I disconnect the brown wire and set the timing to 6 BTDC, right? I'm a little confused. The ecm sets it to 6 degrees so should I set it to 0 after I disconnect the wire or to 6 degrees? I set it to 6 and got some spark knock running 93 octane. I backed it to 4 BTDC and it's a little better. I still have a little ping at WOT but the car does have over 130K. So am I actually setting it at 10 degrees when the light says it's 4 BTDC?

 

If you set the timing to 6* BTDC with the brown ESC wire disconnected, then when the car is running the ESC/ecm advances the timing according to a table depending on rpm and throttle position. If the knock sensor detects knock it takes timing out, then re-advances till it gets to where it wants to be or hears knock again. Disconnecting the ESC wire is like removing and plugging the vacuum line on a vacuum advance distributor.

If you get knock at 6*, but not at 4* then I would set the timing at 4* assuming everything else is in a good state of tune. I didn't do a very good explaining the advance I am afraid...but it's the best I can do this late at night.

Good luck

Bob

 

Hmmm..... ya shouldn't truly be getting knock like that. What does the decal say your timing should be? I take my wire off, time it to where I feel the most power(8* with my setup) and plug back in. When I did have a problem it turned out to be a weak magnet in the pick up coil assembly. I couldn't time it had my life depended on it. It was throwing the time off all over the place. The computer would throw 40* of timing at the motor and I would disconnect the wire, and it would die.
There is something else going on in your motor. Need more slueth work.

 

First, you *might want to try using 89 octane gas the next time you fill up for experimentation purposes only. Since you said that you still have spark knock, I am under the assumption that you know what it sounds like and have a good ear. By running one tank of lower octane gasoline, you are merely going to be testing the knock retard circuit of the ECM/ESC module. Sometimes, there is not enough knock for a lazy sensor with a high grade of gas. A sensor can go bad if it has been tightened down too much.

Next, you might want to start scoping out other problem areas:

You could have a lot of carbon buildup in the heads/top of the pistons. This could effectively raise your compression ratio (you mentioned over 100,000 miles). There have been posts on how to use GM Top Engine Cleaner products (and others like SeaFoam).

Your EGR system may be malfunctioning. It is a PITA to get to, but valves can and do stick after time. There is also a solenoid and a temp sensor. Just because you don't get a code doesn't mean that your system is working correctly.

Your cat could be clogged. Give it a laxative :eek:

Your engine will only run as well as the sensors that feed the ECM. If you have a bad sensor input, you will have bad ECM outputs. The first sensor that comes to mind in a knocking situation like this is the ECT (engine coolant temp) sensor, which is on the front of the lower manifold, under the throttle body, next to the cold start switch. Note that this sensor directly feeds the ECM and does NOT feed the dash readout...that is a sensor in the head.

Your MAF sensor or burnoff/power relays (behind the battery) could be going south. A tap test on the MAF (rap it slightly with the handle of a screwdriver when running and note for RPM change). If the ECM is seeing the incorrect amount of air input d/t a bad MAF, then it could be using the wrong output values for fuel.

Also, an O2 sensor could be to blame. Yours has a non-heated one, which is generally replaced every 45,000 miles.

Something simple like incorrectly gapped or dirty plugs or even a dirty air filter.

Hopefully you won't have to check all of these things, but they are something to keep in mind if the problem worsens! Good luck, -Matt-

 

I'll try the 89 octane with the next fill up. I have a new EGR valve in but have disabled it. It would never open properly. I had a long post experience with it a few months ago. Anyway, no codes, I relocated the temp switch to the exhaust pipe and now use an AIR eliminator bracket also.

I'll look into the top engine cleaner, but when I had the intake off it appeared clean, or atleast no large amounts of carbon build up.

It still has a Cat on it. How can you tell if it's clogged? When you say cleaner you mean eliminator I"m guess. Not a problem for me, I was thinking of that anyway.

The ECT sensor was replaced last week when I broke the old one. I don't think that is the problem.

I'll try the tap test with the MAF, but it runs and idles well. No code 34 since I changed the starter to eliminate a dragging start problem.

New AC delco plugs and filter within 2k miles. Actually runs a little better since then and the old plugs had normal wear and coloration.

Now, about the O2 sensor. It's probably got the one that came on it. I've got a snap-on diagnostic scanner. What should the 02 readings be? Is there a value to look for? Should I just replace it and see what happens?

Oh, about the octane and the knock sensor. Where is this sensor you think is maybe lazy or been tightened down too much? Any info on that would be cool.

