dieseldave24v

99 Cummins 2500 In the middle of closing on a new house and the murphy came to visit with his law.....Here is the deal. My guages have been acting funny for over a year I found out it was a bad connection on the back of the insturment cluster...no big deal. Last week the truck would have a slight miss at idle only when cold, by the time I made it to the end of the street it was fine. Then the check engine light came on, before I could pull the codes I noticed that my fass pump was VERY loud, my guages stopped working, and I had the NO BUSS message in the odometer. I smelled somthing so I poped the hood, one of my batteries had started leaking acid. I put all this together and decided it was overcharging. Checked it with my multi meter and I was around 16 at idle and 18 at 2K rpm. After some research I find out the the regulator is in the pcm. I have pulled the pcm and opened it up. Nothing looks burned or broken and it doesnt smell that way either. I am 90% sure it is the PCM. What do you guys think.......

also if it is the PCM I can order it from the local auto parts store, but does it come programed...Thanks

Almost forgot, the last time I drove it the tranny started taking higher revs to go from 1st to 2nd only did that once or twice.

sweeney186

It does sound like a pcm issue.Checking the codes would be a good idea.Not sure about the auto parts store availability-but most just need vin # insertion & are ready to use even without it-but you might have some other lights come on if you don't

dieseldave24v

Thanks for the reply. Sounds like I will order one this evening. Anyone else have any input?

j-fox

Overcharging can be from a bad ground!
Check them all. Check ground at the pcm, it is the voltage regulator.

patdaly

Before you get goofy with a PCM do a bit of troubleshooting, here is something that was posted here, not my words but easy way to diagnose:

"I had to troubleshoot my charging system recently and came up with a fairly simple way to isolate the problem. Here is a step-by-step way.

First you will need a DVM to measure voltage. Also the batteries need enough charge to start the engine, so use a battery charger to get them charged enough.

The charging system is made up of the PCM mounted on the firewall, alternator, and don’t forget the 120 amp fuse in the PDC on the driver’s side fender well.

1) Start the engine and measure the battery voltage at one of the batteries. It should be more than 13 volts but probably less with a charging problem and that is why you are here.

Measure the voltage at the alternator output terminal (B+) leaving the DVM negative connected to the battery negative post. It the measurement is greater than 13 volts then the fuse in the PDC should be checked or the nut holding the heavy gage wire on the alternator is loose
If you get this far then the next step is to measure the voltage coming from the PCM. The two small nuts on the back of the alternator are the ones to measure with the lower one positive and the upper one negative. These are the field terminals on the picture. If the voltage reading is greater than 8 volts the PCM is calling for full charge and your alternator is bad and not putting out. If the voltage is less than 3 volts your PCM is toast or the wiring between the PCM and alternator is broken. The normal voltage reading at the field terminals will vary from 3 to 6 volts when working correctly.

It’s always a good idea to clean battery terminals and check for bad grounds before spending money on replacement parts.

My alternator turned out to be bad and I had 9 volts at the field terminals. It was the diodes inside that were bad."


I wouldn't personally replace the PCM for it either, you can use the older external regulator look for Infidels posts on external regulator.

dieseldave24v

Thanks I will look into that. I jumped to the PCM because of my guages not working and the tranny shifting weird, I will look into all that. thanks for the input.

patdaly

Whoa, check the Crank sensor before you go any further........ Make sure your PCM is getting the 5V , because if the CPS is shorting to ground, it kills what you are describing....... I could be wrong on the terminology, I mean the sensor that reads the Tach signal at the front.

Your PCM has a circuit that protects the PCM by killing the 5V in the case fo a short.

Sorry I did not catch the gauges not working part the first time.....

busa

9 times out of 10 it will be a alternator problem in the chryslers. I have changed hundreds of alternators and only a handfull of ECM's.

Dave Miller

Yeah...it's called a Crank Position Senser (CPS) or also an Engine Speed Senser (ESS).

It is a magnetic type senser which has 3 pins on it (GND, 5 vdc from PCM, and CPS output pulse signal to PCM). On my 97 it gets 5 VDC from PCM but I have heard it is 8 VDC on some trucks. It is located above the dampner bolted to the block with a gap of 0.050 inch. It senses the 2 recessed slots on dampner to create the pulses (using the 5 vdc from PCM) whose frequency varies with engine speed. It has a about a 2-3 foot pigtail that connects to the wiring harness on the front of engine on top...kinda in front and to left of the inj pump on my 97.

Try unplugging it and plugging it back in. Verify the wires are not chaffed or rubbing against something, especially above the dampner at the senser and verify the gap with a bronze (non-magnetic) feeler gage or use a business or credit card.

Try measuring the voltages at the CPS connector pins (with CPS connected) and if the dc voltage is missing from PCM then unplug the CPS and measure the 5 vdc coming from the PCM to see if it comes back with CPS unplugged. If CPS is shorted this will bring back some gages on my dash. If its not shorted it could still not be sending pulses to the PCM. The PCM needs the pulses to provide ALT charging, Tach and other functions. If CPS is bad you usually do not have any charging voltage at all, from what I have seen so far. In your case it sounds like you are over-charging so I'm not sure the CPS is at fault here.

Also the 99 truck has an ECM (I believe) in addition to a CPS and PCM. It copuld be a problem source. I'm not sure of its functions. Someone will chime in. And you thought this would be easy...sorry...its a little complicated.

dieseldave24v

One note I forgot to include, I unpluged the PCM, and started the truck to see if the CPS was bad. this imay or may not be the right way to do it, but when I did the only guage that does work is the tach. If I plug the PCM in no guages work to include the tach.

Dave Miller

To check CPS I would unplug the CPS not PCM as stated above in my LONG description. With CPS unplugged you will not get ALT charging, tach etc but some gages should work and when you turn key on the MIL light will work and dash gage check will light all the lights. If CPS is shorted (and plugged in) you will not get the MIL light and assorted dash lights when key is initially turned on.

dieseldave24v

Well its raining right now or I would go out and check all this stuff. Thanks for the help, I have one question. If the CPS was bad wouldnt the tach not work?

Dave Miller

That's correct...at least on my 97. If the CPS is bad the tach and alt charging would not work. If your tach is good then your CPS is probably good too.

sweeney186

Crank signal tells the pcm that the engine is running-w/o that input(bad sensor)you will not have any charging to go with the no guages

dieseldave24v

Well tommorow I will get to look at my truck, work has been hell this week. I will let you guys know what I figure out. Thanks