Hello forum,
I have a few questions regarding ECM code 41. First I will give you a run down of events leading to this post. It started when my 1993 Coupe began stalling at random times with a crank , but no restart condition. After about 20 minutes it would usually start. I swapped the ICM with another one I had and this didn't seem to make much difference. The ECM was setting a code 41 "Electronic Spark Control Circuit Open" and after reading about others who cured this by installing a new (re manufactured one in my case), I replaced the ECM with no change to the stalling condition. This began a series of shotgun purchases, some of which were needed anyway. I installed a new fuel pump (the filter was only two months old), a new ignition coil, coolant temperature sending unit, and battery, with no change to the random stalling. Then I installed a new ICM and began a new problem. The car starts, runs for about two seconds and dies. It starts every time, and also dies every time. I notice the wires on the coil connectors were getting beat up by a coolant hose in the area so I replaced one of the plugs and the other tests good for continuity, I do recall several months back that my tach needle was bouncing a little bit at idle, jumping somethings as much as 300 rpm. This led me to the tach filter, an object said to be unobtainable at a parts store.

Here are my questions:

Does anyone know how many ohms of resistance there should be from the negative terminal on the coil (white wire on gray connector) to ground? I measure 75,000 ohms. It seems there should be some resistance because when I attempted to bypass the tach filter to ground I quickly blew the 10 amp ignition fuse. However 75,000 ohms seems like it might dim the spark just a bit. I'm going to Pick n Pull this morning to hunt down a tach filter but I saw where one guy, don't recall the exact post, said a person could build their own tach filter but no reference to requirements. Does anyone know how to build a tach filter that will work in this application?

Does code 41 include any communication failures between the ECM and the Optispark? How about knock sensor circuits?

My CCM sets an occasional code 72 but it is intermittent. About 3 months ago the courtesy lights mounted in the rear view mirror quit coming on when the doors were opened although they could still be lit manually with the key in the run position. The courtesy light relay was making a horrendous noise. The noise stopped with the new battery however the rear view mirror lights still do not come on when the doors are opened.

I cleaned the IAC valve and the valve seat and the air throats of the throttle body. I found that if I really concentrate I can keep the car running past its usual 2 second run time but it will not return to idle and is very difficult to keep running.

When interrogating the CCM I find:
1.2 06 Pass-key (A\D) counts = 181
1.3 01 Pass-key fuel = 1
1.3 06 Key in ignition = 0
1.4 12 Starter enable relay is cycling.

I guess 1.3 06 Key in ignition = 0 is rather confusing considering the other information.

My Optispark is about two years old. I quit washing the motor long ago after the first Opti replacement. This one is the second . The motor has roughly 20,000 on a complete rebuild.

Any ideas to resolve these issues would be greatly appreciated. My main concern obviously is the ECM code 41 and the 2 second run time.
Thanks for anything you can tell me, and yes I realize that it would have been to my great advantage to have purchased the FSM for this car when I bought it 12 years ago. Maybe I'm just getting used to torturing myself. I have the troubleshooting pages for a CCM code 41 from the FSM but not an ECM code 41.

 

Might get some info here on no start
http://www.mainstreamtopics.com/foru...rt-diagnostic/

 

ECM DTC 41 is a problem with circuit 423 a White wire from
ECM Gray connector pin 12 to the Ignition Control Module White wire Pin B.

DTC 41 can set if voltage is detected on circuit 423 when the ignition is on and the engine is not running or cranking.

Can also set if the voltage is greater than 4.6 volts and the engine speed is less than 1500 rpms. Normal voltage during cranking or running should be 4.5-.5 volts.

To eliminate the tach filter, poke its pin out of the Coil Gray connector Pin A or cut the wire and see if that cures the starting problem. The Tach signal is used by the dash cluster and also the Electronic Brake and Traction Control Module.

If the Mirror courtesy/map lamps work with the switch but not in the courtesy switch position. At the mirror you need to measure the voltage on the Orange wire shown as circuit 740. It gets 12 volts from the RH CTSY fuse which is hot all
the time. The ground on the White wire circuit 156 comes from the Courtesy Lamp Relay which closes when either door is opened.