Otherwize the car is starting and running good. It was at zero before I moved it to 4 BTDC so I'm already seeing some performance gains. Any more help is always appreciated.
Thanks,

 

I can not say this from personnal experience because I never tuned my 85's chip when I eliminated the EGR valve, but I have read posts by some pretty knowledgeable guys about the spark tables needing to be changed if EGR is omitted. Think about it like this...the EGR can 'recycle' and add up to 15% of exhaust directly into the plunum air. This alone might cause problems. Do you know if it ever ran without pinging once the EGR valve was replaced?

There are a couple of ways that you can test exhaust backpressue, which can tell you if your cat is clogged. One uses an AIR pipe orientation and another is to use a manometer at the tailpipes. Or, you can run a straight pipe for a while. Problem is, I think on the 86, the cat is not a complete bolt-up like on the 85. It makes it a little tougher to check.

O2 readings on a scanner should show (at idle and normal driving) all kinds of readings between 200 and 800 mV. This is called transitioning about 450mV, which is required because the O2 sensor we have on our cars is cheap (like all the other ones for the most part) and it can only accuratly read one value, which is 14.7:1 AFR. If you have a value called crosscounts or O2 transitions, this number should vary a bunch. I think it resets at some magic number (128 or 256) and then counts up again. A lazy O2 sensor is best tested with a scope, so by the time you hook it up (or have to pay someone to do it), it is almost cheaper to pop a new one in :yesnod: A lazy sensor will not swing or will actually just give more of a DC feed than an AC feed (from what I can remember...this was about a year and a half ago that I scoped a couple different styles).

Knock sensor is passenger side block, about the size of one and a half oreo cookies stacked. Usually has a blue wire. Has to be gotten to from the underside of the car because your manifold will be blocking it. Maybe the wire came off when you did the starter??? This would often set a code 43 though. If it is tightened too much, the housing will spin on the inner body and the sensor won't properly do it's job.

I forgot to mention this...your balancer could have slipped and your mark may no longer be accurate. Also, put the inductive pickup on #6 spark plug wire and check to make sure it shows the same reading on the balancer when checking timing (since 6 and 1 fire 4 apart from each other, it will work ;) ). Good plug wires? -Matt-

 

I'm reading all this and thinking...

I have seen a few 383's that had to bypass the EST function by wiring a resistor in place of the knock sensor or they would get to about 3500-4000 RPM and start running like crap ( blow out black smoke from spark retard and limp home from the EST knock sensor signal ).

My car does it a little at WOT and hi rpm's, I have backed my timing to about 4º ( who knows if that is even right since I have the original balancer with 109K miles...could have slipped a little ). I am thinking about disconnecting it.

I do have my EGR and all stock emissions equipment working ( except for the abscense of a cat ). One thought I had was, since I have that many miles, everything in the motor is loose...I mean from AC compressor bearings to idler to water pump ( which does make a little noise ). I know some engine noises are from stuff other than spark knock...and I think that's triggering the EST crap.

 

Just to elaborate on some of what has already been mentioned. You said the engine "knocks". Do you hear the engine rattling? Or are you observing knock counts on your scanner? If the EST system is working properly, you should HEAR little or nothing. Although I never heard any knocks, my high milage '84 was throwing knock counts on a scanner. I put the highest octane gas available in it and retarded the spark to zero. I still got counts, just revving it in neutral. I haven't isolated it yet, but something else under the hood is triggering my I knock sensor. I disconnected the sensor, and now, rely on my ear. I am currently running 14 degrees advance on 85 octane gasoline. I DOES rattle a little lugging under a heavy load, but it is quiet at WOT. I just don't let it lug. Maybe this helps? It's at least an angle to consider. Good luck.

 

There are 2 causes or effects of this.

The first cause is a 'loose' valvetrain that is usually due to someone wanting more RPMs out of the engine. The additional valve noise and or looser piston in bore clearances that some racers use to speed up engine breakin can be enough to fool the rather prudly tuned KS on our cars (GM appears to have come out with a better setup for the LS1's and can now pull spark out of only the offending cyl if it so desires). This will of course trigger the knock and retard the timing, thus sending a plume of unburned junk outta the tailpipe. Here, the person usually disconnects the sensor and uses an appropriaely sized resistor to fool the ECM when it does self-diagnosis routines.

The other case (as was mine when I removed the sensor from one engine block and put it into the one that I had now) is that the sensor or ESC module is toast. When I took mine out, it was siezed to the point where the inner housing spun and then it was rendered useless. When I hooked it up, the ECM did the timing advance at 194 degrees F and since the sensor was a bum sensor, the ECM went into limp home mode. The ECM expects to see the KS activate and when it doesn't, the system sports a code 43. This method would always give me a code 43 and flip me into limp home mode, which is terrible if you have any kind of cam different than stock. -M-