Hey Everyone,

I've done the required 50 hours of research but still cannot figure out whats wrong with my new purchase of an old 1993 W350 4x4 5-Speed Flatbed. I got this at auction so I don't know much.

What I do know:
Most, if not all the wiring is stock. There is no External Voltage Regulator. When I jump the car, it starts right up, but the battery gets no charge. Inside the cab there is a warning buzz and I see the ABS light quickly go on and off and a few other lights, but the Wait to start does NOT shine up. I do live in So.California so it may just be because its not cold. I also don't think this odometer has works since 174k because I drove it around and it doesn't have Speedometer and Odometer doesn't work. I am not sure if the issue was the reason the last owner got rid of this truck. Seems like it was a farm truck and by the Carfax, only had one owner. Could be that the PCM went out and he just decided to write it off. Anyway...

Current Symptoms/Problem/Issue:
I have no charge at my battery. Before you say CPS, or Alternator, I can tell you that I've checked my fusible links and I even removed the stock plastic that was covering each side, they check out fine. I get power all the way to the Alternator. I checked and cleaned all the major grounds. I checked the CPS as best as I could. I basically unplugged the CPS cable on top of the intake and checked Black/blue tracer (ground wire.) OHMs read close to zero to the battery ground. Seems the Tan/yellow tracer is not getting proper voltage. It reads like .05 Volts when the car is on. I went ahead and checked the resistance all the way to the PCM and it read 0. On the PCM I Checked pin #3 (unswitched) and pin #9 (switched) for power and they have power from the battery. I checked pins # 11 &12 for good grounds and they are fine too. I've gone around and checked the wiring as best as I could and didn't find any issues.

Is it the PCM? I have no Full Fielded the Alternator because I do not know how and after reading every forum everywhere, its still not absolutely clear how to do so... at least to me.

This is absolutely super frustrating because I don't know why the CPS does not get that 8 volts it needs from the PCM. It could only mean the PCM is bad. Unless you guys can help me figure this out.

Please, I don't wish to mickey mouse it to an External Voltage reg if I don't have to , and would love to first find out what else could it be if it isn't the CPS.

Thanks,

Manny

 

If anything, having a computer in a truck with a mechanical engine and manual transmission is mickey-mouse. External regulators were successfully used for decades. I would be trying an external regulator....

https://ramchargercentral.com/diesel...your-dodge%27/

 

I think so. I just wish I knew what was wrong. I also wouldn't mind knowing how fast I am going without having to change that too.

 

Have your replaced the ASD relay on the inner fender? I have issues in the past where through a multi meter tester everything looked fine, but the relay/switch was actually bad regardless of what the meter was telling me.

 

Im praying for this. Will let you know. I cant really find the relay through part numbers. Most forums say its a standard 4 pin found everywhere. But for some reason I thought it was 5 pin. My truck has no AC so there is no swapping. I will let you know soon. Thank you for everything

 

Seems to me that key switch power goes to PCM. PCM then drives the ASD relay, which lights up the ASD circuit which feeds another pin on the PCM> That 12V from the ASD relay also goes directly to the alternator field. If it is present on one of the field terminals, grounding the other will full field the alternator. There is no danger of hurting the PCM when you do that. Shorting the field connectors together is a no-no however.
After the ASD powers the switch power terminal on the PCM, it puts 8V power to the CPS, and 5V to the TPS, and looks for signal coming back. The CPS toggles from about 5V to near, but not 0 v. With CPS signal proving the engine is running, the PCM then fields the alternator by pulling that terminal toward ground, and runs the other stuff, like intake heaters, tachometer, etc.

The Dodge Powertrain Diagnostic Procedures manual is infinitely helpful for both understanding and troubleshooting the PCM and related components.

