Strange jolt at 50mph

[StevesTruck]

Has anyone any ideas?
Bought a 5th wheel camper and towed it home last night. It weighs around 6000#. The truck towed very well for the couple of hundred of back country miles, but twice going up a very slight incline at around 50 mph there was a sudden jolt like being lightly rear ended. No power loss and no warning lights. I only have stock gauges but oil pressure and coolant temp hardly moved throughout the trip.
Any thoughts would be greatly appreciated.
Steve

[Hubert]

Do a search this is somewhat common and to some extent a little normal depending on severity and frequency of the problem. Sometimes these trucks do a little adjustment and sometimes you feel it. Could be the torque converter locking up or unlocking and a fuel metering adjustment. Just once I would ignore or you'll spend a lot of money chasing a ghost. Its related to the precise fuel metering for smooth operation. It could be either the PMD going, a bad lift pump, clogged filter, or sticky fuel solenoid. Could be a bad oil pressure switch. Or the IP. ect ect.

My guess if its completely random intermittent problem then its the pmd going. Most other causes will make the problem more severe and/or more predictable. Towing generates heat under hood that causes the PMD to act up. Sometimes they act up cold.
Has it ever cut off for no reason and would crank back up immediately?
Ever cranked a long time then finally started and run normal?
Any codes? If so PMD more than likely.

[StevesTruck]

Thanks Hubert for the info.
The truck starts great and runs great. It's never cut out.
I will change the fuel filter and see what happens.
Steve

[damork]

StevesTruck,
I've been experiencing the same thing for some time and am quite certain I recently learned a bit more on what is happening.

You may have some fuel issues, but I'd be more inclined to say it is related to the infamous grounding issues we have with the 6.5 electronic diesels.

My most recent issue was TCC cycling and I was focused on the transmission. From time to time I was getting jerks while going down the road - out of the blue and no warning with no codes being set. It rained, or I washed the truck and acted up. Anyway, I learned the brake pedal switch could affected the TCC as well as the trailer wiring may be corroded and affect a bunch more.

I started with the trailer wiring and what a mess. I cut off the old plug and cleaned it up, installed a new plug along with re-cleaning as many ground wires as I could find. I've run a week now with absolutely no hiccups or cycling. The fix was immediate, so it helped me. I think it may even help to find ground wires under the dash and check them with an ohmeter to ensure they truly are grounded, and if not find out why and make them grounded. Something to consider.

[StevesTruck]

Damork,
It's not the first time I have had a grounding problem so it could be coming back to haunt me!
As soon as I replace the filter I will start on checking the ground straps. Thanks for the idea.
Steve

[Hubert]

Steve,

My first response was to ignore a single episode. Well I think I am experiencing the ole FSD failure and it started with a jolt and a few long cranking events. An intermittent nagging nusiance really not an all out stall like many report.

Check your grounds and clean them good maintenance can't hurt but you should start rounding up parts for a back up FSD & remote mount. I was working on one and didn't finish before it left me walking. Can't say how long it will act up before quitting.

[DickWells]

Steve: As someone said above, it could be any one, or more, of many things, but the PMD and the grounds are the most common sources, in my experience.
Checking out the PMD is well documented in the DP. Sounds like you are well versed in checking the grounds, too. But, the one that is often missed, and the one that gave me the most trouble, is the one on top of the frame, just outside of the starter. GM's use of a self tapping screw at that location is pretty much a Mickey Mouse affair. I ended up running a 4.5" SS 5/16 bolt through the frame from the wheel well, and double nutting the two ground tabs inside the frame. That ended the poor ground there. The other ground, (The only one that ever stopped me cold) is the one at the right rear of the engine, by the transmission dip-stick bracket, on the manifold tab, is hard to pin down, sometimes, but is easier to fix.
I finally gave up on the electronics, well, somewhat, last Summer and put in a mechanical marine pump. I'm now between 17 and 18 thousand on the new pump, with NO hiccups! That's a new record, by about 14000 miles, for me.
Good luck.
Dick Wells

[StevesTruck]

Thanks Dick. I'll get cleaning!
Steve