royta

Thanks Dualler. I know, I know, I guess I'm just looking for a replace a part and it's all fixed kind of answer.

Just after my 1:45PM post, I did a bunch of work to the truck. I reset the ESS to .040". I checked my TPS voltage. 5.0 VDC across the outside terminals. 0.9VDC @ idle and 3.5VDC @ WOT. I drilled the hole and cleaned the TPS, removed the screw sleeves, and set to 1.2VDC @ idle and 3.7VDC (or so) @ WOT. 1.2VDC was the most I could get @ idle. If I wanted more, I'd have to trim some plastic off the inside of the screw holes. We'll see how this works. I won't hold my breathe too long, but it would sure be nice if the problem went away.

royta

Well, I had to go on the freeway this evening. Unfortunately, the ESS problem is still around. I guess I better start tracing out electrical wires. Bummer. I only get the trans T/C locking and unlocking problem occasionally, so I'm not sure if that problem is still around or not.

Dualler - I was thinking the TPS might be the reason behind the T/C unlocking and locking. That seems like a completely different problem than the one where it feels like the ESS has been disconnected and reconnected over and over at a high rate of speed. I was hoping that if it were in fact the TPS, maybe it was introducing noise into the system, and causing the flaky tach issues. Just a thought.

royta

new TPS did not fix it. I can have my wife sit in the cab and watch the tach while I jiggle every single wiring loom in the engine compartment, and there is zero tach flutter. I've even jiggled the wiring looms under the dash. I would think that if it were wiring related, the moving of the looms and the wires where they enter the connectors would cause the tach to start dropping. Maybe I have to have the truck in gear at the same time. I'll try that tonight.

darrenG

I would be checking grounds all over the truck. Check the cab and the engine compartment. This screams of loose ground to me. I'd start looking around where you last did electrical work for installing, under your dash.

Take the grounds off and re-attach them firmly. Any that look dirty, clean the crap out of the wire and where it grounds.

I had a weird electrical problem with my jeep cherokee that when I turned the heater or AC on the blower would short and my jeep would shift into 2nd and stay there. highly annoying. It was cus of 1 ground in the engine compartment.

royta

OK, I spent some time yesterday and today doing some troubleshooting. In the following post, I will be referencing connector, connector pin, ground, and splice numbers, which should mean something to you if you have browsed section 8W of your Factory Service Manual. What I originally found, is that even with the Throttle Position Sensor (TPS) disconnected, the electronics are still causing driveability issues. After studying my FSM, I realized that both the Engine Speed Sensor (ESS) and TPS get 5VDC from pin A17 of connector C1 (black connector at PCM), and sensor ground from pin A4 of connector C1. So, I figured the TPS connector would be an excellent source to measure voltages while driving.

I inserted an 18 gauge wire in both the 5VDC feed and ground pins of the connector, fed them through the firewall, and connected them to the leads of my Fluke 87 digital multi-meter (DMM), which I set to min/max mode. This mode measures, and holds, the minimum and maximum voltages for later retrieval. When the tach was dropping, and the trans was acting strange (easier felt than described), my 5VDC would drop anywhere from 2.88 VDC to 2.00 VDC. I then changed my ground reference point to the ground on the underside of the dash panel, near the fuse block (I believe this is G201). Same story. I then changed my ground reference point to the ground terminal on the driver's side battery. Again, same story. At this point I'm convinced my PCM is acting up and having difficulty supplying the 5VDC. I mean, after all, what better ground then directly at the battery. To rule out splice S137 (the 5VDC splice for the ESS and TPS), I decide to measure my 5VDC directly at pin A4 of connector C1 of the PCM. I left my ground at the battery and suffered the same problems. Now I'm completely convinced that the PCM is at fault, and not supplying 5VDC. Then it dawned on me...the PCM more than likely needs a good ground in order to complete the circuit necessary to convert the 12VDC supplying the PCM to the 5VDC that supplies the sensors. After all, the PCM is solid state; I highly doubt there is a standard resistor inside that reduces 12VDC to 5VDC. So, I decide to measure continuity between pin A4 of connector C1 at the PCM, and the ground terminal on the driver's side battery. When the tach measures 0 RPM's while driving, my DMM would measure infinite resistance. In other words, a completely open connection. There is one flaw with the continuity test though. The PCM receives it's ground from pins A31 and A32 of connector C1 (original source is ground G119 which is on front of head just to the passenger side of the front of the inj pump). There may be some switching involved inside the PCM in order to get ground from pins A31 and A32 to pin A4. You'd think with all of my note taking, that I would remember whether or not the sensor ground at pin A4 was a direct connect to chassis ground. If it is a direct connect between pins A31/A32 and pin A4, then my problem is ground related. However, if there is in fact switching taking place inside the PCM to supply the sensors with sensor ground, then the problem could very well be either a problem with the PCM supplying 5VDC, or a problem with the PCM supplying sensor ground, or even both. I believe my next tests are to measure voltage at pin A2 of connector C1 at the PCM for 12VDC (from ignition switch) and also at pin A22 of connector C1 for 12VDC (from battery +). I've already removed, cleaned, and reconnected ground G119. It was immaculate to start with. There are, however, three splices (S150, S151, and S139) before reaching pins A31 and pins A32 of connector C1 at the PCM.

