Gripenfelter

I have a very high knock count. It will roll over after 2 mins at idle. The numbers change so fast that its in the thousands within a couple of seconds.

This is what I've done so far:

Changed O2 sensors (they were old).
Running new NGK TR6 plugs.
New wires (burnt old set).
Drained gas and filled up from another station with the highest octane I could find.
Re-sealed Intake Manifold.
Changed the coil.
Disconnected the Accel ignition.

So it is not fuel related. My oil pressure is excellent. Exhaust smells fine...for an LE2 cam with no cats. It happens after the car goes into closed loop (5 mins idling).

The car will surge at idle and try to rev up to keep the car running. When I turn the car off, you hear a very fast metallic rattle for 1/4 of a second as if the timing is off or something.

While the car is in open loop, it sounds perfect.

This is a 93 so its not the MAF.

MAP sensor? Knock sensor?

My laptop's diagnostic software is corrupt so I can't scan it. I have an Auto X-ray as well which I have never used since I had the laptop.

Suggestions?

Dave '97 Z28 M6

If something is rattling, the vibrations could easily be picked by the knock sensor, and then interpretted by the PCM as knock.

Demus

That'd be the first thing I'd check for. Any exhaust parts rattling along the torque arm or something similar. Also, loud exhaust will cause false knock. I would see lots of false knock with open headers.

1racerdude

The pulse noise in the headers,capped up, will cause retard. Your RR's will cause it. Any noise that the sensor hasn't been tuned for will cause it.
Have it desensitized and put it on a switch with a resistor and use it normal on one side and shut it off on race night on the other side.
I have posted how to do it in the past so a search may turn up something ya can use.

Gripenfelter

Thanx, I'm familiar with how to wire in a switch. I read your post before on this subject.

I just want to rule out everything else first. I want to make sure this isn't a case of the timing being too advanced etc. The rattle when I shut off the car almost sounds like a timing issue.

I'm considering unplugging the KS for a bit because I can't figure out this problem. If that cures it, I'll desensitize the sensor.

http://members.shaw.ca/skin_industries/knock.gif

Zeueses 97 RamAir

Theres wires that run from your headers well right by your headers on the passenfer side if you have long tubes that side will get eaten up by heat

Gripenfelter

Which wires? O2 sensor? PCM? KS?

Zeueses 97 RamAir

Its running down the side firewall theres about 10 wires those run to your pcm including the knock sensor wire... You will see it its the closest one to your headers not the abs wire whicj is running down by your tire

Gripenfelter

If the knock sensor wire was severed, would that give me a rolling knock count? Some how I don't see that happening. Maybe a check engine light instead.

I know this is a sensor issue because I had this problem just before I did a complete rebuild on my motor. And its still there.

New opti as well btw.

I've looked under the car a thousand times and I can't find anything rubbing or rattling.

My only guess is that my true duals, which are very loud, are causing knock unless its a defective knock sensor.

I guess I'm wondering if there is anything in the motor that would cause the knock sensor to see thousands of knock counts per minute.

Injuneer

Are you getting any knock retard, or just the rapidly increasing knock count?

If the KS wire was defective, you would get a code/SES light and you would see almost constant knock retard since the PCM defaults to a table of knock retard reflecting engine operating conditions.

Is it possible you have a high voltage wire (e.g. - plug wire) running very close to and in parallel with the KS wire?

Have you checked for a loose motor mount on the passenger side of the engine, right next to the KS?

OBE1 95Z28

Run some 100 octane gas and see if your knock count changes. If the high octane eliminates your knock, you have true knock and need to correct the issue (timing, tuning, tune up). If the octane doesn't reduce your knock counts, chances are it's false knock to be corrected by replacing the knock sensor input with a resistor.

Gripenfelter

I was running 91 octane last time, switched to 92 octane Ethanol blend, currently running 94 octane Ethanol blend which is the highest octane I can find.

Each time I completely drained the tank. Car always shows 0.1 or 0.2 degree retard on the laptop last year with a continuously rolling knock count. I guess I could check with the Auto X-ray as well.

Injuneer: Good suggestion about the plug wire. I'll check it tonight.

Would a bad PCM do this? Somehow, I don't trust the last shop I was at. Found out afterwards that they mess up a lot of cars. They did exhaust work on my car. Maybe they fried the PCM somehow?

Injuneer

Did they do any welding on the exhaust? Did they disconnect the battery cable before they welded?

Gripenfelter

Yes they welded. And no I doubt they disconnected the battery. Which is why I mentioned it. I just don't know what kind of damage it could do to the PCM.

As soon as I left the shop I had surging at idle but thought it was cam surge because they installed an LE2 cam for me as well. Then it got worse to the point where it almost stalls.

93 PCMs are also harder to come by so I don't have anyone to swap PCMs with either.

Gripenfelter

Update: Disconnected the knock sensor. No effect. Car still tries to die.

It sounds normal at 1100 rpm and higher. When it drops down to 500 rpm (in park) it sounds like marbles in a can. If you rev it up it sounds fine.

Isn't not being able to maintain idle a symptom of a bad PCM?