My friends 90 IROC L98 has some serious issues! He has replaced the distributor,cap,rotor,wires,etc. No luck. It does have chip in it....Hypertech I think. He also has an SLP cam..not sure which one. The car is just doggy as hell. The timing just moves up and down at idle. Nobody can figure it out. I know ZERO about GM's so I thought I'd ask in here. He is getting sick of the car. Has all new motor and has not been able to get it running right yet this summer..now it is all over!

 

Has he replaced/checked the knock sensor?

 

He did that as one of the 1st things he replaced.

 

Is the timing being checked with the ECM wire connected?

 

Don't think so..I'll have to ask..

 

Check this out........my experience was @ idle my timing mark was jumping all over the place and I checked everything but ONE THING!!!!!! seperated my plug wires with a good set of looms and the mark went back to normal. It was just that simple.



Brian

 

The '7730 ECM used in '90-'92 cars uses timing to control idle speed along with the IAC motor. Timing can move as much as + or - 10 degrees to control idle speed. I wasted alot of time checking for problems before I learned that this is normal for these cars.

Regards,
Gary Anderson

 

What about the idle speed? Is it steady, or does the tach "flutter" up and down a bit?

I'm in a situation right now with my 2.8 V6 where, whenever I put a timing light on it, the timing mark jumps randomly all over the place for each rotation, making it nearly impossible to set the timing exactly. The best I could do was to "average" in the middle of the many places where the mark appeared, between the extremes.

In my case, it's likely due to a stretched timing-chain. If he's got a high-mileage engine, that might be a possiblilty.

But definately have the timing (tan/black) wire disconnected before trying to set the base timing...

 

try checking or best if high miles are on it to pull the didt out and replace the pickup coil my 92 z28 with a vortech supercharger acted up the car never responed to timing i went to o'reilly auto parts and bought a new dist for about 130.00 and it fixed it the pickup coil in the dist was erattic and the shaft had some play in it

 

He already put a new distributor in it. I'll have to talk to him...