 

Thank you vetteoz. I looked over the information on the page you linked to and I believe it will be very helpful in resolving my issues.

 

Thank you Hooked on Vettes. Those are the exact FSM pages I was hoping to find. I was under the impression that the coil needed the grounding through the tach filter to operate. I think I need to relearn how the coil operates because you are saying that it will work without the white wire on the gray cap being connected at all. Thank you again for your time. It has been my experience that this website is the most valuable source of information and helpful people on the Internet.

 

I believe Pin D at the ignition control module and the other end of the
White wire goes to the Black connector Pin A at the coil is what makes
and breaks the primary coil magnetic field to fire the coil. The tach filter
wire is also White but is on Pin A of the Gray connector at the coil.


Follow the troubleshooting flow chart.

Also verify you have a good ground from the ICM pin C to the engine block.

This is a schematic that shows the tach filter for a L98 not a LT1.
It shows on the left side what the filter looks like.
A 5.6k and a 10k ohm resistor in series with the signal.
Also a .10 MFD and 100 PF capacitor from the signal to ground.
So there is no DC path to ground. Only a AC path to ground.

 

I believe I just isolated the problem. Although there is no damage to the insulation, it appears that the ground wire for the ICM has an internal break. Checking the pin (b) contact on the ICM plug to ground I see 20-30 ohms of resistance. Shaking it around a bit cause the resistance to jump to 300-400 ohms and then eventually I saw a completely open circuit. Since all the parts houses want $16 to $20 ($50 for an AC Delco plug) it looks like I will be out at Pick n Pull tomorrow anyway looking for this plug. Thanks for all your help, it was greatly appreciated.

 

Well I thought the plug for the ICM was the problem and I did replace it today, but to my dismay I still had the same problem. That's when I took a trip back to Autozone to have them retest the ICM I had purchased from them over a week ago. The guy working there noticed that the part number for the ICM they had sold me was the right number if I was looking for parts for a 1994 Corvette, but mine is a 1993. Although the units look nearly identical there is one small difference, the part number. If you have a 1993 Corvette the ICM from a 1994 WILL NOT WORK in your car! I returned with the "right" part and installed it. The car starts and continues to run, and run, and run, and then dies at random times when out on the road, like it was doing before. Only now it is doing it with a rebuilt ECM, new fuel pump, new coolant temperature sending unit, new coil and new ICM. So I guess it's back to checking wiring. Does anyone know if a bad TPS will kill a running motor? It seems to die when I've lifted off the throttle.

Also, the car is not setting any codes at all. It starts easily and runs good until it dies. So far, since putting the correct ICM in the car it restarted within 10 seconds of cranking after its last random stall (happened while waiting at a stop light).

 

In the first post you said the engine would stall with in 2 seconds
after starting and set ECM DTC 41.

You installed a ICM that you had and the problem didn't really
change. So does that mean DTC 41 still set during cranking or
did the engine now run and randomly stall?

You installed a re-manufactured ECM and the symptom
stayed the same?

Purchased another ICM from Auto Zone which was the
wrong one. Was the wrong ICM causing the DTC 41?

The car now runs with the correct ICM but randomly
stalls?

Did you install heat sink compound on the back of the new
ICM?

 

In the first post you said the engine would stall with in 2 seconds
after starting and set ECM DTC 41.

The initial problem was the car was stalling at random times during driving and would not restart right away. I was exchanging the two ICMs I had with one another looking to pinpoint the cause of this condition. I was seeing DTC 41 being set after a stall would occur. It wasn't until I went to Autozone to buy a new third ICM, they gave me the wrong part which caused the car to start and then die within 2-3 seconds.

You installed a ICM that you had and the problem didn't really
change. So does that mean DTC 41 still set during cranking or
did the engine now run and randomly stall?

Maybe this will answer your question. I never had a problem getting the engine to fire up

You installed a re-manufactured ECM and the symptom
stayed the same?

Yes.

Purchased another ICM from Auto Zone which was the
wrong one. Was the wrong ICM causing the DTC 41?

