Chevy Impala SS Forum banner

1 - 20 of 26 Posts

·
Registered
Joined
·
87 Posts
Discussion Starter #1
I have a roadmaster limited and I'm dealing with a intermittent issue. I have upgraded the coil to a 96 and got a 96 ICM. I started dealing with this issue of misfiring this month and it isn't constant. I figured I would get the DUI ICM and seemed to work and ran great for a short drive yesterday. Issue came back today and it was intermittent and engine light came on then went off. I did purchase a new connector for the ICM but haven't installed it because I decided to do some research on this code. From what I gather, it could be the wiring, ICM, or PCM. From there, I went to gold ss wagon website to follow the wires for the ignition and after following all three pages of wiring diagrams, I noticed that the white wire for the ICM goes to the PCM and also noticed that the pin for white in the connector on the PCM is right next to the ground pin for sensor ground. I am definitely not leaning towards the PCM being bad but I do suspect that the wiring in the black connector is bad and reason why I say this is because I recently received my PCM back from Moe and I'm thinking when I plugged the connector back on, I might have caused a disturbance with the connector or the wires in the connector. Has anyone ever dealt with this issue and was it a wiring issue at the black connector? Fun part is trying to figure this out outside during the winter
 

·
Registered
Joined
·
1,352 Posts
I do suspect that the wiring in the black connector is bad and reason why I say this is because I recently received my PCM back from Moe and I'm thinking when I plugged the connector back on, I might have caused a disturbance with the connector or the wires in the connector.
The PCM connector would have to be in bad shape to cause a problem. If you cleaned the outside of the connector shell of dust and grime before unplugging and did not allow dust and grime to get on the pin sockets when it was unplugged this is probably not the problem.The shell holds the pins securely and there are weather seals for the wires.

RemovePCMpin.JPG


The first test you should try is a "wiggle test". With the engine running,and care to stay away from moving parts start at the PCM and grab the wire harness and lift,push and bend it. Do the same at any connector. If the engine rpm changes or stops while you are doing this you have found your problem. Connectors are usually the weak points and I am personally unimpressed with the ICM and coil connectors.They carry a lot of current and the contacts should look clean and new.

I have upgraded the coil to a 96 and got a 96 ICM.
Does this mean you had problems before you added parts?
 

·
Registered
Joined
·
87 Posts
Discussion Starter #3
The PCM connector would have to be in bad shape to cause a problem. If you cleaned the outside of the connector shell of dust and grime before unplugging and did not allow dust and grime to get on the pin sockets when it was unplugged this is probably not the problem.The shell holds the pins securely and there are weather seals for the wires.

View attachment 196912

The first test you should try is a "wiggle test". With the engine running,and care to stay away from moving parts start at the PCM and grab the wire harness and lift,push and bend it. Do the same at any connector. If the engine rpm changes or stops while you are doing this you have found your problem. Connectors are usually the weak points and I am personally unimpressed with the ICM and coil connectors.They carry a lot of current and the contacts should look clean and new.


Does this mean you had problems before you added parts?
I upgraded to the 96 coil because I came across people saying that the 94-95 coil connector are known for going bad and found out that upgrading to the 96 connector is actually better which is what I did. Car ran fine. As for code 42, which from what I read is a short to ground, I was thinking there was a issue with the connector for the PCM. I have done a wiggle test more towards the ICM to see if anything happens but nothing
 

·
Registered
Joined
·
87 Posts
Discussion Starter #4
By the way, did the upgrade last year. As for code 42, didn't start until after about a week the PCM was installed
 

·
Registered
Joined
·
87 Posts
Discussion Starter #5
The PCM connector would have to be in bad shape to cause a problem. If you cleaned the outside of the connector shell of dust and grime before unplugging and did not allow dust and grime to get on the pin sockets when it was unplugged this is probably not the problem.The shell holds the pins securely and there are weather seals for the wires.

View attachment 196912

The first test you should try is a "wiggle test". With the engine running,and care to stay away from moving parts start at the PCM and grab the wire harness and lift,push and bend it. Do the same at any connector. If the engine rpm changes or stops while you are doing this you have found your problem. Connectors are usually the weak points and I am personally unimpressed with the ICM and coil connectors.They carry a lot of current and the contacts should look clean and new.


