07 5.9 cruise control bucking

[Crunch]

Does anyone here have the definitive answer for the "bucking" that some owners, like me, experience with CC engaged, cresting a hill typically as the cruise reaches a point that it's feathering the throttle?

Can't say this is definitive, but I have a similar problem (I think my cruise control is crapping out on me), and @cerberusiam pointed me to the APPS as a possible culprit. I haven't had the time to dig into it, but the continued smooth running of the engine while it happens leads me to believe that the APPS could definitely be the problem.

 

[G Ogre]

It's been a couple of years, but the time has come to update this topic.

Several months back my truck, with only 111K on the clock, started smoking at idle and launching frequent black clouds on acceleration, way more than normal. I first tried a clean air filter which seemed to help for a short time, but really didn't. Due to my recent move out of state and resulting chaos with garage/tools/unpacking, I brought it to a local diesel shop for a consult. They noted the smoke and also pointed out an intermittent miss. They felt worn injectors were most likely the issue, so I pulled the trigger. Additionally, the #6 hold down was broken, and had them replace that tube and the #4, as well as a leaking valve cover gasket and seeping rocker box gasket, and did the valve adjustment which was overdue.

Result is the engine running better and smoother than it ever has, and the cruise control bucking is now gone! Idle smoke and belching are gone too. Hated the thought of paying someone to do the job, but $700 labor vs. working in my driveway in the mid 20s without special tools and experience seemed like a no-brainer. They also replaced all the blue fuel line for the FASS Titanium pump...the hose was cracked badly over the full length.

Can't say whether injector replacement will solve the bucking for everyone, but it did for me. The result really makes me think that there's been an injector problem since I've owned it (bought at 34K about 10 years ago)...I don't think it's ever run this well.

 

[Motorhead]

G Ogre, What injectors did you use in your truck?

 

[Cloudmaster Don]

Thanks for the report, G O. It sounds like you found a competent shop. Not wanting to work in the driveway in 70° weather without the experience and special tools you mentioned, in addition to being really, really short on knowledge, I hope I do as well here in San Diego. I just may have to finally bite the bullet and head way across county to the big bucks shop to hear what they have to say.

 

[EDankievitch]

I had this bucking issue with my 05. It ended up being a bad fuel injector. It was over fueling the one cylinder and the computer would cut off/ back the fuel when it saw the crank acceleration faster than needed. Drove me nuts until I replaced all the injectors.

 

[DaveH77]

My 2004.5 was bucking on light throttle, level or slight downhill, from the time I got it at 220,000 miles.
Then cc would cut out completely and not work again until truck was shut off and restarted. Definitely had some slack in the drive train and possibly original injectors.
To their credit, the used dealer paid for local Lithia dealer in Kennewick to "fix it". Lithia made multiple attempts with the vac pump and cc actuator replaced, but it still bucked and quit cc. Finally they replaced the apps unit, bracket and all.

That new OEM apps unit made in Mexico fixed it completely for about a year, no bucking or cc cutting off.

About 230 or 235,000 miles it started bucking again, and sometimes on warm afternoons, it was so bad I would wonder if it would get me home, but it always ran good with throttle applied or uphill, or under any load. It only bucked or surged on level or slight downhill with very light throttle.
I ran a bunch of different injector cleaners for months with only slight improvement.

A good Dodge Cummins friend said lots of factory apps are faulty when new or very short lifespan and asked if my fuel mileage was also in the toilet compared to before. Yes!

I talked to Timbo and bought one of his apps units, a bit apprehensive about installing it myself. No worry, easy, simple, no adjustments were needed. Straight bolt in!
At the time I didn't realize Geno's also sells them. Timbo was a great resource, as I know Geno's staff are as well.

With the new Timbo apps installed, my truck has not bucked or surged at all ! Evidently that expensive OEM apps was junk in less than a year.
Now at 284,000 miles, the slack in the drivetrain is not better, lol, nor are the injectors, getting a bit more smoke lately, but the bucking has not returned.

Both explanations of DT slack and injector imbalance sound like truly viable and likely probabilities, but in my case it was the apps.
As I posted before in my '04 surging post, anytime there is a throttle issue, bucking, surging, flat pedal, etc... it is well worth considering a Timbo apps unit.

Now I have to start saving up for a set of BBI injectors and more filtration. Right after I fix my transmission leak and a few other Dodge problems.
I love the Cummins but I wish the rest of the truck was as good as the engine.
At least I'm not far from John at Dynamic Transmission, another awesome resource for our trucks. Can't wait to have him rebuild my AT.

Thanks to everyone who contributes here, the knowledge base is unbelievable and greatly appreciated.

Cheers, Dave

 

[G Ogre]

G Ogre, What injectors did you use in your truck?

They were Bosch remans from Oregon Injection...wanted new but they were not available, and since the shop had a solid track record with these I went with them.

 

[cerberusiam]

Twanted new but they were not available

Whomever told you that lied, a bald faced whopper of a lie at that, they *should* know better. It is unbelievable how much a supposed Bosch authorized shop does NOT know about the product they sell. Tends to severely reduce the confidence in doing business with them.

 

[G Ogre]

Let me rephrase...they weren't available from whoever his supplier was, and that call I witnessed since he made the call after I asked him to check on new ones. Probably could have held out for something different, but the truck was getting worse every day and the feedback from everyone I talked to was positive on the OI remans. If I guessed wrong, hopefully the next time they crap out it'll be warm and sunny, and my garage will be back together. In the meantime, couldn't be happier with the result.