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Discussion Starter #1
Hello all, I was curious if my cruise control is just annoying or if there is something to be done to make it less so. Simply put, when I engage the cruise control, the vehicle surges slightly to keep up the speed, ie: set at 105 km/h then the truck fluctuates between 100 and 105. Speeding up, slowing down...so annoying.

Is this normal or is something up. I did check the bellows and the vacuum line to the mechanism, all seems well.

Any ideas?
 

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Most likely you have a very slight leak on one of the vacuum hoses so it tries to hold the bellows at a set position but slowly drops back so has to open the throttle to maintain speed giving you the fluctuation. They are very susceptible to an out of adjustment cable too so it might be worth adjusting that as per RAVE.
 

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Discussion Starter #3
I will attach my vacuum pump and gauge on there tomorrow and see if the bellows are indeed tight. I haven't ever messed with the cable, so that's probably worth looking at too. Thanks.
 

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Bellows rarely give problems, usual source of leaks is the hose that goes to the brake pedal, it perishes and splits where it goes through the bulkhead. So you need to vacuum test the whole thing, hoses included.
 

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There's also some small pipe inside the actuator that attach to the mini vac-pump and the vacuum release valve, which is actually like a small relay with tubing attached. These pipes get hard & brittle and can leak, but easy to replace. Best is to remove the whole actuator assemble & dismantle on bench.
 

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Discussion Starter #6
Thanks guys. I think I will remove the whole thing, plug the ends up and vacuum it down to see what I find.

Chad
 

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1995-2002 Range Rover P38A
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Is this the GEMS or THOR?

GEMS is old CC ECU which stuff up almost always, you can do the conversion to the thor one, I have done this, and now it works perfect. Can't recall the part number; Err or erm 5100 or 5700.

I also did this conversion with my Disco 1, and it works now, but far from how it should...


What's said before, check your vacuum lines, also the actuator at the brake pedal.

Depends how handy you are, you can do it by powering your vacuum pump with a battery charger, it soon shows if the vacuum lines are good or not.

I must say, this system works ok, but mine also goes up and down in speed a bit, in about the same way you mention, but that's including going up and down hill.
What engine do you have? That can make a difference too I guess.
 

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Discussion Starter #9
Thor 4.6

I did get a chance to adjust the cables. I’d say they were close to 3mm clearance...not good. I brought them back closer to the tighter end of spec and I think the surging actually got a wee bit better.

I will at some point connect my little vac pump and gauge to the system and see what happens. I’m not on the highway this week so it’s less of a concern, lol

Thanks for the ideas gentlemen.
 
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