Does this mean you had problems before you added parts?
After seeing your pic of the PCM connector, I can definitely rule that out as a issue. I removed the wire loom so I can see the wires better and I looked at the connector for the ICM and can definitely understand what you are saying and can definitely picture in my mind that it could ground itself in the connector. I also found the white wire that was under the loom and was bent in a 180 degree. Seems a little stiff but when doing the wiggle test, nothing changed. I am going to go ahead and change the ICM connector because I definitely don't like the condition of the white wire. I am definitely suspecting that wire with that bad of a bend. You can definitely say if I should change it or not. I'm all ears on this
 

·
Registered
Joined
·
87 Posts
Discussion Starter #6
The PCM connector would have to be in bad shape to cause a problem. If you cleaned the outside of the connector shell of dust and grime before unplugging and did not allow dust and grime to get on the pin sockets when it was unplugged this is probably not the problem.The shell holds the pins securely and there are weather seals for the wires.

View attachment 196912

The first test you should try is a "wiggle test". With the engine running,and care to stay away from moving parts start at the PCM and grab the wire harness and lift,push and bend it. Do the same at any connector. If the engine rpm changes or stops while you are doing this you have found your problem. Connectors are usually the weak points and I am personally unimpressed with the ICM and coil connectors.They carry a lot of current and the contacts should look clean and new.


Does this mean you had problems before you added parts?
I think I found the problem and I am going to bypass the ground junction point and run it straight to the grounding point on the block. The code now comes on every time I start the car
 

·
Registered
Joined
·
1,352 Posts
You posted while I was typing so have a look at this post with that in mind..I am working from the FSM not hands on knowledge.

If the ICM has a good signal unplug the ICM harness and with a test light check for a good ground on C cavity (black/white). A volt or ohm reading is not a good way to test the ground. A test light puts a load on the wire which is needed. This is a common problem mentioned on this forum, The ground to the head by the coil bracket has to be in good shape

The description of the code is shorted or grounded circuit. BUT BUT BUT the diagnostics do not look at wires shorting. They focus on missing signals, bad ground, and bad power.

The white wire is the PCM to ICM signal. It says the PCM signal is 0.5 volts to 4.5 volts(while running) It will vary as it pulses with RPM. If the ICM loses this the engine can do anything from stopping to "not feeling right" depending on how long it loses the signal or if the signal is low. I would want to test this.

You can also test the ICM to coil signal, ask if you want to.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #8
You posted while I was typing so have a look at this post with that in mind..I am working from the FSM not hands on knowledge.

If the ICM has a good signal unplug the ICM harness and with a test light check for a good ground on C cavity (black/white). A volt or ohm reading is not a good way to test the ground. A test light puts a load on the wire which is needed. This is a common problem mentioned on this forum, The ground to the head by the coil bracket has to be in good shape

The description of the code is shorted or grounded circuit. BUT BUT BUT the diagnostics do not look at wires shorting. They focus on missing signals, bad ground, and bad power.

The white wire is the PCM to ICM signal. It says the PCM signal is 0.5 volts to 4.5 volts(while running) It will vary as it pulses with RPM. If the ICM loses this the engine can do anything from stopping to "not feeling right" depending on how long it loses the signal or if the signal is low. I would want to test this.

You can also test the ICM to coil signal, ask if you want to.
I was thinking it was the ground until I looked up the code for it to refresh my memory and I disagree with myself about th
You posted while I was typing so have a look at this post with that in mind..I am working from the FSM not hands on knowledge.

If the ICM has a good signal unplug the ICM harness and with a test light check for a good ground on C cavity (black/white). A volt or ohm reading is not a good way to test the ground. A test light puts a load on the wire which is needed. This is a common problem mentioned on this forum, The ground to the head by the coil bracket has to be in good shape

The description of the code is shorted or grounded circuit. BUT BUT BUT the diagnostics do not look at wires shorting. They focus on missing signals, bad ground, and bad power.

The white wire is the PCM to ICM signal. It says the PCM signal is 0.5 volts to 4.5 volts(while running) It will vary as it pulses with RPM. If the ICM loses this the engine can do anything from stopping to "not feeling right" depending on how long it loses the signal or if the signal is low. I would want to test this.

