06 with bucking cruise control during downhill coast

[BILLVO]

I work with a friend and also carpool with him in an 06 SB Auto 4X4 with 50k miles and having not seen it would have never believed it he gets 20+mpg all the time with it. Runs lucas oil and fuel additive.



Anyways he has had a problem with the cruise while going down hill the cruise causes the pickup to start bucking really bad, he hates to take it in if its an ecm update he doesn't want to loose his milage and I don't blame him. I have not checked for codes either but will do it next week. It is really annoying. Is there an update or has anyone had a problem with this in the past?

 

[jelag]

When the truck goes down a grade and the speed increases the transmission usually will lower the pressure in the torque converter and let it coast so that no matter what the cruise is doing it's sort of coasting... . if the truck has an exhaust brake on than the pressure will remain...

I own several trucks... we've not seen this, on the sticks. . But when an auto goes down hill, could it be hunting for the right gear with the transmission be hunting 2 gears instead of the cruise...

I'd suggest you try the same hill and do it either 10 mph fast or 10 mph slower and see if the transmission is the problem...

I'd also suggest a move either into tow/haul or out of tow/haul and see if this takes care of it... .

 

[BILLVO]

transmission is in same gear no up or down shifting at all, its the engine rpm that won't stabilize the speed on the downhill coast. Speed doesn't matter will do it at 55 or 85. The engine rpms are what causes the bucking. No exhaust brake either.

 

[raksasa]

On my truck, that I believe is the same as your friends, my cruise control (ecm) will force a downshift in order to maintain speed if the truck accelerates more than 10mph over the set speed. It's in the owners manual for details.

The problem may lie in the ecm somewhere. I checked the FSM and didn't find much troubleshooting info for non-servo cruise control, so the codes may have to shine the light on his problem.

I wish I got 20mpg instead of 14.

 

[foolkiller]

transmission is in same gear no up or down shifting at all, its the engine rpm that won't stabilize the speed on the downhill coast. Speed doesn't matter will do it at 55 or 85. The engine rpms are what causes the bucking. No exhaust brake either.

my 07 auto does the same thing... . i think i noticed it after i advanced the timing though. does your friend have any mod that would advance the timing?



i travel in october and will return to stock timing to check this.



either way, the cruise cont bucking i'm feeling is not enough to damage anything. it's very subtle and my 99 did it too. i've spoken with others with the same truck when refueling and some of them have mentioned it. i bet alot of folks are getting this and not noticing it or disregarding it.



j

 

[HBarlow]

I work with a friend and also carpool with him in an 06 SB Auto 4X4 with 50k miles and having not seen it would have never believed it he gets 20+mpg all the time with it. Runs lucas oil and fuel additive.



Anyways he has had a problem with the cruise while going down hill the cruise causes the pickup to start bucking really bad, he hates to take it in if its an ecm update he doesn't want to loose his milage and I don't blame him. I have not checked for codes either but will do it next week. It is really annoying. Is there an update or has anyone had a problem with this in the past?

It is normal. It occurs when the down grade is just sufficient to cause the cruise control to fuel very slightly then back off repetively as it tries to maintain speed control. My '01 and '06 did it and several years ago similar posts from other members questioned the same situation.

 

[JMusso]

my '07 5. 9 auto does the bucking also. I always thought it was the converter locking and unlocking?

 

[BILLVO]

I could see it if it was a slight surge but it literally can not stabilize the rpms even on the slightest of downhill coast starts at the crest and gets to bucking really bad like jumping a clutch and the driveline is loaded and unloaded several times before he kicks the cruise off at times.



It is definately cruise / engine ecm related not transmission related.



He said it came on all of a suuden one day and has done it since. He has a Bully Dog programmer also loaded on a lower setting but he can't find the programmer due to being packed away while in limbo from Wyo to ND.

 

[foolkiller]

I could see it if it was a slight surge but it literally can not stabilize the rpms even on the slightest of downhill coast starts at the crest and gets to bucking really bad like jumping a clutch and the driveline is loaded and unloaded several times before kicking the cruise off at times.



It is definately cruise / engine ecm related not transmission related.



He said it came on all of a suuden one day and has done it since. He has a Bully Dog programmer also loaded on a lower setting but he can't find the programmer due to being packed away while in limbo from Wyo to ND.

That's definately not what i'm experiencing... . i don't know enough about how the cruise control works to help you but i'd start, as i'm sure your friend intends to, by removing the bully dog program.

 

[jakprince]

Mine does it too and its a manual. I dont know why though.

 

[JamesStevens]

My 07 5. 9 auto does it too, and it is just the cruise kickin in and out. Have to be going down just the right hill to get it to kick in or out

 

[Red Rocket]

Mine too

My '06 does it too, my 98 didn't, and neither did my '01. It's really not that bad when it does happen, and most passengers won't notice it. I would like to find a cure, but I have posted on this about 6 months ago, and no one came up with anything on it.



Nick

 

[DBentley]

I noticed my 06 doing this for the 1st time this weekend its not to bad but it bucks and shakes a little.

 

[steved]

If everything is working right, they shouldn't buck/surge... but no one wants to listen to me, so I'm not wasting my breath.

 

[BILLVO]

If everything is working right, they shouldn't buck/surge... but no one wants to listen to me, so I'm not wasting my breath.

Yeah what he said ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^.

 

[GaryOwen]

New APPS cured mine. APPS kept getting worse until I finally broke down and bought an OEM. Have since bought the "timbo" replacement version as a backup. Not sure if recalibrating the APPS would help, but is worth a try. Might try cleaning APPS connection also.



Gary

 

[BHaner]

My 07 does it as well...



The downhill is not as bad as being locked up in 3rd gear on flat ground. It will get very violent.



Doubt it could be the APPS on the 05+ trucks... . When the cruise is on, I don't think they are doing anything like on the older "TV" cable auto trans trucks.

 

[BILLVO]

6 bad injectors

Well the surge was getting worse so he finally took it to the dealership and they said that all 6 injectors are bad, its under warranty so he is waiting for the dealer to get a set ordered up for it but they wouldn't let him take it, they held it until it gets them. so he wasn't impressed about that. Wierd thing is it ran super and gets excellent milage still. Has about 60k on it.

 

[foolkiller]

i'd like to bet a dollar this doesn't fix the cruise control issue. not that i don't wish your friend luck.



did it surge with the foot control?? i don't see how injectors could do this only when cruise control is set.



j

 

[steved]

Hmmmm, then I guess my bucking cruise, that was cured with new injectors, shouldn't be cured either.



It boils down to the fact that the fuel system can't compensate for the leaking injectors.