[Drewkeen]

I have a late 2003 48re auto truck.

The cruise control when set causes the truck to sure terribly to the point I do not use it. It spees up 5 or more MPH then then slows down.

We checked vacuum and it is good. The line doesn't leak anywhere and the servo holds vacuum as well. We also put an orifice in the tube and a restrictor and neither of these made it better at all.

We also did some datalogging on the dyno and rail pressure stays steady. The increase in fuel is caused by the APPS commanding more fuel. It drives great using just your foot to control the accelerator.

I also tried to do the cruise relearn I read about on here and that made no difference.


Is cruise controlled in the ECU or the TCU?

I'm basically out of ideas here, any thoughts would be greatly appreciated!

 

[rghavana]

ECM which contains TCM controls speed control.
Any ECM or cluster codes (EMIC)?
Speedometer/brake switch/lights working properly??

Strange, sounds like ECM is seeing an accel command, from some where.
If no codes I would verify good connections including grounds to ECM, APPS, rear speed sensor, brake light switch and speed control switches themselves.

 

[Drewkeen]

I thought the ECM was on the side of the engine and the TCM was mounted on the passenger side of the truck on the firewall?

No ECM codes, I'll have to see how to check cluster codes.

Those are all working correctly. The cruise stays engaged as long as I want it to, it just does to accel/decel thing continually so its not like the system is cutting off from the brake switch.

I can go through and check grounds, but I don't think it would be so consistent if it was a ground. The acce/decel rhythm is fairly consistent not something that is worse at times that others. The only time it isn't as bad is pulling a grade with a load behind the truck.

 

[rghavana]

I thought all late 03/48re had only ecm, if pcm on firewall then yes that is trans control/speed servo.
I have late 11/03 date of manufacture and just ECM/TCM on engine.
Cluster code test is easy
key off press and hold trip button , turn key on, dont start
gauges start sweep, light test , release trip button codes will show in odometer 00,00 format
first 2 characters code, second 2 digits, number of time code tripped. 00,00 done

post or search for codes in FSM

 

[naterenfo1]

I have an 03 as well and have the same problem - cruise control surges badly. Do you have a tuner on the truck? after I removed my Bullydog and went with a stock tune cruise was much better, but not perfect. I can pretty much only use cruise when I have a trailer hooked up.

Following for a fix!

 

[jon-d]

Same here. I can se the throttle imput surge on my BD when on level ground. Works better when towing up a grade.

 

[cms829]

It may very well be the vacuum pump. Or a slight leak somewhere. Its on the pass side inner fender by the hood strut. My vacuum pump is shot. MY cruise will work for a little while and then stop and wont work again for a while.

 

[rghavana]

Could be but OP says he checked it, my bet is on APPS issue, bad design, very delicate/sensitive.
I got a Timbo APPS to avoid common unexpected breakdown, kept original as backup.

 

[cummins creep]

New here, but have experience with this problem. on my 04 it turned out to be the the transmission speed sensor. Being the true dummy Iam I changed the ABS sensor in differential as well, oh well only 25.00 bucks. When I started out My vacuun pump was burned out due to the fact I had a hole in my vacuum line due to Pack Rats...."I Hates Pack Rats!!! Any way working better than ever now.

 

[rs72z]

I had a bullydog on my 03 and with torque management( i think thats what it was called) turned off it would do the same thing.

 

[2012mciga]

I have an early 03 that does this as well. Doesn’t seem as noticeable when going 45 and under. Was hoping somebody had found a solution to this