There was only one purchase of an ICM at Autozone, the wrong part and then an exchange last night. The ECM set Code 41 with the wrong ICM (for a 1994) installed and I believe it was the cause as the last time I checked there were no codes being set with the new ICM (for a 1993). Even after a stall. I also believe the ICM I took out of the car right before the wrong ICM went in, was also failing as it was leaking dielectric grease from its housing and the back plate became separated from the housing when I was removing it.

The car now runs with the correct ICM but randomly
stalls?

Correct.

Did you install heat sink compound on the back of the new
ICM?

Yes I did.

Here's something that might be of interest. The last time I had a water pump go out some moisture got into the Optispark. I cleaned up the Optispark and sealed the the distributor cap to the housing with some silicone to prevent this from happening again. My Opti had a fresh air port on the lower side of the cap to which I attached a piece of vacuum hose which I routed up behind the power steering pump and back along the left bank cylinder head, under the fuel injector wiring. My thought was to keep it away from any splashed water and on top of the motor where the air might be drier. I live in California's Central Valley where we don't have high humidity very often. I have heard of Optisparks forming condensation under the cap. Maybe my silicone and two foot long vacuum hose are preventing the Opti from drying out as any moisture that would have run out the vent port would now be faced with an 18 vertical climb to reach the end of the hose. Do you think my self-engineered solution created a bigger problem?

Thanks for your time.

P.S. I think my vacuum hose idea was half of an original idea of having two ports on the cap. One attached to manifold vacuum and the other attached to a restrictive air flow device (to limit vacuum loss) and then a small air filter. Or better yet install a small 12volt fish tank style air pump (if they make such a thing) to force dry outside air through the Optispark while the car is running. Either way putting a single hose on the only port maybe created a bigger problem.

Also, since the new battery went in the car my map\courtesy lights are working properly. Amazing isn't it? The one problem I haven't yet got around to tracing out and it's already fixed.

 

Heat sink compound is usually white in color and is used on the back
of the ICM to transfer heat from the ICM to the engine.

Dielectric grease is almost clear in color and used to prevent moisture
from getting into the electrical connectors.

You've eliminated the wiring, the ICM with the new one so the only things
left is the ECM, Optispark, Coil (not likely with your symptoms) tach
filter which you can eliminate by disconnecting it..

Was your original ECM repaired or did you exchange it?
If your original ECM was repaired, I wouldn't trust it.

A very common problem with the 92-93 ECM is circuit board flex problems
or heat related problems. For the flex problem with the engine running
you bang on the ECM housing with your hand. For the heat problem, remove
the circuit board from the case and run it like that.

Takes some work but last resort would be to examine the Optispark
Cap for carbon tracking, verify the rotor is secure, no corrosion on the
timing disc. and cranking the engine to see if there is any wobble in
the timing disc. That eliminates the Optispark except for the optical
sensor which can really only be done by using an oscilloscope.

The ECM can only detect if the High or Low resolution signal is missing
and sets DTC 16 for a Low resolution signal problem or DTC 36 for a High
resolution signal problem. It can't detect if both signals are missing which
could happen if something is wrong with the optical sensor.

Engine will still run if the High resolution pulse is missing.

Engine will run with the Throttle Position sensor disconnected but
throttle response will be degraded. (DTC will probably set).

As for the IAC there is really no feed back that the IAC motor is working
properly.

If the engine is stalling at highway speed with continuous throttle I don't think the IAC is your problem. If letting off the gas and coming to a stop
and stalling, could be a bad IAC or dirty throttle body. (You said you cleaned the Throttle Body and IAC pintle and bore).

One way to verify the IAC is working is at idle turn on the AC. The engine
idle rpm should increase to compensate for the extra load on the engine
from the AC compressor.

To verify fuel pressure you need to attach a gauge to the fuel rail, tape
it to the windshield and drive it. I believe you can rent one from Auto Zone.

Last question. When the engine stalls does the engine misfire or just shut
off as if you turned off the ignition?

 

This sounds very much like the issue I'm trying to work through on my 93 so I'm very interested in the outcome.

 

Heat sink compound is usually white in color and is used on the back
of the ICM to transfer heat from the ICM to the engine.

The compound I used on the ICM was white and came with the module.

