Fergavs

I just picked up another 1st gen for real cheap because the PO left his vehical over charging and started the wiring under the hood on fire. Most of the wiring on the passenger side is fine but every thing on the drivers side went up in flames. So...

What is the vehicles computer used for in our trucks exactly (91.5 IC) I basically want to know if I can rewire the truck and not use the computer.

Can anyone repost the pics for the info in the sticky for intercooled trucks
(seen here: https://www.dieseltruckresource.com/...d.php?t=128911 ) it would really help me identify some of the chared mess.


The engine part of the harness is mostly fine its the truck part (headlights,computer,etc.) that is smoked. If someone has a parts truck they would like to strip for me see here: https://www.dieseltruckresource.com/...t/22279/cat/21

BC847

- Running +12v to the fuel solenoid will make the engine run.
- An external regulator for the alternator should take care of that.
- A push-button for the grid heaters if you're in to them.
- The ksb is temperature controlled so no PCM needed there.

The in-cab stuff should be as easy; aftermarket cruise if wanted etc.

So say the voices in my head.

Fergavs

I currently have the truck running on 3 HD switches. 2-35 amp for starter and grid heaters and a 25amp for fuel solenoid. This is however only temp as I want to put the truck back together properly. Can I still have all my gauges and such with out the computer. Im fine with most of it but what about stuff like the grid heaters? I guess I could do a timed relay.

Ace

Let us know if you figure out how to get the speedometer working without the PCM. That is the only thing preventing me from completing a PCM"ectomy" on mine. I suspect it merely passes the signal through on the pins marked "SCI," but haven't tried to confirm this yet....

I theorize SCI is the Dodge acronym for Speed Control Interface - "human" interface.

Once that's gone I plan to re-do the alternator wiring and eventually eliminate virtually all the OEM underhood wiring.

Fergavs

I will be looking into the speedo but I am not to concerned as I use a GPS and it has speed displayed on it already.

wannadiesel

The speedo doesn't need the PCM. Some automatic trucks have a 3-wire VSS that needs a power feed from the PCM, but those can be replaced with the 2-wire style.

Fergavs, if this is the '91.5 in your sig, you will need to do something about the OD control. I think the slickest setup I've seen is using a pressure switch in the governor test port.

I'd run the grids off a momentary push button. Hold it down for 10 seconds when it's around 0 C, 30 seconds if it's -10 C or colder.

Ace

So how come when I disconnect the PCM the speedo no longer works?

wannadiesel

How many wires to your VSS?

Ace

Didn't know I had a VSS, but it's definitely not an auto trans. I asked this same question over on 1st gen, no response. I've been all up and down the pinout diagram for it, looks correct, all the same pins in my plug as shown.

Don't want to get too cavalier shorting pins or applying voltages on the plug before I have a pretty high degree of confidence I know what I'm doing. I tried supplying 5v a couple places that were labeled as such, but that was as far as I went with that experiment. One thing I am curious about is the ones labelled SCI. There's an innie and an outie for something called SCI. Suspecting that may be what I'm looking for, but dunno.

Montana2x2

My 91.5 does the same thing, not sure how many wires on it, I'll have to check.

Ace

Is the VSS what I call the signal generator that attaches to the trans (Getrag) with a threaded collar and sends a wire or two with the speed voltage/signal somewhere? I thought VSS was an auto thing.

TruckU

Vehicle Speed Sensor. Yes, it's the thing attached to the speedometer output on either Stick or Auto trans

Fergavs

Yes the 91.5 in the sig. The pressure switch is a good idea but on my other 1st gen I just run a switch. Cant I just do the same on this one. I like being able to switch in and out od OD when ever I want. I just went to the 3 wire harness on the 47rh for lockup and OD, I assumed the older trans had a connector for OD as well.

As far as the grids I think I'll just do a timed relay off of ignition as its cold here and I use my command start a lot. When the relay sees the ignition wire turn on it'll automatically fire up the 10 second timed grids. This way I dont have to go out and push the button.

So is there really nothing important the computer does that I cant do with a switch or a relay? I won't lose any gauges or anything similar?

As far as the pics under the hood go, even if some one doesnt wana take close ups to put back in the sticky could you just post some good quality drivers side fender wiring pics here. I really need to identify whats there so I can go buy what I need. Thanks for the help so far guys.

Ace

You won't have a speedometer without the PCM until we figure out how to bypass it.

Fergavs

Again, not worried about the speedo as I use a GPS. Anything else?