Surging Cruise Control

[DaveHess]

I have noticed this from the beginning but I have never posted about this problem.



My cruise control will surge ever so softly when running on a level highway. I watched the gauges when this is happening. The tach and speedometer look like the needles are painted where I set the cruise but as I watch the boost gauge it will go up and down about 3 PSI. I know it is not scientific but I can feel the surge in the seat of my pants. As soon as you hit a grade it stops surging until the truck is again on flat level road. When pulling the trailer it never surges and runs smoothly. I noted the problem, if it even is a problem, before I ever added mods to the truck. This truck has the vacuum pump on the passenger side engine compartment. It is not a big deal and is mostly an annoyance since I can feel the truck doing it. It is also rhythymic. My first instinct is the vacuum pump. Any other suggesstions???

 

[Turbo Kidd]

Join the club... . Mine started doing it about 3,000 miles ago and I can't figure it out yet.



Good Luck

 

[steved]

Two most common causes for a surging cruise are a failing FCA or worn injectors...


Further, I had this after installing cruise in my 04. 5... the injectors were replaced after one failed, curing the surge.

 

[mxaaron]

That is what my 01. 5 did right before the injection and lift pumps died.

 

[JJPage]

My 03 has done this since new while running empty(just the truck), towing the surge vanishes. The big single turbo's I once ran, made it worse, now with the BD twins, it act's like it did stock.



Exactly like DaveHess states, while cruising on flat land you can feel and see boost drop, then a small burst of fuel, boost goes up, fuel backs off, boost drops, you get the picture. I have found if I set the cruise while pulling a slight grade, the surging is minimized and sometimes remains non-existent until I have to brake, or coast, then hit resume, it's back.



Smarty will also enhance the surging, if on any tq management over 1. I have replaced my FCA about 3 times, without a positive affect on this particular problem. I have pretty much resigned to driving without the cruise unless I'm towing, then it's fine.

 

[EDankievitch]

I've noticed the same as the truck has worn in it's gotten much more noticable the serge that is will not do it when towing or if I'm running B100% Biodiesel is the worst on reg diesel. It's almost as if the computer DROOP setting is set too high. I've replaced the FCA only to see it was a waste of money... .

 

[DaveHess]

Hmmm. Well, at least I am not alone. I trully is just an annoyance and I don't consider my "butt feeling" in the seat to be a solid indicator of a problem but the boost gauge doesn't lie. I have a FASS on now but the problem was also there with the stock lift pump. The fuel pressure gauge at the FASS remains steady and the rail pressure gauge does its normal thing. That is the only gauge I regret spending the money on. It gives me more heartache worrying about what it is doing. I wish I had the ability to just leave things alone. Is this an OCD type thing??? Anyhow, I have not noticed any change even with the Smarty Jr on board. I leave it on default Tow all the time. BTW, the fuel mileage on this last trip that I am writing about was about average. The trip was 202 miles RT and I managed a 17. 8 MPG (hand calculated) at 75 MPH. The surge is not enough to affect my mileage.

 

[NavyDood]

I've felt it also since I bought my truck 5 yrs ago. It only does it to me in the 45-55 mph range and then it is hit or miss when it happens. I have 130,000 miles on the truck now. I guess my injectors, FCA or Injector pump have been on the fritz for 5 years now.

 

[NavyDood]

see above post

 

[Slow Six]

Mine has always done this also. It does this when truck is in a "coast" mode and levels out as soon as there is load on the engine. I just chalk it up to a cruise characteristic rather than an engine problem as I have changed injectors and engine runs fine otherwise.

 

[KKaminski]

I've felt it also since I bought my truck 6yrs ago. It only does it to me in the 45-55 mph range and then it is hit or miss when it happens. I have 130,000 miles on the truck now. I guess my injectors, FCA or Injector pump have been on the fritz for 6 years now.

I'll second this. My truck has 151,000+ on it and since I bought it with 85,000 on the clock I've had this same issue. The local Dodge dealer said there was nothing wrong. It's just annoying that if I stop the cruise and use the foot-feed, the problem disappears.



I'm thinking that maybe its a vacuum leak.

 

[steved]

3rd gens don't use vacuum for cruise... .

 

[Kry226]

3rd gens don't use vacuum for cruise... .

Steve, I'm not usually one to prove points, etc, but I must disagree, at least partially. Per the 04 FSM, there are a host of things to look for when diagnosing the cruise control system, to include a malfuntioning speedometer. I have posted the discription of each system (since there are significant differences between manual and automatic transmission equipped trucks) and associated troubleshooting. Obviously, there may be differences between model years too.



5. 9L Diesel Engine With Manual Trans.

Vacuum is not used for any part of the speed control

system if equipped with a diesel engine and a

manual transmission.



