I hope someone can help with a stupid but very puzzling problem.
My 1989 XJS 5.3 V12 has been in storage and barely used for a decade or so. Putting it back on the road and it is running very rich.
When looking at the ECU in the rear of the car we found that the vacuum pipe comes out of the ECU a T joint and one end disappears towards the front of the car but the other pipe has come off somewhere and we can’t find out where it has come from!!
Been driving us mad for a couple of days - any ideas

 

Yours is an '89 so I could be wrong (mine's 87) but the 'T' is odd. Should be a single pipe (rubber-steel-rubber) to the manifold cross pipe. There's a metal pipe under the car that joins to the rubber one in the boot. The rust makes me think that it used to connect to the metal pipe maybe. I think you should trace the one that goes forward and see what it connects to.

 

Welcome to the Forums.

When the beast is sorted please do an Intro in the New Members Area.

Yours being a Marelli car, I reckon that hose goes to the Marelli ECU, and when the coffee kicks in downunder, Warren will sort it quick time.

OR

4th coffee kicked in

That bit of steel pipe in the end of that hose looks like the end of the steel pipe that runs under the car FROM the engine bay TO the boot, and enters the boot under the battery (memory).

I feel some investigation is about to take place.

Might pay to add "UK" to your location, coz I thought you were in Newcastle Downunder.

Good luck.

 

As Grant said, the reason your car is rich is because the ECU thinks the throttles are wide open because the vac signal is absent.
Look under the car, and you will see a number of pipes on the UK driver's side floor towards the rear:
A brake pipe going to the rear cage on the driver's side,
A fuel pipe that enters the boot at the front RH lower front corner just behind the RH wheel,
Another pipe that enters the boot in the same area at the fuel pipe. This is the vacuum pipe from a spigot on the cross pipe at the rear top of the engine.

Pull out the carpets etc etc in that corner and you will find that pipe. It should be connected to the ECU pipe in your photo, it looks as though it is not. If in fact the vac pipe is properly connected to the ECU, and your photo is an unknown loose end, then block it temporarily, and see if the richness goes. Then you can find out what it should be doing as the next step.

 

IIRC the Marelli ECU sits behibd the dash and gets it's signal via a small red tube directly off the intake manifold (A bank).

 

My 89 Marelli does not have a T for the FI ECU vacuum. The Marelli ECU as Daim said is up front in the passengers footwell on the door side, the Vacuum takeoff in the engine bay is separate from the FI ECU.

The fuel injection setup on a Marelli is exactly the same as pre-Marelli, with ONE exception the tach signal the FI ECU sees is different. In a Marelli car FI ECU, the signal conditioning inside the ECU is different because the signal is a squarewave from the Marelli so the ECU's are not interchangeable.

The only thing I can think of is someone has added that to fit a gauge to diagnose a problem. I would get rid if it as this will affect the vacuum for the ECU.

I would make sure the metal pipe to the engine bay is good and does not leak and get rid of the T.