I just replaced the rubber bushing in the rear transmission mount on my 1990 XJS Convertible V12. After reassembly, I started getting a loud clicking noise from the transmission area only when the car was in gear. The problem was that there is small metal tube that runs from the engine to the rear of the car up in the transmission tunnel held in place by one plastic clip that had broken. The metal tube was under tension when under the clip and so it sprung forward when the clip broke and was able to rub against the front u-joint and "clicked" everytime one of the high points of the u-joint came by. I replaced the clip with something a little more sturdy. The question is what is that tube for? It is just above a black rubber hose that I believe is the gas line. I suspect it is the vapor recovery tube from the gas tank to the carbon canister but I can't easily trace it on either end and I can't find it in the shop manual. Anybody know? Thanks. Tom.

 

its your Vacuum hose that provides vacuum to your ECU.

 

That tube is carrying the vac signal from the cross-over pipe to the ECU in the boot. The "black rubber hose "you mention is the full-on 12v major feed from the battery + post to the firewall connectors that feed the starter and other systems.

 

Thanks to both M90power and Greg for the response. It's good to know now it's the ECU vacuum line. It's also good to know that the black hose is not a hose at all but the 12v feed to the engine compartment.

Is my ECU vacuum line the only one with a single plastic clip holding it in place or is that common?

Thanks. Tom.

 

Hello, probably my response comes a little late (only 8y after your post).
I am having right now exactly the same problem on a 89 Conv. and confirm that there is only one clip that holds this pipe in place. Its located pretty close to the u-joint and hold by a rivet. I found onle one zip tie that holds the pipe to the cable that can be also found in the tunnel.
No idea, why the Jaguar engineer thought that the pipe remains intact even after 30y by using only one plastic clip.

 

Oh dear. I'm guessing all the cars with aforementioned problem are US spec? It seems you're talking about pipe that connects the fuel tank vapour valve and the engine. When engine starts -the solenoid opens and pressure vape from the fuel tank goes to the engine's inlet directly, not through the carbon canister. I'm not sure if that's so simple - something like it. Only US spec cars are having this system due to emission regulations. European cars are venting to the atmosphere (through the rear pipe/solenoid in the boot).