Electronic ignition module?

[Daddio]

Hello friends. My 1978 Datsun King Cab 620 is having issues. Can anyone tell me what the symptoms might be like when the electronic ignition control module goes out? Thank you. Daddio.

[datzenmike]

There will be no spark from the coil and the engine will not start.

 

 

What's it doing, or what's it not doing???

[Daddio]

It acted like the alternator was going out: Instantly died. Then restarted but ran very rough, as if two of the plugs were not firing, then would not stay running, then the starter would crank but not fire off the engine. Plenty of fuel, fuel to carb, new coil (had a good spare coil, which I swapped out, no difference), good distributor, good starter, new battery(two weeks old). Was getting spark but does not seem to be getting spark now. Recently serviced and was running well. The electronic ignition module is original. My hunch is that the electronic ignition module is most likely the problem. I recently replaced the alternator in my Subaru, which had similar symptoms, however, this time the relatively new battery in the truck wasn't drained.

 

That is why I was looking for symptoms for a failing electronic ignition module. 

[datzenmike]

Pull the coil wire off the cap and hold close to the head or any ground. Have someone turn the engine with the starter. Got spark???

 

If yes then the module is working. Now check one of the plug wires. If no spark look at the rotor, cap or ignition wires.

 

If no, it would be a shame to replace this $100 plus module to find out later it might be one of the following...

 

The distributor must be firmly electrically grounded. Some EI distributors even have a separate ground lug and wire.

Check for 12v power on the positive coil terminal in the START and RUN ignition positions. Could be the ignition switch.

 

[Daddio]

Many thanks for the insight. Soonest I can work on it will be Sunday. Let you know what I find out. 

Ignition switch? Hasn't given me any trouble. No symptoms. Died and gave me a bunch of weird symptoms but the switch seemed the least of the problems. 

Switch now gets the starter to crank over the engine without problem, but I know there are other symptoms that could be switch related. 

We shall see. It would actually be great if it was the switch. Easy (easier) fix than the module. 

[Daddio]

To test for spark, by myself, I've rigged up a piece of heavy duty insulated copper line and attached a tweezers to the end of it. It inserts well into the lead from the coil. I can also use it on spark plug leads. Then I run the copper line over to my driver's side window and tape it onto to my rear view mirror support on the side of the truck with a slight air gap. This way I don't have to hold the wire. If it's got spark, I don't want to be part of the circuit. Ouch. BTDT. When I crank the engine, if there is spark it arcs over to the grounded metal on the mirror support. Good way to test coils for spark. Now, a good way to test the module as well. 

[Stinky]

I had a Civic oncst....it would die....no spark.  if you pulled the cap, and put it back on, it would run just fine.  The distributer got changed.  I don't know what was wrong w/it.  It was something in there...and the ICM was on top of the "Usual Subjects" list.  It would run for hours, then die.  Once it cooled it would run like crazy for the next week or 2.  

 

That is was a bad ICM does....usually no spark.

[Daddio]

Update: Pulled the wire off the coil that goes to the distributor and connected a lead from from the coil near to a ground source. Tried to start the engine. No spark. Tried it with another known good coil and same result. Again, the symptoms do not point to a bad ignition switch. The ignition switch cranks the starter beautifully which is useless since there is no spark. Upstream from the coil, if I recall my schematic properly, is the ICM. I've looked for this particular ICM and found only one place that advertised it:

 

1. When they do have them they are $295 and free shipping. (JDM car parts)

2. .......and they are currently out of stock. 

https://jdm-car-parts.com/products/ignition-module-for-datsun-280z-and-other-models-nos

 

oempartsonline only go back to 1984.

nissanoempartsdirect also only go back to 1984.

My local pick-a-part wrecking yards have NO models this old on hand. All have been recycled. 

 

It has occurred to me that If I try and have this ICM serviced, it will likely be more expensive than the value of the truck to get it fixed. The 1979 models, a single year older than mine, are extremely different and retrofitting is next to impossible.

 

I would rather it NOT be the ICM, but I'm not sure what else it could be. 

