Volvo cruise control - help figuring it out please!
 

Hi Folks,

I've got a '740 wagon which I've been trying to fit cruise control to.

I fitted all the wiring, pump etc, no problem, but on test drive the cruise didn't operate. When I investigated, I found the electric pump was getting voltage, but I couldn't get the pump and bellows to move the throttle arm. It just doesn't seem to have enough strength. I wondered if this was partly because I was adapting parts (throttle wheel) from a petrol (gas) car.

I got desperate enough that I (last night) bought a scrappy 940 diesel with (non working) cruise control. The seller told me the cruise used to work if you lifted the brake pedal towards you a bit before applying the cruise. However, this setup seems to have exactly the same issue - the pump doesn't move the throttle arm.

What I'm doing is applying 12v to the terminals on the pump which activate the motor and the cutoff solenoid. This, wired direct to battery, doesn't give enough 'pull' to move the throttle.

Does anyone have any thoughts, or a car with working cruise that they could try the above (connecting 12v to) on to see if the throttle arm moves? I'm really running out of ideas now :o

Thanks,
Jim

What about that brake (vacuum break) switch? On mine that was what was causing all the problems. Switch plunger o-ring was gummed up and not quite making good enough seal.

Thanks for the thought :)

With mine, I've tried connecting the pump direct to the throttle diaphragm (so no brake switches to present problems) and with the pump given 12v to the top and bottom terminals, and the central terminal earthed, the pump still can't pull the throttle.

It just seems the throttle springs are too strong for the pump to overcome.

I've got the same problem on two cars having tried 3 cruise control pumps, 2 injection pumps/springs, and two different throttle reels...

Would you be willing to try connecting your pump as above (just with the connector removed and a couple of jumper leads to the pump from the battery) to see if your pump opens the throttle fully when connected up? :)

Thanks,
Jim

I should be able to try that this weekend.

Can you get yours to pull the throttle by pulling a vacuum with a Mityvac attached directly to the dashpot? To test the condition of the dashpot?

Thanks :)

I don't have a Mityvac (so can't measure the force required) but if I suck directly on the tube I can make the throttle open. If I cap the tube the throttle stays in the same place. So I suspect the pneumatics beyond the pump are good...

So today I tried the cruise on my 740, having replaced a couple of vac lines and the throttle spindle on the weekend. It now works fine - so I'm very happy :D

Thanks ngoma for the help, much appreciated. I'm still not sure whether it was just my not connecting the pump correctly that meant that it didn't work on test...

Very happy with it, it made the 120 miles this morning go even quicker than usual!
Jim :)