I appreciate the suggestion about the ignition switch being a possible culprit, but I believe I have completely ruled out that as a problem. When measuring 5VDC at the TPS, I noticed that even after turning off the ignition switch, I still measure 5VDC for one to two seconds. So, even after the truck is completely shut off, there is still 5VDC supplied to the ESS and TPS. If you try this test without starting the engine first, you will be able to hear a relay click when the 5VDC finally goes away. More than likely, the relay opening is removing 12VDC supplying the PCM. So, I'm thinking that if it were an ignition switch problem, there would still be a that 1 to 2 seconds where 12VDC was still supplying the PCM, which of course supplies the 5VDC to the sensors.

8/15 edit #1 -- I just realized that not having continuity between chassis ground and pin A4 on the PCM doesn't necessarily mean that ground is not entering pins A31 and A32 properly. If the PCM does in fact supply ground to pin A4 by some fancy switching inside, than a failed (or failing) PCM might cause a loss of Sensor Ground at A4.

8/15 edit #2 -- I just got off the telephone with somebody on this forum, and was told that Sensor Ground at pin A4 is actually being supplied by the five individual sensors. So, a break between splice S161 and pin A4 would cause the problem I am experiencing. Obviously, this doesn't necessarily mean that is the problem, but it is one more thing to check. How nice.

infidel

At this point only things I can recommend is checking that your meter probes haven't enlarged any female connectors. This is what had happened on the truck that we needlessly replaced the pcm. When the enlargement occurred it wasn't noticeable, the probes fit in easily. It took the owner several hours to go back over all the female connectors that had been probed and squeeze them tighter. Just a slight bad connection that a meter can't register is enough to cause a problem.
Other than that it's pcm time. If you know someone with a donor truck make a swap. I've been told by several reliable sources that you can't damage the pcm from the donor vehicle by swapping.

royta

OK, I did my final testing, and I believe it is definitely the PCM.

I connected a jumper between negative terminal on driver's side battery to G119 (ground point on front of block). G119 is the ground feed to pins A31 and pins A32 of the PCM. I wanted to bypass the Sensor Ground altogether, so I connected my DMM negative lead directly to the negative terminal of the battery. I back fed pin A17 of connector C1 at the PCM with a paper clip so I could measure my 5VDC. I went for a drive and measured voltage with my DMM. When the problem was acting up, my voltage would drop down to the 2.00 VDC to 2.88 VDC range. Could the PCM problem be intermittent though?

What do you think?

infidel

The pcm could be intermittent or the + power supply to it could be intermittent.
Have you removed the pcm and looked at it?
Any signs of overheating or shorts are visible though the resin.
Sure hate for you to throw an expensive part at the problem to find out it isn't the problem.
Any luck with junkyard pcms?

royta

I tried All Dodge in Rancho Cordova, CA. They had one last week, but not now. Their price would have been $300. I know an old Cummins tech who purchases a lot of parts from Moss Bros Dodge in San Bernadino, CA. He told me to drop his name to the parts guy there so I could get a discount. Normal price for the PCM is $515, but I'll get it for $453. Of course there's tax and another $80 for flashing. At the time of the flashing, I'll pay for a diagnosis and hopefully find out that the PCM is in fact the problem. It's funny how I hate dealerships because I'm afraid they'll just throw parts at it until the problem goes away, when I'm doing no different. I think I'm learning my lesson though. I talked with a copule dealerships today (after I had already ordered the PCM), and they both had a tech that has been working on the Dodge's with Cummins engines since the '89 model. One dealership's guy only works on the diesel trucks. Nothing else. If it's not the PCM, I'll certainly have learned my lesson, and will bite the bullet and have it fixed by somebody else. I think it's better to pay a lot now, and get back to work to recuperate your costs, rather than pay a lot over a longer period of time, and continually have problems over that period.

royta

Here's the latest information on this problem. The PCM did not fix it. I know, I know, that's a shock for everybody.