 

 

Maybe you fine folks know of another reliable source for these ICMs or a better way to test them. Please let me know. Thanks, Daddio

 

[Dguy210]

1 hour ago, Daddio said:

Update: Pulled the wire off the coil that goes to the distributor and connected a lead from from the coil near to a ground source. Tried to start the engine. No spark. Tried it with another known good coil and same result. Again, the symptoms do not point to a bad ignition switch. The ignition switch cranks the starter beautifully which is useless since there is no spark. Upstream from the coil, if I recall my schematic properly, is the ICM. I've looked for this particular ICM and found only one place that advertised it:

 

1. When they do have them they are $295 and free shipping. (JDM car parts)

2. .......and they are currently out of stock. 

https://jdm-car-parts.com/products/ignition-module-for-datsun-280z-and-other-models-nos

 

oempartsonline only go back to 1984.

nissanoempartsdirect also only go back to 1984.

My local pick-a-part wrecking yards have NO models this old on hand. All have been recycled. 

 

It has occurred to me that If I try and have this ICM serviced, it will likely be more expensive than the value of the truck to get it fixed. The 1979 models, a single year older than mine, are extremely different and retrofitting is next to impossible.

 

I would rather it NOT be the ICM, but I'm not sure what else it could be. 

 

 

Maybe you fine folks know of another reliable source for these ICMs or a better way to test them. Please let me know. Thanks, Daddio

 

 

Where are you located in Oregon? These are not valued much on the used parts market. 

 

2 choices. You can replace it with almost any generic HEI module, or find a used one. They are not worth much.

 

OR go to a matchbox distributor instead. 

 

If you're anywhere near Oregon City I'll just give you one I get extra in a box of 620 parts.

Edited August 5 by Dguy210

[Daddio]

LOL! I'm in the extreme south end of the state. Ashland. I'd be happy to mail you funds to ship it. It would cost me $113 in fuel and 9 hours of time to get to you and back. 

I'd like to replace the original module first. Adapting an HEI module or replacing the distributor are slightly above my paygrade and experience. Thank you very much for reaching out!! Much appreciated. 

[datzenmike]

One last check:

 

On 8/2/2024 at 7:09 PM, datzenmike said:

Pull the coil wire off the cap and hold close to the head or any ground. Have someone turn the engine with the starter. Got spark???

 

If yes then the module is working. Now check one of the plug wires. If no spark look at the rotor, cap or ignition wires.

 

If no, it would be a shame to replace this $100 plus module to find out later it might be one of the following...

 

The distributor must be firmly electrically grounded. Some EI distributors even have a separate ground lug and wire.

Check for 12v power on the positive coil terminal in the START and RUN ignition positions. Could be the ignition switch.

 

 

The ignition switch has to send power to the coil positive terminal as well as the module. Use a test lamp and check for battery on the coil positive.

 

If the remote igniter under the dash is bad and it looks like it you can convert to an HEI unit off an older GM vehicle...

 

(ignore the 1.6 ohm coil just use yours.)

 

[Dguy210]

48 minutes ago, datzenmike said:

One last check:

 

 

The ignition switch has to send power to the coil positive terminal as well as the module. Use a test lamp and check for battery on the coil positive.

 

If the remote igniter under the dash is bad and it looks like it you can convert to an HEI unit off an older GM vehicle...

 

(ignore the 1.6 ohm coil just use yours.)

 

 

Thanks for posting this. I initially went looking for that image got distracted and didn't end up tracking it down. This is probably the simplest fix.

[Daddio]

I'll do that tomorrow. Too dark now. Thanks for letting me know. 

[Daddio]

UPDATE on the ICM saga. 

Did as recommended and disconnected the positive line off the coil and attached it to the positive lead on the VDC scale of my multimeter.   Black lead to battery negative battery terminal. If there was current coming from the ignition switch, it should register some voltage. 

 

Nothing. Made sure all my connections were good. Nothing. When I turn the ignition switch on, it is not sending anything to the coil. 

 

Ignition switch?  

[datzenmike]

When ignition is on do the wipers, heater fan work????? 

 

On the right inner fender is a black plastic box. Put your ear near it and have someone turn the ignition on off on off. You should hear a clicking sound from the ignition relay. Is there a clicking sound???

