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my first gm hei conversion has failed

Old 06-11-2018, 07:15 PM
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my first gm hei conversion has failed

Well, 212 days ago I completed the hei conversion on my blue 1977 Dodge W200 (360 5.9L).

Here is my original post regarding this mod:

Sunday that system failed, luckily in the driveway before I left to run an errand . I got it going again (I THINK, haven't driven it far yet) but, not before replacing both the module and coil.

The engine was running and then it just quite and wouldn't restart. In the process of troubleshooting it started blowing the 15A fuse protecting the ignition circuit. I replaced the coil first since I already had one, no dice. Then scrambled to get a replacement module at the auto part store. Checked to make sure it was still dead.. Installed the module and she fired right up. So, I decided to put the old coil back on... dead again. Put, the new coil back on.. it lives!

So, from what I can tell one component failed and killed the other. I'm guessing the coil since it was super hot when I first touched it.

Both the failed and replacement coils are Motorcraft DG470.

I compared the resistance of the two. The resistance of my meter leads was about .3 or .4 ohms.

Good coil:
Primary .7 (Subtract .3) = .4 Ohms
Secondary 7.96K Ohms

Bad Coil:
Primary .4 (Subtract .3) = .1 Ohm
Secondary 7.58K Ohms

As you can see they have different readings. But without specs I wouldn't know if it was good or not based on ohm readings alone. From what I can tell acceptable ranges vary greatly for hei coils depending on their intended application or whether their stock/oem vs high performance/aftermarket.

On the bad coil wouldn't the primary basically short out the module? From what I understand this shouldn't be higher than .5 ohms, higher will lower output power.

And there's like a 380? Ohms different between the secondaries. Not sure what that means.

The failed module was a NAPA TP45 and was replaced with a BWD CBE4 from Oreily since my local NAPA was already closed for the day.

I'm concerned about the quality of CBE4 as I've read the TP45 is one of the better aftermarket modules and is comparable to the GM 990 (high performance series module). It has circuits for variable dwell and current limiting which cheaper modules do not implement. Out of curiosity I'm thinking about writing BWD concerning this matter but, ultimately I'll probably switch back to the TP45.

I'm still wondering why my coil failed (if that's what caused this). I went with an OEM coil instead of aftermarket in hopes of better quality and reliability.

Wonder if it was a lemon or maybe the way I've mounted these device is negativity affecting their lifespan? (Pictures in my other thread linked above)

Anyway, I lucked out this time. You see I never got around to purchasing a spare coil and module after I did this conversion. The coil I had was intended for my second hei conversion and I had no spare module. I'll fix that for sure!

Last edited by dodgem880; 06-11-2018 at 07:28 PM.
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Old 06-17-2018, 07:39 AM
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Well, I turned my bad coil and module in on warranty. I already got the replacement module from napa. Still waiting for the coil.

The truck didn't seem to run as well as I recall with the CBE4 module,so I swapped it out for the TP45. That seemed to fix that.

When I first switched over to hei, I immediate noticed a rapid tick/buzzing sound as the engine idled. I assume I'm hearing the e-coil fire or arcing in the distributor. That noise was quieter with the CBE4. So, I'm guessing the TP45 must produce hotter spark? I don't know.

At least now I have a spare coil and module on onboard.

Last edited by dodgem880; 06-17-2018 at 08:08 AM.
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Old 06-17-2018, 07:53 AM
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I carry a ECU and a Ballast with me.... Now that I have had one in the truck as a spare. I've never had to use
Murph's law I guess...
Glad you got your back up and running.... Keep us posted...
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