5. 9L Diesel With Manual Trans.

The speed control system is fully electronically controlled

by the Engine Control Module (ECM). A

cable and a vacuum controlled servo are not

used if the vehicle is equipped with a manual

transmission and a diesel engine. This is a servo-

less system. The controls consist of two steering

wheel mounted switches. The switches are labeled:

ON/OFF, RES/ACCEL, SET, COAST, and CANCEL.

The system is designed to operate at speeds above

30 mph (50 km/h).



5. 9L Diesel Engines With Automatic Trans.

If equipped with a diesel powered engine and an

automatic transmission, an electric vacuum pump

and vacuum lines are used to supply vacuum to the

speed control servo. A vacuum reservoir is not used.



DIAGNOSIS AND TESTING - ROAD TEST

Perform a vehicle road test to verify reports of

speed control system malfunction. The road test

should include attention to the speedometer. Speedometer

operation should be smooth and without flutter

at all speeds.

Flutter in the speedometer indicates a problem

which might cause surging in the speed control system.

The cause of any speedometer problems should

be corrected before proceeding. Refer to Instrument

Cluster for speedometer diagnosis.

If a road test verifies a system problem and the

speedometer operates properly, check for:



- A Diagnostic Trouble Code (DTC). If a DTC

exists, conduct tests per the Powertrain Diagnostic

Procedures service manual.

- A misadjusted brake (stop) lamp switch. This

could also cause an intermittent problem.

- Loose, damaged or corroded electrical connections

at the servo (if used). Corrosion should be

removed from electrical terminals and a light coating

of Mopar MultiPurpose Grease, or equivalent,

applied.

- Leaking vacuum reservoir (if used).

- Loose or leaking vacuum hoses or connections (if

used).

- Defective one-way vacuum check valve (if used).

- Secure attachment of both ends of the speed control

servo cable (if used).

- Smooth operation of throttle linkage (if used)

and throttle body air valve.

- Failed speed control servo (if used). Do the servo

vacuum test.

 

[steved]

Yeah, after you said that, I remembered that only applied to the manual trucks, which is what I have.



However, typically, from those threads on this forum, its been injectors.

 

[mwilson]

My 06 will do the same thing going down a slight grade with the cruise on. I am 99% sure that my truck is all drive by wire, no servo or vacuum on it.



One thing that will cause a surge is if your foot is touching / applying even the tiniest bit of pressure to the throttle pedal with the cruise engaged. Truck will go half nuts until you set your foot down on the floorboard.



Son does it every once in a while when he is driving.

 

[EricBu12]

My old 01 did the surge as well. . The way I was able to fix it was cut the vacuum tube and insert a smaller tube inside, then seal up together. . The surging was almost eliminated on the flat

 

[JJPage]

My old 01 did the surge as well. . The way I was able to fix it was cut the vacuum tube and insert a smaller tube inside, then seal up together. . The surging was almost eliminated on the flat

So you are saying, that by restricting the vacuum source you were able to eliminate the surging?



Seems like a simple enough exercise, I'll give it a try. But why cut the line, why not just remove it from one end or the other, insert a "snubber" and reconnect?

 

[NavyDood]

3rd gens don't use vacuum for cruise... .

03 and 04 automatics do.

5. 9L Diesel Engine With Manual Trans.
Vacuum is not used for any part of the speed control system if equipped with a diesel engine and a manual transmission.
5. 9L Diesel Engines With Automatic Trans.
If equipped with a diesel powered engine and an automatic transmission, an electric vacuum pump and vacuum lines are used to supply vacuum to the speed control servo. A vacuum reservoir is not used. ​

 

[KKaminski]

I kinda thought it was a vacuum problem. I'm going to try to replace all the vacuum lines associated with this an see what happens.

 

[JWChessell]

I have the exact same problem with my '03 5. 9L with auto trans. HOWEVER: Mine does NOT surge. The speed drops off slightly, then resumes. Neither the speedo nor the tach move at all, but as one gentleman said, "you can feel it in the seat of your pants;" when it's more pronounced the upper half of my body will lean forward slightly as the truck decelerates just a little.



I bought the truck new; current mileage is 132,500; this problem did not start until approx 100,000 miles. Also, the problem does not occur until I have been driving the truck at least about 40 mins to 1 hour on the highway at 65 MPH or above; no dealer has been able to diagnose it because they just take it out on the highway for a quick 5-min spin, then come back and tell me "everythings OK. " 40 mins down the road it starts again. Not so pronounced when towing a trailer, but stilll there.



Again, it's NOT a surge; it's a slight decleration that becomes more pronounced the the longer any single highway driving session lasts.



Any thoughts? Thx.