[Daddio]

Okay, just tested it. The relay seems to be activating when turned to the on position. Can't tell if the relay is actually doing it's job, but it does click on when turned to the on position. 

[Daddio]

Also, almost forgot, YES, the wipers and fan work just fine. 

[datzenmike]

Well the power that turns the ignition relay on off also goes to the coil positive terminal. It would seen that power goes that far at least.

 

If wiper, fan, radio are working then the relay is working.

 

The coil wire should be Black/White stripe.

The power to the relay is the same Black/White wire. Find the relay and check to confirm... it has to have power.

[Daddio]

Well, I'm stuck. The ignition relay seems to be fine by way of all the other things it sends power too are working. The positive lead to the coil I've traced back to the ignition switch and all seems good. Ignition switch seems to be operating as expected, but no power coming out of the lead from the switch to the coil.

 

Should there always be current coming from the ignition switch in the "on" position, to the positive coil lead? Ignition switch malfunction or ICM?  Am I missing something?

 

All of the other components check out. No damaged wiring. No fuses blown. Plus, the symptoms of stalling, then restarting roughly, then stalling again, then sounding like it was missing, then the engine refusing to stay running, then not starting at all, indicate to me an issue where there was a cascading catastrophic breakdown of an electrical system. That doesn't sound like the ignition switch.

 

By process of elimination, it seems to point to the ICM or possibly...maybe.... the ignition switch. But how do tell which it is? A simple solution would be to plug in and test another ICM, but I don't have that option, yet. Don't want to replace the ICM with and HEI module and new dizzy only to discover that wasn't the problem in the first place. 

 

Thank you again for all your insight and help. You folks are a lifesaver. I've learned so much!

[datzenmike]

Wiring diagram shows B/White strip wire going to the transistor box module, the ignition relay and then to coil. The ignition relay is working so the coil should have power.

 

Well possibly your test was faulty. Use a test lamp connected to ground and touch probe to coil positive terminal. You don't have to disconnect any wiring. Key on should light the test lamp.

 

You could also make a jumper and run battery power to the coil positive and try starting.

[Daddio]

Worth a try. Let you know after I try it. 

[Daddio]

Hi Datzenmike, Found my 12 volt probe test light. Attached it to the positive lead on the coil and to ground. When I turn the key to ON it lights up fine. Evidently I had done it incorrectly before. Not sure how but I did. Now that I know the coil is getting current and nothing is happening, what's next? Does that leave the ICM as the likely culprit? 

[Dguy210]

1 hour ago, Daddio said:

Hi Datzenmike, Found my 12 volt probe test light. Attached it to the positive lead on the coil and to ground. When I turn the key to ON it lights up fine. Evidently I had done it incorrectly before. Not sure how but I did. Now that I know the coil is getting current and nothing is happening, what's next? Does that leave the ICM as the likely culprit? 

 

Check the coil itself. The coil goes bad way more often than the ICM.

Easy way is if you have a multimeter and can check the resistance of the primary and secondary coil.

Other option is if you have a spare coil to just swap it in. 

[Daddio]

Thank you,

I keep a spare coil on hand, because it has been known to eat coils. Put in the new coil a few days ago and there was no difference. No spark. Man, that would be great if it WAS the coil. That is a cheap, easy fix. 

[datzenmike]

If you have power on the coil positive just briefly ground the coil negative terminal. When you remove the ground the coil should spark.

 

 

You can't go wrong with a test lamp, it works even if backward.

 

A/ Take the cap off and see if the rotor is turning.

 

 

There are a couple of checks you can do with a multi meter at the transistor box under the dash...

 

1/ Check between Black (ground) an the Black/White wire. Should read 12v with ignition on.

 

2/ On the 50 volt range check between the Black (ground) and the Blue wires with ignition on. If the wire and the coil are good you should read close to battery

 

3/ Pull the plug and on the 10X resistance scale check between the Red and the Green wires. Should be about 720 ohms. If far less or more than this the pick up coil in the distributor is bad and should be replaced.

 

3a/ On the 2.5 voltage range (with coil wire off so engine does not start) check again between Black and Green while spinning the engine with the starter. Meter needle should deflect up/down slightly if generating a pulse. Be sure you do A/ above first.

 

Anything else you need an oscilloscope