Surging with cruise control

I have a '91 Explorer. When the cruise control is operational, the vehicle surges while attempting to maintain the selected speed. What could this be? The vehicle runs perfect, other than that.

1991 EB

Check the vacuum hose for an obstuction or leak.
I recently installed a new cruise control hose with one having a larger internal diameter which improved overall control performance.

Well, I inspected all hoses involving the cruise control. No damage or blockage found. I applied vacuum and the cruise diaphragm seemed to hold. What gives? HELP!!!

I received an e-mail from someone recently regarding the odometer and the cruise control. The e-mail suggested that the speedometer sets the stage for maintaining a speed using the cruise.

I found this hard to believe but today I may have confirmed this. At 55 mph my speedometer is steady, as is the speed using the cruise control. AT 68 mph, the speedometer fluctuates 1 to 2 mph. When I set the cruise control at this speed, the vehicle too surged and fluctuated.

Any other input on how the speedometer communicates with the cruise control? I thought that the speed sensor regulated the cruise. Am I wrong?

Doug

Hey Doug,

What is the condition of your vac. mod. on the tranny? The cruise control started doing a bunch of strange things right before mine went out on my 91EB. Check your trans fluid level and see if the vac. line from the trans is wet with fluid. Fluid loss in the trans and oil level gain is a sign of this also.

Engine surge in cruise control

The speed sensor in the transmission has a plastic gear on the end. Mine had one tooth broken off and several others worn. Replacing the gear cured the surging and erratic speedometer readings.