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Thread: GM HEI Module Install

  1. #1
    Registered User sscanf's Avatar
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    Default GM HEI Module Install

    Installing a GM HEI Ignition Module into a 1976 280Z (which already had a ZX ignition)


    This article describes how to upgrade a ZX ignition module to a GM HEI module. In this particular case, the ZX ignition module happened to be installed in a 1976 280Z which had been upgraded to a ZX distributor/ignition module using the Atlantic Z Club instructions. The purpose of the HEI install was to fix a sudden engine cut-out problem and a jumpy tach problem.


    Heat Sink
    The first thing I needed was a nice heat sink and, afters scouring the basement and considering attacking an old Western Electric telegraph test set with a hack saw, I laid eyes on a stack of these:

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    Which is an old tape format from the 80's/90's (we called the streamer tapes back in the day). I still have a SCSI drive that can read/write these things (but haven't tried in at least 10 years)... Anyway, these tapes are build like tanks, the back plate is .1 aluminum - I knew I saved them for a reason. The following pictures illustrate the transformation of one of these tapes into a nice heat sink for this HEI conversion project.

    Add some quality time with a hack saw and drill to get a nice heat sink...

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    Don't forget to use heat sink compound (I used the stuff my module came with). Note to self: add part numbers here.

    Disconnect the old Ignition Module

    Pull the distributor and yank the old ZX module (this 76 280Z had been given a ZX upgrade by PO). I figured the neatest way to do the job was to open the old ignition module case, cut the connections, and jumper the distributor wires to the external connections (note that I misapplied some opening force to the old module and had to glue it back together - this was not necessary - observe that access to the guts is not at the bottom but at the top - see photos).

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    Pull the distributor then disconnect the distributor wires from the old ignition module: two spade connectors - a gentle yank with some plyers should do it - clean the connectors/terminals while you are there - I sprayed a little DeoxIT and worked them on/off a few times. Pay attention to which side the wires go to (but the rubber boot they plug into is marked red/green if you forget). Remove the two screws that hold it to the distributor.

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    Disconnect the old module and crack it open (I did this a little too literally)

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    Clip off the connections to the board, then jumper the posts as shown. Clean the posts then you will need a lot of heat (I used an 800 deg F iron, nicely tinned and laid into the post and wire for a good 10 seconds before applying rosin core solder). What is that goop in there?

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    Don't forget to check your work. Make sure you have continuity where you should and that nothing is crossed.

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    Fixed the case with some super glue and JB weld.

    Wire it up

    Wire up like this (note: the left image was stolen from another thread):

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    Profit!
    Last edited by sscanf; 12-09-2013 at 09:41 AM.

  2. #2
    Z geek at large FastWoman's Avatar
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    I wish I had taken better notes on my stock '78 system when I retrofitted it with HEI. Here's what I recall I did:

    1. Remove the stock ignition module, which is under the passenger kick panel. I just unplugged it and left the connector hanging. My objective was to make the retrofit as reversible as possible, so I wanted to leave OEM wiring intact.

    2. Remove the wire from the (-) post of the ignition coil that originated from the IM. I folded this wire back on itself and wrapped it neatly into the wiring harness with electrical tape.

    3. Wire as diagrammed above. Note: It is also very important to have a good continuity to ground from the mounting holes of the HEI module.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

  3. #3
    Rust Free'ish zKars's Avatar
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    Please do not take this as raining (or ice storming or snow dumping, depending on where you are this past weekend) on your parade, but these GM HEI ignition modules can be "less good" than the stock ZX ignition modules. Your solution to keep the stock module but to "wire it through" is great to keep the dizzy sealed. Most just remove it entirely and splice into the two remaining wires, which does not solve the hole in the side of the dizzy problem unless you goop it up with somethin'

    They are definitely "More good" from the point of view of cost and sourcing a new one when the old one fails, no question. However their performance, especially at higher RPM's (above 5K) can be much worse than the stock module. There was a discussion on HybridZ about this, and it was pointed out that there are better high performance versions of this module available (from MSD I believe) that are designed for higher RPM and spark performance. http://www.summitracing.com/dom/part...5596/overview/ is the simple one, http://www.summitracing.com/dom/part...2000/overview/ for a real flame thrower!

    You must also be careful with your coil selection when chosing the HEI ignitor, (ohm internal resistance = 3ohm for most) to provide reasonable life with both the module and coil.

    Don't forget the simpliest and most modern approach of all, the now common Pertronix upgrade (discussed at length here), that combines the rotation pickup and ignitor in one tiny package inside the dizzy.

    So if the HEI upgrade makes your car run the way you like in your operating range, then great. Nothing more to do. If it gives you noticable problems at higher RPM's , then consider upgrade to a "better one". You chose the device.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
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    www.xenonS30.com

  4. #4
    1978 280Z (stock) TomoHawk's Avatar
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    HI Bill,

    There's nothing wrong with commenting about how an "upgrade" may not really BE an upgrade. The knowledgeable enthusiast should definitely know the facts from all points-of-view, to weigh them according to his experience or expectations, and then decide.

    As you mentioned, I would probably do this upgrade because of the lack of new or replacement parts, and if that one part (the ignition unit) fails, the whole car is useless, but for a big paperweight (or trophy?)....

    the alternative would be to wire in a different ignition system (like points) or to swap out the engine.

    Besides, this is a discussion forum, so go discuss things!

    BTW-
    During some of my online research, I read that the GM ignition module is actually capable of going to the higher RPMs, but that the coil was what really limited the performance.
    Drive Responsibly.
    enjoy classic Rock music.

