Crank but no fire for 90 2.4 MM

[MitsuMini]

Hey Guys!

Recently bought a beautiful 1990 Mitsu Mighty Max, shop said the ECU was bad but a visual inspection of the ECU board didn't show any scarring or anything concerning (def no popped caps). I went out to the truck with the ECU and plug it in and the truck cranks very well. I tested spark and I noticed I wasn't getting spark through the wires. So I replace the wires and plugs but still no success. Fuel gets to the cylinder as well as spark but I still dont have any kind of firing. Engine has low miles and its in pretty good shape but this issue is what parked it a couple years ago and it's been sitting in a yard since.

The mechanic thought it was the ECU but I don't trust his opinion as he isn't a very successful mechanic. That being said after this most recent event I am suspect of the ECU again. Anyone whos had a ECU fail on these trucks, have you guys seen a similar issue? Crank but no fire? Everything appears to work and i've been slowing going through the ignition system and testing with a multimeter, it looks like most of the electronics are functioning. The only issue I found was a burnt out wiper blade so far. When I turn the key I get a click from the ECU (or that other control box down there) and it really wants to fire but something is just missing. Ive also check most of the fuses, the ones on the battery lead and in the cab for sure.

I don't hear a fuel pump hum when the key is in the ignition, is the fuel pump a noticeable noise or pretty quiet?

One thing to note, when the key is in the ignition the buzzer is blaring a constant buzz. I was wondering if this was because something was wrong in the electrical system, but google didn't help me out there. I disconnected it because it was unbearable to listen to but it was any time when the key was in the ignition.

I want this thing to run so bad! It freaking mint!

Thanks guy! Love the forum and Love these trucks! :))

[noahwins]

ECU is probably the #1 thing to fail on the early FI trucks. Failure can be catastrophic, like melted circuit board or invisible like solder joints cracking and the electrolyte inside the caps degrading over time. I'd get it remanufactured. There are a few threads on where/how to do it.

[noahwins]

Also, finalfighter found a very clever way to get later ECUs that aren't susceptible to this problem to work. Look for his thread. Very clever. Turns a $200 rebuild into a $40 purchase at the junkyard.

[camoit]

It can only be a couple of things. You need to start with the basic. If it has spark at the coil and not the plugs it might be the wrong cap or rotor. But if the spark is at the plug then fuel and timing is the next step. It's just a process of elimination. Has it ever run for you? It would not be the first time someone has gotten a MM with the cam timing off.

[MitsuMini]

Hey thanks Guys!

I like the timing idea and I was thinking it myself. Do you think I could get away with putting the same belt on just to move it and get a timing kit soon?

Here's some pictures of the ECU inside and a video to the no crank. The buzzer is loud AF and I have since ripped it out. 148451484614847


Here's a video to the cranking.

https://youtu.be/RtPsIdQccy4

[geezer101]

If you are going to re-use a timing belt it has to have relatively low mileage on it and it has to be installed the same rotational direction from which it was removed. Belts are cheap enough and the only reason I could justify using an old belt is if you were in a jam and couldn't get your hands on one. And camoit is right about getting timing belt installs wrong. If someone thinks setting the timing up on it simply means having the alignment marks facing upward it's not going to turn over. I got caught on a 1.8 Family II engine where the bottom pulley alignment mark was this tiny pointer sticking out of timing case at 2 o'clock. Til I spotted it, this thing kept popping like a lawnmower with the spark plug out of it.

[finalfighter]

your ecm is missing some caps, thast probably the problem.

[finalfighter]

14848
these ones.

[MitsuMini]

Thats crazy, no one had ever opened it before me and I didn't have any broken caps fall out. Ill have to look for a stock image but I dont know if im going to get one. I should plan for a new ECU either way.

[geezer101]

Oh craaaap. I have never heard of capacitors going AWOL. They should've been floating around inside the ECU casing doing even more damage, so there's something fishy going on with this ECU. My bet is those were the non-functioning capacitors and this thing was sitting on a bench waiting for new ones to be soldered in - and some tool forgot about it and sealed the case back up. If you can find the corresponding value caps this ought to be an easy fix.