Downhill Engine studder with cruise set

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Matthew Pederson

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Great site! Been reading and following site for a while and need some help. I have an 01 sprt trac with 100,000 miles and Xcal performance tune on it. I havent made any changes or mods to anything for a long time so I would have no reason to suspect the tune, but have developed an issue that was never there before. When I have cruise control set at 65 or so and hit a good downhill descend the truck feels like its studdering or having issues with fuel. It only does it on a good downhill with cruise set. Its like it cant figure out what to do with its self...I can see the speedometer moving around with the studder. No change if I take overdrive off either. It runs perfect with the cruise off on a down hill. It works fine on flat surface and uphill with cruise on. No check engine lights on and there are NO codes pending. No problems with tranny or engine acting funny besides this. Flushed tranny 10,000 miles ago and have synthetic in. Has a new fuel filter also.

I've read some one thread about the torque converter possibly being the issue. Any thoughts to the problem??? Thanks



 
That's not a stutter you feel. I believe it to be the cruise control trying to maintain the speed. For me, it only happens at certain speeds in association with specific downhill grades. The slope is just shallow enough to not quite maintain the set speed you have set into the cruise control so it applies a little gas. Only, now that it has increased the speed, it is now too fast and lets off the gas to slow down a bit.The only trouble is that it just seems to oscillate between these two conditions and becomes annoying. You begin to wish it would either flatten out to stay on the gas or steepen up so that gravity would maintain your speed and the cruise control would stay out of it.

 
One additionsl point to what Uncle_Bob said: That is when the cruise control is maintaining the speed you have set going downhill it will apply the brakes, and when the desired speed is reached the cruise control will let off the brakes. Therefore the oscillation you are feeling. Hope that helps.
 
My 01 started doing the same thing after the dealer installed the "repair" for the cruise recall.Never had an issue prior to that!
 
Hey Tom B, did you have the cruise control brake sensor replaced also?. I did notice that the stutter started after the dealer put in the new cruise control brake sensor! Is this the probable issue? Thanks for all the responses
 
Dingo is correct. The Speed Control Servo maintains vehicle speed by controlling throttle linkage position through the actuator cable. It is deactivated by steering wheel speed control switch, the brake pedal position switch, or the brake pressure switch (in the brake line) should the pedal position switch fail.
 
Yup, only the high dollar mercedes and few others have the braking tied to the cruise control.
 
Mercedes has a system called "Distronic Plus." It's K-band radar from the front of the vehicle that senses other vehicles in front of it. It then slows the cruise control to match the vehicle in front.
 
Now that I think about it I guess you could call it braking by wire. IDK maybe it's just me but when I think of samoehting as "by wire" it means that the mechanical aspect has been taken out...ie throttle cable or when talking about brakes a direct link between the drivers foot and the master cylinder. There are some systems out there that do use the brakes with the cruise control but this is usually on higher end vehicles. For example my Lexus has adaptive cruise control, you set it and it won't run over the car in front of you if they are going slower, in that case the system applies the brakes to slow the vehicle enough to accomplish this.
 

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