Cruise control acting up

[91K5]

Hey guys,
On my '91 the cruise control has always acted funny, now that I just got back from a 1,400 mile roadtrip, I want it to work right from now on. What happens is I'll set the cruise. It will hold the speed for a while, and then a while later, it will just start slowing down. It doesnt turn off, just slowly decellerates. While it does this, If I hit the resume button, it wont do anything, just kinds of stops responding. If I tap the gas, it will go back up to wherever it was set, but If I have to tap the gas pedal like every 2 minutes, I might as well just not use cruise in the first place. There seems to be no certain condition that causes it to happen (like going up or down hills, etc.) I havent checked around under the hood yet, was going to see what you guys think might be the problem, or where to start. Thanks!

 

[sapper]

you might have a pinhole in the servo letting some air out slowly??

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[Can Can]

Does a 91 have electric cruise or vacuum cruise?



<font color=blue> WE WILL NEVER SURRENDER<font color=blue>

 

[91K5]

I was kind of suspecting a air leak somewhere in the crusie... what exaclty is the servo?

 

[sapper]

look on the driver side of the engine. it will have linkage going from the tbi to the firewall conected to a round black rubber thingmabober(servo).this is how it is on my 89 dont know if yours is elec or not. hope this can help

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[91K5]

I just ran outside to look at it, it is a vacuum operated unit. Got the servo behind the throttle body, and hoses running over to a big black bulb looking thing. I'll have to check the hoses and stuff tommorow. Thanks for the help.

 

[txbartman]

I had a similar problem in mine. It was a cracked vaccuum line. Be sure to check them out if yours is vaccuum controlled. If they look the slightest bit weathered, replace them. Vaccuum lines are cheap.

Brian
Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!

 

[Overdrive]

Just got a price quote for mine

My 89 Cruise Control is broke The linkage from the carb to the servo has worn loose on the servo ( so the linkage just falls out of the servo). Just priced a new servo from Chevy $290! I saw on NAPA's website that they have replacements for under a $100... Hope the NAPA unit works because I don't want to spend 300 bucks!

Overdrive

 

[Thunder]

Also check the cruise cut out valve that is activated by the brake pedal. if it is leaking or out of adjustment you will loose vacume there. it is located under the dash by the brake pedal. If you cant find any vacume leaks. The problem could be in the cruse controll module. It is located under the dash between the gas pedal and the brake pedal. If you look under there you will see a rectangle black box. The black box is a cover it slides down and reveals a PC board that plugs into the wireing harness. My 89 is doing the same thing as yours Chevy quoted me $250 for a new module so I have been living wihout cruse for a while. Till I can find one at a junk yard.
Another thing that can cause it to loose speed is:
Short in the cruise controll circut. This will most likely occur in the multi function lever(Blinker lever) beings your resume doesn't work the problem is probabally in the electrical parts.
One more thing. Does your speedometer needle bounce around when going down the road? If it does the cable needs to be taken out and lubed or replaced. if the needle is bouncing around while going down the highway it really screws up the vehicle speed sensor on the back of the speedo. These bad siginals overwhelm the Criuse module and it shuts down.

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[bigk]

The cruise on my 88 Surburban just up and quit. Is mine electric or vacuum? Are the previously mentioned solutions things I should check, too?

Karl
Temporarily Unemployed Underwear Model
87 3/4 ton

 

[Can Can]

Just so you know, I had a very similar problem with my 83 6.2 half-ton. Cruise would engage, and then after a while it would just fade off. My problem ended up being caused by a weak vacuum pump(diesels dont create vacuum on their own so a vacuum pump is installed in the same place as the distributor on a gasser). I replaced the vacuum pump = lots of vacuum, and the cruise has worked great ever since.

A good way to know if you have a vacuum leak is to see how well the rest of your vacuum-operated accessories are working. Chances are if one isn't working properly, the reat might have issues as well.......



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[dyeager535]

FWIW, I believe all of our trucks (73-91) have a vacuum cannister, the electric part comes from where the cruise gets its speed reading. Later ones are VSS, (electric) earlier ones were the transducer(?) on the fenderwell. The cars used identical systems, just went to "electric" a few years earlier.

Dorian
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