Slight surge/buck in Cruise Control

[betterthanstock]

I disagree... if it is working correctly, there will be no bucking or surging.



My drivetrain had 143k on it when the injector failed, so it is far from tight. Once repaired, the cruise never bucked/surged until recently, when I started having fueling issues again at 168k. When it worked correctly, even having a 5k RV in tow made no difference... it was as smooth downhill as it was uphill.

We need to define bucking/surging.

What I meant is that at a certain speed, on a certain slope, the engine will need just about zero HP to maintain cruise speed. When the speed starts to go up, fuel injection is completely shut off. Then it slows down, and it adds back a minimal amount of fuel (like at idle). If you're sensitive enough, you can feel that. I did not refer to severe bucking, like with a bad clutch, and a novice driver, nearly stalling the engine... A bad FCA might be more to blame than an individual injector, since it is the FCA's job to shut off the fuel.

With a healthy engine, one click up or down on the CC will usually cure the normal bucking that usually occurs on the same downhill at the same speed.

 

[jackrather]

I also have the problem with the cruise control and if you notice if you put just a tiny bit of pedal the problem goes away. I thought it might be the TPS but have not figured this one out yet. I also have the full banks kit installed on the truck. I am curious to see if anyone has figured out the problem yet as well My truck is a 2007 3500 Mega cab 4x4 with 16,000 miles and have only had the condition on the last two trips.

 

[steved]

Mine did exactly what you describe... just adding a bit of throttle made it go away.

Injectors, not an FCA, cured mine... and I did replace the FCA in an attempt to cure it.

I believe the computer is mapped to a set of parameters for new injectors that are not the same parameters a set of leaking injectors provide... thereby causing the truck to "search" for the correct speed/rail pressure/rpm/etc.

I still think its the computer seeing the rail pressure, the FCA builds rail pressure to compensate for it being low, the added pressure causes fuel to "leak" faster and the truck lunges... the computer sees this lunge and shuts the fuel off, and the process starts all over again. Before injectors, my rail pressure varied quite a bit, after injectors it varied very little...

 

[jackrather]

Hey Steve, so even if my truck has only 16k on it I could have injector problems? I have a good source for DDP injectors so I might pull them and send them up to Lenny to check them out.

 

[steved]

Anything is possible... there's a guy on another board with bad injectors and only 5k... pressure boxes don't help.

If I were you, I'd start cheap... replace the FCA for $100, then have the injectors checked.

You might be able to talk the dodge dealer into fixing it under warranty, or are you your own warranty station now?

 

[EDankievitch]

I'm having the same problem with my stock 05, 6 speed. Funny though I also had a slight stumble at idle. I just got a 50/50 mix of BioDiesel and after a week of running the mix fuel and letting it sit a few days both problems have seemed to go away. There is a test where you mix some two cycle outboard oil with your fuel and run it through to se if the FCA valve is bad. I wonder if the Biodiesel mix is doing the same??? Guess I'll be replacing the FCA next chance I get.

 

[BILLVO]

Just went through this with a friends rig and here is a link to what was posted on the same thing, Turned out to be injectors also.

 

[amsoilman]

I have the 03' HO with 6-speed NV-5600 that has done this same thing on and off since it was new. Sometimes it is a bit more noticeable, but I don't worry about it, as the truck has run flawlessly, gets great fuel economy, and I now have nearly 80 K.