Ignition control module question
Ignition control module question If this schematic is correct:
http://shbox.com/1/95_ign_system_schematic.jpg
How can this be correct?
Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
Something is not making sense to me.... Is the schematic wrong or the write up? Or is it me?
Al 95 Z28
http://shbox.com/1/95_ign_system_schematic.jpg
How can this be correct?
Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
Something is not making sense to me.... Is the schematic wrong or the write up? Or is it me?
Al 95 Z28
The schematic is correct although this is the first I heard of such a detailed description about that code. However i've had that code pop up a few times and it was 2 wires that I didn't solder correctly to the module that caused the dtc.
Now I'm wondering what the heck the ignition module is used for at all with a MSD. And how or why it would have anything to do with setting a code. Other than the input (Pin B) open or shorted. If that happened you would have a no start condition.
Better start hunting for a better explanation.
Al
If the PCM is providing pulses when it wants a spark a very simple interface would work. I'm sure the ICM is doing all kinds of wonderful stuff, like current control and so on. But the MSD does not need any of that.
Found a troubleshooting guide for DTC 42 but it's a jpeg and not very readable. I'll slosh though it today, again time permitting. This car is a nightmare, ripping off everything and going with a aftermarket controller is starting to look better and better. Even fitting a good intake and carburetor in there is starting to look good.
I've spent so much time trying to learn about all the different systems it's starting to overwhelm me.
Thanks,
Al
73 Z28, 489" BBC, Ron's Toilet, MSD crank trigger, Dedenbear Glide, Dana 60. 9.00 @ 155 MPH, a real car!
TECH Veteran
Joined: Dec 2008
Posts: 4,144
Likes: 61
From: Little Rock, AR
I realize that. However I don't see a reason for it. Today I will, time permitting. put my scope on it and see what it really does. I'm guessing it's just an adaptation of a HEI module.
If the PCM is providing pulses when it wants a spark a very simple interface would work. I'm sure the ICM is doing all kinds of wonderful stuff, like current control and so on. But the MSD does not need any of that.
Found a troubleshooting guide for DTC 42 but it's a jpeg and not very readable. I'll slosh though it today, again time permitting. This car is a nightmare, ripping off everything and going with a aftermarket controller is starting to look better and better. Even fitting a good intake and carburetor in there is starting to look good.
I've spent so much time trying to learn about all the different systems it's starting to overwhelm me.
Thanks,
Al
73 Z28, 489" BBC, Ron's Toilet, MSD crank trigger, Dedenbear Glide, Dana 60. 9.00 @ 155 MPH, a real car!
If the PCM is providing pulses when it wants a spark a very simple interface would work. I'm sure the ICM is doing all kinds of wonderful stuff, like current control and so on. But the MSD does not need any of that.
Found a troubleshooting guide for DTC 42 but it's a jpeg and not very readable. I'll slosh though it today, again time permitting. This car is a nightmare, ripping off everything and going with a aftermarket controller is starting to look better and better. Even fitting a good intake and carburetor in there is starting to look good.
I've spent so much time trying to learn about all the different systems it's starting to overwhelm me.
Thanks,
Al
73 Z28, 489" BBC, Ron's Toilet, MSD crank trigger, Dedenbear Glide, Dana 60. 9.00 @ 155 MPH, a real car!
Again, the MSD does not have the capability to replace the ICM (not that I know of, anyway). So, the ICM must stay in place.
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Verdad Gallardo Checked everything again. No reason for the DTC 42, yet. Waveforms at the ICM we're as expected. The computer sends a high to the ICM and the ICM outputs a low. Dwell is determined by the PCM, not the ICM. For MSD use it's a simple inverter, one transistor and a few resistors, no big deal.
Also checked the high and low resolution outputs of the Optispark, all are good.
So I'm stumped. So far I've found three bad MSD wires. 2, 4 and 5, repaired them and ordered a new set. Think the miss I started out chasing is gone.
