Hey guys, I have a 1989 ranger with factory cruise control. Whenever I use it the RPM's surge from 1000 to 3000 no matter what speed. I have checked for a binding actuator cable, kinked vacuum lines, and I even tried adjusting the cable. Anyone have any ideas as to what it is...
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cruise control surge
- Thread starter Cole
- Start date
There is a check/release vacuum valve on the brake pedal in the cab, this is a mechanical valve to release vacuum pressure in the cruise control module in case the electric shut off for the cruise control fails.
Diagram here: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Cruisecontrol_1of2.JPG
It is called the Vacuum Dump Valve in above diagram, if this is disconnected or leaking then when cruise was engaged you would get a vacuum leak and RPM changes
Diagram here: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Cruisecontrol_1of2.JPG
It is called the Vacuum Dump Valve in above diagram, if this is disconnected or leaking then when cruise was engaged you would get a vacuum leak and RPM changes
In '89 a speedometer cable was still being used.
Is your speedometer needle steady or does it fluctuate?
You can pull off the cable at the transmission end and inspect the plastic gear
Pictures here of what it should look like: http://www.therangerstation.com/tech_library/speedometer.shtml
Not sure what year they added the VSS(vehicle speed sensor) to the mechanical cable, but both were used at the same time until '94.
The VSS signal was used by the computer and cruise control.
In '95 the cable was eliminated and only a VSS was used
Is your speedometer needle steady or does it fluctuate?
You can pull off the cable at the transmission end and inspect the plastic gear
Pictures here of what it should look like: http://www.therangerstation.com/tech_library/speedometer.shtml
Not sure what year they added the VSS(vehicle speed sensor) to the mechanical cable, but both were used at the same time until '94.
The VSS signal was used by the computer and cruise control.
In '95 the cable was eliminated and only a VSS was used
It does fluctuate below 25 mph. The cable has been replaced and the gear looks fine. I also checked vss resistance and it was 210. The manual said it is supposed to be between 180-250
Just to see if it is the computer(PCM) or cruise control that is causing the RPM issue, open throttle all the way and remove the cruise control cable.
Then drive and set cruise control, if RPMs change then the computer is doing it, perhaps via IAC.
If RPMs don't change then I would hit the wrecking yards for a new cruise modules
Then drive and set cruise control, if RPMs change then the computer is doing it, perhaps via IAC.
If RPMs don't change then I would hit the wrecking yards for a new cruise modules
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I will try that tomorrow. It is raining like cats and dogs here now and the truck doesn't go outside if there is a cloud in the sky. So if the rpms are normal then I need a servo or an amplifier?
Yes, but I wouldn't think the servo could "think" on it's own, unless it is a failed vacuum internally that unseals and reseals because of cable movement.
So Amplifier would be best guess, misreading VSS signal maybe???
Here is the page 2 of the Cruise diagram: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Cruisecontrol_1of2.JPG
Both pages do include some ohm readings
So Amplifier would be best guess, misreading VSS signal maybe???
Here is the page 2 of the Cruise diagram: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Cruisecontrol_1of2.JPG
Both pages do include some ohm readings
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