Awesome info Dave. Thanks very much! (Had not been covered)

Ray

I checked the Control Relay. Opened it up and its pristine inside. Looks brand new. I manually operated the relay contacts and confirmed good continuity. I think its fine.

So now I think its the ECU. I rechecked it and its giving a replace code now. I've replaced all the e'lytic caps already and I don't see anything else on it that looks suspicious. If I get a chance today (have to work) I'll check for spark at the plugs again. Should be no spark now I suppose...

Anyone local (or not) have a spare '91 ECU that I could buy or rent? Once I know that's the real problem I'll spring for an AV-Pro rebuild.

This would potentially be the 2nd ECU failure for this truck. Should I be looking at the ISC as well? I think I read soomewhere a bad ISC can kill an ECU.

Ok, so I caved and sent the ECU to AV-Pro to be refurbished. Finally got it back today, installed it, and...KAPOWWWW!!!



No change <img src="/forums/images/graemlins/barf.gif" alt="" />




Still turns and turns. No fire. So f-ing frustrated. I was just sure she'd fire right up. I was holding back a grin as I turned the key...

So where am I??? What am I missing?

If:

-ECU is known good (based on AV-Pro's great rep at least)
-Control Relay looks good (I hear it clicking when I turn ignition, insides look pristine, continuity checks good)
-Fuel Pump comes on when fed through test jumper, and sounds strong and continuous with no sputters, etc
-FUEL SMELL OBSERVED AT TAILPIPE (***this contradicts what I thought I observed early in the process)
-Recent new distributor cap and rotor (installed last year, and ran with no problems)
-Fresh charge on battery
-Spark observed white-blue at plug (I have to admit, I have not RECHECKED this since I did it early on, and I only checked one at the time)

What would be your next move? Craigslist? <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

Some things I have not checked (mostly bc I didn't know how):

-ISC
-Distributor Function
-Ignition Coil Function
-Test for vacuum leak (beyond mere visual)
-Anything Else?

IDIOT CHECK: My passenger floorboard components have been disassembled for so long I worry I'm missing something simple in reconnecting the ECU. I d/c'd neg battery terminal, plugged the 3 big connectors into the back of the ECU, connected alligator clip from the ground wire coming from one of the ecu connector to chassis, reconnected neg battery connection, cranked, hurled expletives...slammed hood...Drank Beer. Correct?

I'm sorry. I know you guys are probably tired of seeing this thread keep popping back up.

I'm not geting tired of hearing about it,,,that's what we're here for...
I'd check spark again.
If your still getting spark it would seem igniter and coil are good,,,and probably means distributors cam and crank sensors are good.
The wires at igniter are notorious for cracking...
I left a main wiring connector unplugged and felt like calling the junkyard once. Fatigue and frustration can make you miss stuff, fur sur.
Check the fusable links(wires) with an ohmeter.
Check the big Fuses at battery with ohmeter. The little windows in mine are fuzzy and I don't trust looking thru them.
I'll try to think somemore on this. Tonite my brains pretty fried over my headgasket.

Thanks Dave.

I checked for spark this morning by pulling a plug, plugging it back in to the wire, and setting the plug down so that the threads rested on the chassis then cranked engine. No Spark now.

I'll check the coil wires more closely and check continuity on those fuses.

I'll also try to do a better spark test than what I did this morning...best I could come up with solo before work.

I also stumbled upon this:

http://easyautodiagnostics.com/mitsubishi_ignition_distributor/ignition_spark_tests_1.php Mitsubishi Ignition

So I'll be digesting and working my way through this tonight.

One thing I'm concerned about...

I wonder, did something kill my ECU or was it just time for it to let go? I am SURE that I had spark when I was initially troubleshooting. But I did get some occasional random starts at the beginning too (none now). Also, the ECU gave steady blinking code (normal signal) at first. Before I sent it off to AV-Pro last week it was giving the "dead" code.

So is the dead ECU a symptom or cause of the problem? Obviously there is more to it because with "new" ECU truck still no starty.

What are some common ECU killers? I've heard ISC, but that's it.

Thanks again!

-Ray

I suspect that the ecu is not seeing a tach signal, so it doesn't inject fuel. Test for a tach signal at the ecu while cranking. Check wires from coil - to ecu. You stated that there is no movement from tach while cranking, right? Get the fwm download and look at the fuel system wiring in the mpi section in vol 1. Trace the wires from coil- to tach and ecu. Pay special attention to the gizmos on the coil bracket besides the coil, and follow the tests for the power transistor as well. The gizmos on the coil bracket condition the tach signal for the tach instrument, and their wire insulation gets very brittle and if they crack, vibration breaks the wire via fatigue at the crack.

Do you have spark with the rebuilt ecu?

I actually did away with the 2 gizmos ( noise filter and condensor) years ago. My tach works fine now without those cracked wires.
The squarish gismo(noise filter) has a grounding signal that goes thru it from ingniter or coil , or both,,, to the tach. As I understand it an inductive signal from that negative wire triggeres the tach. The tach has a + wire going to it from the ECU feeding it juice.
.
And , not to forget, cracked wires can allow things to work sometimes and sometimes not.

Thanks for the tips fasteddy. To answer your questions, I see no movement on the tachometer while cranking. I HAD spark when I first started troubleshooting, but no spark now, even with the rebuilt ECU (which is giving a "good" code now).

I smell fuel at the tailpipe now. I don't THINK I did at first. Would I smell fuel at the tailpipe if ecu was not injecting fuel?

Visual inspection of components in that ignition pathway doesn't show anything suspicious-looking. Will scrutinize a little more and get the multimeter out.

OK, still at work...will post more tonight.

Ok, more thoughts.

If you have a fuel smell at the tailpipe while cranking, it is injecting fuel.

We need to test the coil. Ignition on, coil plug disconnected. connect the coil connection that goes to the black/white wire to 12v from the battery using a jumper wire. Using a second jumper wire, make and break the connection from the other coil terminal (the one connected to the white/blue wire) to ground while holding the cap end of the coil wire with a paper clip in it 1/4" from a good ground and observe for spark.

If this tests ok, time to test the power transistor.

POWER TRANSISTOR
the power transistor has 3 terminals. With the catch at the top, they are 1, 2, and 3 counting from the left.

Connect the negative (-) terminal of the 1.5v power supply (AA battery) to terminal 2 of the power transistor, then check whether there is continuity (ohmneter used here) between terminal 2 and terminal 3 when terminal 1 and the positive (+) terminal are connected and disconnected.

The power transistor is an electronic switch which makes/breaks the connection of coil- to ground. When 1.5v is applied to terminals 1 and 2 (neg to 2, pos to 1), it opens the switch and there should be a current path between 2 and 3 (ohmeter shows some small resistance). When the current to 1 and 2 is interrupted, the switch is open and there is no connection between 2 and 3. When the engine is running, the ecu breaking the ground circuit by removing power from 1 and 2 causes the mag field in the coil to collapse, generating spark.

If the coil and power transistor check out, it's time to test the distributor output (crank position sensor inside the dizzy). I don't have the test procedure for this, but it's been posted on here before. I know the red wire to the dizzy should be 12v+. I think white and green should have pulsing voltage while cranking, one faster than the other.

Many thanks krazydave and fasteddy.

Chomping at the bit now. I'm going to get on this as soon as the rain lets up today.

fasteddy, thx for taking the time to spoonfeed those test prodedures. <img src="/forums/images/graemlins/baby.gif" alt="" /> I am learning, though. Never knew how an ignition coil (or the much of anything about the fuel system) worked before this. Now I do!