 

John,

Thank you for the PM. I'm so stupid. I went and opened the ASD relay and left it opened without the cap on to see what happens when I turn the key. I noticed the thing did not activate upon first turn. I turned the car on, and hooked up a volt meter to my battery terminals... and then STUPIDILY hot wired the ASD relay buy activating it manually, noticed that the battery started getting a charge, which excited me, BUT, immediately a small puff of smoke came from the Computer, thus making me shut everything off. Thats where I am now. I am sad. I feel like, I found out the issue, the ASD isn't getting power, but at what cost.... I dont know what I've done at this point. I know the CPS works and so does the ALT. Sad day but learned.

 

If you fried your PCM then maybe take a look at this thread....

https://ramchargercentral.com/diesel...your-dodge%27/

 

So sorry to hear that.
I suspect you did some real damage to the PCM. There must be some reason for the power sequencing routine, that is the PCM is partially powered, then energizes the ASD relay, which then powers a second pin on the PCM. When you manually operated the ASD relay, you powered the second pin without some prerequisite being met, probably key power to the first pin.

That's why it's important to have the right tools. In this case the powertrain diagnostic manual I mentioned, as well as a fundamental knowledge of electricity and electrical control in general. Even with very basic knowledge, following the MAPS in the manual won't lead you astray or cause damage.

There are places that repair PCM's. and I'd be willing to bet you're not the first to let the smoke out in this way. I suspect you fried a relay driver integrated circuit, and that wouldn't be either hard to find or repair is set up to do so.

Taking this as teaching moment, unfortunately at your expense:

If you're troubleshooting and something that is supposed to happen doesn't, (In this case the generator didn't gen) don't immediately try to force it to happen, but instead find out what is missing and why.
In this case, if you would have probed the field terminals, you would find that 12V is missing, and both terminals are at ground. That indicates no 12V from the ASD relay.
Next, probing the relay, you'd find 12V at one contact, and 0V at the other, indicating the ASD relay is either bad or not activating.
Swapping relays around would quickly eliminate the bad relay theory.
Probing the coil terminals on the relay, you now would either find both at 12V, or both at 0V.
Further following the problem you'd either find a broken wire (very common by the way) or that the PCM wasn't driving the relay.
and on until you get to the fault. So far, following this sequence you would have sorted out 32 to 64 possibilities with 5 or 6 tests.

The plan to proceed is best laid by the inventor(s) of the machine in question, thus the service and diagnostic manuals.

My truck once failed in this way. I found that I had the right voltages in the coil wires near the ASD relay, but the relay did not actuate. One wire was broken between where I probed it and the relay, which was found by close physical inspection. The wire failed at that point because it had been pierced (probed) previously and not repaired. (painted over with liquid electrical tape) Years of salt did their thing on the copper conductor until it parted.

That said, I don't think it's all that helpful to say that is what to look for. There are many other faults that will have the same final symptoms, Iie nothing computer works.

Hopefully, this whole thread will help someone else avoid the pitfalls and effect a repair on their truck. Actually I know of one already. I have 2 trucks, and one is slow to actuate the ASD relay when it's cold. I was entertaining the idea of rigging some way to actuate the relay to "help it out", but not before I researched it some more. This thread shows me that I should not do that. Thank you.

 

I'm going to read this again and again. I just wanted to reply quickly to show you that I appreciate every moment you spent reading and writing this. Thank you.

Manny

 

Wire in an external regulator and use a cable to shut down the truck. At least it will be useable. Wasnt there a place in FL that sold remam computer reasonable?

 

Or a guy somewhere that has good PCMs sitting in his shop for Cummins trucks??

If it gets to the point where the OP needs an original PCM or wiring harness for that truck, I save those things in my shop.
PM if in need.

 

Im having similar issues 1993 D250 5 speed Getrag..everything was fine went to clean battery terminals and then after no crank no lights in dash except for oil and very dim dome light..I've replaced the terminal with good military grade ones and nothing checked the ASP relay and I get power when I turn key on on A but nothing otherwise..thinking maybe the ignition switch but have no idea HOW to check that plus I suck at electrics!
I've poked to see if have power on both sides of fusible links and it seems to have power to back of inside fuse box so it is getting there but...
HELP Lol..it's my daily driver and I am bicycling to work..thank god it's only 1.3 miles