You can also test the ICM to coil signal, ask if you want to.
I was thinking bad ground because after I installed the new ICM connector, I started the car and the engine light came on. I shut it off and then restart the car and it came back on again. I shut off the car to check and make sure I connected the wires in the right spots. I messed with the ground wire a little at the junction and tug on my connections to make sure it is tight but found the white wire had a little play in it. I am going to replace the connection at the white wire and see if that helps. If not then I will replace the connection for ground and move it to the new location that I did last year and put it on the block itself instead of the head. Reason I did that last year was to make sure, all the grounds were good. When I moved the grounds to the block, I noticed that my under hood light got brighter. By the way, yes, I'm running the innovative wiring battery cables and they definitely help.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #9
The biggest problem I was having is that it intermittently act like it was getting choked out or act like I was repeatedly pressing on the gas when in reality I was pressing on the gas firm and steady. Next step light it was fine. Cruising along it would be fine but act up a little then be fine again.
 

·
Registered
Joined
·
1,352 Posts
At some point I think I checked all the wires that ground to the head. One of them is the PCM I seem to remember. I think I just ran a 6ga from the battery/block point to the grounds on the head. Should not have to do this but it gives me piece of mind. I add star washers and dielectric grease or copper coat to stop corrosion from starting.Painting over the ground works as well, no oxygen=no corrosion.

I find as a car gets to the 20-30 year old mark the grounds need attention. On the pre-PCM cars this meant ensuring the alternator, regulator, ignition module, and windshield wiper motor.had good grounds. Any ground to sheet metal can be a problem.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #11
You posted while I was typing so have a look at this post with that in mind..I am working from the FSM not hands on knowledge.

If the ICM has a good signal unplug the ICM harness and with a test light check for a good ground on C cavity (black/white). A volt or ohm reading is not a good way to test the ground. A test light puts a load on the wire which is needed. This is a common problem mentioned on this forum, The ground to the head by the coil bracket has to be in good shape

The description of the code is shorted or grounded circuit. BUT BUT BUT the diagnostics do not look at wires shorting. They focus on missing signals, bad ground, and bad power.

The white wire is the PCM to ICM signal. It says the PCM signal is 0.5 volts to 4.5 volts(while running) It will vary as it pulses with RPM. If the ICM loses this the engine can do anything from stopping to "not feeling right" depending on how long it loses the signal or if the signal is low. I would want to test this.

You can also test the ICM to coil signal, ask if you want to.
I went ahead and cut the ground wire from the junction and ran the ground to the head. So far the car seems to run better and doesn't feel like it is misfiring. I'm letting the car sit right now to cool off so I can see if the light will come back on again or not. I was going to use my test light only to find out that it doesn't work. I sure hope it is the ground wire cause I really don't want to rewire the car, LoL. I'll keep you posted if this changes anything or not. I do know this much, I am considering replacing that ground junction point so it can have better ground.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #12
At some point I think I checked all the wires that ground to the head. One of them is the PCM I seem to remember. I think I just ran a 6ga from the battery/block point to the grounds on the head. Should not have to do this but it gives me piece of mind. I add star washers and dielectric grease or copper coat to stop corrosion from starting.Painting over the ground works as well, no oxygen=no corrosion.

I find as a car gets to the 20-30 year old mark the grounds need attention. On the pre-PCM cars this meant ensuring the alternator, regulator, ignition module, and windshield wiper motor.had good grounds. Any ground to sheet metal can be a problem.
Yes, the grounds from the PCM do run to the ground junction and then the head. The other reason why I moved my grounds from the head to the block is because I have aluminum heads and I know that aluminum can conduct but I also know it can corrode over time so I decided to move it to the block which is a metal surface and I trust it more than I do aluminum
 

·
Registered
Joined
·
87 Posts
Discussion Starter #14
I think tomorrow I will go to the auto parts store and pick up some connectors and white wire and replace the white wire from the PCM to the connection I made for the new ICM connector so I can eliminate that circuit. The ground for the ICM is now on the head but I will move it to the block with the other grounds. If this doesn't fix it, I might consider rewiring at the coil and the harness for the optispark
 

·
Registered
Joined
·
87 Posts
Discussion Starter #15
At some point I think I checked all the wires that ground to the head. One of them is the PCM I seem to remember. I think I just ran a 6ga from the battery/block point to the grounds on the head. Should not have to do this but it gives me piece of mind. I add star washers and dielectric grease or copper coat to stop corrosion from starting.Painting over the ground works as well, no oxygen=no corrosion.

