Mopar ecm issues. Why wont they work?

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69moredoor

69moredoor

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Ok folks. The stock mopar ecm on the 80 apsen leaked it’s ooze all over the place. It still worked! Ordered a new one from rock auto. A standard (red/white box). Installed. Wouldnt work. I know people complain about the aftermarket ones so I figured it was just a bad one. Yesterday went to Napa. Got one of theirs. Started car today with no problem with the old one. Installed the Napa one…nope. Nothing. I had a third new one that I bought for the d100 project. Another standard one. Same thing. Nothing. But the original one works. Figured maybe a grounding issue. Ran a separate ground right to the battery and put the grounding star washers under it. Nope. Still nothing. So what’s the story? What should I be doing?
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Did the nut come off of the center post on the original one and stay in the plug? I've had that in the past keeping the terminals from making contact?
 
Nope. The original one the nut stayed. The aftermarket ones came off but were easy to get out

and no idea why the pics posted multiple times
 
What's wrong with using the old one? Just want to keep a spare?
 
cudamark said:
What's wrong with using the old one? Just want to keep a spare?
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The old one leaked all the goo down the fender. Exposing the board. Wanted to use the original as a spare. Dont want the original going out on the race
 
Some guys have expermented with repotting using epoxy or sand and epoxy.

As to the new ones. It would seem like they were manufactured very consistantly.
wink-gif.gif
 
Just to grease the knowledge wheel with some humor….the team name will be
***-pen


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I’ve never gotten multiple dead units, but I had a bunch that would start to miss and break up past 3,500 rpm or so. Aftermarket ones, Mopar replacement ones, etc. I cleaned terminals, ran ground wires, same results. That was years ago and the quality of the ECU’s was already getting bad, I had a few “chrome boxes” that would work but the standard and orange boxes were junk. I ditched them entirely and went with “ready to run” distributors that don’t need the external ECU. Cleans up the engine bay, most of the ones now have better curve adjustment, and you’re still dead in the water either way with an ECU failure since both depend on a board somewhere. Plus most of the ready to run types ditch the ballast resistor too.
 
69moredoor said:
The old one leaked all the goo down the fender. Exposing the board. Wanted to use the original as a spare. Dont want the original going out on the race
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I haven't seen bad potting resin having any effect on whether the ECM works or not. I've had brand new ECM's (both Mopar and aftermarket) leak resin right in the box sitting on the shelf. I've had nasty looking used modules missing most of the resin that worked fine, and as you found out, I've had perfect looking new ones not work at all. If you're going to race, get and MSD system and not worry about it.
 
I've learned to keep all the ecu's I have as there doesnt seem to be a 100% tried and true method for determining good or bad.
What's the part # on the gold/black Napa units? They look like Standard LX101
 
Maybe you have a distributor pickup on the ragged edge. Any chance you have a spare working distributor?

Make absolutely certain you have scraped the box mounting ear for electrical contact.

Also try this: with the box GROUNDED and the harness connected, turn the key to "run." Rig the coil wire with a test gap and separate the dist. connector. Repeatedly tap the bare end of the 2 wire connector from the engine harness onto a ground. Each time you do should produce one single hot "snap!" spark.

Check voltage at coil positive terminal with the key "in run." Voltage should be well below battery, AKA somewhere around 5-10V. If it's lower, you may have low voltage. If it's "same as battery" IE about 12V, the box is not conducting current through the coil. Move to the ballast. Check both ends. One end should be 12V "same as battery" and the other end should be same as what you just measured at the coil. If the battery end is low, check for harness drop. What you are trying to do with these last tests is to determin 1: if the box is conducting current through the coil and 2: If the system is getting adequate voltage through the key/ ballast

You might work the ECU connector in/ out numerous times, maybe some oxidation in there.
 
How to help determine if the boxes are "maybe better" or "maybe worse" quality:

One thing is that many of the really cheap boxes use fake transistors on the outside to make them "look", and the real transistor is a smaller device INSIDE

IF the previous test showed the coil is conducting, then with the thing connected and key "in run" see if there is any voltage on the heat sink/ transistor. It should be same voltage as coil NEGATIVE terminal. If it is zero, it's a fake transistor. That is, the "real" ones---the heat sink and transistor are not grounded. They are insulated with mica, and the "real" boxes would give you one heck of a "tingle" on a running engine.
 
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Thanks hops. will read that. To add confusion (before I read it). I played parts swap with the 79 d100
Two of the new ecus worked fine (did t try the third)
The hood one from the d100 (318)—older unit made in maylsia (see pic) worked in the aspen!
Retried the new ones and yup. Work in the d100 but not the aspen. So…new units work in 79 318
Old units only work in the 80 slant
how’s that for confusing
 
I think it's time to go by the factory manual to check the ECM plug socket and distributor pickup coil terminals for voltage and resistance readings.
 
My 80 slanty Volare leaked it's jelly out in the early 90s, But kept right on running even on the day I sold it last summer. I even borrowed one day when my Orange-box died, and subbed it in for my 367HO, which ran fine on it until I got a new one for the Barracuda. It's probably still running on it. That's about 30 years on no jelly.
 
Is the transistor case 'hot' with the engine running? I was under the impression that this was connected to coil neg, so 200-300v back EMF. Have not been brave enough to stick my finger on it to find out...
 
By "installed" did you actually clean the metal on the fender and bolt it down? These have grounded.


 
Bewy said:
Is the transistor case 'hot' with the engine running? I was under the impression that this was connected to coil neg, so 200-300v back EMF. Have not been brave enough to stick my finger on it to find out...
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The coil is fed by switched and ballasted battery voltage.
AFAIK the ECU is just an amp and a translator for the magnetic pick-up, and the transistor is like a glorified set of points, being a fast-acting ground-interrupter. I can't see how anything over battery voltage can come out of the ECU, and I can't even see how any voltage at all could go into the coil.
The box just needs a ground for translator/amp that turns the magnetic trigger into a signal shape with enough strength to turn the transistor on and off. Oh yeah and a ground for the coil primary side, lol.
Buy what do I know, lol.
 
If you have triple checked the ground and they ecu's are for sure grounded and none of them work id start looking elsewhere. The chances of having 4 bad ecu's are slim. Check for spark at the distributor. Check your coil and check for power on both sides of the ballast. Del has an awesome step by step write up on here. He helped me when I was getting no spark. Ill find the thread and post it here
 
Ditch and go Mallory. Ill pass up a 6AL box at a swap meet for $20 (Nah, Ill flip that SOB faster than a slap shot). Mallory may not be the highest performing but they are rock solid reliable.
 
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