66mule

Here is the story in the most condensed form, 1992 LT1 coupe.
-purchased a few eeks ago, 137,300 miles, ran pretty good
-washed engine, got opti wet, dried with wifes hair drier for 2 hours and ran fine, passed CA smog the following day
-decided to change out opti, H2o pump, wires and plugs for assurance
-first a cheap Ebay opti, Maxx Performance 8mm wires, Bosch+2 plugs
_ Washed all grease and oil from front of engine with everything removed, figured it would be the best time, car would not start, hair drier on coil and icm, started 30 minutes later then died, code 16 low pulse problem from opti
-Installed new coil and icm from Napa, no good, will not start
-Dismantled Ebay unit, opti wheel base is machined to shaft and timed off a bit from factory, no way to relocated shaft position
-Ordered GM opti from Summit, fired right up and idled for 30 minutes while burping the coolant system, took it for a test drive and died within 1/2 a mile, would not start
-removed opti, dried everything, reinstalled with new H2o gaskets, restarted, ran 45 minutes at idle, purred like a kitten, stepped on the throttle and died
-Checked fuel psi, a bit low, changed filter, now between 38-43psi
-started back up with a very slight hesitation, drove it and it died a mile down the road
-Summit sent me another opti, installed along with AC 14 RF plugs, and 7mm wires, fired up but ran bad, like timing, a bit rich also, then died and wont start, cranks then fires badly and shakes violently
-Code 41, open est stored, checked all connection points at icm, coil and opti, all clean and tight.
-12 volts at coil connection, 2.4 volts AC to icm from opti, fuel at 40 psi and holds after pump is off
-reset codes, fired once then died, code 41 again
-installed original icm, same problem

Pulling my hair out, today I will unpin each connector and look for any weak or broken connections.
Can a bad tach filter cause a code 41?
Can just a few broken wire strands in a harness or connector cause this?
If nothing found, i guess it will be time to send it to the stelership, losing my patience very quickly!!!!!

FICINJECTORS

just something you should try for the hell of it.. ohm check the injectors. on your year if the ecu picks up voltage through the ground trigger wire going to the driver circuit it will shut down the ecu. the injectors should be around 14-16 ohms. if any are below 10 disconect it and see if it runs. if you have any below 5 they are dead shorted. At least this wont
't cost you any money unless you need injectors. Multec failure is a common problem which is overlooked.

66mule

Tried the injectors, all between 11.9 and 12.2, changed the coil connectors since they looked pretty bad, even though they had continuity. Fired up, but not smooth, this was with the old icm. Reinstalled the Napa unit, and code 41 again. Napa said they cant test the icm?

FICINJECTORS

i think most autozones can check the ICM.. your injectors are all low, was that test cold or hot, if you can get them hot then test them you might see them below 10

66mule

Cold, it will not run long enough. It throws the 41 code with the Napa icm only, runs really bad with the original unit, that is falling apart. My Napa unit is the same one they sell for the 94 Impala, which I have read will not work. I will go to my local Chevy dealer tomorrow for the correct unit.

larry00

Make sure to let us know the outcome as your having an expensive lesson.

The OPTI is a great unit and it's not it's fault for the position it's in . LOL
I fought electrical gremlins on my Hot Rod LT 4 for a while bought all the same stuff but it turned out I had a bad connection from the MSD 6A to the coil , that was all.
Still need to solder that thing but I've been having too much fun driving it to work on it right now .

BrianCunningham

Could be the pump starting to go.

They run fine for a while, then they overheat.

At least check the sock on the end of it.

tim32920

I have the same exact problem and have replaced the pump and injectors gm optl icm coil you name it...im about to go postal!

Mines due in the shop next week for paint,and I hope someone on here can help me as well

BrianCunningham

How are your wires?

Have you tried the "under hood light show" test?

Start the car at night
lift the hood and
see if you see arching

66mule

Wires are good, pump is a possibility and next on the list of assurance replacement parts. The old ICM started coming apart when i removed it, the back wanted to stay with the grease. Anyway it fires right up with this ICM, but runs bad, I get a code 41 when I install the Napa unit, and no fire at all.

66mule

Installed the new GM ICM, no start and code 41 again. I unplugged the icm and plugged in the old unit and started, ran rough but it ran. I just had the old icm sitting by the heater hose, when i attempted to move it, the engine died. I restarted it, and wiggled it around, same results. I unplugged it after a couple minutes, boy does it get hot, twisted the connector 2 times and plugged into new unit, crossed my fingers and it fired up. I cut off the plug, unpinned it, made new pig tails with new Metri Pak ends soldered on, and but spliced back on car with heat shrink. Car now runs great, going to drive it to work for a test.

NEVRL8T

Hope you fixed it.

BrianCunningham

Nathan Plemons

Sounds like you got it. What you were describing sounded a lot what mine was doing when the ICM died. Since you were able to find an obvious short, I'd say you have it. I thought mine was the coil. I changed the coil with a used one, no luck. I hunted around and found one of my friends had the whole assembly from a '96 Z-28. I got it from him, I was going to try the coil. The '96 coil is different so I couldn't try it. Since I had it already I decided "what the hell" and tried the ICM. It firred right up and ran great. I bought it from a him cheap and was done with it. That's been probably 8 years ago and it's still running strong.

You mentioned how the ICM gets hot fast, you'll notice that the coil base that it mounts to is designed as a heatsink. I'd say it's that way for a reason and I wouldn't run it for too long without it firmly attached. It also wouldn't hurt to put some heat sink compound between the ICM and the heatsink.

Good luck!

66mule

Thank you to everyone for all the help, it runs great!!!!
What a pain in the , but better than paying $110 hr to the stealership!! Now time for beers!!

BrianCunningham

66mule

Tonight I changed the oil, and the cheap Napa coil with a MSD Blaster from Kragen ($48). What a difference, hits a lot harder than my 66 Impala with a 396 (about 500 HP). This thing is a blast, already thinking about a rag top for me, since this one is for the wifey poo!