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    Just offering a counterpoint - there are numerous discussions around the internet also about the possibility that the high RPM weakness is either just a myth or is an early problem that was solved quickly. Many, many stories out there about no signs at all of high RPM problems. The cynic in me says that the aftermarket ignition module and coil companies have benefited greatly from this myth, and actually keep it alive with their unsubstantiated advertising claims. If you search, I think that you might find one decent article about the GM HEI system having a high RPM problem. I looked all over and there's very little real evidence of a problem, just repetition of something heard (no offense).

    I also found a reference somewhere quoting the guy who inadvertently started the initial rumor (might have been David Vizard) saying that his initial comments had been blown out of proportion and the GM HEI system was a good one. It was in a newer fuel injection tuning book in a book store so I may never see it again though.

    Edit - here's a link to a comment about Vizard and what might have been the book I was browsing. Not FI, but small-block chevys - http://cyberdave.org/HEICoilInfo.html

    If you read the whole link though, you end up with someone postulating again, with no evidence. It's like the perfect endless discussion topic. Lots of evidence for and lots against, and infinite combinations in between.

    On the coil - GM actually made an external coil for the early Novas and trucks (late 60's). You can buy it from Rock Auto or a parts store. This gives you the actual GM system, except for the triggering system in the distributor, which is based on the same principle.

    I have the standard (BWD, not high performance) HEI module and the GM coil on my engine and it works fine with no issues. Not even a sign. But my stock L28 is done pulling by about 5,500 RPM so I never go higher.
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    Last edited by Zed Head; 12-09-2013 at 01:29 PM.
    1976 280Z, with some minor modifications

  6. #6
    1978 280Z (stock) TomoHawk's Avatar
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    That seems reasonable... To use the high-performance coil that is made to work with the high-performance ignition unit!

    I would try it only after getting the other stuff to work, and confirming there is some "high-RPM" loss.

    Will it hook up like the stock coil? the ECU needs the spark pulse to feed gas to the engine.
    Drive Responsibly.
    enjoy classic Rock music.

  7. #7
    Registered User sscanf's Avatar
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    It looks to me like the same procedure would work with either of those modules. At the moment I'm happy to have a working ignition system. Not even close yet to going above 5K RPM but who knows, maybe some day. Nice to know there is a drop-in replacement if I have trouble in the future.

  8. #8
    Z geek at large FastWoman's Avatar
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    Here's a nice page about HEI retrofits for Mopar slant 6 engines:

    Slant Six Forum, :: View topic - HEI Electronic Ignition Retrofit How-To

    I haven't thoroughly digested it, but they do note the importance of a good ground, and they suggest a relay to provide good power to the unit. They discuss coil options and recommend a coil like Zed Head shows.

    Apparently they think quite highly of the HEI. Following the links, it is suggested that GM put some really great engineering into the module back in the early days of catalytic converters, because they didn't want misfires to melt down their already frail and junky converters, resulting potentially in fires from white-hot escaped catalyst pellets.

    I think there might be a few different versions of the HEI with different performance specifications -- different RPM ratings and dwell angles. I got the common variety of 4-pin unit, and it works fine. I don't rev my engine that high anyway -- probably 5k max. Something to keep in mind is that an 8 cylinder engine has more sparks per revolution than a 6 cylinder engine, so if an HEI made for an 8 cylinder engine is rated at 5500 RPM, hypothetically, it would be good for 7333 RPM in on a 6 cylinder engine.
    Last edited by FastWoman; 12-26-2013 at 10:29 PM.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

  9. #9
    Registered User madkaw's Avatar
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    Boy-o-boy- all these L motors not going above 5krpm- what a boring life they lead-
    The worst thing I have read about my research is that the HEI is touchy when it comes to voltage and grounds , like Sarah pointed out.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  10. #10
    Registered User sscanf's Avatar
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    Default What not to do

    So I have learned what not to do with these modules: Don't replace a Z coil made to work without a ballast with a GM coil that is made to work with a ballast. Result: Dead HEI module after about 4 seconds of engine run time. An example of a GM coil that can kill your HEI module in this configuration is the DR35.

    I hated that it was not running, so, in my haste to verify that this was the error in my ways, I checked Rock Auto and found that they sell a rebuilt 1979 ZX distributor (A-1 CARDONE Part # 31619) with the ignition module included for $90 and and OEM coil for $15. I installed them over the weekend and it works great: tachometer is rock solid with this module - maybe even better than with the GM module. I have no idea if the built in ignition module on this unit is a fully functioning original unit or if it has been somehow updated by Cardone. I doubt the latter. Their web site states that they test and update electronics as necessary during the rebuild process. Once I have two known good distributors, I'll pry the cover off of this unit to see what, if anything , has been done in there.

    At the same time, I also ordered a new GM ignition module and am planning on using it to do a cleaner retro-fit with my old distributor. Stay tuned.

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    Last edited by sscanf; 12-30-2013 at 06:59 AM.

  11. #11
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    Quote Originally Posted by sscanf View Post
    So I have learned what not to do with these modules: Don't replace a Z coil made to work without a ballast with a GM coil that is made to work with a ballast. Result: Dead HEI module after about 4 seconds of engine run time. An example of a GM coil that can kill your HEI module in this configuration is the DR35.
    Thanks for the story. I had looked at those coils, since they look identical to the others, but found that resistance was typically 0 - 0.1 ohms, compared to 0.7 for the "right" coil. Even though the 4-pin module has current limiting circuitry it didn't seem like a good idea. Better to use the balanced system as it was designed. I can see how you would get burned though, on appearance. Those later coils are typically used with the 7-pin modules that rely on the computer to control timing and current flow.

    I can understand the "hated that it's not running". 1979 specs. about 0.40" plug gap so Nissan probably has similar high-energy technology in their module. Spark potential is probably just as strong. The main reason to go GM HEI is that it's cheaper, and allows you to keep your distributor timing curves. It's also fun to experiment.
    1976 280Z, with some minor modifications

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