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Duraspark to HEI Module- Another Writeup

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  • Duraspark to HEI Module- Another Writeup

    I know this has been covered before, but I did not find all of the information that I needed in one place, so here is my experience swapping the Ford ignition module to the GM HEI ignition module:

    Pretty simple swap. Gutting the old module is time consuming, but pretty straightforward; I didn't bother heating it up in the oven as others suggested. The sandy goop inside was really not all that hard to remove at room tempterature. There are two screws holding the aluminum plate burried in the goop that are not obvious and were not mentioned in the other write-ups I found. Dig around and find them on the edge opposite the wiring inlet before trying to pry the plate out.

    I cut the wires as long as possible, crimped terminals on the ends and then screwed the HEI module to the inside of the original module's housing as a heatsink. The wires are not quite long enough for the blue strain relief block to be secured in its intended location, so I just left the wires hanging out the bottom between the box and fender instead of grafting extensions to the wires.

    The other write-ups were a little confusing to me because they would sometimes reference the wire colors on the module (ford) and sometimes the colors in the jeep harness, but never the two together.
    Here's a breakdown of the wiring connections with respect to a 1990 wiring harness referenced from the wire colors on the Duraspark Module:
    In the two-wire plug:
    • White on the original module is for the duraspark cranking retard and is the one that is not used on the HEI. It corresponds to Green in the harness.
    • Red on the original module is power coming in, corresponds to yellow in the harness. Connect to B on the HEI.

    In the four wire plug:
    • Orange on the original module is Distributor Pickup Pos. Corresponds Light Blue in the harness. Connect to W on the HEI.
    • Purple on the original module is Distributor Pickup Neg. Corresponds to White in the harness. Connect to G on the HEI.
    • Green on the original module is Coil Neg. Corresponds to Green w/ White Stripe in the harness. Connect to C on the HEI.
    • Black on the original module is Distributor Ground. Corresponds to Black in the harness. Connect to Grounding Terminal on HEI.

    I was always confused about distributor pickup pos and neg. How can you tell which is which? My distributor plug disintegrated a long time ago and I always wondered if I had it hooked up right. I tried it the other way once and the coil got smoking hot so apparently it does matter... Well, the wires on my distributor are Black w/ Orange Stripe, Black w/ Purple Stripe and Solid Black, which correlate with the Ford wiring colors of Orange=Pos and Purple=Neg.

    Some said that TFI conversion was prerequisite, but I'm not convinced that it is. The HEI system was designed to work without the resistance wire to the coil, but that resistance wire only effects the voltage at the coil, the ignition module gets its power upstream of the resistance wire. I had already done TFI, so my coil could run 12v, but I did not dig out the resistance wire so I'm not getting as much spark as I could. I will probably take it out eventually, but I'm not in a big hurry.

    The new HEI module changed the timing considerably and I had to advance the timing to get it back to spec.

    If I were doing it again I'm not sure I wouldn't just get a generic ford duraspark module and graft the jeep plugs onto it. The regular ford module is a lot cheaper than the jeep specific module. The only difference is the type of plug connecting it to the wiring harness.

    Check the attachment for a diagram with jeep and ford colors.

    Here are some resources I found useful:
    A nice concise wiring diagram with the ford colors on it:
    Concise diagram with Jeep colors:
    A bit more detailed write-up, but not jeep specific:
    This is a pretty common ford mod; google "duraspark hei" and you'll get a lot more references.
    Last edited by Walt; 08-29-2009, 06:35 PM.
    90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!

  • #2
    Oops, found a mistake on the originally attached diagram. Revised diagram attached.
    90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


    • #3
      The cap and rotor from a TFI system should be used in the event you have a higher voltage coil. Module will work either way.
      Mark B. Jones

      Originally posted by GrandWag&Prix
      Actually, now that I think about it, that could be either awesome or really terrible.

      '79 Cherokee Chief "Junaluska"


      • #4
        You just created the Jaguar ignition module used in the 80's. A black box that costs over $200 that, if you open up, contains a GM HEI module that you can buy for $20.
        David "If all else fails, read the instructions."
        83 Wag Lt,BJ's 6"lift,360/727/Pinned229,D44/trac-lok,AMC20/lock-right,35/12.50 Baja MTZ,Pro-Jection EFI.
        10$ NP229 fix


        • #5
          Duraspark to HEI Module- Updated- Now a year and a half later...

