I bought my '90 Montero in January this year. It had a lot of work done on it, and was running great. My neighbor, who had commissioned the restoration, decided to switch to an automatic vehicle and I jumped at the chance to buy it. Then in Feb, it started to randomly die. Usually it would do it a couple times until it got warmed up, but then got worse until it consistently dies within 45 seconds of starting.

I was on a trip in the Montero when it started dying consistently, and took it into a shop. They said that for some reason the fuel injectors were being shut down and so it was stalling. It was below freezing that week, and I told them when the ecu got warmed up, it usually ran OK and so they put a little heat on the ecu with a heat gun, and it did the trick, so I drove the 300 miles home without stopping (well once for gas). I don't know if this is significant or not. It's warmer now, and still stalls out.

I had some diagnostics done at another shop after I got home, and was told that my ecu was bad. So I got a reman unit from ebay. It fixed the stalling problem, but now when I start it up, it idles high (~1800) until it warms up, and then starts "loping" (bouncing between ~1500 & 1900 rpms) at idle. If I turn on the AC, it will drop down to a normal idle for a few minutes but then start revving up again. If id drive with the AC on, then it will either rev high or bounce between the 1200 & 1500 rpms when I stop.

I'm interested in getting more mechanical, but I'm a real novice. I've looked at the "Solving the 3.0l V6 Idle Problem" article, cleaned out the throttle body, replaced the isc motor, replaced the ignition control module, tried to check for vacuum leaks, checked for cracked wiring and bad connections, but haven't found any problems.

I don't know why the two different ecus would give two different behaviors. The one idles fine, but dies after 45 seconds, and the other runs, but then idles high and does the surging (revving, loping, not sure what to call it).

I sent the first ecu in to be remanufactured, and it was worked on and bench tested, and should be good. But the vehicle still dies. The second ecu is the "newer" kind that isn't supposed to have the capacitor problems the original had.

Any insight would be appreciated. Anybody seen this kind of thing before? Where should I look next?


Thanks.

Just call me Captain Obvious, but it sounds like it was misdiagnosed on the first ECU, and that isn'tthe problem. The second one sounds like it has it's own issues. You're a newbie you say? You want to learn? I recommend you go to mitsubishilinks.com and look/print the fsm for your truck. Check out the " 89 3.0 driveability manual" to your printings. Follow the steps/procedures in those. Another thing you can do is a "haztoys wiring tune-up" google that. Have your white vinegar and water spray bottles handy. While cleaning figure out what all the connectors are, notice their locations.

My $.02.

Thanks. I've downloaded the powertrain diagnostics PDF from mistubishilinks.com, and I also have a Haynes manual which has a list of possible causes for the erratic idle of the second ecu.

The driveability pdf is for the '87. How much of that is applicable to the '90?

I'm working through the checklists, but wanted to know if there was anything obvious to someone familiar with the vehicle that might be happening.

Thanks.

I was going through the wiring and found a part with some exposed wiring. Not sure if it would cause any problems. I can't get the part number off the part. The part is attached to the wiring by the ignition coil and ignition control module, but on the back side, mounted by where the throttle attaches to the intake manifold. Anyone know what this is? The wire covering is sliced open on both wires right at the base of the part where it comes out of the metal casing. I'm trying to attach a photo....

Thanks,

Alex.

There were two driveabilty papers in mitsubishilinks. One for the 87 carbed vehicles, and one for the 89.

I don't see an '89 driveability PDF there now.
However, I've been trying to trace the problem today, and discovered while switching out the ECUs that if I wiggle the wires a bit that are coming out of the middle connector of the ECU, I can cause a stall or recover from a stall when it starts. I'm not wrenching on them, just poking them a bit to move them. Seems especially to be the blue/Green wire in the corner of the connector. I don't know if this would indicate that the wire has a short in it or if the wire is not making a good connection in the connector, or if the connector is letting current across wires and causing issues, or what. And it may or may not explain why the newer ECU is idling high and loping.

So that's where I am at right now. Not sure how to check the connector. The wiring harness is pretty tight up in there under glove box. Don't know if I should cut the ECU connector out and splice in some longer wires or what. Any opinions?

Thanks.

OK. I downloaded that one earlier and have looked through it. Is there a way to get the codes without the diagnostic reader? I hooked up an analog meter to the pins on the diagnostic connector, but it's giving me a steady pattern, so that means no error codes are being thrown, right?

Thanks.

that i dunno. i asked about that on here and never got an answer

Remove the ecu connector and make sure all the pins are pushed all the way into the connector. Clean the connector with white vinegar. If the wire is loose in the connector, pull it out and bend the little spur out furter so it hangs when inserted. Read the electrical section intro stuff about how to take the wires out of the connector. The 89 fsm has a better section on this than the 90fsm...

A single steady pulse is the indicator of a healthy ecu with no stored codes. Flatline is a dead ecu. Codes are long and short pulses.

The pictured part is one of two components on the underside of the coil bracket that comprise an "LC filter", which conditions the spark signal for the tach. If grounded, that circuit can kill the spark. Use liquid electrical tape to reseal and insulate.