I brainstormed with a tech at the dealership this morning, and he said it almost sounds like the 5VDC supply is shorting somewhere. However, the voltage does not drop to 0 volts, like a short would cause. Because it wasn't dropping all the way to 0 volts, he agreed it sounded like a PCM problem. So, I change the PCM in their parking lot and took it for a test drive. The problem stayed. I pulled over at another parking lot and checked voltage coming from Fuse 8 in the Power Distribution Center. When the problem was acting up, there was still full voltage reaching pin A22 on connector C1 at the PCM. Removing the fuse, does not kill the truck, but it does kill the tach, speedo, alternator charging, A/C relay, basically everything that drops when the problem is acting up. I imagine that this 12VDC entering the PCM is what gets regulated down to the 5VDC leaving the PCM. OK, so now (at that particular moment) I'm thinking a sensor is bad, causing some heavy restistance, and lowering my 5VDC. Not exactly a short, but as close as you can get to a short without dropping to 0 volts.

During my travels during the rest of the day, I disconnected a couple sensors one at a time, and continued driving. I started with the Rear Wheel Speed Sensor, but all that does is illuminate the ABS and Brake lights on the dash. I then moved to the Vehicle Speed Sensor at the transfer case. I'm guessing that all the 5VDC supplies are interconnected inside the PCM, regardless of which connector they leave the PCM from. My 5VDC was still dropping in and out. I then reconnected the VSS and disconnected the Transmission Solenoid Assembly connector at the top of the transmission. The Transmission Temperature Sensor is located in the Transmission Solenoid Assembly, and also receives 5VDC from pin B31 of connector C2 at the PCM. My 5VDC is still dropping off at the PCM.

Here is a list of sensors that I have changed, that receive 5VDC from the PCM. Engine Speed Sensor & Throttle Position Sensor.

Here is a list of sensors that I have disconnected that receive 5VDC from the PCM. Vehicle Speed Sensor & Transmission Temperature Sensor (via the Transmission Solenoid Assembly connector). I've disconnected the Throttle Position Sensor a day or two after changing it out, and I'll still lose my 5VDC from the PCM.

Basically, what I'm trying to do is disconnect sensors supplied by 5VDC, one at a time, until the problem goes away. Disconnecting the Engine Speed Sensor forces the problem into full time, instead of the jittery, flaky condition it is currently in.



Am I missing something? Does anybody else have a Factory Service Manual that they could look at (preferrably a '96 or '97, as they both have the same electronics & 47RE transmissions) with me and we could brainstorm together? Could it still be a short on the supply side, despite the fact that 5VDC isn't dropping to 0? I've connected a jumper directly between the negative battery terminal and ground G119 at the front of the head. This is where the PCM receives it's main ground. Unless there is actually a break in the wire between G119 and pins A31 & A32 of connector C1 at the PCM, the PCM is definitely receiving full power.



This is seriously killing me. I'm just sick over this. I'm stressed beyond description, I'm trying to turn a profit in my new business, and it's real tough to do when I'm working on my truck. I'm about to get some cab to axle measurements on the 2005 so I can see if my service body will fit on a new truck.

royta

I just disconnected my ESS and took a drive. I can tell when the problem would normally act up, as my 5VDC voltage will still drop out.

I'm starting to think the only way I'll find the problem, is by cutting the 5VDC supply wires that leave the PCM, approximately 6 inches from the PCM. If my 5VDC no longer drops out, then I know it is being caused by a short on 5VDC supply wire somewhere in the loom. If the 5VDC continues to drop out, then the only explanation would be a bad ground to PCM. I've already checked voltage going into the PCM, and used the negative terminal of the battery as a the ground reference, with no drop whatsoever of the 12VDC supplying the PCM.

I hate the thought of cutting up the loom, especially if the problem is being caused by a sensor, but at least I can narrow down where I need to look.



Does anybody have any suggestions?

Donz455

what was the fix?