First I am going to apologize for the length of this post but I want you to have all of the details.

We purchased a used 02 24v 3500 dually just about a year ago.

It had been sitting so we got it going and just did the basic services, fluids etc.

my son drove it about a month and in mid September it developed a weird rough idle after warming up but no other drivability issues.

Changed both fuel filters with napa units and no change

about a week later the frame broke in half from rust so we parked it.

Fast forward to January 26, cab and bed removed, new frame from down south, blasted and painted. truck goes all back together with all new parts, brake lines, fuel lines, shocks, bushings, all frame wiring cleaned up etc. Drivetrain was cleaned up while it was out and any leaks addressed etc, new tires, really fun winter project for us.

Mid March, trucks back on the road. Rough idle was gone after we put truck back together. Assumed it was a bad connection, dirty ground, terminal etc.

After about 800 miles it comes back so we really start digging in.

At this point the truck has never had a code other than we first got it had no communication with Inj pump and turning on headlights would kill motor.

That was corrected by redoing the grounds behind the drivers headlight.

So no codes and rough idle after warm up

Change ECT for good measure

cleaned all grounds again

Batteries and terminals were all new with rebuild

blue chip diesel hot wire test on pump after truck is up to 180 and idling poorly returns truck to smooth perfect idle. this tells me pump, injectors, and fuel delivery are not a culprit

truck has airdog pump and Edge monitor with Fuel pressure gauge always steady at 17psi

performed WT ground mods

remove fuel pump relay to swap with horn and note some green corrosion on main terminals

open up PDC and removed 30 and 87 terminals. cleaned thoroughly and reinstalled

put brand new fuse in fusebox for feed to fuel pump relay

double checked all grounds behind headlight while battery was out for the pdc access

Truck runs great, assume all is well. my son drives the truck daily for about a month. 1000 miles or so, towing, etc

After a couple day rainy stretch issue comes back.

my son claimed he opened underhood fuse box and pushed on fuel pump relay, checked oil, and when he started truck it was fine again.

next day rough idle is back again

I opened the fusebox and tried messing with relay and then swapping it back with horn, no change.

This was about a month ago, still no codes of any kind or any other driveability issues other than idle

Since then I have opened the pdc and removed all the fuel pump relay terminals again and cleaned them even though they looked perfect.

tested pin 6 and 7 wires from pdc to vp44 no issues, added extra power and ground wires for testing, no change.

visually inspected all other wires in pdc for damage and found none, no presence of rodents etc

Completely removed EDGE at various times in troubleshooting with no change.

sent ecm out for testing and repair to keyworks in Virginia, no issue was found but I did have him follow through with the rebuild, change common failure parts etc.

ecm reinstalled and no change in running.

performed PCM ground mod with no change.

Tested all sensor circuits, 2 and 3 wire. good 5v reference to all

tried unplugging one sensor at time with no changes. I did get appropriate codes for each sensor when it was unplugged

The only sensor I never unplugged was the cam sensor under the pump

inspected all the loom on the harness and didn't see any issues, chafing etc

used contact cleaner on connections at pcm, and the two high up on the firewall, also any other connections or sensors I opened

one interesting thing to note, the black with a blue trace wire at each sensor is listed as the sensor ground from ecm, this wire has continuity to battery ground at each sensor but that goes away once the ecm harness is disconnected. Is this normal? I always thought sensor ground and body ground were different? Does the ECM connect body ground to the sensor ground pin internally? I also put my meter from sensor ground at ect to battery ground and thoroughly wiggled the whole harness to see if continuity beep stopped. It di not stop Until i removed ecm plug

I am at the end of my list of things to try. Anybody got any ideas lol?

We love the truck and just want it back to normal.

7 hours ago, kevinmacd said:

First I am going to apologize for the length of this post but I want you to have all of the details.

A long post with lots of detail is much better than a short post with little detail.

7 hours ago, kevinmacd said:

Does the ECM connect body ground to the sensor ground pin internally?

Many sensors ground through the ECM - you can see this in the photo below (terminal #11 on ECM).

When the engine has the rough idle, can you tell if all cylinders are affected, or just one cylinder?

Have you checked the mechanical idle stop condition - loose, out of adjustment, etc? I would expect a code, but not necessarily. The APPS is a closed loop system with the ECM and there is an idle validation switch inside the APPS. It is possible that if the APPS adjustment is marginal, the ECM may not see the idle validation switch signal (the ECM controls idle).

• John

Edited 47 minutes ago47 min by Tractorman