What causes an ECU to fail?

[carter davidson]

My 1977 M882 quit last week as I was driving out of my driveway, fuel tank was full so I checked the spark and found none. After replacing the unit I began to wonder what caused this, anyone know the answer?



I'm melting!

[Gordon Maney]

One or more internal components failing, internal connections failing, external connections failing. Physical damage from vibration or heat contributing to any of the above mentioned possibilities.

[ram fan]

I always figured it was just the electronics inside failing over time, much like the voltage regulator. Voltage surges probably don't help either. I always keep and extra coil, VR and ECU handy in the toolbox, as you know, you can never tell when they'll fail.
Craig

[ram fan]

BTW, pull all the Mopar (factory) units you find in the salvage yards, as they are MUCH better than todays China junk. I had a new (China) one on my '77 M-883 that I put in a few years ago, it already went bad. At the time I had a '74 PW that hasn't run in years that I was using for parts. Inside the '74 was the original or at least very old Chrysler unit complete with rusty outside. I thought I'd at least try since the truck was at home anyway. I pulled it out and put in the '77. She fired right up and have been running on it for over a year now!
Craig

[The Other Ross]

As stated before on this forum the answer to all things electrical regarding these trucks is GROUND Everything.

[712edf]

as stated before on this forum the answer to all things electrical regarding these trucks is ground everything.

amen!

[carter davidson]

Thanks all, I will add a ground strap and look for some American made ECUs and keep spares of possible failure items as mentioned. I thought maybe the failure was the result of some specific shortcoming in the ign. or something in the electrical system that I had overlooked. I did notice when I pulled the old one that the screw was missing from the plug and possibly that was the cause of the burnout due to lost elec. contact although the plug seemed tight on the unit when I removed it to install the new one, the screw has been replaced and I hope that will eliminate future problems.

The ECU that failed was one that came with the truck.

Thanks again guys. Carter

[KRB64]

The ECU that failed was one that came with the truck.

Thanks again guys. Carter

You mean from like 1977? I'd call that good!

Even the new Mopar ones don't last (maybe they are same as made in china?). At least that was my experience. The $4X unit from Dodge lasted about a year.

Like posted here, it could be that we are blaming the unit when it is only a symptom, not a cause (poor ground, faulty alt, etc?)

[carter davidson]

Can't say it's the factory installed one, it was on the truck when I got it in 1998, the milage at that time was 21,372 and today 24,831. The AutoZone replacement was assembled in the USA from "imported" parts, most likely China.

[jakenok]

Google "HEI swap" for Dodge and take a look at the simple process of replacing the box you showed and the ballast resistor with an HEI module from a Chevy. It allows full voltage to the points, is cheap, and an afternoon job.

[MoparFreak69]

EEK, Chevy parts in a Mopar? I'll pass.
Like others mentioned above, as long as all your connections are tight/clean and grounds are good you can run one of those modules practically indefinately.
HEI units often (as in like clockwork) burn the coil leads out of the cap because the ground is a small trace taken from the distributor housing itself. You also will find yourself replacing the cap and rotor way more often on an HEI unit than the stock Mopar jobber. Yes the HEI is nice to have everything in one unit, but the sheer bulk of the thing means you arent really saving any space at all, its all just packed on the back of your intake and the size of those things can make some situations impossible.
Like Ram Fan mentioned, go to your local junkyard and grab a couple outta any old Mopar and keep it laying around. It will be screaming cheap, will probably last you a lot longer than a new replacement, and if your connections and grounds are good might last you the rest of the life of the rig. My '68 Dart had its original (as evidenced by part number) when I picked it up several years ago. Before I tore the car down I started it up and it ran just fine. Cant beat that for reliability.

[carter davidson]

Thanks for the education fellow posters, I have the truck starting and running well now with the new ECU installed and grounded but have not had the time to check out the local yards for US made used units, that will have to be put off until the white crap on the ground melts.

I won't be installing a GM HEI at this time unless the new ECU fails and I am unable to find any used orig. OEM ones. I did Google the swap and it looks simple enough to do and might do so when all else fails, but for now since all's well I will leave well enough alone and run what I have.

Thank you all for taking the time to read and answer my question. Your help is appreciated. Carter