Hi All!

I I am still troubleshooting and keeping dim hope alive in trying to get my 91 LWB Monty going. Starting a separate thread for this topic so it doesn't get buried in the original gargantuan thread ( Stranded... ).

So...

--Caps can leak electrolytic fluid, dissolve traces, etc.

--ISC coils can short causing excess current to fry the driver card.

--Wire / harness shorts? Anyone have any common culprits?

What else? My original was rebuilt by AV-Pro AFTER my Montero no-spark problem started. The truck has not run since that fateful day. When I got the rebuilt ECU back from AV I plugged it in and it gave the "A-OK" signal at the test connector. That did not fix the no-spark problem. Now after only cranking the ignition sporadically during troubleshooting over the last few months I noticed that the ECU is no longer giving a signal (not even solid "on"--which is the code for dead ecu). Just nothing.

Backup ecu still gives "A-OK" code, but I don't want to risk harming that one until I figure out what happened with the rebuilt one.

I don't have a spare ISC, and the current one tests out fine. I know you can have good test readings and still have a bad ISC, but before I replace it I'd like to explore other possible causes.

Thanks in advance!

Did you ever trace the on/off signal from the ecu to the power transistor?

I'm pretty sure I observed a pulse with an led. I'm going to do some testing tomorrow so I'll confirm that.

The PT control circuit wire is white, and goes to position 28 in the center connector at the ecu, the only white wire on that connector. There are no intervening connectors in the circuit.

Ok. Thanks Eddy. I confirmed I do have continuity from ecu connector to PT connector.

In examining the ECU I noticed discoloration on the top, middle pin of the small connector slot. There is corrosion (blue) on several pins, but on this middle pin its dark and, though its not 100% clear, it looks burnt. could be rust though. Either way it seems worth tracing. I'm going to stare at the wiring diagram some more and see what that goes to. Hopefully ISC, then at least that would point to something broken!

Pics:

[urlhttps://lh4.googleusercontent.com/-pk0ygYq4Q1I/UbahPO2ws0I/AAAAAAAADIc/F_DH-zgoeiA/w405-h720-no/IMG_20130610_225955_837.jpg]connector burnt?[/url]

OK. Turns out that those pins in the above pic go to unlikely ecu killer candidates. Best I can tell they are pins 45 and 50 and go to fuse #1 and Inhibitor Switch / MPI Relay respectively.

I did pull my ICS and found that it is toast. Pins 1&2 and 4&5 test open on my multimeter (new one tests 42ohms at those points). I could have sworn I tested it before and it tested fine. Either it has since died or I suck at diagnostics. I'm leaning toward the latter...

So I have at least one explanation for dead ECU. However, I thought that happened over time. The ECU had been rebuilt and ASSUMED good AFTER my problems started. So that means that if the ECU is indeed dead again then just the occasional cranking during troubleshooting killed it. Can it happen with that little amt of exposure to the turned-evil ICS???

Does this...SPARK...any ideas for anyone? <img src="/forums/images/graemlins/butwiggle.gif" alt="" />

The ics can be a quick killer. It's basically a short back to the ecu when it dies.

What FE said.