Crossy's son

So i got this 91.5 4x4 5spd yesterday and today i put another battery in it because the one that was in it was dead, and i've had it running all day.

All of a sudden smoke is pouring from out the hood while its running so i shut it down and open the hood to find a fire at the fuel filter area.

i put the fire out and found that the wiring going to the fuel heater were peeled back and bear copper, there appears to be 2 wires going into the heater

so i had buddy turn the key on for like a second at a time and every time the key was turned on the fuel heater wires would glow orange and i'd quickly turn key back.

so i unplugged the fuel heater wire plug and turned key on and every thing was normal in the cab but it wouldn't crank? no cranking at all.

Now i turn the key on and I see the PCM glowing orange inside the fins and smoking! so turned the key off and looked for bare wires around the computer and nothing. turn the key on 1 last time for 2 seconds and this time i get a loud POP and some smoke, and now i have NO message center, no pillar gauges, no blower motor.......but i have headlights, gauge lights, and power windows and everything work ?????? still no crank.

I'm pretty certain i blew the computer, i can deal with that and cry about it because it was my dumb mistake, i should have fixed the fuel heater wires before turning the key back on again but WHY WHY would it not start when i unhooked the fuel heater and before the POP ?????

WHAT DOES THE PCM ON A 91.5 CONTROL ?!?!? i know its gonna be hard to find a replacement but i just want the truck to run!! i dont even care about the fuel heater.

MY THEORY IS THIS---- fuel heater went bad creating short circuit which melted fuel heater wires, which then were touching each other since they were bare copper and my dumbass keeps messing with key which shorted the whole fuel heater system right back to the pcm which fried the pcm ??? sound spot on ??

If anyone has this Pcm please pm me and if anyone has any idea what i should do please help!!

i know i can run power to the shutoff solenoid and jump the starter to get it running but i won't start with the key and i have practically nothing in the cab, the guage cluster needles are'nt even moving

BearKiller

I see the truck is a 5-speed.


Were it mine, this is what I would do :

Dig out and toss the PCM.

Do away with the fuse-link mess and route the wires instead through breakers or Maxi-fuses.

Being a 1991.5, it should already have the external fire-wall mounted voltage regulator.

Gut/bypass that silly RWAL gizmo back near the rear axle.

Eliminate the fuel-heater with one of the filter studs made for that purpose.

Eliminate the WIF gizmo with an integral-drain filter, such as a FS1221 or equivalent.

Investigate the fuse-block and wiring for any more melt-down and address accordingly.

Gut the shut-down solenoid and install a kill-cable.

Put the starter on a button, instead of the key-switch.


Doing all of the above should eliminate whatever caused the problem and any after effects.

BearKiller

Also, I forgot, bypass the clutch "safety" switch if you don't accomplish the same when adding the push-button starter.

Crossy's son

I would love to ditch the PCM but at the same time i want the key to work and all that...

I just don't understand why the truck wouldn't restart after the little fire at the fuel heater. It's almost as if the PCM went bad first THEN the fuel heater wires caught fire?

And i swear i heard the pop from the PCM but my other buddy leaning over the driver fender swears it was in the grid heater area (which happens to be where the fusible links are!!!) and saw smoke, but don't see anything abnormal in that area at all?

I don't get it. I'm about to convert the WHOLE system to Non i/c style and be done? if they're any better.... i know they use no pcm.

Crossy's son

I think the A/C goes through the PCM as well and i need that to work. right now it does nothing.

Basicly i have no power going into the cab to run anything besides the lights and the windows/locks/mirrors.

No gauges, (not even the aftermarket pillar pod gauges come on) and no blower/hvac stuff

Crossy's son

Yea i finally get my VERY OWN 1st gen after being ragged' on for years....and 1 day of ownership and it catches on fire.....

Polaraco

First of all, I'm betting the relay to the heater is stuck.

The PCM is the body computer. 91 didn't have electronic controls

It is probable the heater burning out shorted something else in the wiring and shorted the body pooter.

Strib the harness apart and look for additional damage. You can always tape it back up later

You should have just cut the heater leads and be on your way. But it's possible the damage was already done.

Boy it's been a loooong time since I had one of those.

12valve@heart

On my '92, there are 2 halves to the fuse block. One part is hot all the time and the other part is hot fed from the ignition. On mine, the wires in the steering column behind the ignition switch burned causing half the fuse box to go dead. Of course, with burned wires at the ignition switch, it wouldn't start either.
You might pull the plastic cover off the bottom of the steering column to check for burned wires there.

I think '91.5 is like the '92 that needs the PCM for AC, Alt, and Cruise. If you want it to start, you can hotwire the shutdown solenoid and jump the starter solenoid.

Crossy's son

Ok it probably was something to do with the grid heater because it was right there.

Still doesn't explain the fuel heater wiring burning up unless they are linked.

Onemoparnut

Don't bypass the pcm you won't have air, cruise, or a speedo. The pcm also won't keep the starter from cranking. It probably burned a usable link and that is why you lost power to stuff and it won't crank. Check the usable links with a test light and be sure they are all good before you rule them out as the problem.

Crossy's son

i haven' checked fuses inside the cab either. I should definely do that too,

Crossy's son

So that's all it controls? I was just wondering......I don't have cruise but I definely want A/C and a speedo.

Even if i did burn the PCM it should still start, So it's definely a fuse or something.

Bill do you know if the 92-93 PCM power check works for the 91.5 as well? there's a sticky for how to test it

BearKiller

I could very well be wrong in my thinking; but, it is my understanding that the 1991.5 is an entirely different animal than the 1992-93s.

The computer has nothing whatsoever to do with the alternator on a 1991.5; it is externally controlled just like the earlier non-I/C trucks.

As best I remember, it has nothing to do with the A/C either; if it does, all it could possibly do is turn the compressor on and off, and that can easily be by-passed, if that be the case.

I can't say for certain on the speedometer, but I don't think it has any bearing on the reading of the gauge, only the control of the cruise-control --- which is always the first function on any truck that I dis-able = dangerous and can and has got people killed.

As much of the over-challenged factory wiring that you can re-route through bigger/better, the better everything about the truck will perform.

Onemoparnut

Maybe my 91.5 is different than some others but it controls my speedo, grids, ac clutch, od and cc. But the computer may net even be bad it may just be a wiring issue. Brandon I am not sure if the pcm power test is the same on the 91.5 as the 92 and 93 trucks. If u want a hand fixing it give me a call.

Crossy's son

Yea I'm thinking that pop sound was the main fusible link that popped....all fuses in the cab are good. Right now i'm trying to use the 91.5 Wiring diagram in the sticky to Re-wire the fuel heater , only 4 wires are damaged, There are 2 big weatherpac plugs right there that i unhooked and have the wires easy accessible

I'm talking to Nick about getting him to get rid of all the fusible links and wire in a little fuse box right there.