240 CIS Failure: K-Jet Constant Idle System

Here is a component failure inside the sealed black box idle control module.







Here is the resistance of the offending idle motor lead which corresponds to the trace from its input to the failed component on the board. Should be 20 ohms. Looks like voltage from green went to ground from a bit more amperage than the component could handle. The idle motor was sucking up the amps according to the board traces. *Poof* Yet another example of heat striking again!



Here is a picture of the voltage regulator in the alternator. It appears that unstable voltage took out the idle valve and the board. I'd say the idle motor was iffy anyway and gave up the ghost under those circumstances. This was a cheap China-made regulator since replaced by a Bosch.




Note to Charlie:

This is why I suggested you test out this subsystem. This is pretty extreme but not unreasonable and you can see that you never know and run the risk chasing your tail for sure if you don't. There are no published test procedures for the black box, as such, plus its sealed; however, you can test the idle motor for resistance, voltage from the the control module to the idle motor, resistance from the coolant temp sensor leads, voltage from the ignition coil lead and continuity from the throttle switch. If all of that passes, you may have a bum module.

I'll try and post up the measurements of a known good module. Without schematics, we have to assume they are correct; put another way, this modue, due to the failure on the green lead, is shot and for sure would not match know good specs on that lead. Without the schematics or opening up the module, it's hard to know. I did smell kinda funny though.

Usually burnt-up control modules aren't the source of the problem, but the victim. From your really fuzzy photos, I'd guess that the IAC shorted to ground and damaged both the CIS module and the alternator. Or maybe the alternator decided to dump +20volts on the electrical system and took out the CIS module that way.

The damage from running a bad harness maybe?

This makes me want to open up my ICU on my LH 2.2 that I pulled recently. To see if something like that damage exists in it, which I think I may find something like it.

I had a couple instances of smoking harness while driving in mist.

Not the kind of thing you ever want to see when 100 miles from home or even 1 mile.

Love it when circuits let the smoke out of themselves...

Happens.

Hay thanks Howard, I just found my problem and I just kept over looking it. It turned out to be engine harness at the middle of the firewall. There were 3 wires that were just making a connection but barely. It was hard to see but the insulation on the female connectors inside the grey connector was falling apart and I guess when pulling and installing the engine the connections got pushed further apart.
I bought wire with connectors from Dave Barton and did the repair today and problem I had was solved. I had bought this replacement harness about 9 years ago and the wiring is fine but it was those clear rubber looking covering on the female connectors that fell apart from heat and allows the connections to move.
Charlie

Yep, wiring every time. Good stuff, Charlie.