ofelas

Hi, on a 91.5 auto 4x4, if I want to do an ECM delete -

1/ Grid heaters - momentary on pushbutton switch - blue wires from heater relays grounded via the switch

2/ TPS - shouldn't make a difference as all it does it set the 3rd to 4th shift point

3/ OD - red wire off the OD solenoid grounded through a 2-pin toggle switch

4/ Speedo - blue wire off the VSS grounded to chassis

5/ Rear ABS - not affected if I unplug the module

6/ Charging - not affected, as 91.5 is regulated externally

7/ AC & cruise - don't have these on my truck

8/ KSB - not sure what the will affect

9/ Fuel heater & water in sensor - use the Cummins delete nipple and go with an integral drain Fleetguard FS1221 or similar)

10/ The FSO shouldn't be affected

The coolant temp switch, trans temp switch and air temp switch can be left connected as they are now redundant

With the harness unplugged at the ECM, the truck starts, runs & turns off just fine, except that the grid heaters and OD don't get a closed ground circuit.

Anything else Im missing?

j_martin

Don't think so. KSB is all discreet wiring as well.

ofelas

About the OD - instead of an on-off 2 pin toggle, how can I use my factory OD switch to complete/interrupt the ground circuit, and can I have it light up when OD off like the factory does it?

And on the pushbutton switch to the grid heaters - makes sense to ground switch the blue wires, do they get grounded by the ECM signal from the input wires orange/black & yellow/black ? If so, couldn't I just put a switch in-between the yellow/black & orange/black wires & ground?

Is there a difference grounding the blue wires vs the orange/black + yellow/black?

Thx

j_martin

The OD switch is a momentary contact switch. It sends a pulse to the PCM which toggles the state of the OD circuit. You could replace that switch with a loading lamp switch, which will snap into the same hole. (I think)

The blue wire is ignition hot. Grounding the black w trace wires will energize the relays. That's what the PCM does.

Why delete the PCM. It does a pretty good job at what it does, like properly cycling the grid heaters on a cold start without burning them out.

ofelas

Tell me more about this loading lamp switch ! :-D
That's why a momentary on starter switch for the grids, so I give it a 15 second blast when needed and don't forget to turn it off.
PCM delete as the threaded insert is loose despite the JB Weld, and it acts up when the weather is hot.
All pins on the harness/plug check out good.
I can't find a 91.5 PCM anywhere, junkyard or reman.

j_martin

On my dash board, there are two switches near each other. One is the OD-off switch, momentary on, and right beside it is the cargo lamp switch, push-on, push-off. They look and mount the same. Connectors are the same, different pins used. The mounting hole is 7/8" (22mm) square, so maybe a commercial push-on-off switch, or a rocker switch would fit.

The stock switches have independent lamp circuits. You'd need that to use the original ground on circuit and have an indicator. You could re-wire it so ground is to the solenoid, and the switch sends power to it, with the indicator built into the switch. (most, but not all indicator switches)

ofelas

You've lost me here.
On the factory OD lighted switch - do I use it as an interruptor on a ground circuit wired directly to the OD solenoid?
And if so - what wire do I connect to have the switch light up during "OD off" ?
Thx

j_martin

The factory OD switch:
When you push it, circuit is closed.
When you let go, circuit opens up.

The Cargo Light Switch:
When you push it, circuit is closed.
When you let go, it stays closed.
When you push it again, circuit opens.
etc.

The factory OD switch provides a momentary signal to the PCM
The PCM turns on the OD if it's off, and vice versa. It grounds the wire to the OD solenoid to turn it on.
The lamp in the switch is driven by the PCM, indicating the state, ie light on means OD is off.

If you remove the PCM, you will have to provide something that grounds the OD solenoid terminal that was wired to the PCM to turn it on. That is if you keep the original power source to the OD solenoid.

You may choose to ground the OD solenoid terminal that went to the PCM and provide power to the other pin when you want to turn it on. This would simplify the wiring of a switch with an indicator.

Look in the wiring diagram to get the color codes. They're in the FAQ thread of this forum.

To clear up a point, no wire goes directly from the factory OD switch to the transmission.

ofelas

I have the 91.5 Diesel supplement in front of me while I read this.

Your point by point explanation was simple, but clarifying.

Thank you!

Rampage1967

Overdrive - -

The OD switch is a monetary contact switch. Each push toggles the control module to right of the glove box to either connect or disconnect the circuit to the ECM. This turns the od on or off . . . A simple toggle switch to bypass the ECM is all that is needed . .or a relay controlled by the little module next to the glove box.

Speedometer - -

The speedometer needs a voltage source supplied by the ECM. You need to connect this wire to power in order for the speedometer to work. It is an 8 volt source if i remember right. I used a light bulb as a dropping resistor on mine (never meant to be permanent).


KSB - -

The KSB is controlled by a temperature switch on the intake manifold. It does need the grid heaters pulsing like stock to work right though. You may want to put a toggle switch in the circuit to turn it off manually after a certain amount of run time.


Rear ABS - - -

It will work fine minus the ECM

AC & Cruise - -

Cruise will not work. Ac not affected.

Fuel Heater & WIF - -

Neither of these involve the ECM. They will work fine after the delete.


Mine has been running this way for years.

ofelas

On the ABS - if functional before the delete, will still work after nixing the ECM ?

Speedo - should I supply power or should I ground out the BL/BK wire from the VSS ?

KSB - Instead of constant 12v like the pre intercooled trucks, I think the 91.5+ only activated the KSB when needed, so its really not affected by the ECM delete ?

WIF - will it still work after the delete? Or is it just not affected/functional after removing the ECM?

Thx

j_martin

1. Don't know

2. Ground. On automatics the tan wire needs 8V

3. You got it.

4. No, involves the PCM

ofelas

Good stuff thanks!

For the OD I'm going with a second gen lever with the integrated OD switch (which I'll replace with an on-off round rocker that fits nicely in place of the original switch.

Daytime running lights - prefer them off :-)

Momentary (on) off pushbutton to ground the grids relays

I prefer leaving things the way they are but due to the lack of a 91.5 auto PCM - may as well go this route.

The only additional switch on the dash will be for the grids. Found a square pushbutton Carling that almost looks factory that I will mount in the hole that the PO has for aux lights.

Shiny

Help!
I bought a '92 CTD dually 5 speed in June, truck is awesome, my 5th 1st gen Cummins truck.
When we picked it up it boiled the battery right afterwards as my son was driving it home. We noticed the speedo and odometer were not working, along with grid heater and few other things. Put a new battery and VR in it, was fine for about 2000 miles then blew the VR again.
I went thru a bunch of the grounds and no change.
It just blew another VR this morning after about 4000 miles...
I want to delete the ECM, is it pretty straight forward with this being a 5 speed, and a bunch of the stuff isnt working anyways!
Thanks!

-Shiny

oliver foster

Might want to chuck the parts store VR and buy a real Mopar one. They last a lot longer.
The parts store ones, I think, are made JUST well enough to get you home in a pinch.