xafalcon

Does anybody know why my cruise control surges sometimes and not other times? Say I turn the cruise on at 100kph, the speed may drop to 98 then accelerate up to 102 and continue to cycle like that (on a totally flat road). Other times it works fine and hold the speed completely constant. Car is a EB 5.0 Fairmont Ghia.

Thanks in advance for any ideas.
Tris

Brentus

My old EL Ghia did the same sort of thing but yeah i got rid of it on an AU2 so i never got it fixed. However is your cruise control slow to take up eg. when you press the button whats the reaction time? Because i also had a problem with that.

Aussiblue

Check for vaccum leaks. It sounds like there may be a small leak in the line between the pump and servo and the pump keeps having to adjust for the leak down.

__________________
Regards Blue

XWish Ute

A mate fixed the same problem in his Mazda 929 (which may be worth consideration. the Maxdas had the same unit as an XF, which may be similar to your EB.

The underbonnet unit contains about 3 vacuum valves operated by solenoids. The solenoids are controlled by the cruise computer. If the car needs to go faster, the computer will send a signal to open one or more valves to apply vacuum to the servo, which pulls a cable attached to the throttle linkage. The more vacuum, the more pull, and the more acceleration.

With age, the rubber seals on the vacuum valves can perish and become sticky. So when the car needs to speed up, and a valve sticks, the computer senses that speed has not increased, and sends a signal to open the next valve. If the first valve then frees itself, heaps of vacuum is suddenly applied to the servo, and surging occurs.

The computer then shuts down all the valves as the car is going too fast, and the process starts again

The fix was to dismantle the unit, apply rubber grease to the seals on the vacuum valves. Only a real light smear was required.

hope this helps!

xafalcon

Thanks for the replies so far Guys. The "reaction time" is good, say about half a second. Where is the servo located? Sounds like I might need to disassemble it and grease up the valves.

Thanks again
Tris

Aussiblue

Under the wiper's washer reservoir bottle.

__________________
Regards Blue