1990 ZR-1 ECU got super hot while idling, white smoke appeared

[1971 Judge]

Hey Guys,

Kinda scary moment today. I started my car to put it into the garage.

When I came to a stop and opened my door, I noticed there was white smoke rising from the left driver side by the mirror - just a small amount. I immediately killed the ignition lifted the hood and couldn't see anything. When I touched the plastic ECU box, it was super hot. I then unbolted the (2) 10mm nuts and pulled it off the metal bracket, then flipped it over and removed the (4) small nuts that give access to the actual ECU. I pulled the EPROM out (Haibeck tune). Yes, it smells like something was burning. Ugh...I have no idea what the root cause is. I haven't tried to start the car, but it was running while it was burning up inside the ECU case.

It's tough to diagnose this stuff, but I thought I would you guys if you had any knowledge on this. Recommendations? TIA.

[Corvette95]

I will be following this thread. It is hard to take chance with a rare ECM. Maybe an email to Haibeck would be in order. If not , I would unplug the ECM and turn on the ignition and see if anything else could be the culprit. The downside of that is the DIS which you don't want to fry. Wish I had more to offer. I would also verify the PROM is seated firmly. Look over the harness connector for any signs of high voltage or short before you turn the ignition on. I recommend disconnecting the battery first.

[1971 Judge]

Thank you for replying on this.

Next steps:
1) Cranked car with out EPROM installed - no start.
2) Installed EPROM, started just fine
3) No smoke, no high heat after 60 seconds of idle (this is what worries me - a possible ghost?)
4) Checked codes: H41 - cleared it
5) Restarted car, no issues, no codes, like nothing happened (again, not happy, don't like chasing electrical ghosts)

I'm lucky, my neighbor is a master electrician with all the toys and he does a lot of customer work for restorations. He's going to look at it this weekend.

(Sigh), we'll figure it out. But wow, it came from nowhere.

Thanks again for chiming in. I was a bit emotional earlier.

[Corvette95]

What I originally thought was that the fusible links are directly below (pretty much) under the ECM but since you said the ECM housing was hot, I didn't mention them.

[1971 Judge]

What I originally thought was that the fusible links are directly below (pretty much) under the ECM but since you said the ECM housing was hot, I didn't mention them.

Appreciate helping me think through the possible issues.

Yes, that damn black box was very hot, like it came out of the oven!

Always learning something new with this creature. Still love it. Typical, huh?

[WARP TEN]

Appreciate helping me think through the possible issues.

Yes, that damn black box was very hot, like it came out of the oven!

Always learning something new with this creature. Still love it. Typical, huh?

Yes we are all closet masochists.....Bob

[1971 Judge]

Guys,

Have an update with good news!

The root cause was water trapped in the latch area where the hood posts lock into. Apparently, previous owner siliconed over the weep hole, so if water gets in the latch area, it has nowhere to drain, but spill over.

When I pulled into my garage, I drive onto my lift and it "bumps" the car, spilling water on the electrical post that sits directly behind the battery causing the smoke (or vapor). Either way, the water splashed down onto the electrical post where the fusible links connect and gave off a strong electrical odor.

I wrapped the wires in electrical tape and then put some A/C insulation around the terminal and fusible links to better shield it from water.

Big thanks to Mark Haibeck for responding to me initial email. I thought I had an ECU problem, and thankfully, that wasn't the issue. Also, want to recognize Bill Schroeder for being a friend and calling me up about the water issue, BINGO!

Got lucky on this one!