Don't see any mention in my factory service manual of this thing that sits on the LH fuel rail and has 2 vacuum hoses. Any pointers would be appreciated

 

Its a vac thermo switch that senses fuel temp in teh rail, and adjusts the ECU fueling to try and assist "hot start".

We no got that item, so I only reply based on what I have read.

We got an electrical switch to attempt the same thing, mostly failed, or got broken and were removed.

Its a "pad sensing" switch, so NO fuel will escape when its removed.

 

almost

it is indeed a vac/thermo switch , but there is no electrical or vac part to inform the ecu , all it does is control the fuel return pressure regulating valve on the manifold , it switched vac on and off thermally

and is there to prevent vapour lock as well

BB

 

And its broken. It should have a vacuum port coming out the side as well. When starting the car hot (fuel rail hot), the thermo switch shuts off vacuum to the left side regulator causing fuel pressure to be higher until fuel flows through the rail enough to cool the thermo switch which in turn allows vacuum to the left fuel pressure regulator.

These switches are NLA new, so finding a good used one is about all you can do.

 

No, both nipples are present and accounted for. One has a hose attached already!


Cheers
DD

 

Yup, it's not broken, I just removed the 2nd hose to see where it leads to - it goes to the metal coolant return line just behind the CTS.




The other hose leads to the front of the intake manifold.

So, either I'm having a hard time understanding how this can alter the FPR, or else the hose has been connected incorrectly



The mystery deepens!!!
My manual does not show any connections to the gizmo behind the CTS either

 

One hose goes from the fuel temp switch to the fuel pressure regulator. The other hose goes from the fuel temp switch to a manifold vacuum source......a nipple at the front of the manifold as I recall

Neither hose should be attached to a coolant line


As I recall, when the fuel hits xxx-temperature (for some reason 157ºF sticks in my mind, possibly incorrectly) the temp switch simply 'opens to atmosphere'...dumping the vacuum signal. No vacuum at the regulator = higher fuel pressure. Higher fuel pressure clears the fuel percolation and/or vapor lock.


Cheers
DD

 

The thermo vac switch with two nipples protruding upwards....sorta like rabbit ears?

That's for the canister purge system as I recall. Again, foggy memory, but I think it allows canister purge on when the engine is cold or cold-ish.

Cheers
DD

 

Thanks Doug, spent some time on the interwebs and came up with the name for the gizmo - it's a "vacuum advance coolant sensor". Could not dig up any details behind it, just this pic:



I assume PO's "jaguar specialist" garage inadvertently switched the vacuum lines. But I'm not clear on all the connections.



So #5 (manifold) goes to #3 (fuel switch) - no change

#4 from the fuel switch needs to be changed and connected to FPR #1 - ok

FPR connection #1 is currently connected to manifold via Tee at #2. I would assume that the "vacuum advance coolant sensor" needs to be connected here instead? It seems like they must have mixed up the 2 lines, simple mistake but I'd like to be sure since I cant find any references to it.

There is also another Tee (topmost circled area) in the cross-manifold hose that has been blocked off - was something supposed to be connected there? This is the closest vacuum diagram I could find, but it is not comprehensive






I'm in the process of replacing aged vacuum hoses, and it looks like most are 4 mm ID, the brake and balance pipe are 8 mm, and the distributor vacuum hose is 9 mm. Anybody know if there is a kit available?

Thanks