UPDATE! MISFIRES, SURGING, AND HESSITATIONS!

[shortstuf212559]

figured out the TACH problem, the plug on the ICM wasnt 100% tight. but the car is still running like poop. i've also noticed i get a misfire in park at 1200 rpm.

[shortstuf212559]

had the crank sensor replaced and aligned using the original GM tool. car ran super good for two days. now running worse than before.

car is very hard to start, with extended cranking time, sometimes no start at all.

found out the car is running on only 4 cylinders there is no spark to the top two posts on the coil pack (magnavox setup) now i've swapped this in from a known good running car. still the same thing.

[MattStrike]

Sounds like it's a wiring issue to me.

Start with the connector and wiring at the crank sensor. Check the terminals on the connectors for corrosion or see if the springy tab on the female terminal is pinched flat. Use a DMM or a test light to verify continuity through the wire or wring out the wiring to check for breaks. Trace each wire from the sensor up to the ICM to make sure they aren't broken anywhere. Continuity should NEVER be broken, even when the wire is wiggled around (intermittants, anyone?). You can get replacement connectors from a junkyard most of the time, or if you're incredibly handy and a little lucky you can fix them yourself.

Another (DANGEROUS, I would **NEVER** do it, but it works) way is to start the car and wiggle the crank sensor connector and wires around and see what happens. If a direct correlation between misfiring and the position of the wiring/connector is evident then you may have wiring issues.
But it would suck to get your hand caught in the serpentine belt so don't do it. I recommend getting a DMM and some alligator clips some random wires with different terminal connections that you can use to test this stuff. That's what I did.

[shortstuf212559]

this is still a ongoing problem. still no spark on cyl 3 or 6. i've done my best to check the wiring from the CPS to the ICM and everything seems okay. i've even wiggled the wiring while the car was running with no change. every once and awhile i will get a slight spark real quick on 6, then it stops right away. it does this without any input from me. no wiggling of wires or change to anything will recreate it. just at complete random.

i also now have a code 42

[alec_b]

Try adding a ground to the mounting plate for the ICM.

Is there a factory ground there? If so check it and make sure it's connected, the ICM needs a really good ground to work correctly.

[shortstuf212559]

is the ground for the icm box used thru the three screw posts used to attach it to the mounting bracket?

[alec_b]

I believe the ICM grounds through the mounting plate. The screws just hold down the coils and sort of "pinch" the ICM in place, but the ICM actually grounds itself through the case and into the mounting plate, which then needs a good ground for everything to work properly.

[shortstuf212559]

Okay, i'll give it a try

[crzydmnd72]

My brothers 90 Lesabre had similiar strange issues, missing occasionally, o2 codes for no reason, tach would come and go, then it started iding at 2500rpm.

After redoing the whole top of the motor, and getting nowhere, we swapped in another ECM. Instant solution. If you have a spare handy its worth a shot