3rd Gen Cruise Control Pulses going downhill

[jbpetersen]

Hi All,



I've got a 2006 5. 9 Automatic, and the Cruise Control pulses when going downhill.



Anyone had this issue and know of a fix or where to start looking?



Thanks in advance.

 

[OBayer]

I have and 08 manual and w/o cruise control on I can get an odd pulsing going down hill with or without the EB running. Never could figure it out. Sometimes worse then others, sometimes not at all. Keep thinking it's some black box program kicking in.

 

[Motorhead]

Hi All,



I've got a 2006 5. 9 Automatic, and the Cruise Control pulses when going downhill.



Anyone had this issue and know of a fix or where to start looking?



Thanks in advance.

Are you running any programmers?

My '07, 5. 9 will do the same thing when I am running my Smarty jr.

 

[HBarlow]

It is normal. They all do it. Apparently cruise control programming is not sufficiently precise to control tiny throttle inputs without causing surges on downhill runs.

 

[NavyDood]

Only time I get the pulse is going around 45 with the cruise on, on my 04. Never have had a pulse going down hill. Sounds like yours is going in and out of TC lock up.

 

[AH64ID]

Is it every downhill or just on certain hills?

This is normal, to a point. When the conditions are just right it will happen becuase zero fuel isn't enough and minimum pulse width is too much. It happens to me on one specific hill on my way home from work, if I slow down or speed up 5 mph it stops.

If it happens on most downhills then it could be pointing to injector issues. I know of several people who have had it happen more often than most and injector replacement fixed it.

You may try an injector cleaner for a few tanks to see if it helps.

Large hp tunes and/or injector nozzles will make it worse. I haven't noticed my Smarty Jr effecting mine, it happens sometimes stock on the same hill. . just perfect conditions.

 

[MTaishoff]

Mine does it. Always has. I've just learned to live with it. If it gets too annoying; I just turn off the cruise.



Never does it under load.



Mark

 

[WOT]

I have the same issue. it's not on all hills, just ones that get the exact right grade for my speed where it seems like it isn't sure if it should give it throttle or not. kick off cc and it goes away. seems to amplify any driveline slack. I'm living with it for now and hope to get the 1 pc driveshaft down the road... maybe that will mask it to some
extent.

 

[AH64ID]

On a side note, I have found a few hills where my car does it too. . Just the nature of the beast with fuel injectors.

 

[JExum]

Mine does it also,like others said with the smarty on#9 and 50hp injector tips its more noticeable. If my rpms are above 1700-1800 its also less pulse. One thing I think do think helped it was when i installed a 165 Airdog lift pump. I was wondering if other members also felt this helped it or not.

 

[EDankievitch]

I had a very slight bucking like what you are describing here. I found that it was a cracked injector. The injector would over fuel the one cylinder just enough to cause the computer to pull back on fueling. What does your over head MPG read? if your showing a higher reading than your getting alot higher like 5 to 10 mpg higher, then that's your problem.

 

[steved]

I had the same issue and it was fixed by a set of injectors. I have not had a single surge or buck on cruise it over 100k miles since the replacement.



It is not normal, and it is most often a injection fueling issue.

 

[jbpetersen]

Hi All, Sorry for the tardy reply back from me - I've been out of the PC loop. My truck is mechanically stock. It started pulsing last year and continues to do so downhill I'm usually doing 65 mph. Anyway, I appreciate all your inputs and I'm going to start with another bottle of BG244 injector cleaner. I ran some through last year at 55k miles before this started happening. On the happy news front, I picked up another set of 17" OEM wheels on Craigslist today to mount up a separate set of snow/all terrain tires for the winter seasons. The Ram's got Amsoil fluids throughout and runs awesome except when he "bucks a bit". Thanks again, Jim

 

[Tinman]

I had this problem with my truck also. It was bad enough I didn't want to use cruise. It turned out to be a bad injector. When I up graded to 50hp DDP nozzles, I sent them to DDP for testing and #6 tested "low flow". The body was replaced and all is smooth now. Search post by my user name and you can get some more info.

 

[Scottyg1]

Are you running any programmers?

My '07, 5. 9 will do the same thing when I am running my Smarty jr.

:{Ditto#@$%!

 

[steved]

:{Ditto#@$%!

I've ran every setting on my Smarty JR, and surge has never returned... I run my cruise for tens of hours at a stretch.



I installed the cruise buttons in my ST truck around 100k, so I don't know what it did from new. But having my injectors replaced (the only variable at that time) with F1s at 145k, cured my surge/buck... been running the JR since about 180k, and currently sit at 258k. I've ran empty, ran loaded approaching 20k GVW, and all the settings on the JR... have not had even a hint of the surge/buck returning.



If/when it returns, I will be looking hard at injector replacement, or one of the other components in the high pressure fuel delivery system. The surge/buck is not normal... just because your truck might have done it from new, doesn't mean its supposed to! Other parts need replaced on new vehicles under warranty, nothing says part of the injection system can't be bad on a new vehicle.

 

['strokeThis_'07]

The bucking is normal. When I bought my 07, before I actually signed the papers, they let me take it over the weekend for a 300 mile trip. First time it did it, I thought I screwed something up on a truck that wasn't yet mine.



It's done it since it had 24 miles on it, and still does it with 96,607 miles on it. It's more pronounced with TNT/R programming, but it's normal.



The 03 has never done it in ~127k miles. Maybe it's a programming thing, or maybe it's the difference between manual and automatic. I don't know.

 

[HBarlow]

All three of my Cummins powered Dodges have done it from low mileage to high. The mild surge results from a minor programming limitation in the way the engine fuels gently when descending grades with cruise control ON.