HEI / Duraspark conversion -or- "I'm a Tard"
PistolDave
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- Lubbock, Texas
- Vehicle(s)
- 1977 CJ-7 SBC 5.7 TBI, TH400, D300, D44 front, D44 rear, 4.56's Detroit / Truetrac, SOA, 35" MTR-K's,
------------86 CJ-7 258 - T5 - AMC20/D30 3.30 open f/r - Dana 300 - 2" BDS wrangler springs - 31x10.5 BFG
************* 83 CJ7 3.8L, T19 5.1:1, D300, D30/AMC20, 4.11's, Chevy TBI, OX lockers, OME 2.5" lift YJ springs, 33x10.50/15 KM3's, Lots of rust and zip ties.
Just learned something the hard way and thought I would share. If this is common knowledge that every one already knows, well, please excuse my ignorance.
I recently got my 401 rebuilt and back together in my -7, and decided an ignition upgrade was in order. My engine was still running a points distributor with an MSD 6a box. I decided to do the "large cap" Ford duraspark distributor using a GM 4 pin HEI module to trigger a TFI coil. After assembling all of the pieces, wiring them up and getting everything installed, I fired the engine up and lo and behold it fired right off! Sucess!!! Or not quite, because as soon as the vacuum advance pot was connected to vacuum, the engine would instantly die. I triple checked everything I could think of and found nothing wrong. Looking at the reluctor wheel, it seemed to me it was a little out of location with respect to the pickup coil based on the position of the rotor. So, i had the bright idea of rephasing the reluctor about 25 degrees by filing a new notch for the roll pin. Ha! now my vacuum advance works properly.
The engine now runs pretty decent, timing advances like it should, everything seems kosher, except i notice my HEI module is awfully hot. I have it mounted on the underside of an empty duraspark case with premium heat paste, and a computer heat sink scabbed onto the top. Over the course of 2 days I go through a couple of HEI modules. What the heck? In the course of researching HEI failures I discover a few things:
1. Not all HEI modules are created equal, you get what you pay for.
2. A 16 gauge wire supplying power to the HEI module pin 'B' is not enough, according to experts on this subject it needs to be 12, or even better 10 ga.
3. Polarity from the pickup coil to the HEI module is VERY important. If I had done my homework upfront I would have discovered that the purple wire from the Dist. needs to go to the 'G' teminal on the module, and the orange Dist. wire needs to go to the 'W' terminal. If I had wired mine this way to start with, rephasing the reluctor would have been totally unnecessary.
Now that mine is wired correctly with the proper wire size and with a good quality module, it seems to be running perfectly. Time will tell but hopefully it is solved.
Too Long, Didn't Read version: Pay attention to the dang instructions.
Dave
I recently got my 401 rebuilt and back together in my -7, and decided an ignition upgrade was in order. My engine was still running a points distributor with an MSD 6a box. I decided to do the "large cap" Ford duraspark distributor using a GM 4 pin HEI module to trigger a TFI coil. After assembling all of the pieces, wiring them up and getting everything installed, I fired the engine up and lo and behold it fired right off! Sucess!!! Or not quite, because as soon as the vacuum advance pot was connected to vacuum, the engine would instantly die. I triple checked everything I could think of and found nothing wrong. Looking at the reluctor wheel, it seemed to me it was a little out of location with respect to the pickup coil based on the position of the rotor. So, i had the bright idea of rephasing the reluctor about 25 degrees by filing a new notch for the roll pin. Ha! now my vacuum advance works properly.
The engine now runs pretty decent, timing advances like it should, everything seems kosher, except i notice my HEI module is awfully hot. I have it mounted on the underside of an empty duraspark case with premium heat paste, and a computer heat sink scabbed onto the top. Over the course of 2 days I go through a couple of HEI modules. What the heck? In the course of researching HEI failures I discover a few things:
1. Not all HEI modules are created equal, you get what you pay for.
2. A 16 gauge wire supplying power to the HEI module pin 'B' is not enough, according to experts on this subject it needs to be 12, or even better 10 ga.
3. Polarity from the pickup coil to the HEI module is VERY important. If I had done my homework upfront I would have discovered that the purple wire from the Dist. needs to go to the 'G' teminal on the module, and the orange Dist. wire needs to go to the 'W' terminal. If I had wired mine this way to start with, rephasing the reluctor would have been totally unnecessary.
Now that mine is wired correctly with the proper wire size and with a good quality module, it seems to be running perfectly. Time will tell but hopefully it is solved.
Too Long, Didn't Read version: Pay attention to the dang instructions.
Dave