          Well, I never updated this post with the disappointing part of the 'upgrade'. I had several problems with the 4-pin HEI module that really had me close to just slapping a duraspark module back in. But I've got a TBI system in the works, so I thought I'd better slog it out withe the HEI.
          My issues were:
          --Rough idle
          --Dies when A/C kicks in
          --When cold, dies going into gear
          --When restarted hot, dies going into gear
          To get around these issues I bumped up the idle. And I found several references on here to others that had similar rough idle/die on A/C problems that bumped up the idle and were just living with it. Like this one:

          It seemed like anything that pushed the idle down below a certain threshold would cause the spark to cut out altogether and the motor would just die; like the A/C load, or engaging the transmission.
          The guy in the other thread says he resolved it by bypassing the resistor wire. But then he goes on to say he was able to reduce his idle from 1100 to 850; and if he still has to run the idle up at 850, I doubt the problem is really fixed.
          I jumpered the coil straight to the battery at one point and it didn't help my problems at all. And the TFI coil runs at stock voltage just fine with the duraspark module, so I don't see how that could be a factor anyway.
          Anyhow... I never did resolve the problems with the 4-pin module, but in the course of putting in the TBI wiring harness, I made a big breakthrough.
          Now I'm running the 8-pin TBI module without the computer hooked up to it (yeah, it will work without the computer hooked up to it!). And apparently there are some differences between the 4 and 8 pin signals. I poked around and found some discussion around the different types of HEI modules on megasquirt's website: apparently the 4 pin module passes a sine-wave signal, where the 8-pin converts it to a square wave. And apparently this square wave works a LOT better for me. Maybe the duraspark pickup doesn't put out as strong of a signal as the HEI pickup it was designed to work with?
          I've got my idle back down to normal, it's smooth and none of the dying problems like A/C, and just after startup.
          So, your mileage may vary, but if you too are experiencing these problems with the HEI module, it may be worth trying out an 8-pin module.
          Last edited by Walt; 02-15-2011, 07:04 AM.
          90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


          • #6
            Another update: I put a timing light and vac gauge on it this afternoon for the first time after having swapped the module. It was idling really well having just been tuned by ear.
            The timing had shifted 3 deg advanced with the module change.
            Played with the idle mixture and I've got it idling well again at 600 rpm (in gear) with 14.5" of vac. No dying issues of any kind, in gear or with A/C.
            I can't believe I suffered with that other HEI module for a year and a half!
            90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


            • #7
              1989 "KRONK"
              Detroit front/rear 4.27 gears
              Ramsey 9000 modified bronco winch bumper
              Built 360/ 700r w/ 241c Lokar floor shifter
              Hydro-boosted brakes
              20" wheels w/ 35" Toyos
              15" Welds w/35" Uncut mud boggers
              Dual Ram Air /MSD TFI Ignition /Dakota Dash


              • #8
                Thanks for updating your thread...

                '43 cj2a
                '51 Willys p/u
                '51 Willys Parkway Conversion
                '68 Panel Delivery
                '74 CJ5
                '75 J-20 Wrecker
                '75 J-20 Cummins service bed
                '77 J-10 p/u
                '79 Cherokee
                '88 Grand Wagoneer
                '98 Grand Cherokee


                • #9
                  Well, now that I look at the wiring diagrams, I am cornfused again...
                  In theory nothing should have changed in the HEI module wiring when I connected the new customefis TBI harness with the 8 pin module. But new harness' reluctor polarity doesn't agree with what the standard ford colors say it should be.
                  I did my homework very carefully and made absolutely sure to connect the reluctor wires with the correct polarity, but now that I look at the info in the megasquirt link below, it looks to me that the reluctor polarity on my new customefis TBI harness is REVERSED from what the ford wiring diagrams say it should be.
                  Now, with the 8-pin module installed:
                  Purple from the distributor is connected to the P(ositive) on the module
                  Orange from the distributor is connected to N(egative) on the module.
                  Standard ford color coding says the trigger wiring is:
                  But this setup is working beautifully wired up 'wrong'. Maybe because our distributor turns clockwise and ford turns counter-clockwise? And signal polarity is reversed? That might make sense.
                  I was so certain about the correct labeling of Pos and Ned coming from the trigger (based on color) that I didn't try it the 'wrong' way with the 4-pin module.
                  Maybe I'll switch polarity on the 4-pin module and try it again, just to confirm that.
                  Here's where I'm getting my information on 7-8 pin modules:
                  That link lays out what each terminal does.
                  Last edited by Walt; 02-22-2011, 09:06 PM.
                  90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


                  • #10
                    Thanks Walt!

                    Great information there.
                    (Ristow) fram....that deserves a ratchet upside the head.


                    • #11
                      Originally posted by asphaltrockdweller
                      Thanks Walt!