I find as a car gets to the 20-30 year old mark the grounds need attention. On the pre-PCM cars this meant ensuring the alternator, regulator, ignition module, and windshield wiper motor.had good grounds. Any ground to sheet metal can be a problem.
Question though. Could a bad wire between ICM and coil cause code 42 to come up or is it something between the pcm and ICM that will cause the code to set??
 

·
Registered
Joined
·
1,352 Posts
Question though. Could a bad wire between ICM and coil cause code 42 to come up or is it something between the pcm and ICM that will cause the code to set??
Anything. Quote DCT42 will set when: PCM detects 84 crankshaft revolutions without any "electronic spark timing" What this means to me is that if the engine slows down when the ICM is ordered to stay steady or increase RPM the PCM will store a 42.

I think tomorrow I will go to the auto parts store and pick up some connectors and white wire and replace the white wire from the PCM to the connection I made for the new ICM connector so I can eliminate that circuit.
The factory wire is 18ga temperature rated for 105C. Cheap car wire insulation could melt. If I ever had to do this I would use 16ga for physical strength and better signal. You could unplug both ends and use a ohm meter to do a wiggle test.

I might consider rewiring at the coil and the harness for the optispark
I would not mess with the optispark harness unless you have proof.

There are tests listed with the DCT42 in the FSM. They use a test light or volt meter. Short version is the ICM and coil, as well as connecting wires are all suspect. A good technician with a good scope would just check the PCM signal and the coil and see if they are sincronized. Not listed but on my list would be a bad high voltage coil to distributor wire. If it were spark plugs or wires I would think it would not get 84 revs without a single spark..

Something that will not cost any real time is to unplug and replug the PCM connectors.(battery off)

Tests are quicker that swapping things.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #17
Anything. Quote DCT42 will set when: PCM detects 84 crankshaft revolutions without any "electronic spark timing" What this means to me is that if the engine slows down when the ICM is ordered to stay steady or increase RPM the PCM will store a 42.



The factory wire is 18ga temperature rated for 105C. Cheap car wire insulation could melt. If I ever had to do this I would use 16ga for physical strength and better signal. You could unplug both ends and use a ohm meter to do a wiggle test.


I would not mess with the optispark harness unless you have proof.

There are tests listed with the DCT42 in the FSM. They use a test light or volt meter. Short version is the ICM and coil, as well as connecting wires are all suspect. A good technician with a good scope would just check the PCM signal and the coil and see if they are sincronized. Not listed but on my list would be a bad high voltage coil to distributor wire. If it were spark plugs or wires I would think it would not get 84 revs without a single spark..

Something that will not cost any real time is to unplug and replug the PCM connectors.(battery off)

Tests are quicker that swapping things.
I am going to get wires and connectors and a test light tomorrow. I've decided not to rewire the optispark. I will be doing like you said about checking from the PCM to the ICM and do the wiggle test and see what happens. I'll do the same for the power wire that goes through the coil and into the ICM and do the wiggle test and see if anything changes. It's probably something simple and I am just missing it right now.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #18
I held off on getting wires and connectors and found a ac delco coil I had before switching it to the blue streak coil I put in. I came across a new problem I have which is code 15. I have a break in the wire somewhere so I will have to find the break and replace the wire. Here's hoping this coil fixes code 42
 

·
Registered
Joined
·
1,352 Posts
If you short the temp sensor out and get DCT14 you are looking for a bad temperature sensor or intermittent open circuit. Do you have live data or just a code reader? With live data you could do a wiggle test and just watch the scanner.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #20
It is definitely a break in the wire. I moved the wire and the engine light went off and it began to read the coolant temp
 
1 - 20 of 26 Posts
Top