Another guy (me) having cruise troubles

[sparks57]

My cruise works ok at 55, but once I get above that, the thing surges a lot when going up and down hills and sometimes on straightaways. Headwinds also make it surge. It's not real bad, but it makes for a very uncomfortable ride.



The other very annoying thing that happens is the stupid thing will be just going along and poof... the cruise turns off.



What's up with this thing?

 

[Philip]

The surging might be a head unit going bad.



The computer reads the TPS (Throttle positions sensor). If it is going bad this could cause it to drop the cruise. You need to check this with a voltmeter. Low side voltage should be in the . 75 to 1. 0 volts. When you move the throttle shaft it should move up the voltage with a smooth steady raise. If it is jerky and shows dead spots replace the TPS.



The computer reads the crank RPM sensor. This is located on the timing cover and reads RPM from the harmonic balancer. This could be going bad. I'll have to dig out my manual and check the way to test this item.



The computer reads the speed sensor signal. Does your speedometer move around when the cruise drops out. If it does you need to check the plug down by the trans for the speed sensor. It has been noted here that it likes to corrode up.

 

[sparks57]

Nothing happens to the speedo when the cruise shuts off. I just had the TPS sensor replaced last winter, so I don't think that's it. That rules out everything but that sensor on the timing cover according to your info... my timing cover is leaking, so I wouldn't be surprized if maybe the sensor got messed up.



Thanks.

 

[Philip]

The sensor is a sealed unit. Oil would not affect it. But a build up of dirt on the balancer would. You might try cleaning the balancer and readjusting the sensor and see if this stops the problem.



Do not rule out the TPS going bad. It could happen. Check th plug on the TPS for corrision to.



Also check the plug on the RPM sensor. It is by the front valve cover. People have found the pins loose in it. The way Cummins installed the wiring on the engine left the wires pulled tight. I rerouted mine to remove the strain.

 

[sparks57]

Ok, I'll keep that in mind. Thanks for the tips.

 

[MFalkinham]

I'm not sure what your circumstances are, but my cruise used to kick off all the time at highway speeds when hitting bumps in the road. The brake pedal arm has some slop in it, causing it to bounce on bumps and hit the brake light switch. I installed a small spring between the pedal arm and dashboard to hold the pedal fully up during bumps, and the problem hasn't been back since.



- Mike

 

[sparks57]

That's a really good point. I will drive over some bumps and see if it is kicking off when I hit bumps.



Thanks.

 

[Case500D]

In my W-250 a bad vacuum booster caused my cruise control not to work. Also had to replace the switches in the steering wheel. They were around $34. I would check to make sure you have good vacuum. My W-350 runs 8-10 lbs at idle and 20-24 going down the road.



Jeremy