Good evening, all
Occasional reader, new user/poster.

The patient:
2001 Ram 2500 5.9L gas, auto, 4x4, 116000 miles. I believe it was a village/small city truck; there is an hour meter in the radiator shroud showing 8313 hours (good Lord I almost hope this is wrong, as it would be something akin to 480000 miles). It did sit for 3 years before I bought it. I downloaded the build sheet and it seems to have been ordered as a basic work truck; ie: rubber floor covering, no A/C, tow package, snow plow package, manual windows & locks, etc. I did search other threads but did not find quite this set of symptoms and believe I have covered the basics that were solutions to other's issues.
The problems:
occasional no start/rough starts, intermittent bucking/misfiring under light load, scanner often unable to communicate with PCM when vehicle is running (communication seems to be more successful when only reviewing codes).
3 startup scenarios are A: crank/no start; B: crank & start but timing sounds very late, idles only 5 - 10 seconds and dies. If you mess with the gas to keep it running, it smells incredibly rich; or C: crank, start & idle correctly
P1391 code.
What I've done so far:
cleaned various ground connections: under battery, on fender by left headlight, at left front of engine block near where A/C pump would be, on right fender and both firewall connections near the cowl. I also ran a piece of battery cable from the right side firewall connection (also where the flat ground strap to the PCM connects) over to the negative terminal on the battery.
Exchanged crank, cam and TPS sensors with working pieces from another truck that does run correctly & with no issues; verified part #s to ensure a "like for like" swap. I'm willing to accept that Mopar sensors work best but I'm not 100% convinced that I have only a sensor problem and prefer to troubleshoot more thoroughly.
Cleaned IAC
Bought refurb PCM - I did originally have a "No Bus" problem but this was resolved with the new PCM. I had thought this would resolve my "no communication" error when trying to view live data but sometimes it works, sometimes it doesn't. Usually doesn't. Reading historical codes with the truck not running is more successful.

One of the times that I was able to view live data, I did notice cam signal count often showed zero, right bank fuel stayed in open loop and right upstream O2 sensor voltage stayed at 4.98 volts. I unplugged this sensor this afternoon and was checking with my meter; readings in the harness connector are as follows:

Pin 1: 1.16 volts
Pin 2: 0.05 volts
Pin 3: 0.05 volts
Pin 4: 14.26 volts

Are these normal? I expected a ground, a battery + and nothing on the other two because they send the signal back to the PCM from the sensor. Or am I totally mis-comprehending this?

I can easily recreate the bucking/misfire. Simply feather the gas pedal to a light, almost no-load condition; doesn't matter if you do this at 75 MPH 2000 RPM on the highway or at 55 MPH 1600 RPM on a surface road. It seems to be "engine load" related, not necessarily RPM/TPS position related. If you either let fully off the gas or stomp it to the floor, it smooths right out. After converting the hours on the meter I was darn near convinced it was a sloppy timing chain (but that wouldn't explain the communication failure on OBDII connector either). I have not yet checked this with the "turn crank & hold rotor" method.

I do currently have the O2 sensor unplugged and it has improved but not eliminated the bucking/misfire. It is Federal Emissions, not CA, and thus has only two O2 sensors.

My thinking is that I have a wiring problem somewhere that is causing the "no communication with PCM" error and may or may not be causing the misfire as well. There is no cover on the under-hood Power Distribution Center. The previous owner said he had been told by a mechanic that the fuse box was corroded and needed to be replaced. By visual inspection I did not see any extraneous corrosion though and am not sure how qualified the previous diagnosis was. Is this a common issue? The bolt on the square white connector gets finger-tight but will strip/pop loose if you try to go any more than that. Will this cause a problem? The connector itself does feel like it is firmly seated.

Thoughts? Suggestions? Your time and input are appreciated.

Huge thanks for having the service manual available!!!

 

I don't think you get a straight shot from the PCM for bus communication.... I think it goes thru the central timer module first..... I think.

You can download the factory service manual here. (I highly recommend that.)

You should be seeing 5 volt reference voltage on one of those pins to the O2 sensor. That may be part of the problem......

1 wire is 5 volt reference signal.
Another wire is signal return to the PCM.
The other two are the heater circuit. (battery voltage, and a ground.) Heater circuit appears to be good. (at least, for supply voltage.....)

Are you getting any misfire codes?

The intermittent loss of cam/crank signal would certainly give you a miss...... Is the sensor in the truck a mopar sensor??

 

Central timer module? No idea what that is but will do some research.
Downloaded the service manual, thank you!!
I read somewhere that there's a chafing issue with the harness by the trans dipstick tube. Per the service manual, there's a splice joint there for one of the wires to the O2 sensor. Seems like a good place to start digging, might be able to revive that 5v signal...
I don't know if the current sensors are Mopar. I'll check them this weekend to see if there are any identifiable markings on them.
I did have time tonight after work to swap the IAC. It did idle differently afterward and I was able to get codes from the odometer by cycling the key. They were 0505 (referencing IAC failure) 0031 and 0132 (referencing voltage irregularities on O2 sensor circuit; these are expected, as I do still have that unplugged) and the infamous 1391.

I did get a spare engine wiring harness with it, although it does have the wrong O2 sensor plugs (round keyed gray ones). It may be easier to use the service manual and verify connections between the sensor plugs and PCM connectors to ensure that it's the same harness. Assuming it is, I may look for replacement O2 sensor connectors (square black ones), change these on the spare harness and then swap the whole thing on the weekend.

This beast is my DD and I'm gone about 11 hours a day due to commute & work, so I typically don't have much time to wrench on it till the weekend; may take me a few days to post updates back here.

 

I now have a randomly clicking relay under the dash, sounds like it's near the lower right side of the steering column. This clicking is not in sync with the misfire condition. I don't know if it's related to the same problem or not, guess I'll be pulling that lower dash panel off and poking around down there.

 

Sorry for the delay, just haven't had time to look at this thing.

The afore-mentioned randomly clicking relay under the dash does indeed appear to be the Central Timer Module. I disconnected it, opened the case and checked for corrosion (found none), reinstalled and have had no issues with it since.

I had been unable to check live data or read codes with the scanner, kept getting a "no communication" error. I was disconnecting/reconnecting the PCM plugs to ensure a good seat when I noticed the cover was bowed out a little. On further inspection, all three cavities had cracked around the center and there was what looked to be heat damage/discoloration in cavity C1. I took pictures but don't know how to post them here yet. I emailed the refurb company that I bought the PCM from but have not gotten any response. I am currently driving the truck with a $100 junkyard PCM. It does still have the same misfire condition, which I can easily recreate. The important thing is that I can now read codes and live data. My oldest son and I took it for a test drive today and I noticed the following:
Right side fuel system stays in Open Loop
Right side upstream O2 sensor stays at 4.98 volts
Right side fuel system stays in rich condition
Ignition timing is around 16 degrees BTC when under even slight load condition
Ignition timing is around 40 degrees BTC when under coast/no load condition/misfire -- this seems a bit extreme; given the 8300+ hours on the meter, I'm inclined to suspect a worn/stretched timing chain.

It doesn't seem logical that a worn timing chain/mechanical issue would also create a right side fuel system problem. I wouldn't be surprised if I have separate mechanical and electrical troubles. I hope to have another truck on the road in a week or so, which will give me a chance to park this one and dive into it. I'll pull the engine harness and spend a few evenings going through it. I also plan to check for excessive play between the crank and distributor. Will post updates as time allows.

 

The O2 sensor should cycle between 0, and 1 volt. The fact that yours is showing five implies that it is internally shorted.