Dielectric grease is almost clear in color and used to prevent moisture
from getting into the electrical connectors.

The stuff coming out of the ICM was a clear gelatin-like substance.

You've eliminated the wiring, the ICM with the new one so the only things left is the ECM, Optispark, Coil (not likely with your symptoms) tach
filter which you can eliminate by disconnecting it..

I haven't tried this yet and I'm glad you reminded me because as I said earlier, my tach needle has been bouncing around near idle. As I learned from attempting to ground the coil by bypassing the tach filter that would cause the 10amp ignition fuse to blow. If the filter is failing or is creating a momentary high-resistance path to ground, I am guessing that it might be enough to disrupt the spark without blowing the ignition fuse. Another note which I did not mention, the tach filter has a black wire coming from it which grounds to the motor block near the water pump. That wire appears to have gotten hot at some point and is missing insulation in a few places where it appears to have melted off. I was just getting ready to pull the Optispark, but I think before I do that I am going to disconnect the white wire from the coil which leads to the tach filter and see if it will stall while driving. I'm going to do that right now and I will return to continue answering your questions if this does not solve the problem.

Well that answered that question. I cut the tach filter wire and started the engine. Before I could get the hood closed to take it out for a drive the engine stalled and would not restart. So much for the idea that something is getting hot and failing. I'm really beginning to think that I'm going to be pulling the Optispark out. Even with the tach eliminated the ECM did not set a code.

Was your original ECM repaired or did you exchange it?
If your original ECM was repaired, I wouldn't trust it.

The original for this car was turned in as a core about six years ago. It was replaced with a re-manufactured one. That one I still have and it's supposed to get mailed off as another core. The latest one is another re-manufactured one from Cardone.

A very common problem with the 92-93 ECM is circuit board flex problems
or heat related problems. For the flex problem with the engine running
you bang on the ECM housing with your hand. For the heat problem, remove
the circuit board from the case and run it like that.

Like I said it doesn't seem to matter which ECM I have in the car, it never seems to change anything when I swap them.

Takes some work but last resort would be to examine the Optispark
Cap for carbon tracking, verify the rotor is secure, no corrosion on the
timing disc. and cranking the engine to see if there is any wobble in
the timing disc. That eliminates the Optispark except for the optical
sensor which can really only be done by using an oscilloscope.

I have an old Hewlett\Packard 8559A Spectrum Analyzer that might work for this purpose.

The ECM can only detect if the High or Low resolution signal is missing
and sets DTC 16 for a Low resolution signal problem or DTC 36 for a High
resolution signal problem. It can't detect if both signals are missing which
could happen if something is wrong with the optical sensor.

Engine will still run if the High resolution pulse is missing.

Engine will run with the Throttle Position sensor disconnected but
throttle response will be degraded. (DTC will probably set).

As for the IAC there is really no feed back that the IAC motor is working
properly.

I can hear the servo in the IAC running when I shut the key off. It sounds kind of squeaky. The guy at Autozone said they have a special lubricant for IAC valves and mine is probably dried out. If at idle the IAC were to completely close wouldn't it choke the engine and cause it to stall?

If the engine is stalling at highway speed with continuous throttle I don't think the IAC is your problem. If letting off the gas and coming to a stop and stalling, could be a bad IAC or dirty throttle body. (You said you cleaned the Throttle Body and IAC pintle and bore).

I cleaned the IAC pintle and the throttle body

One way to verify the IAC is working is at idle turn on the AC. The engine
idle rpm should increase to compensate for the extra load on the engine
from the AC compressor.

My A\C system is not charged. The compressor needs to be replaced.

To verify fuel pressure you need to attach a gauge to the fuel rail, tape
it to the windshield and drive it. I believe you can rent one from Auto Zone.

I'm considering buying one.

Last question. When the engine stalls does the engine misfire or just shut off as if you turned off the ignition?

It's curious that you ask this because it does seem that when the engine stalls while rolling, braking it just shuts off. I often don't know until I see the check gauges light or try and turn the steering wheel. However when it dies at idle, transmission in drive, it feels like there is a very brief miss-fire and the motor goes down with with a "thump" if that makes any sense.

