Ignition control circuit
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
you've opened a subject for great discussion on this site, but this is your next 'easy' fix.
http://www.ecklerscorvette.com/corve...1986-1996.html
http://www.ecklerscorvette.com/corve...1986-1996.html
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Thread Starter
Intermediate
Joined: Dec 2011
Posts: 27
Likes: 0
Check out Ghost in the Machine by me. Was told VATS system will not shut down car while running. New distributor, new coil, new ignition switch, new ICM, rebuilt ECM, new VATS keys. Security light does not come on when trying to crank the engine. Do I need a Pastor or a Priest????
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The ICM then grounds the coll which creates a high voltage to
fire the spark plugs.
If the voltage level on the signal line from the computer to the
ICM exceeds 4.6 volts DC, DTC 41 sets and the fuel injectors are
disabled.
Normal voltage on the line should be .5 - 4.5 volts.
The ICM is located on the passenger side, front of the engine
head and behind the ignition coil.
It has a four pin plug.
Pin A is a Pink/Black wire and comes from the coil. This is 12 volts to power the ICM.
Pin B is a White wire and is the signal from the computer to the ICM.
Pin C Is a Black wire and is ground.
Pin D is a White wire and is grounded by the ICM to trigger the coil.
Unplug the connector and verify there is no corrosion on the pins.
Trace the wires as best you can and verify the insulation on them
is good. Verify Pin C a Black wire has a good ground.
If everything checks out, replace the ICM.
If you do replace it, make sure to use some heat sink (thermal paste) compound (it's white in color) on the back of the ICM so the heat gernerated by the ICM is transfered to the heat sink.
If no heat sink compound is supplied with the new ICM you can purchase a small tube of it at Radio Shack.
ICM Looks like this.
Last edited by Hooked on Vettes; Feb 19, 2012 at 11:13 AM.
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Follow what Hooked on Vettes said. Not sure why all the talk about VATS when it does not have anything to do with the ignition system, as far as stopping it from operating. Radio Shack sells the heat sink paste for like 3 bucks, FYI. Get the simple white stuff, you don't need the paste for fixing your Xbox.
I cannot believe we have a code and no one bothered to open up the FSM to follow the diagnostic tests listed for code 41.
Thread Starter
Intermediate
Joined: Dec 2011
Posts: 27
Likes: 0
All wiring is fine. I have already tried a new ICM, car is going to die after 8 to 9 miles of driving. Wait 5 to 10 mins and it will run fine for the rest of the day, even after being parked at work. It will go the 35 miles back home with no problem. When the "ghost" shows up, no spark whatsoever to the plugs. It is my belief that my car is possessed!!
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
Are you saying every time the engine stalls and you have no spark, DTC 41 is set?
Reseat the electrical plug/connector on the PCM (Bottom plug closest to the engine).
That's the plug that contains the Ignition control line.
When the problem occurs, (no spark) unplug the 4 pin plug at the ICM. With a volt meter set to read AC volts, place one probe on Pin B White wire and the other probe to ground or you can use pin C Black wire.
Crank the engine and you should see a AC voltage changing from 1 to 4 volts.
If you don't, the PCM is not sending the ICM trigger voltage. Could be a bad PCM or could be the Optispark (but not likely since you don't see a low or hi resolution code set).
If you have AC voltage verify you have spark at the coil output wire.
If no spark it points to the ICM, Coil, tach filter or the wiring.
Before you swapped out the original ICM did you have this exact same problem with DTC 41 being set?
Don't know about a 94 but on a 95, this code does not turn on the
Check Engine/Malfunction indicator lamp.
Reseat the electrical plug/connector on the PCM (Bottom plug closest to the engine).
That's the plug that contains the Ignition control line.
When the problem occurs, (no spark) unplug the 4 pin plug at the ICM. With a volt meter set to read AC volts, place one probe on Pin B White wire and the other probe to ground or you can use pin C Black wire.
Crank the engine and you should see a AC voltage changing from 1 to 4 volts.
If you don't, the PCM is not sending the ICM trigger voltage. Could be a bad PCM or could be the Optispark (but not likely since you don't see a low or hi resolution code set).
If you have AC voltage verify you have spark at the coil output wire.
If no spark it points to the ICM, Coil, tach filter or the wiring.
Before you swapped out the original ICM did you have this exact same problem with DTC 41 being set?
Don't know about a 94 but on a 95, this code does not turn on the
Check Engine/Malfunction indicator lamp.
Last edited by Hooked on Vettes; Feb 20, 2012 at 12:25 AM.
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
You stated that the wiring is find. How do you know this? How did you test it?
Are you getting code 41 consistently?
The FSM also states, "If all wiring and connections are OK, check the ignition coil or the ignition coil voltage supply. Check coil fuse for being open."
The ICM gets power via the coil power supply and via the coil itself.
You could have a coil that is faulty. Try spraying some water on the coil/ICM while the car is running see if anything happens.
Are you getting code 41 consistently?
The FSM also states, "If all wiring and connections are OK, check the ignition coil or the ignition coil voltage supply. Check coil fuse for being open."
The ICM gets power via the coil power supply and via the coil itself.
You could have a coil that is faulty. Try spraying some water on the coil/ICM while the car is running see if anything happens.
