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Hello. I'm new to this forum.
I need some help finding a part for my 1989 XJS Jag.
I have no idea of the part name or what is for, but i will leave some pic of the part needed.
Thank you so much. I hope this works.!
That is a sensor that is meant to help the engine fire when the fuel rail is hot. When hot, the vacuum tubes connected to it affect the fuel pressure regulator and help to guard against fuel evaporation.
As said above this is a thermal vacuum switch. When the fuel rail is hot it dumps the nearside fuel pressure regulator vacuum signal to increase fuel pressure and overcome vapor lock. Many have broken the switch, and many have done away with it, given how pricey a new one is. There have been varying reports of its efficacy on the forum; but what it seems to come down to is if you are in a super warm climate it probably helps on hot starts, but otherwise is unnecessary. This switch is not exposed to fuel, so you can remove it from the rail without issue.
It looks like someone has put teflon on the threads of the switch. This is not necessary and may in fact insulate the switch from the rail and prevent it from functioning properly anyway.
I'm sure you've got better things to do than go and waste your money on a New one of those (just seen a secondhand one on ebay for £75!)
As has already been said, its a Fuel Enrichment Valve that has a Wax Thermostat Sensor, that speaking from experience is a lot more trouble than it is worth as if you were to unscrew it, no Fuel will come out as the hole it is screwed into is Blanked off
All it does is to Control the Vacuum to regulate the Fuel for a 'Hot Start' Less Vacuum More Fuel or More Vacuum Less Fuel
So Broken as it appears to be now, your Car will be running Over Rich and possibly back firing in the process, where as such all you need to do is pull both those Tubes off it and then Join them together or just replace them both with a Single Tube
Then you will be good to go!
As in Practice this Thermal Enrichment Valve isn't really needed
Just make sure those Vacuum Tubes are not blocked up with Broken Debris
Hmm. I've always wondered about this switch. Mine is gone, removed, as folks have discussed here and for them reasons. Actually forgotten about (and how it was configured) BUT,,, and there is always a but...
Looking at the larger photo of the OPs engine bay I see that the SWITCH is in the line between the LH intake manifold, using a feed off the intake as a source of vacuum, first into the switch then BACK around to the FPR on the outlet of the rail...
Here's my issue and confusion. The way I routed that line POST delete of the sensor/switch is to run a line directly from the spout on the LH intake, a short loop around, and to the back of the LH FPR... FPR operation in direct relationship with intake vacuum.
I guess what has me scratching my head now (doubting) is ---- is the switch always OPEN allowing vac freely to the FPR until the fuel in the rail gets hot enough (thus providing intake manifold vac signal to the FPR) OR is it always CLOSED until it gets hot enough which then provides an intake pressure signal to the FPR?
To put it shortly - Does the switch close when hot there by interrupting vac or OPEN when hot providing vac to the FPR?
In normal, non-hot start mode, the FPR has a vac source from the manifold. The general idea of the vac source to the FPR is so that as the throttle opens, the vac declines and the FPR enriches the mixture as a result; thus ensuring a richer mixture at higher revs and loads, and a leaner mixture at lower revs and loads.
The hot start gizmo closes off the vac when the rail is hot, thus enriching the mixture regardless of load and throttle position, equally this helps pull possible fuel vapour from the rail more quickly, in the hope that this process will allow the injection system to access liquid fuel more quickly, and thus allow the engine to fire more easily.
Last edited by Greg in France; Apr 7, 2022 at 06:40 AM.
In normal, non-hot start mode, the FPR has a vac source from the manifold. The general idea of the vac source to the FPR is so that as the throttle opens, the vac declines and the FPR enriches the mixture as a result; thus ensuring a richer mixture at higher revs and loads, and a leaner mixture at lower revs and loads.
The hot start gizmo closes off the vac when the rail is hot, thus enriching the mixture regardless of load and throttle position, equally this helps pull possible fuel vapour from the rail more quickly, in the hope that this process will allow the injection system to access liquid fuel more quickly, and thus allow the engine to fire more easily.
Understood... And as usual, Greg. Thank you very much...
To babble a little bit more. I find similar "looking" switches on the LH and RH water rails with vac tubes going to places. The one on the RH side I don't think about too much BUT (and there's that word again) the one on the LH,,,, I've been trying to figure out whether it would be worth it or possible to hook it up to what remains of my vapor recovery/fuel tank venting system.
I can't remember but I think I have a line coming from the fuel tank up to the LH fender and,,, if the LH sensor gizmo is a heat controlled on off switch, is there anyway to run a small vac line from the intake, to the switch on the rail, then TO the blanked off line in the front fender to SUCK UP some of the fuel vapors (can be strong at times) from the tank...? Is that rail switch OPEN when hot,,, or OPEN cold?
If y'all think I should start a new thread just say so, especially the OP...!
New thread. Such a question needs a diagram or a photo! But, if you are getting fuel smells, then the vapour/tank breathing system needs fixing. blocked Rochester valves are not uncommon.
New thread. Such a question needs a diagram or a photo! But, if you are getting fuel smells, then the vapour/tank breathing system needs fixing. blocked Rochester valves are not uncommon.
Engine Part
