[chrisjessc]

Anybody have a new/used pcm for sale out there?or a pin out diagram?have no overdrive, no intake heater,over charging,no cruise,only .8 volts at tps.no voltage at blue wire on voltage regulator. can anyone help that has had same problem?

 

[9297oldram]

Have you checked your grounds , battery clamps and regulator case to make sure they are
clean and tight?

Check to see if you have a burn't fusible link on top of the left fender well.

 

[chrisjessc]

Block,frame,body,and regulator have good grounds.I found 2 links going too intake solienoid.is there more?

 

[chrisjessc]

Do you know what cavitiies on pcm plug have power

 

[9297oldram]

Dodge Diesel - Diesel Truck Resource Forums - View Single Post - Fusible Link Abatement 2nd picture in this link shows the fusible links.

http://www.cumminsforum.com/forum/89-93-tech-articles/155693-testing-crank-position-sensor.html Is your CPS good and have a .050 air gap.

The ECM (PCM) doesn't have anything to do with the alternator since it has a external regulator.

I don't have a FSM for a 91 so I don't know the pinouts.

 

[Steve g]

I lost function of cruise control, grid heaters, and od and my speedo acted wierd. You should not have lost power to the reg. I suspect you may find the key on voltage to the ecm to also be dead as both those are key on power.


3 is Batt voltage, 9 key on ign voltage, 11 & 12 are ground. Unplug the connector from the ecm and test them from the plug end. Use a voltmeter and ensure you have batt voltage with no drop. If all inputs check out it is safe to assume the ecm has crapped out.

Although lots of suppliers show a part number for it, I had no luck finding an in stock ecm for my 91.5. I was able to have it rebuilt by Cardone at the price shown in the catalogues, about $265 CAN my cost.

Steve g

 

[Steve g]

Pinout attached (hopefully)

 

[Steve g]

Had to reduce the scan too much for it to still be readable. PM me with an e-mail address and I will send you a full size copy.

Steve

 

[simplysmn]

Check relay on fender wall of driver's side of truck

 

[chrisjessc]

Your wiring looks really nice and clean.i just might have to copy that.what does that relay on fender control?thanks you guys for the info.plan on doing more test and poking around tomorrow.you gotta love these trucks

 

[chrisjessc]

pcm/ecm

tested ecm plug for power and ground.All checks out good.looks like ecm is bad.What is the relay for on drivers side fender?Also on my external voltage regulator there is a green and blur wire,is one suppose to have ignition key on power and one have battery voltage?

 

[Steve g]

There are a couple of relays on the inner fender. I don't know which one was being referred to, but as far as I know or can tell from the wiring diagram none have anything to do with the ecm. One is the starter relay and there are the two grid heater relays.

Without looking at the wiring diagram I can tell you that one wire in the reg plug will have battery voltage with key on only ( I believe this is the blue one) and the other runs to one of the field terminals on the alternator. The other small wire on the alternator should have batt + with key on also.

The circuit is key on batt voltage to one field wire in the alt. That current runs through one brush into the field windings in the rotor then passes out through the other brush then on through the green wire (I think green) to the regulator. The regulator grounds that circuit thereby completing it and energizing the field magnet. The key on power wire at the reg provides operating voltage to the reg and batt sampling voltage so that it can regulate the voltage to 14.2 by interrupting the field circuit.

The only connection I can see to this circuit and the ecm circuit is the key on batt+ is common to both. But if your #9 pin on the ecm is showing battery volt with no drop I can't see there being any connection.

You can go one step further by grounding the #15 then #16 pins and confirm that the grid heater relays click. That leaves only the ecm and the temp sensor input as possible faults in the grid heater circuits.

Do you have cruise control and is it also out?

Steve g

 

[chrisjessc]

I do have cruise but it isn't working.i only have about half a volt at tps.im guessing that's why it doesn't shift into od. ECM?

 

[Steve g]

It's not as simple as the low voltage to the tps. That's only part of it. Even if the tps had adequate voltage the ecm still has to do the calculations and ground the od solenoid. If the ecm is dead the low voltage is only a part symptom.

When I went through all this a month ago I did the pinout checks that you've done and the one I suggested to confirm the grid heaters were working. I also stuck a 1/16th cotter pin in the #55 terminal and ran a wire from it through the firewall and left it hang by the steering column. Drove the truck to speed and grounded that wire against a dash screw. Shifted into od. In as much as all these functions went out together, cruise, grid heaters, and od, and actuating the heaters and od by grounding their respective pins in the plug caused them to work, and all my inputs tested okay I went with the assumption the ecm died. Pulled it out and had it repaired. Installed it and my diagnosis was confirmed.

I couldn't drive it without od, 4.10 gears and highway ride to work. Also too cold to start without grid heaters. So while the ecm was away I wired the #55 pin to an on/off switch that grounded it in the on. I Used cotterpins and connected the two grid heater pins to a wire and ran it through the firewall and just let it hang.

Go out in the morning , turn the key on, ground my heater wires for about 15 seconds and twist her tail. Operated my od with the switch. Lived without cruise.

Steve g