Vannin' Home Forums Dodge Performance (Dodge) ICM?

mine looks pretty old but having no issues with it. i was at the wrecking yard and seen 2 that were new looking and could probably get very cheap as a backup but was wondering about the different colors. Both were blue, is that just something the different companies that made them do is paint them different?  

I'm all for spares!!

There are several different colors, from different manufacturers, and for different applications, such as daily driver, street/strip, and full on strip.

Some (most new ones now...) are quite cheaply made Chinese products... most likely the plain silvery steel cased ones. Their connector pins may not even be the correct diameter to mate reliably, if at all, with the original ECU connector on the wiring harness!

The oldest ECUs (1972-1979) had 5 pins in their connector. You could tell them by the black painted body and dual ballast resistor with 4 terminals on the firewall. The newer ECUs only contain 4 pins, and use a single element ballast resistor with 2 terminals.

The now missing 5th ECU pin was just a wired ground. The newer ECUs only use their metal case for ground, so they need very clean surfaces on the firewall, frequently requiring periodic maintenance of the ground surfaces.

The main precaution I'm aware of with ECUs aside from their source is that since these are capacitive switching type ignition modules, they have a pretty firm top end in terms of how many RPMs you can run and still have sufficient energy for the coil to generate a spark. (Dwell is fixed in these - not adjustable)

For performance and race applications MOPAR sells a special ECU with a shorter dwell so it can run at higher RPMs. These ECUs are best identified by their part number...

The black or orange painted ECUs are apt to be original MOPAR ECUs, and are good up to around 6000 RPMs, as are the blue anodized replacement ECUs. If it's original MOPAR, you'll see the little Chrysler Pentastar symbol near the part number. The orange ECU claims a hotter spark than the black or blue units.

The silver ECUs, if Chinese, who knows what RPM they're rated for! If USA made, up to around 8000 RPMs. They claim an even hotter spark than the orange ECU.

Some of the gold anodized ECUs are in the 6000 RPM range, while some shiny (polished) gold ones are in the 10-12,000 RPM range! The highest RPM units are strip only ECUs. They have a very short, very hot spark.

-You can see where part numbers are a must to tell what you've got!

ok, then does this look incorrect? my van is a '75. the wire harness plug has 5 wires going into it. The ECU has only 4 pins and the ballast resistor has the 4 terminals.

The 4-pin ECU *should* work in that system; the extra pin was just a wired ground. You can use a 4-pin ECU in a 5 pin ECU application, but not vice-versa; the 5-pin ECU needs the dual (4-terminal) resistor, the 4 pin ECU doesn't care.

They got cheaper/more clever later on and relied on the bolts through the chassis as the ground. This ECU was very likely a replacement unit, since you have the dual resistor.

Anytime you take one of these ECUs off, scrupulously clean the metal flanges where the bolts go through, and likewise clean the surfaces on the firewall which will make contact with the flanges, and clean the undersides of the heads of the mounting bolts. A bit of dielectric grease on these clean surfaces and the bolt threads will go a long way towards keeping your ignition system reliable.

If by chance you should ever strip out one of the mounting bolt holes through the firewall sheetmetal, just move the ECU over a bit and drill new holes, cleaning up the new location.

Thanks for the info. I did read on other forums also that they said it would work.