Cruise control vacuum pump

Post by **Caspar** » 14 May 2016, 14:11

Hi,
my cruise control does not work - never did since I own the car. Sometimes, when I try to switch it on, the car will apply a little bit of throttle, but only at low speed, for short.

I tested the system according to the 850 work shop manual I found here. Using jump wires, I can switch pump and relay. The gas pedal moves, but not very strongly, or at least pretty slow and weak. Once displaced, it will stay where it is for more than a minute - vacuum seems to be tight. Press the brakes, and the gas pedal jumps back to idle - brake switch ok.

So this seems to be fine. I wonder if the pump is simply too weak. If I feel the vacuum it creates, it's pretty weak also. Way less suction than on the manifold vacuum lines, for instance. Is the pump supposed to have more power?

And if so, I wonder if it is repairable. Anyone opened and tinkered with one of those before?

Thanks, Caspar

Post by **Caspar** » 14 May 2016, 14:19

Oh, it also makes a terrible sound when running

Sounds like an ancient fridge compressor. Maybe no surprise.

Post by **Ozark Lee** » 14 May 2016, 14:31

That sounds like a candidate for a pick-n-pull replacement. They typically run forever so I a junk yard version is pretty low risk.

There is, by design, an open port on the pump and many people freak out about it. Double check that someone didn't put a plug on that port thinking that they were plugging a vacuum leak. That port is where the pump exhausts air to draw the vacuum.

...Lee

Post by **Caspar** » 14 May 2016, 14:41

Hey Lee,

yeah, did check that - one port is open, and on the other one is slight vacuum.

Will try to get a junkyard pump.

Thanks,

Caspar

Post by **Caspar** » 14 May 2016, 14:42

"so I a junk yard version is pretty low risk."

That's what I wondered, good to hear.

1337 · Post by **1337** » 20 May 2016, 22:57

The pumps also go for about $30 on eBay (used), if you're not in the mood for a trip to the junkyard.

To test the rest of the cruise vacuum system for leaks, you can connect a Mityvac or other air pump to the vacuum line running from the cruise control pump (under battery) to the plunger above the gas pedal. If you apply vacuum to that line, you should be able to look in the foot well and see the pedal has moved near the floor.
If the pedal doesn't move (or if the Mityvac gauge shows no pressure), you may have other leaks.

Post by **Caspar** » 22 May 2016, 03:57

Bought a pump on ebay - 19 Euro. Replace the old one - now I have cruise control! Hurray!

So it seems sometimes those pumps do age and fail. My old pump still was pumping, but apparently too weak.

1337 · Post by **1337** » 22 May 2016, 11:25

Nice work!