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. 

19 hours ago, sethreesh said:

I deploy tomorrow. I'm gonna pull the ECM out and have the wife send it for testing and coordinating that. Who do you recommend I send it too. 

 

Auto Computer Specialist in Florida...

https://www.google.com/search?q=auto+computer+specialist

Hey guys I'm back from deployment.

 

My wife sent in the ECM to get looked at by auto-computer specialist. Still having issues. They had me replace the crank and cam sensors prior to reinstalling the ECM.

 

The dash cluster is showing that the engine is cold running and when you plug in a DTC to the OBDII port it reads -40 but will occasionally flash to about 180-190. I have had the ECM rebuilt by autocomputer specialist and they sent it back with some repairs done. I have replaced the injection pump, upgraded the fuel pump to a FASS, replaced the APPS with a TIMBO, cleaned up alot of the wiring, new alternator, new batteries. Do you think I could have a short in the same problem causing the PCM to send that it's -40 and the ECM sends a bunch of extra fuel causing the surge. When the gage cluster is reading the right ECT the surging goes away. When the ECT tanks out or doesn't respond at all the surging stays present? Please let me know your thoughts.

 

I sent the truck down to the local mechanic shop they seem to be stratching their heads too. But I was trying to save some of my own time as my ship is now in port at the shipyard up here in Washington and I'm spending most of my days wrenching on a submarine instead. 

Welcome back.

Did you get a chance to check S165? According to the wire map Mike posted, it's a splice that serves many sensors, including the ECT, IAT, and Cam sensors. Do you have an OBD Link LX, MX, etc., to check live data? Would be interesting to know if the IAT  and ECT sensors wig out at the same time.

The coolant sensor may be bad and needs to be tested.   The sensor is a thermistor and the voltage to the sensor is 5 volts.  When the temperature is low the resistance increases with less voltage going back to the PCM.   With an open circuit in either the sensor or it's wiring no voltage is getting back to the PCM which will give a reading of -40 and no temp gauge movement.  To test check the ohm resistance of the circuit.   The resistance will decrease as the temp increases. 

10 hours ago, IBMobile said:

With an open circuit in either the sensor or it's wiring no voltage is getting back to the PCM which will give a reading of -40 and no temp gauge movement.  To test check the ohm resistance of the circuit.   The resistance will decrease as the temp increases. 

 

Actually an open circuit is going to cause a high volt code being there is no ground. The +5V and sense at the ECM will see +5V and hi volt code is thrown. Now if the if its shorted to ground now the voltage goes low and now will trip the lo volt code. So an open circuit will make the gauge go hi in value, and shorted to ground will make the gauge value go down.

 

This should help explain this...

 

+5V & Sense -----> ECT Sensor <------ Return to ECM Ground.

Edited January 4, 20223 yr by Mopar1973Man

I finally watched the video and see that the oil pressure 'gauge' doesn't move when the engine does its thing.  So, maybe that splice isn't a problem.  Or it could be that only the ECT wire is the only one not making consistently good connection.  Considering the shoddy work we've seen related to such splices (W-T's photos prove it), I'd start there as it costs about zero pennies to check, and not many minutes to take apart, inspect, and reapply electrical tape, etc.

LorenS 

 

On a live data the IAT is showing no indication of failure during the surging. On the graph you will see the ECT go low while nothing else changes. However with the ECT sensor unplugged the surging stays present. You’ll get the hi voltage error code that way though. 

IBMobile

The sensor was replaced. With a multimeter the resistance tracks as it should with a change in temperature.

 

I almost think there is a short to ground somewhere interrupting communication causing it to load up on fuel. I just don’t know where. I know the ECM, PCM, and data link all eventually tie in together at a ground. Maybe it’s the common ground splice under the air box or there is a wire that is rubbing that the vibrations of the engine running make it contact and short then regain signal.

 

I know the ECT is recieving the 5V signal. And the 5V wire was replace from the ECM to the ECT it’s currently out of the harness loom as a standalone. 
 

Still the only error code I get is the companion 1693…

Edited January 4, 20223 yr by sethreesh

I typically verify the ECT to the IAT values on live data tools. Cold engine, key on engine off, then read both ECT and IAT values typically they match at first key on cycle. 

Hey guys in with a update. I traced and replaced every possible bad wire in the harness. Cleaned it up a lot. Still surging. Pulled the PCM and sent it off. They just got back with me they replaced 3 blown capacitors. It’s in the mail on the way back fingers crossed. 

PCM installed still surging. I think they missed something with the ECM still on the scanner you can see the ECT open circuit and return to normal. Pulling ECM sand PCM and sending back to ACS for them to look at. 

Hey guys back with another update. Got the ECM/PCM back again from ACS it’s still surging. The only value that changes with the surging is the ECT. I replaced every wire that comes from the battery. Cleaned all the major grounds. The only sensor I haven’t replaced is the oil pressure sensor. Any more thoughts. 
 

The 1693 is completely gone now though. It was still there when I got the computers back but after I replaced the ground wires and completed the WT mod and the PCM ground mod it went away. 

Edited March 17, 20223 yr by sethreesh

The graph shows the temp going to -40°F; that's an indication that there is either an open circuit or bad sensor.  Test the wires from the coolant sensor to the ECM and the coolant sensor by itself.   Be sure to test/check where all the ground are spliced together (see diagram below).

 

  

IBMobile how would you test at the splice? You’re talking about the S165 right? That’s the one in from of the ECM just behind the injection pump? 
 

With the ECT unplugged the truck runs perfect. 
 

It has 5V constant at the tan/black wire at the ECT sensor plug. 

That surge you are hearing is the timing going nuts most likely. Going from -40 timing to operating temp timing is a 4-5+ degree difference if I remember correctly.

 

Check wires then check the sensor.. 

Edited March 17, 20223 yr by Silverwolf2691

 

 Here’s a live view of the ECT and surging. 
 

I’m going to dig into the s165 splice and see what I find 

 

The shop I left it at couldn’t figure it out and want to say it’s the ECM I can’t imagine after it being looked at twice by ACS that it’s the ECM 

So a little more digging on the s165 the apps ground, ECT ground, oil pressure ground, cam ground all read at 6 ohms, the IAT ground read at 5 ohms and the pin at the ECM (pin 11) was 5 ohms. The ECT is the only on that seems to change the live value on my scan tool. So it looks like I need to go into the loom and see if I need to repair that connection…

Edited March 17, 20223 yr by sethreesh

7 hours ago, sethreesh said:

Here’s a live view of the ECT and surging.

The Calculated Load also jumps.  Causation or correlation I have no idea.  The video starts with the ECT at -40 and the engine is at 0% load, then jumps to 16 and even 20% later in the video.  As said a few months ago, that S165 needs to be checked.  It may just be that only the ECT sensor's wire is loose and the others are fine, etc.

Do a jiggle test.   Engine off, ohm meter on the suspect wire, grab the loam and jiggle it.  See if the meter shows open circuit.

 

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

From FSM: S165 (Diesel) Engine Harness, Near Engine Control Module