The truck 1998 ram 1500 sport 4x4 5.9l auto.

So ever since I got the truck I've been fighting vacuum issues. I got them all fixed now. Verified at work by one of the techs when he fixed the last issue that was one of my check valves was bad. Now my vents aren't all over but my cruise has never work correctly. I can set it and it will hold speed and accelerate only under light loads. If I get on a decent hill or in a good wind it can't maintain speed and forget towing with the cruise. According to my aftermarket display the cruise can't get above 35% throttle, this is right at the point where it would downshift to third. If I manually put it in 3rd with the button it can do 39% throttle. I put in a new cruise vacuum servo and I'm just perplexed at this point. How it can work but not work all at the same time? Is it the tps sensor throwing me off? I can't find this issue anywhere else.

 

Poke the button so the O/D OFF light comes on.

 

is the cable from the servo to the throttle body stretched?

 

Thats what I have been doing but I believe in getting it back to original working order, makes long trips nicer. I will check the cable and see if it has an adjuster like the throttle does. I may throw a tps in it just cause it looks like the original and they go out so common.

 

That is original working order. Overdrive is intended for unladen flat ground cruising. If you want it to stay in overdrive on hills, you need to get more power out of the engine at cruising RPM than the factory configured the thing to provide.

 

I don't quite think you're quite understanding what I'm saying, my bad. I am driving hills where O/D can do them but the cruise can't. If I'm pulling a trailer, I'm in O/D off, and the cruise can't handle the mildest hills then either. I'll let you know what I find later this week. I have a big p-chem test Thursday so I won't have much free time for this til then.

 

Cruise control should be able to get very near wide open throttle. Sounds to me like it just has limited travel, for whatever reason.

 

I am not sure "limited travel" is the best description.....mysteriously poor CC operating condition that is not VAC related is not as uncommon, as what it is simply commonly undocumented.

The cruise components are half vac and half electronically controlled, but you seem to know that already.
There is no adjuster for the cruise cable.

The operating process reads/measures the intake vac pressure, and then pretty much winds the cable up with a on a spool....
This is why a properly working cruise system will usually ease the throttle up about 150 RPM or so +/- over what you have the pedal at, and then backs down to match the vac pressure that was present at the time of actual CC engagement.

Aside from a stretched cable, you might want to double check the connecting point on the Throttle body, as it is possible it is partially misrouted or slipped off of the guide cam, or the guide came being plastic is now MIA.

5.9 V8 Auto & Cruise Throttle Body, and cable Linkage

Don't let the green arrow mislead, that is roughly where the pedal connects to the assembly on the inside where it is not visible in the pic.

 

Yeah my durango would pull the pedal a little then back it off as you described. My ram doesn't do that though, that has me puzzled. Oh on top of the vacuum system being all checked out I put in a new mopar cruise servo a few months back.

 

I would suspect mostly a mild conflict of routing then.......Be sure to check out the black plastic cam on your TB control linkage plate ( as indicated in previous reply post) and update us.
and the pedal drop, and faint RPM surge and fall back is So normal for properly operating CC systems that the fact it don't do it, definitely indicates a cable issue, especially being you replaced part of or all of that specific module.