Hey guys. New to the forum here. I have a 1998.5 Cummins that has been in my wife's family since day one. My wife grew up getting to drive the truck to high school when her Dad wasn't using it for work. He also used it to tow his mega truck "Crawldad II" to events in the southeast. Anyways he passed away 2 years ago and my wife wanted me to make the truck my daily driver a remembrance of her dad. When I got back from deployment this past spring we flew to TN and proceed to drive the truck from TN to WA with no issues. I only flushed/changed the fluids/filter and replaced the brakes. Outside of that the truck drove great. About a month the truck started surging at idle. When it surges the ECT will immediately drop to zero. First I replaced the ECT sensor and the issues continued. Then the VP-44 and lift pump decided to quit. I thought this may of been the problem. Replaced the VP-44 (from thoroughbred diesel) and installed a 165 FASS pump. When I did the pump I also did a timbo apps sensor. The surging problem continued. I thought it may of been due to old batteries. I replaced those. Still there. Replaced alternator as it had excessive AC noise before and after I did the ground mod. I have replaced the Tstat with a cummins Tstat and burped the system for about 30 minutes. The surging continues and the ECT drops with it or even fails to respond with a change in coolant temp. The tan and brown wire for the ECT sensor has 5v at it. The sensor itself shows a change in resistance for coolant temp (decreasing as the temp goes up) I found the vacuum line from the power steering pump to the manifold to be missing (this explains the blow by/not going into 4wd/only having defrost on the AC) replaced that line with a flexible rubber hose with clamps. Solved that problem but the surging continues. It happens in park and drive. I have videos of the surging if needed. I'm at loss. It's throwing no engine codes. The WTS light always comes on immediately. With a scanner it reads everything at the right value expect the ECT will flash from NOT to -40, or will stay at -40 for long periods of time. I am assuming the ECT is causing the surging due to the changes in fuel delivery and timing.

 

Any advice would be greatly appreciated. I am trying to get this fixed before I deploy again later this week.

 

There are no mods done to the truck besides a larger horn for the intake. It had a banks engine calibration module but nothing was plugged in and I don't know anything about it so I took it all out. 

11 hours ago, sethreesh said:

Loren do you know exactly where that is in the loom I have the loom opened up from the ECM to where it begins to dip below the power steering pump and I don’t see it

I'm afraid I don't know, just that it's supposedly by the ECM.  Your method of starting at the ECM (or elsewhere) and removing loom is what I'd do.  Personally, whatever I opened up I'd just replace with new since it gets all brittle.

I may just make a entire new ground line that goes from the ECM to each associated sensor to eliminate it from being a problem. 

Personally I would pull the ECM and the entire engine loom and then send it to @Auto Computer Specialistand have them test both the ECM and the wiring loom which they can do both including repair of the wiring loom as well. That way you don't have a hacked wiring loom with future problems. 

1 hour ago, Mopar1973Man said:

pull the ECM and the entire engine loom and then send it

That ECM will have racked up some serious frequent flier miles!

Haha you’re telling me looks like I’ll pull it off on Sunday and send it out…

Well guys here with an update I got the ECM and PCM out along with both harnesses out. It's currently on route to @Auto Computer Specialist. Should be there this Thursday. Let's hope they are able to figure out this rouge electrical problem. Those harnesses get pretty nasty I pulled all the old brittle plastic insulation off cleaned off all the old tape. The splice looked in good condition but I didn't break into it. For those wondering splice S165 sat just below the power steering pump on my truck. 

 

While all that stuff is out for the next few weeks any one have suggestions on what I should do to continue making this baby shine? I have a BHAF sitting waiting to be put in when I put everything else back in for the electrical problems.

Have you thought about the actual sensor being bad? I know you already sent it out though.. 

 

Unless i missed where you mentioned your results with the sender  

1 minute ago, Silverwolf2691 said:

Have you thought about the actual sensor being bad? I know you already sent it out though.. 

 

Unless i missed where you mentioned your results with the sender  

I did that as my very first step of troubleshooting. Put in a ECT from NAPA still had problems. Did a bunch of other troubleshooting. Thought maybe the NAPA one was bad so I pump in one from Cummins still had problems. With it unplug and multimeter on the ECT sensor you can watch resistance change as temp increases.

