Cruise Control Issue - Info Requested

Aye Up,

I’ve read a number of threads on here re ‘technically’ testing various items in the system but before I follow the route of testing the cruise ECU with a volt meter, does anyone know the answers to these practical tests on other parts of the system?

First of all -
All perished vacuum hoses have been replaced;
On a road test switching on the system at approx 50mph and pressing the set button seemed to have no effect apart from the vehicle slowing down slower than I might have expected with my foot off the accelerator but I might have imagined that;
At home -
The vac pipe to the brake pedal switch was clamped so as to isolate any fault there;
The cruise pump was taken out and disconnected from the loom wiring but with the vac pipe still connected to the throttle bellows;
A remote 12v source applied to the motor contacts shows that the pump motor runs and is sucking to some degree;
I haven’t investigated the Tx box speed sensor yet;

Qs:

1. With the cruise pump removed from the loom and a remote 12 volt source applied across the motor contacts, how far should the accelerator bellows contract - fully or partially? (My assumption is that the cruise ECU varies voltage to the cruise pump in order to hold/increase/decrease pump suction - and that on full 12v it would/should suck the bellows completely in?)
2. If I manually open the throttle linkage to a midway position to simulate cruising speed and then apply power to the pump, should the bellows be able to contract and at least hold the throttle at the set position? (Mine won’t suggesting poor pump suction or leaking bellows?)
3. I notice that the housing of the cruise pump has an easily removable end cap giving access to the internals - does this imply scope for some kind of adjustment?
4. The pump mech looks fairly simple - is it serviceable - has anyone done it it?
5. Has anyone been involved with enough failed cruise control systems on any vehicles the age of mine (1997) to be able to say what the most common failure after perished vacuum hoses is?

Thanks

Is your Disco 1 a diesel or V8?

1. The bellows should contract fully, I’ve test my pump in the past from the ECU electrical connector by bridging a few terminals and the bellows disappears into its plastic cup and stay there while the pumps running.
There’s not much suction from the pump to start with, so I think the suction isn’t variable, but then I’ve never had the need to be interested in the ECU function.
2. The bellows should contract to the limit stated by the position of the throttle and then hold it.
3. The cap that u mention can be pulled off if not careful but there’s nothing to see other than the tip of the motor shaft and it’s bearing so press it back on so that clips properly to keep any water out, the rest of the pump is sealed therefor not intended to be serviced.
As for a common failure, like any ECU they have a service life so the original one lasted me 20 years, the eBay replacement just 18 months so now I’m on number 3 another eBay item, also as the pump seems to be identical to the items fitted by other vehicle manufacturers, it’s the D1/RR P38 item appears to be rare so I now have a disco pump on the garage shelf as a spare incase my original pump fails.
The rubber vacuum pipe failed years ago, so was replaced with the silicone version.

Aye Up agin,

Thanks for the replies.

Juke it the v8 efi.

Discool, thanks for the info. On the strength of that it looks like it’s the pump that’s got asthma then :-(
(I have replaced with silicone hoses too)

Is anyone aware of whether any other vac pump will work or is it the case that the ECU will only work with the originally fitted type?

I don’t know the Disco 1 cruise control system.
On my V8 Disco 2 the cruise control stopped working after I added LED bulbs to the brake lights.

Enzian said:

Aye Up agin,

Thanks for the replies.

Juke it the v8 efi.

Discool, thanks for the info. On the strength of that it looks like it’s the pump that’s got asthma then :-(
(I have replaced with silicone hoses too)

Is anyone aware of whether any other vac pump will work or is it the case that the ECU will only work with the originally fitted type?

Click to expand...

There’s not much of a suck from the pump, my original is different from the spare I have, but as it’s sucking into a closed system both are functioning to operate the system, go on eBay search ‘cruise control pump’ and you see the identical looking item to the D1s pump from a VW plus a few other German vehicles, after all they are made in Germany by Hella.

Well Juke, that’s because your ECU doesn’t like LEDs.

I’ve upgraded my interior lights with LEDs and added one to the shut face of the rear door (which when open hides the offside tail light cluster and which IMO should have been spotted by LR etc during trials!) neither of which appears to have interfered with the ECU - (because the ignition/engine is off?)
However I have seen on this site whilst researching whether to swap out my stop/tail/indicator filaments for LEDs that the ECU don’t like ‘em. In fact it doesn’t like a lot of things for example if I run my motor with the MAF plug disconnected the ECU makes the speedo behave like the rev counter! :-0 :-0.

Out of interest anyone know whether the D2 vac pump is compatible with the D1 or whether there is a cheap source of D1 type pumps that were used on other marks i.e. ovloVs?

Aye Up Discool,

Just read your latest reply after having responded to Juke.

Thanks for the update, I will have look on Ebabe tomorra.

Cheers