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Ignition control module (ICM)


z_ya

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The car is a 1978 280Z during lunch break today I pulled it and tested it on the machine. The tester had failed it at low rpm but passed it at high rpm. The car did die twice today when i came to a complete start and was a pain to start. I do have one on order that should arrive Wednesday. Is it normal for it to pass a high rpm an fail on low?

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The ICM is a "black box" device. I was having very random issues- rough running, stalling (no start), tach going haywire...

Had an electronic tech friend compare a new with the old. No discernable difference. Replaced the old, suspect ICM with new. No problems since.

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There is a recent thread about installing a GM HEI ignition module into the '78. People have reported success with it, and the OE ignition box is no longer needed. It's cheap enough you can buy lotsa spares for what the OE ignition box costs.

Edited by TomoHawk
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I tried the HEI conversion without any luck. I know that others have been successful with, I just could never get it working correctly.

I wound up replacing the Ing Module and the Key Lock switch and that licked the problem. You can find a Ign Module here:Standard LX513 Ignition Control Module Datsun Nissan New | eBay

No need to pay more than $100 for a new one since there are plenty of them out there.

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Andrew, did you have the tach/ECU wire connected? If not, the ECU wouldn't have been triggered, and it wouldn't have delivered any fuel.

Tomo, if I recall correctly, you keep the + wire intact. Then on the - side of the coil, there will be two wires. One will go to the old ignition module. (You can disconnect that one.) The other will go to the tach and ECU (see above). You need to preserve that one. And then there's the connection you add from the HEI unit to the - of the coil.

I took my ignition module completely out, but I kept the plug and wiring intact, so that it could be easily re-installed or replaced with OEM. As I recall, I simply folded back the ground wire to the coil and taped it up.

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I may try this again, I believe the HEI solution is the best and people should try it. Sarah, maybe (please ;)) you could do a write up with pictures of what you did to your Z. There are a lot of instructions on the web, but none of them are thorough and few have pics from a later model S30.

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Tomo, just trace the wires with a multimeter! You might need an assistant, but hold one probe on the ECU #1, and the other on one of the disconnected mystery wires. If you've got continuity, that's the one.

Andrew, I hate to say I'm in "life gets in the way" mode right now. We start building a dock on Thursday, and that's only the beginning of all our fun, including landscaping, grading, armoring of our shoreline, waging WWIII on an invasive species of marsh grass, adding on to our home, alternative energy, and probably a few things in the "etc." category. So I can't promise you a good, illustrated writeup anytime remotely soon. Until then, this will have to do (all from memory, so I might have an inaccuracy somewhere):

1. Remove the passenger kick panel, and uninstall the ignition module. Leave the wiring in place, in case you want to revert to OEM configuration in the future.

2. Locate the terminal block (a tiny black clamshell on the inside driver's fender) where the distributor's pickup coil connects to the wiring tree. Take apart the connections, and remove the terminal block, making sure to save it for later reversion to OEM. You may use the same threaded mounting holes to mount your HEI module.

3. Disconnect the wires from the (-) post of your ignition coil. Identify the wire that has conductivity with the #1 connector on to your ECU (beneath the driver's side kick panel), and reinstall it on the coil. Fold the remaining wire back on itself, and wrap it up in electrical tape. You may pull this wire back out later if you wish to revert to OEM.

4. Mount your HEI module to a good heat sink, and mount that heat sink to the fender, using the old terminal block's threaded mounting holes. Use heat sink compound between all mating faces. It is very important to have a good ground between the module and the body.

5. Replace the pickup coil's ring connectors with female spade connectors. Connect red to "W" and green to "G" on the HEI module. Lube all connectors with silicone dielectric grease, both here and below!

6. Install a wire from the HEI's "C" to the (-) terminal of the ignition coil.

7. Install another wire from the HEI's "B" to the (+) terminal of the ignition coil.

Additional notes:

See Tomo's diagram in post 19 of this thread for pin positions:

http://www.classiczcars.com/forums/engine-drivetrain-s30/45070-gm-hei-upgrade-78-280z.html

One person on this forum once swore that you should run a very beefy wire directly from your IGN+ circuit to the HEI's B terminal. However, the heavy current handling of the HEI is only from the coil to ground. The B terminal merely feeds the module's internal circuitry, so I don't think it has to be particularly beefy. You'll run the same +12 to the coil via the supply wire that was there to begin with, and it is heavy enough to support the current demands of the coil. The HEI module can simply be supplied with a small'ish branch off of that, perhaps 16 gauge.

I used a square, finned heat sink for a power transistor to mount my module. I did this out of conservatism. Others (Steve Blake) have said no heat sink is necessary and that mounting directly to the fender is adequate. This makes sense, as the module is ordinarily in a pretty hostile (hot) environment, crammed inside a distributor.

There are different versions of the HEI module. They all wire the same way, but some are higher specification (e.g. for very high RPMs). I used a very cheap/ordinary one, and it's worked great.

My own successful installation was based on this writeup for a 240:

GM HEI retrofit

Edited by FastWoman
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3. Disconnect the wires from the (-) post of your ignition coil. Identify the wire that has conductivity with the #1 connector on to your ECU (beneath the driver's side kick panel), and reinstall it on the coil. Fold the remaining wire back on itself, and wrap it up in electrical tape. You may pull this wire back out later if you wish to revert to OEM.

OKay so do i take the #1 wire from the ecu and mount it to the negative on the coil?

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FastWoman wrote her instructions from memory, and might have added a wire. I think that there is only one wire connected to (-). The wire branches to other places like the tachometer and the ECU, it's not parallel.

The wring diagram shows only one for 76 and 78 (my car and hers).

The wire ends that are extra and that you need to worry about are the ones at the stock factory module location. One or more will have power when the key is on and one will still be connected to the (-) post of the coil (because of the branched circuit). Make sure that those are separated from each other and insulated from ground. 1978 is easy because it's a plug-style connection, 1977 and earlier use ring terminals and screws.

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I pulled it and tested it on the machine. The tester had failed it at low rpm but passed it at high rpm. ...

Is it normal for it to pass a high rpm an fail on low?

Assuming that "it" is just the ignition module. What machine/tester did you use to test it?

I've not heard of an ignition module testing machine. More info would be interesting, even if it doesn't help answer your question.

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Oops. The answer would be yes. But the blue wire from the negative on the coil already goes to Pin #1, and the tachometer and the original ignition module.

If you leave the blue wire on the coil negative in its original spot and just add a jumper wire from the coil negative to the C terminal on the HEI module, you will have things connected right. The jumper wire is a new branch to the new module, and the branch that connects to the old module isn't used anymore. You can run a jumper for the B terminal also from the positive post.

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I installed it and noticed a MAJOR increase in drive ability and its much smoother rpm drop when changing gears. I took the red and green and connected it to the module and for the coil I hooked it up off of what i call the "soapbar" ballast resistor. The only thing i noticed was that when I would rev it up the tach would jump around a lot but if i do it slowly it won't. Also after doing the swap it was a little difficult to start up (possibly be the ballast resister causing issues? Can i eliminate the resistor without any negative effects?) But other than that I am highly satisfied with this. Thanks for all the pictures and explanations I truly appreciate the help.

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The ballast is there to protect the coil and the old module. If you swapped in a 78 or later coil, or a GM external HEI coil, you could get rid of the ballast. You'd have the full HEI setup.

Are you going to describe the module testing machine? I'd still like to know what it does and who has them.

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