I’m helping my son prepare a '90 XJS convertible to sell (long story). We are on the home stretch, but cruise control is inoperative and, I believe is missing a part. Or, maybe we are missing a part of something else, but this seems like a good place to start. Can anyone identify the part in the picture? It has two three pronged plugs, but I can’t find anything to plug them into, other than each other, which makes no sense. Appears to be a vacuum switch of some sort. Is this supposed to control vacuum to the cruise bellows?
There should be a bellows just to the right of your pic. Sits to rear of a/c compressor and cable runs to accelerator pedal. Does not appear to be there. Three prong plug socket arrangment is what it uses.
Bellows is present. Looks like the blue thing is an electro-mechanical vacuum switch with one vacuum line going to the front of the right side intake manifold and the other to the cruise bellows. My question is, what is the vacuum switch wired to? Seems like it should be some sort of module that senses speed of the car and regulates the amount of vacuum to the bellows accordingly. Maybe somebody could look at their car and take a picture of whatever those wires are plugged into?
The blue switch is the result of a recall. It’s purpose is to rapidly bleed off vacuum to the c/c bellows. The bellows in your photo appears to be mounted upside down- as we are seeing the underside of the heat-shield. Undo three bolts, and turn the heat shield over, and you should discover the wiring actually connected to the bellows. I believe the blue switch should be connected in series with the bellows. (My car does not have a blue switch, as the PO ignored the recall, I guess.)
Hope that helps.
Thanks Dave, that was it! Turned over the bellows, exposing both the vacuum and electrical connections. I plugged the blue switch into the connection from the harness and the one on the bellows, as the vacuum from the manifold was routed through it. Will see tomorrow if it works, and, if not, will route vacuum from manifold directly to bellows and connect bellows plug directly to harness.
Craig,
Since your cruise control actuator was incorrectly installed upside down, it is quite possible that the rubber bellows is old and cracked and won’t hold the vacuum. The part number for the rubber bellows is AEU4090 and they are readily available on eBay and also from the Jaguar parts suppliers for about $20 US.
We own an XJ-S, an XJ6, and an XJ12 all with essentially the same fully functional cruise control system. I use cruise control all the time and have found it to be very reliable, but there are several parts that can fail including that blue vacuum switch, the rubber bellows, the brake pedal “kill” switch, the two solenoids in the actuator, the vacuum hoses and the set switch. There are lots of posts in the archives from people who had cruise control problems and fixed then and I also believe that Kirby’s “Experience in a Book”, downloadable for free from Jag-Lovers, has a section on how to test the actuator solenoids.
Even if they are in good shape they leak where the round metal plate joints the rubber, the fix is to apply some silicone sealant.
This is recommended even with new bellows.
Simple bellows check is to apply 12 volts (+ & -) via the two outer contacts on bellows plug and apply vacuum directly.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
9
To explain that a little further. Originally, there was a connector where the wiring harness connected to the bellows assembly. There are two valves inside there, one that closes a vent to atmosphere and one that opens a port to engine vacuum. Obviously, both valves have to work for the cruise to engage.
Evidently someone sued, and the result was this blue solenoid valve. It was designed to be easy to connect; just unplug the wire from the bellows and plug it into one of those connectors, and plug the other connector back into the bellows. That’s why the two plugs plug into one another.
If you have trouble getting the cruise to work, you can just undo that recall and omit the blue valve and connect up the bellows directly, as it originally was connected. It’s not likely the blue valve is the problem, though. Far more likely the problem is the valves inside the bellows assembly. If you pop the bellows off you can see them. On the very end of each plunger is a small rubber disk that serves as the seal that closes off a port when that valve is closed. On my '83, both of those little rubber disks had fallen off and were wandering around in the bellows. I made new rubber disks by punching holes in an old bicycle inner tube, glued them to the ends of the plungers, and even sanded them a bit to ensure they were smooth enough to seal.
There are also electrical issues, of course. The Book includes a simple test circuit for determining if the control circuit is actually working as intended.
Thanks guys, incredibly helpful and a very impressive level of knowledge and familiarity with the 5.3. Although a couple of 4.0 XJS’s have passed through my hands, this is the first V12 and I feel a little out of my depth. The cruise control doesn’t actually work yet, but at least it’s hooked up correctly and I have a clear path to start diagnosing what’s going on with it. Fact is, I need to remove it again to access a leaking right side cam cover. My fault… I had it off previously and, although I installed a new gasket, I didn’t tighten the bolts adequately. I assume they are 8.8 grade and would thus be torqued to 9 Nm. Sound right? Also, gasket appeared to be treated with something so I did not use any sort of joint compound. Is there a recommendation for this? I’ve tried to find “Experience in a Book” but the links I followed took me to a site that directed me back to this one. Again, I appreciate the guidance and prompt responses.
Craig
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
11
There are LOTS of recommendations for that! None of which you have apparently read yet. So, two basic options:
Omit the gasket entirely. Install cam cover with sealant or “gasket maker” such as Loctite 518 or Permatex Ultra Black all the way around and around the rubber half moon seal. Toss the OEM “triangulated thread” screws, purchase new socket-head alloy screws one size longer than the originals. Put a split ring lock washer and a small OD flat washer under each head. Make sure that the flat washer is small enough to sit flat in the recesses in the cam cover. Remember that Ultra Black must be finger tightened and then allowed to set for an hour before fully tightening the screws. This arrangement will remain leak-free until the rubber half moon seal dries up and falls out in crumbles. The genuine Jaguar part will reportedly last longer than the aftermarket parts.
Toss the rubber half moon seals, and install aluminum half moon seals instead. There are people on this forum that machine up a bunch every now and again. Apply Loctite 518 or Ultra Black around the underside of the aluminum half moon seal while leaving the top side clean and dry. Install cam covers using gortex sandwich gaskets, a thin layer of aluminum with gortex on both sides. Again replace the OEM screws with socket head alloy screws one size longer with split ring lock washers and flat washers. This arrangement will remain leak-free until the sun burns out.
Or, you could install the cam covers as Jaguar intended with rubber half moons, paper gaskets, and triangulated thread screws with no lock washers. You’ll be lucky if it remains leak-free until you get the first quart of oil poured into the sump. Jaguar did some fine engineering, but there’s no contesting the fact they didn’t know squat about sealing an engine.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
12
Oh, and while you’re in there: There are two sizes of head studs, big 7/16" suckers around each cylinder plus rows of smaller 3/8" studs along the inboard and outboard edges of each head. One by one, remove each 3/8" nut along the outboard edge, replace the thin flat washer with a 1/8" thick flat washer, and put the nut back on and torque it to spec.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
13
