I've got a weird(?) problem that occurs intermittently.

When towing our big travel trailer, then coming to an idle condition, the engine will occasionally run rough and stutter/flare up erratically. It almost always keeps running, but will idle pretty roughly.

Strangely, if I turn off the key and then re-start the engine, it idles normally.

The problem never occurs after normal driving. In fact, the engine normally idles very smoothly when warmed up.

Any ideas? What should I monitor?

 

What year? Check ipr% at hot idle.

 

2005. August 2005 production, so definitely a 2005 engine. I've got an Edge CTS monitor, so I think I can set this up to monitor IPR%(?). I may also monitor FICM voltage, just in case.

 

Changed the Edge CTS Insight to show Injection Pressure Regulator % and FICM Voltage. I also added the Injection Pressure. Nothing of interest to look at yet.

I have to wait until I stress the engine for a while towing the big rig, I assume.

 

Same problem recurred night before last. I had just towed my 10,500 lb trailer from one storage location to another (about 5 miles). Ex had to idle a fair amount while I unhitched.

All was fine, and I left to drive home. About 8 miles later, I pulled up to a stoplight and the truck suddenly DIED. This motor just simply never does that.

In this case, I was monitoring the IPR% on my Edge CTS. I was able to restart the engine. It sputtered a couple of seconds and then ran smoothly for the remaining 3 miles to the house.

The really odd thing is that the display "IPR%" became stuck at 14% and stayed that way for those 5 - 6 minutes to get on home. When I got it in the garage, I restarted the engine and the IPR% displayed a more normal fluctuating value (about 21%).

The next day, the truck ran fine and the IPR% fluctuated normally.

Advice?

 

If your ipr was stuck at 14% then your icp sensor or pigtail may be sending a false reading and the truck thinks it has more oil pressure than it actually does. A quick check is to see what your icp sensor is reading koeo and if your truck acts up like this again the simplest way to test this is by unplugging your icp sensor. If the engine suddenly runs better once the icp sensor is unplugged then I would go ahead and replace the sensor and if that connection has any oil in it then it's time to replace the pigtail as well. As a rule your ipr (and other sensors) should not hit there max or min values while in operation, for the ipr that means never hitting 14 or 85 while running

 

Thank you kindly. I am still trying to understand this a bit better. It sounds as if the IPR% (Injection Pressure Regulator % open(?)) is a 'command' that results from the measured injection manifold oil pressure (ICP?). Is that about right? I added IPR% to my Edge CTS. I think I can also display ICP reading.

Would it be wise just to replace the ICP and pigtail without further diagnosis?

 

i guess you could just go ahead and replace it but i would first look into a few more things first. the hard part about an intermittent problem is it really has to be "acting up" to help diagnose the problem (thats why i suggested pulling the icp sensor connection when the truck is running rough) and if not properly diagnosed you could end up going down the "throw good parts at it road till its fixed" road = $$$. if you pull the connection and the truck smooths out and idles fine then you found the culprit, if nothing changes when the connector is pulled and still runs like crap then it isn't the icp that's causing your problems (and the bonus is that this test cost you squat to do). you want to look at your icp volts and icp pressure koeo. they should read about .24V and 0psi and ipr should be 14.8ish (i will add some of diesel tech ron's vids explaining this better than i can type the info out to you and why its important).

the ipr valve is essentially a dump valve to our high pressure oil systems. 14% is fully open (dumping all the oil it can) and 85% is closed (sending all of the oil pressure from the hpop to the tops of the injectors). the ipr opens and closes based on how much oil pressure is desired at that particular time (at a warm idle sitting in traffic it only needs about 600psi of oil pressure so the ipr opens or closes to get that 600psi which on a healthy high pressure oil system is around 23-24%). now when your towing your trailer going up a grade spinning 2500rpm's you need higher oil pressure to get you up and over that hill so the ipr valve closes sending more oil pressure to the tops of the injectors.

the truck knows how much oil pressure is in the system via the icp sensor...so if thats outta whack then its trying to run off of false readings (thinking it has more oil pressure than it actually does). in this case it would actually be better to run it with the icp disconnected running off of its default values to get you home (it will/or should run better and you wont hurt anything by doing this).

just as a side note, the ipr % value is the commanded value and may not be the actual position of the ipr valve. sometimes this is important to know when trying to diagnose a no start or suspected weak oil pump where instead its debris holding the ipr valve open dumping all of the oil.


if you haven't already spend some time on his youtube channel...LOTS of great info!

 

Cam Phasers! It will run good for a bit then go to crap. Turn it off and back on it runs good again, but not for long. Eventualy it wont run good after restarting, then it will finaly just run like crap. My top left chain guide was chewed up and n the oil pan as well.

 

 

LOL, I just think that he is excited that his 5.4L is running right again! Been there and done that w/ the 5.4L.

 

LOL. We know he isn't Spock. Spock always just used the neck pinch thing. And Cap'n Kirk preferred to duke it out. Scotty was back on board manning the beamer. Could it be that doctor character. I know Uguru? used her phaser a lot.

OP, while you're looking around, it's not that much to just yank the IPR and clean it. Prolly won't fix, but could, and lets you know if any chain guides tore through the screen.

 

Totally cam phasers......







.....just kidding.

 

When i had this issue, it was a faulty injector. after replacing it everything smoothed out.