Another clue... if the ground side is lost it will peg at 240F. (High volt code) If the +5V is shorted to ground the temp will fall to -40F. (Low volt code). I'm going to assume you have a short to ground between +5V line.

18 minutes ago, Mopar1973Man said:

Another clue... if the ground side is lost it will peg at 240F. (High volt code) If the +5V is shorted to ground the temp will fall to -40F. (Low volt code). I'm going to assume you have a short to ground between +5V line.

 

I'm really interested in where the short is at. The tan/black wire from the ECM to ECT is a brand new pinned in wire. All the sensor grounds tested less than .2 ohms each last night from the ECM plug to the sensor. I sat on the kitchen floor with it all laid out and tested each point. This is driving me. Interesting that I am not getting any codes from this. Only way to get a code is to unplug the sensor. The P1693 was stuck in for a while but when I did the W-T mod that went away. But hey at least I'm not paying diesel prices in WA right now....have to find the bright side. 

Edited March 22, 20223 yr by sethreesh

Again if you would do the diagnostic for the error code the testing would have you unplug both the ECT and ECM and now check from pin to GND. This will show up on the 5V lead not the black tan.

So tan/black to battery ground? Just making sure I understand. You’re saying the short could be in that signal causing the error. And it’s probably a small break so it’s intermittent 

Edited March 22, 20223 yr by sethreesh

Don't confuse the sensor ground for frame ground. They are not the same.

 

Tan/Black is +5V signal. If this is shorted to ground (body) will produce you issue. So I'd you unplug both the ECT sensor and ECM then measure ohm between black/tan to block should show a short (0 ohm) but being intermittent it may not. Still in all the black/tan goes directly to the ECM.

 

Black/light blue is sensor ground back to the ECM this is shared by other sensors (APPS sensor, WIF sensor, cam sensor, etc.)

Hey guys while the ECM/PCM/Wiring Harness are at the @Auto Computer Specialist shop I am reviewing the grounds again just to triple check and make sure I have all the major ones. Want to check with you guys to see if I'm missing anything. So far I have cleaned up:

 

Outside The Cab

1. Driver side battery ground to engine just below the power steering pump on the timing case.

2. Driver side battery to frame mount for the front bumper

3. Driver side battery to body on the fender

4. The G100 just behind the driver side head light

5. Additional ground by G100 (two leads going to it; which one is this?)

6. Just aft of the PDC bolted to ABS controller coming out of wiring harness (not sure which one this is to)

7. Passenger side battery to PCM

8. Passenger side battery Engine

9. Passenger side battery to Body

10. Just above starter below ECM

11. W-T mod on timing case

 

Inside The Cab

1. Two sets on driver side kickplate

2. Centerline in dash frame below radio

 

Let me know what I'm missing. Thanks guys.

 

Oh my Gawd. 

 

The only one is the passenger battery lead. The rest of those are lights and nothing major. W-T ground wire mod deals with this directly. Again passenger battery negative covers ECM, PCM, and VP44.

 

Being all sensors rely on ECM internal ground this means the W-T ground mod resolves most of this. 

 

Again being that ECT is not pegging out and dropping this is the ECT shorting to ground. If you did the W-T ground you would have the loom exposed most of the way to the ECM. Even having @Auto Computer Specialist do the testing too will resolve this.

Edited March 31, 20223 yr by Mopar1973Man

Oh I’m just cleaning up the engine while the loom is out for testing. Like your crank case breather mod I need to do that as that vent has made everything below it absolutely disgusting. 

Got my harnesses back. @Auto Computer Specialistdid a bang up jump cleaning them all up. Going to install tomorrow evening or Saturday weather depending. Anything to look out for when I put them back in? 

3 hours ago, sethreesh said:

Anything to look out for when I put them back in? 

In my case, squirrels. Tore up a big chunk of my harness! Critter Ridder applied every couple weeks didn't prevent another nest, but no more damage. Now trying moth balls tied up in an old sock...

I shouldn’t laugh but that is humorous 

That is a stellar looking engine harness. Could you possibly tell me what you paid for that service? Being up here the ranchers tend to butcher the electrical and sometimes the only way to fix it is to just pull the wiring out and let @Auto Computer Specialistdeal with it. After seeing that above I'm sold... Very professional looking.