So, after a ton of diagnostics and much help I have ( I think) a handle on my crank/no run issue. I seem to have 2 problems: the main pump does not time out, so I think I have a bad "clock" (oscillator) in the PCM. I also seem to have no signal to the injectors. Are they related?

The ignition system looks OK. New cap and rotor (needed anyway), new NGK coil. Plug wires and coil wire all pass the test. Plugs are good.

PCM and fuel pump relay test good. All the fusible links appear intact. 45 psi at the the rail.

Motor tries to run with starting fluid but doesn't want to keep running (again, points to no signal to the injectors--maybe?)

I have a Haynes manual, poring over engine electrical schematics.

Still hunting...any advice much appreciated. TIA.

 

Yes that indicates the PCM has failed.

 

Crap. Any advice on finding a new one? My PCM model ends in BM1B. Thoughts on new/refurbished? And what caused it to fail? Only 89K on this beast, well maintained. Also FWIW, I have an adapter for my OBD2 reader and it is telling me it " cannot establish a link" with the ECU and it also says it reads only 5.9V, though the Interstate is good @ 12.7V.

 

Q?:
Can I hack it? Can the oscillator be replaced? What controls the FI system? Any other tests I can do to confirm the problem?

 

OK, found a PCM with my specific PCM's model # (E8TF-12A650-BM1B) in hand. 460, 3spd auto. RA has one. P&P, already flashed. Does the "12A650" matter? And it's listed as a "BMB", not BM1B. Does it matter? Does anyone out there have one to sell me? Again, TIA.

 

Get the exact tag
No flashing or programming for your 1989 processor is possible or needed
You could sure replace the caps in your processor and possibly fix the problem
As far as a timer or oscillator, no reference to any of that in any of the literature I have read
Just inspect your caps and the board to determine how bad the traces are on the printed circuit board and go from there
I found a JAG1 processor for my van and am now very pleased withy how it runs
I did save my old processor to repair later maybe

 

At 35yrs old this ECM is past it best before date, the electrolytic caps have leaked and the fluid corrodes traces and other components on the citcuit board. Sometimes this is repairable but most times not since those other components have long since been discontinued.and are not available.

Yeah that won't work these old EFI computers are far too primitive to communicate with a modern scanner, you need an Equus 3145 code reader.

 

[QUOTE= And what caused it to fail? Only 89K on this beast,[/QUOTE]

I’ve had some luck before replacing the caps but that’s hit or miss. Bad grounds can shorten the life of these so I would be sure and check all the grounds involved with this and all the pins in the connector. I always clean these with contact cleaner when apart personally.

 

Thanks for all the input. Many have suggested a wonky ignition switch. I have one coming and will install it Monday.

I've rechecked and cleaned all the grounds. The ICM is new and correct. The fuel pump relay is new. The ECM relay is good. Lots of dielectric grease everywhere. New coil, cap & rotor, plugs. Secondary wires all pass muster. Fusible links intact. Fuel pump makes 40psi before the new fuel filter, 37psi at the rail. Fuel pressure regulator looks good, no vacuum leaks, no fuel in the vac line, no external leaks. Maybe relevant: the system does NOT hold pressure over night (I have a guage on the rail) but it comes up fast and holds.

Anything else come to y'alls mind? What have I overlooked? TIA

@conanski: yes, I have that OBD-1 scanner. It's not showing any codes. I'll disuse my OBD-2 unit. Thanks.

 

I have a solid direction to go in: I don't think the injectors are getting their ground signal to fire. But it's intermittent. I had the truck running 4 times, but it was rough and died in about 3 minutes. I have a FP gauge on the rail and it fluctuated about 5 psi. And, it leaked down quickly, so I replaced the regulator. Pressure now holds steady, doesn't leak down but a tad. But it still doesn't want to run.

The thing starts right away with starter fluid but, again, everything points to the injectors not getting their ground signal to fire.I'm pretty sure I have a bad ground somewhere. Today I'm going to reinspect the FI-related grounds. My question is: how exactly to check the pins at the PCM/ECU harness? As I understand it, they're 58 (right bank) and 59 (left bank). I also want to check pins 20 (case ground) and 40 and 60 (power grounds).

PIcs: with the battery in frame: I believe the 2 wire connector near the battery is to the ECU, pins 58 and 59. Yes? I HAVE checked it, cleaned and greased, good "click" when it seats. Also, the tools I have; good multi meter, a digital test light and an old school light bulb "dumb" one. Also a pic of the new ICM and FP regulator.

All connections reinstalled with dielectric grease.

And to set the timing: book says get to temp and unplug the ICM, then set timing set to 10° BTC, then reconnect the ICM. Correct?

Thanks again for all y'alls help.

 

Pins 58 and 59 go to the injector batches so test for continuity from end to end... disconnect injectors and the PCM and put a test lead on each end. The injectors are fired when the PCM grounds those two pins so yes the PCM grounds need to be solid as well.


NO, you remove the spout plug to set base timing, it's a little 2-wire plug in the ICM wiring harness.

Also note that correct use of dielectric grease in to apply it over top of clean metal to metal connection, there should be no grease between the two metal contact points as this grease is an insulator.

 

SPOUT plug, correct? Remove the end-plug to disable it, reinstall after timing is set.

And, yeah, I may have been too liberal with the dielectric grease. Will inspect and clean as neccessary. You've been a tremendous help. Thank you.

 

Yes that is it.

 

Did I miss the part where you replaced the defective PCM/ECM?

 

@My4Fordtrucks yessir, replaced the bad PCM. Main pump times out just like it should.

Now cleaning all my connections of too much dielectric grease. I was too liberal.

Also checking continuity from the injectors to the appropriate pin(s) at the PCM harness and double checking all my grounds. Fingers crossed...