Slight Bucking Sensation at Highway Speed

[Alan Reagan]

I just completed an 1800 mile round trip running almost entirely interstate miles. At speed, occassionally I will get a slight bucking sensation like the truck has a momentary miss. Cranking and idling are fine and I haven't noticed it at lower speeds on the two lane roads. I can't tell if it is the suspension, drivetrain or an actual engine miss.



Suggestions?

 

[BIGNASTY]

When mine goes to buckin and thats not very often!! I just put some spur to it that stops that BUCKIN I TRIED TO BY-PASS THE CUSSING FILTER right now!!!



SORRY I JUST COULDNT HELP MYSELF

 

[Alan Reagan]

I tried that, Bignasty. It worked until I settled back to a "normal" interstate speed. It may have been those sorry roads in North and South Carolina. Especially North Carolina. If you spur too much in that state, you will get airborne.

 

[MChrist]

My '06 does the same thing, and it has been mentioned by several people here with various years, so it doesn't seem to be a 4th Gen issue.
It makes my wife ask "What's wrong?" every time.

 

[Alan Reagan]

Makes me wonder if it is the suspension. The tach isn't moving when it does it, no codes. Does it with cruise or without cruise. I have to go to St. Louis on Monday. Maybe the Tennessee roads will tell the tale.

 

[MChrist]

Makes me wonder if it is the suspension. The tach isn't moving when it does it, no codes. Does it with cruise or without cruise. I have to go to St. Louis on Monday. Maybe the Tennessee roads will tell the tale.

Perhaps, but mine happens while on cruise control going down a slight decline. Feels like drivetrain lash.

 

[AH64ID]

Are you on pavement or concrete?



I know that my friends with CC LB 4th gens say that the wheelbase makes expansion joints very uncomfortable, relative to the QC LB wheelbase of the 3rd gen. My 3rd gen will buck on them a little, but nothing like a 4th gen.

Perhaps, but mine happens while on cruise control going down a slight decline. Feels like drivetrain lash.

That may or may not be the same issue. My 3rd gen does this as well. On the perfect decline the truck cannot inject little enough fuel to maintain speed, so it oscillates between minimum fuel and zero fuel and gets a slight surge. Oddly enough the only hill around here that my truck does this on is also the only hill my VW Jetta 2. 0 gasser does it on also.



If it happens at higher fuel rates it can be indicative of injector issues.

 

[Alan Reagan]

AH64ID, I was thinking injectors at first but it is so intermittent. I happens suddenly and then nothing. It's like hitting a bump that you don't see. I have to go to St. Louis on Monday so I'll see how that trip goes. Like I said, NC and SC roads are the roughest in the Southeast. Hopefully that's what it was. I'm running 65 PSI in the front tires and 55 in the rear. Since I will be running unloaded, I may drop my pressures a little and see if that changes anything.

 

[Cummins12V98]

Unloaded I would run 72 in the front and 45 in the rear. I have gotten 120k on two different sets on my 98 4x4 12V running those pressures. One set Michelin and the other BFG 3rd gen factory take offs.

 

[rscurtis]

That's excellent tire life on a second generation truck.

 

[Bob4x4]

Light load is 60 front 45 rear. Seems to work pretty good on the trucks I see

 

[Alan Reagan]

I may have discovered the issue. I normally don't add any additives on this truck. I always used Stanadyne on my previous diesels. When I changed my fuel filter last week, it was extremely dirty. To the point of a fine black dust looking coating on the top of the old filter. When I wiped it with a shop cloth it was black. Wiping the element turned the cloth black. It was dirty. So I picked up some Stanadyne and added it to the a fresh tank of fuel and 100 miles later, the bucking appears to have stopped. I must have had an injector that needed some additional lube to free up. So far so good. Apparently, I picked up a bad load of fuel in the great state of Florida last week. I'm going to change my filter again today to make sure I got it all.



I will post more after my trip to St. Louis on Monday.

 

[RonD]

My guess your fuel filter was way over due for service, mine never looks like yours when I change it 15,000 miles tops on replacement

 

[Alan Reagan]

My guess your fuel filter was way over due for service, mine never looks like yours when I change it 15,000 miles tops on replacement

I never go past 15k before changing the filter. I was at 14k about to do a 1400 mile round trip. I am sure I got a bad tank of fuel on the trip back from Tampa. The filter has never been dirty like this.

 

[Alan Reagan]

Just returned from St. Louis. The problem got worse during the trip. Additive didn't solve the problem. While I was up there, I cranked up one evening and while I was waiting to get out of my parking space, the engine sound kept oscillating between normal and the sound you get when the EGR is cycling. Suddenly the engine stalled but didn't quit before it came back to life. Scared the devil out of me. Idle returned to normal. As I pulled out on the service road the engine suddenly dropped to idle and I had no throttle control. I coasted off the road and again the engine came back to life.

Today, I took it to the dealer. No codes and, of course, the problem could not be duplicated. I've known the mechanic for 14 years and he knows I don't bring in my truck for minor stuff. After we talked for a while, he said the dying was a symptom of a failing EGR. He is thing that it is intermittent as the EGR is cycling and not opening all the way when it should. Tomorrow the new EGR and a couple of other parts are going in.

I will keep this post updated as to whether or not this is the fix. It did seem a lot worse in cold weather so hopefully he is on to the problem.

Almost forgot, he did a flash update that was the full meal deal. Apparently, the have been several updates to the software, one of which solves this bucking problem. I could tell after the flash, that the acceleration was smoother and a little more torquey starting off.

I guess I will know tomorrow if the EGR is the culprit.

 

[Bob4x4]

Egr does not make a stalling condition on a Ctd. You can run 100% egr flow at idle and it will still be smooth There are many dtc's for various egr system failures

 

[Alan Reagan]

Egr does not make a stalling condition on a Ctd. You can run 100% egr flow at idle and it will still be smooth There are many dtc's for various egr system failures

I would have thought the same thing. Supposedly the reflash has to do with the sticking EGR butterfly. According to the mechanic, it will cause the stalling like I experienced. The engine doesn't quite, it just has no power when I push on the go pedal. The cold morning when the engine almost quit, I could hear the exhaust changing as the EGR was cycling. When it went to the final "jake brake" sound is when it almost died. When I pulled out of the parking lot it did it again. In reading thru some of the Cummins ISX stuff, they state that a malfunctioning EGR can cause stalling and misfiring.



I don't know the answer to this yet, but they are replacing the EGR this morning.

 

[Bob4x4]

The tech may be talking about the throttle body not the egr valve

 

[Alan Reagan]

You are probably correct since he said he is replacing the throttle body as well. I just hope it solves the problem. I dropped it off at 0730. Should get it back before lunch.

 

[g_dog1]

It definitely sound like an electrical connection is loose, or damaged. What modifications do you have? Anything that would rub a wire harness, like a fifth wheel hitch?