hear it really good then. Even the guy running the dyno said so.
I have a high compression right now its like 10. to 1
vortec heads, 24lb injectors, intake big tube runners and ported base.
full exhuast headers back.
Cam is 210/214 duration and .474/.474 (comp cam)
car seems like its not making the power it should, 220hp 280tq with all this garbage done to it.
Somtimes i have really nice power and somtimes its like it was when it was stock.
I hear the det when the engine is under load.

CFI-EFI

That compression isn't really all that high, even with iron heads and that mild camshaft. Are there any codes set? If you can beg, borrow, or steal a scanner to confirm knock counts and/or timing retard, it may end up being quite revealing.

RACE ON!!!

cplonner

yeah it looks like thats what im gonna hve to do. steal or.....steal a scanner
How detrimental can detonation be to an engine? I know its bad but how bad?

CFI-EFI

Other than burn holes in the tops of pistons and melt valves...not too bad. I forgot to mention bearing damage, too.

You didn't say if you had any codes set.

RACE ON!!!

bjankuski

Your knock sensor circuit may not be working and it may not set an codes. On the 1986 Vette the system checks for errors by advancing the way past where it should be and then listens for knock, if no knock is detected the check engine light will be set. The only time it does this check is when the engine is started when the water temperature is above 195 degrees and then floored for the first time after the start. If you have a low temperature thermostat and the water temp is not above 195 on the start-up then it will not run the test and it will not show a check engine light. I learned this procedure the hard way on my 1986 vette when I was having knock but my scanner was showing no knock. I could hear the pinging but my scanner showed zero knock counts. I then purchased a Howell manual (Best money I ever spent) and trouble shot my knock circuit and ended up having a bad knock module. I replaced the module and my scanner showed knock!!

dlmeyers

"Other than burn holes in the tops of pistons and melt valves...not too bad. I forgot to mention bearing damage, too."

Cylinder pressures can exceed 3 to 4 times the normal pressure. Profoundly hard on your engine. Your piston is trying to go up, and the gasses are trying to send it down. Not good.

I occasionally smoke a Dominican cigar, the ashtray is a piston with collapsed ring lands, scarred skirt, and the cylinder this slug cam out of required a .040 bore. The idiot owner (me) failed to do much about a slight ping on acceleration.

Let us know.

dlmeyers 90 coupe zf6 3 speed shocks

65Z01

Pull the stored codes; if there is no knock sensor code:
-the knock sensor is faulty
-the ESC is faulty
-wiring in the knock sensor circuit is faulty

What was the A/F ratio on the dyno pulls?
Did it drop from 14.7:1 to 12.6:1 when the operator went to WOT?

cplonner

I havent got any codes, the a/f ratio is at 13.5 at the higher rpms (3500-5000rpms)

MBDiagMan

Use a test light on the knock sensor circuit. You can disconnect the connector at the knock sensor and use a jumper to complete the circuit and to connect a test light. Ground the other end of the test light and with ignition on, rap the right side exhaust manifold with a medium size hammer and you should see momentary change in test light. If not, replace the knock sensor.

Good luck,

comp

test

cplonner

ill give it a shot, thanks