                      Great information there.
                      Don't thank me yet! I still don't understand why it didn't work before!
                      If the 4-pin problem is a polarity issue, it shouldn't work any better with the 8-pin hooked up reversed. The timing only shifted 3 deg when the 8-pin module went in. A polarity problem should have been a much bigger shift.
                      Here's another megasquirt manual page that says the 4-pin W terminal should be Positive:
                      Which 'should' correspond to Orange in the Ford color scheme.
                      However, the megasquirt info also says "The 4-pin HEI uses a negative-to-positive transition, while the 7/8-pin uses a positive-to-negative transition". If the Ford module is ALSO uses a positive-to-negative transition, that would explain why the 4-pin module works so badly for me.
                      But it doesn't explain why the 8-pin module works so well hooked up opposite!
                      I'm inclined to believe the reason the 4-pin module didn't work is something else. Like, maybe the 4-pin module is just not triggered very well by the ford pickup coil, at least not near idle. Where the 8-pin converts the sine wave from the reluctor into a square wave that is much more reliable?
                      Last edited by Walt; 02-23-2011, 07:55 AM.
                      90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


                      • #12
                        OK, I have confirmed that my 4-pin wiring did indeed connect the Orange/Blk reluctor wire (that Ford says is Positive) to the W terminal on the 4-pin module (that GM says is positive). And that did work..., but I couldn't get it to idle below ~800 and had issues with the motor dying at various times.
                        The new TBI harness with the 8-pin module has the Orange/Blk reluctor wire connected to the N(egative) terminal on the 8-pin module. Which makes sense, if the 4-pin HEI uses a negative-to-positive transition, and the 7/8-pin uses a positive-to-negative transition. If the 4-pin module was connected properly, then the 8-pin would need to be reversed, or it would be triggering off of the 'dirty' transition.
                        So, to summarize my findings:
                        The 4-pin module worked badly for me. YMMV... I didn't try another 4-pin to rule out issues with this unique module, so it may be just one bad module. Given others' experience with the 4-pin module, though, I don't think it was a one-off thing.
                        The 8-pin module is working beautifully in place of the 4-pin module with only 5 of the pins connected (4 pins plus ground).
                        Reluctor polarity is REVERSED with the 8-pin module. ie.- reluctor Orange/Blk connected to 8-pin module N(egative) and reluctor Purple/Blk connected to 8-pin module P(ositive) utilizing the original duraspark module's 4x plug.
                        Other wiring terminals:
                        8-pin "+" is connected to switched 12v+ supplied through the original duraspark module's 2x plug.
                        8-pin "C" is connected to Coil Negative terminal through the original duraspark module's 2x plug.
                        8-pin "G" is connected to ground
                        8-pin "B", "R", "E" are N/A (mine are currently not hooked up to anything, until I get the ECM installed and complete the TBI install).
                        Last edited by Walt; 02-23-2011, 08:45 AM.
                        90 G Wag.- New Motor/Trans/TC...Soon to have TBI!: CS-144 Alt; Parallel Flow A/C Condenser; Read this BEFORE you install an HEI ignition module!


                        • #13
                          Great write up, you put in a lot of time an analysis, here are some notes from my seat of the pants hillybilly work.

                          I have in 4-pin on Gonzo with the stock dizzy (TIF cap)
                          8 pin in thumper, tied into the TBI computer, and the stock dizzy locked out.

                          Both trucks run/idle great.
                          Both trucks had issues when I set them and I had to change the polarity on the wires from where I started. I don't remember if I started with them correct or reversed, or one each....I would have to check the wires to see how they are set up currently....
                          I can also tell you when I pulled the TBI off my CJ (360/MSG dizzy) and put the stock back in I had the wires one way at first and had to reverse them, it would idle but not rev up with the advance hooked up.
                          (And to redneck it up my DOG told me to reverse the wires on Thumper to get it to run correctly, I was stumped took the 2 for a walk and was venting to Cherokee the older one on why it would not run, he then crossed leashed with Diva, I uncrossed he looked at me and crossed again, very unusual for him, this happened a couple more times and I said out load, "switch the wires on the module?" and he stopped crossing leashes.....)

                          The modules will fire the coil in either polarity but it messes with the timing, one way fires early and the other latter, if you have issue put a dial timing light on and watch how the advance works as you increase rpm's, start with the vac advance disconnected.


                          • #14
                            Walt, great write-up! I have always wondered about the distributor polarity wiring differences between all the diagrams that you find on the net.

                            A test you might want to try is to check distributor phasing by cutting a window in an old distributor cap (between the number one spark plug terminal and the coil plug terminal). Then as you set your timing check how close the rotor is pointing to the number one plug. Check mechanical advance by revving up the engine and then use a vacuum pump to check vacuum advance.

                            Remember the distributor turns at 1/2 crank speed. So 5 degrees of rotor movement equals 10 degrees at the crank. If the rotor is getting too close to the next terminal while idling or at full advance then you may want to switch your trigger polarity or re-index the reluctor wheel on the distributor.
                            1991 GW 401 /727TF/NP229 /4" Skyjacker /EBL TBI /CS-144
                            1981 J10 401 /727TF/NP208 /6" Superlift /CS-144


                            • #15
                              Now Im really confused, I have read about 12 pages about doing this. I want the 8 pin set up. What are all the parts I need to buy?
                              87 grand wag, 84 cj7