This 42 code is not keeping the engine from starting, or stopping the spark advance. So maybe I should just forget about it and move on. Car has a mail order tune so I'm assuming I may be fighting a non issue. May build a simple ICM and see if the code goes away, something about the very high impedance of the MSD input instead of a coil on the output may be causing this. Or, some of the MSD's hash may be getting back to the PCM through the white wire as it is in the loom with the lead from the MSD to the coil.
Thanks to all who endured this. I'm going to start a new thread for some help leaning this thing out.
Al
Also checked the high and low resolution outputs of the Optispark, all are good.
So I'm stumped. So far I've found three bad MSD wires. 2, 4 and 5, repaired them and ordered a new set. Think the miss I started out chasing is gone.
This 42 code is not keeping the engine from starting, or stopping the spark advance. So maybe I should just forget about it and move on. Car has a mail order tune so I'm assuming I may be fighting a non issue. May build a simple ICM and see if the code goes away, something about the very high impedance of the MSD input instead of a coil on the output may be causing this. Or, some of the MSD's hash may be getting back to the PCM through the white wire as it is in the loom with the lead from the MSD to the coil.
Thanks to all who endured this. I'm going to start a new thread for some help leaning this thing out.
Al
TECH Veteran
Joined: Dec 2008
Posts: 4,144
Likes: 61
From: Little Rock, AR
This was the thread I was referring to:
https://ls1tech.com/forums/lt1-lt4-m...eshooting.html
You may know more that I do about the electronics, so maybe you can come up with something that works for you.
On rare occasions, a DTC 42 seems to be opti related, though it is usually accompanied by an opti code.
https://ls1tech.com/forums/lt1-lt4-m...eshooting.html
You may know more that I do about the electronics, so maybe you can come up with something that works for you.
On rare occasions, a DTC 42 seems to be opti related, though it is usually accompanied by an opti code.
This was the thread I was referring to:
https://ls1tech.com/forums/lt1-lt4-m...eshooting.html
You may know more that I do about the electronics, so maybe you can come up with something that works for you.
On rare occasions, a DTC 42 seems to be opti related, though it is usually accompanied by an opti code.
https://ls1tech.com/forums/lt1-lt4-m...eshooting.html
You may know more that I do about the electronics, so maybe you can come up with something that works for you.
On rare occasions, a DTC 42 seems to be opti related, though it is usually accompanied by an opti code.
Just for information, I'm very careful NOT to cut up wiring. I was able to remove the little rubber seal on the ICM connector and get the signals right off the pins. Used short lengths of # 22 copper wire stuffed in the connector from the back.
Got the Opti signals from the connector on the right side of the injector.
Thanks for the link for troubleshooting the DTC codes. Great info., that I really can use. Now if I can just take a pill and wake up knowing how to program the PCM
Al
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Joined: Feb 2006
Posts: 1,025
Likes: 1
From: CT/NJ
The description you posted for DTC 42 is for a DIS car like a 3100 or 3800 V6.
If you follow the link shbox posted, you will find the correct description for an LT1 car. PCM is looking for ICM activity, most likely thru some sort of feedback created by the high current switching of the coil. It would follow logically that this code may set on a car with an aftermarket coil charging box like an MSD, all that it appears to need is an extended crank (84 crankshaft revolutions). It goes on to state that fuel injection will be disabled when this code is current so, if your engine runs, this code is not set currently.
Conclusion, clear the code and forget about it.
If you follow the link shbox posted, you will find the correct description for an LT1 car. PCM is looking for ICM activity, most likely thru some sort of feedback created by the high current switching of the coil. It would follow logically that this code may set on a car with an aftermarket coil charging box like an MSD, all that it appears to need is an extended crank (84 crankshaft revolutions). It goes on to state that fuel injection will be disabled when this code is current so, if your engine runs, this code is not set currently.
Conclusion, clear the code and forget about it.
