I just finished overhauling the distributor on my '90 IROC 350, and I put a new ignition control module and pickup coil in it. The ignition system has been replaced from plug to distributor. I set the timing with the ESC bypassed to 8 degrees BTDC, and the white mark on the balancer didn't move at all under the strobe light. However, when I hooked the ESC back up after I shut the car off, I rechecked the timing and I find that it is real erratic, hovering all over the place between about 14 and 20 something DBTDC. The car still has the same rough idle and jumping tach symptoms. No codes. I've been through alot on this beast. My question is, what would make the electric spark timing so erratic? More specifically...what are the sensor inputs to the ignition control module because it did this before with the old pickup coil and module, so the new ones are likely OK. I'm thinking knock sensor, but your input is appreciated. Thanks guys!

 

Jethro,

Try unplugging the knock sensor and installing a resistor to ground in place of the sensor. Try about a 5K ohm resistor. You can restart the engine to see if the knock sensor may have been picking up detonation and retarding the spark.

I've noticed that my timing at idle is not rock-steady either, but I don't experience a rough idle. It does wander a couple degrees, but not wildly like yours apperently does.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

God bless you Vader! I think I am narrowing in on my problem, and hopefully I can get the old "Canary" running right soon because there's plenty of mustangs to spank and my baby Blazer can't do it (on the road, at least)! That timing is as fidgety as a frog in a hailstorm. Is there any other input to the spark timing that could cause something like that besides the knock sensor? I appreciate your help, man.