 

Well, that does it. I'm pulling the Optispark out.

 

After the engine stalls does the engine start right back up
all the time? In one of your posts you said sometimes you
had to wait 20 minutes.

I was wondering when the engine stalls and it doesn't start
back up can you verify it has spark?

Or if you can't do that can you shoot some starter fluid in
the throttle body and see if tries to start to eliminate a fuel problem
when it won't restart?

One way to verify the ECM is pulsing the coil is after a stall and it
doesn't restart is to look at the tach while cranking. (Assuming you
reconnect the white wire).

The tach should show some rpm while cranking which would indicate
the ECM is pulsing the coil. I would think that would indicate there is
a problem with the secondary of the coil or the high voltage section of the
Opti.

With engine running tug on the ECM wiring harness connectors and around
the ICM. With your hand bang on the ECM housing. Yes I know you said
you have two ECM's displaying the same symptoms.

Pull the vacuum hose off of the fuel pressure regulator and verify
there is no gas in the hose.

Ohm out the injector coil windings.
Should measure around 12 ohms. If one injector coil is shorting out it
can cause problems with the other injectors connected to the circuit.

Check the resistance with engine cold and hot. But from your description
the problem occurs both when the engine is cold or hot.

If all else fails put it on Craigslist.

 

After the engine stalls does the engine start right back up
all the time? In one of your posts you said sometimes you
had to wait 20 minutes.

Sometime it will restart right away, about 25% of the time. Most times it will not. You can run the battery dead trying but I've learned that if it is going to start it will start right away and if I have to crank it more than 5 seconds it's better to just wait it out. The night it left me standing on the side of the freeway it wasn't going to start at all, even after someone came and gave me a jump start. Tow truck was the answer that night.

I was wondering when the engine stalls and it doesn't start
back up can you verify it has spark?

I haven't verified spark but used starting fluid and it would not fire.

Or if you can't do that can you shoot some starter fluid in
the throttle body and see if tries to start to eliminate a fuel problem
when it won't restart?

That was my thought exactly.

One way to verify the ECM is pulsing the coil is after a stall and it
doesn't restart is to look at the tach while cranking. (Assuming you
reconnect the white wire).

The tach should show some rpm while cranking which would indicate
the ECM is pulsing the coil. I would think that would indicate there is
a problem with the secondary of the coil or the high voltage section of the
Opti.

Honestly I don't recall. I will keep my eye on that from now on.

With engine running tug on the ECM wiring harness connectors and around the ICM. With your hand bang on the ECM housing. Yes I know you said
you have two ECM's displaying the same symptoms.

I will try this.

Pull the vacuum hose off of the fuel pressure regulator and verify
there is no gas in the hose.

Did that and it was dry.

Ohm out the injector coil windings. Should measure around 12 ohms. If one injector coil is shorting out it can cause problems with the other injectors connected to the circuit.

Did that and all injectors measured between 12.1 and 12.3 ohms.

Check the resistance with engine cold and hot. But from your description
the problem occurs both when the engine is cold or hot.

Haven't tried this. Have to keep it running long enough to get it warm.

If all else fails put it on Craigslist.

I'm sure whoever bought it would hunt me down and try to shoot me if I didn't disclose this car's problem.

I'm starting to consider the price of a new engine harness.

Here's some more information. I'm looking at the Optispark sitting on the bench in front of me. I disassembled it and found it had ingested a small amount of motor oil through the three vent holes drilled in the aluminum back plate at the bottom of the Opti. It appears I have a pan gasket leak near the front of the motor. The high-voltage area appears to be dry and there is no traces indicating a cracked cap. The oil did make its way up the back side of the metal plate that covers the optical section of the distributor. The disk does not appear to have any visible oil on it nor does the optical encoder. I was reading that the optical encoder can be cleaned with rubbing alcohol on a swab. I am guessing that the presence of oil in the optical section means that the entire area would have a thin coating of oil on all of the parts. Do you know anything about cleaning one of these?

