Iceman0502

Okay lets see if I can stump you guys.

First I'll give some background. I had a 91 Z28 with a 350 TPI and automatic tranny, which was in an accident and bent the body of the car, turning it into scrap metal. So I went out and bought 89 RS with a barely running V6 but a great body.

Now I had a 4 year project. I basically made a Z28 clone in a RS body, transfering all the components over. Engine, harnesses, interior, etc. and even threw in a T-56 tranny while I was doing it.

Now here is my problem. The car is finally at a point where it is working better and the tuning has taken place but the car bogges down when driven in the low rpms. My mechanic I hooked up his new ultimate scanner to the computer and found out that the knock retard timming is jumping up almost 20 degrees when the car is given gas. So pretty much when the accelerator is depressed, the car has major hesitation until it starts getting some speed and the rpms hit around 2500 and then its fime. It feels like a missfire, that gets so much better when the rpms are higher.

So here is we changed so far.
Plugs and wires were change and boot insulators were added to eliminate any burnt wires.
We thought it had symptoms of Cats. So the new ones were replaced for some new ones. (you read correctly) - No change
Then we figured the pickup in the distributor. So a new distributor cap, rotor, coil, and ignition module were installed.
Then the ECM was replaced for a remanufactured one, we kept the same PROM. - Nothing

Now here is the funny part when the scanner is hooked up. When you look at the knock sensor, the readings cycle through the 0 up to 250, very quickly and then returns to 0 and back up to 250. It never stops. Also when you hit the gas to rev the engine the Knock Retard Timing jumps up to 20 degrees. This happens when the knock sensor is disconnected as well.

So we started trouble shooting from the manual. There should be between 1.5 and 3.5 volts at the pin on the ECM - we got 2.2 volts.
The resistance at the knock sensor should be between 3300 and 4500 - We got 3900.
Should be 5 volts at the connector terminal - we got 4.9 volts.
We even checked for continuity from the pin on the ECM to the connector terminal and we were good.

Does anyone have any ideas on what it might be or have they had the same situation before.

I just want to drive my car again while the weather is nice. It been out at his shop for 3 weeks now and this is really starting to get me mad.

I appreciate any feedback.

Atilla the Fun

I can give you some proven band aids, if not the answer you want. If it's pulling timimg for no good reason, undo the sensor from the block, wrap the threads in teflon tape, and reinstall as loose as possible. This will make it a lot less sensitive. It could be the sensor is damaged internally and is over sensitive anyway, plus GM has made them with identical-looking knock sensors having different sensitivities for different engines. I haven't ever had reason to try this, but try a LB9 sensor, an LG4 sensor, et cetera, from GM, not from AutoZone. Each application should have a different part number, though maybe all 305s use one PN while all 350s used another, This would make sense, but again, I never researched it.