 

Inside the Opti:
You can clean optical sensors with Isopropyl alcohol. Other alcohol types might fog the plastic sensor lens. Oil inside an Opti is usually a death sentence to the optics. It puts a thin film on everything in there. If the fresh air vent is more restrictive than the vacuum applied, you might be running the Opti in too much negative pressure and sucking oil past the drive seal and through the bearing. It doesn't take much oil to make a nice vapor in there and coat everything with a thin film. Your fresh air vent (top) should always flow more than your vacuum inlet(bottom). If you reverse the air flow, you won't pull any oil or moisture out the top port till the opti is full, and it will die long before that happens. You just want a slight breeze through there to clear out ozone and moisture and maybe just a little cooling for the sensor. If you put much vacuum in it, the cap will distort and can even cave in and crack. (Like sucking a plastic pop bottle flat)
Sometimes it takes the optical sensor a while to die.(intermittent stuff will make you crazy) If you already have the thing out, save yourself a lot of future grief and put a fresh one on there.

 

Might as well try cleaning the optical sensor with isopropyl
alcohol.

Isn't the opening just a slit and you really can't see much?

If that's the case, take a piece of lens tissue and dab it
with some alcohol and do the best you can to clean it.

Before complete reassembly after cleaning, you can bolt
the Opti back on. Leave the water pump and crank balancer off and
see if the engine fires back up. Someone also mentioned if you reattach
the cable for the optical sensor,, the coil wire and one spark plug wire,
turn the ignition On and manually turn the Optispark it should fire
that plug.

Is the sensor made by Mitsubishi which is the company
that GM used? There was a company rebuilding Optisparks
and claimed they used Mitsubishi optical sensors in
their units. Someone bought one and discovered the
sensors were clones made in China. To bad Mitsubishi
will not sell these sensors to the public.

 

Well I cleaned the Optispark the best I could and sealed it back up with a little clear silicone and re-installed it. I guess in one aspect I'm satisfied, satisfied that I believe I've finally located the source of the problem. On the other hand it looks like the opti project is not over. After putting it back together it didn't want to start. I didn't try for very long before checking the codes and it set a DTC 16. I thought oh great, I've done it now. The battery was low so I charged it up a little bit, cleared the code and tried it again. It fired right up and has fired right up every time since then. I just drove the car on a trip half way across the county and it didn't die once. However, the car is running like crap. It has a sporadic miss at idle and under acceleration. Reminds me of the days before I learned about washing the motor at the do it yourself car wash and thinking I would never make it home. On closer inspection of the cap and rotor there was significant build up on the center electrode of both. The rest of the cap looked pretty good. I'm going to write this distributor off to the junk pile and start looking for a new one. Any suggestions on what to buy? I know usually you get what you pay for and I'm going to assume the GM factory replacement would be the best choice but I just don't feel right spend over $300 on a distributor that I know will eventually fail long before the engine spins out it's life. Any recommendations?

 

Anybody want to buy a used Corvette? Just kidding, after all this work I have to keep it. However I do need to find a new distributor. Hooked on Vettes you were explaining the finer points of having a ventilated optispark (i.e. a retrofit kit to make a 1993 like a 1994\95. I said that my cap had a port to which I attached a piece of vacuum hose but I was not suggesting there was any vacuum at the other end. I was merely describing the type of hose I used. Sorry for the confusion as it is perfectly understandable given the application why you might have been under the impression that I had install a kit. What I did (apparently, as I don't really recall) was bought a newer optispark with the vented cap but never followed through by getting the kit OR devising my own (working) system to ventilate the unit. I know this shows how much I was paying attention , but it wasn't until I pulled this optispark last night did I realize there are three small holes drilled in the aluminum back plate at the bottom of the unit. I understand now that if I had hooked my hose to a vacuum source, not only would I have had a terrible vacuum leak to deal with but I also would have created a small Hoover that would have sucked up every sort of fluid and debris, probably enough to kill the opti long ago and scar the cylinder walls from all of the sand and dirt I would have picked up. It's a good thing I did a half-assed job.

I'm seeing $400+ for a genuine AC Delco unit. I also see many people are happy with the MSD opti. A friend of mine said he found a complete opti online (cap and rotor included) for $105. Surely this unit was built in China and we all know what that means.