Greetings

I have a 1984 XJS V12 HE. Had the car about 12 months, noticed not that long ago that there is “No” Full Throttle Micro Switch on the Throttle Turntable. I cannot see anything to say one was fitted, ie redundant wiring or mounting plate.

The car has a Throttle Vacuum Switch Fitted.

The car is a British compliance vehicle that was imported to Australia.

Did the Brit cars come with the Throttle Micro switch….i recall reading somewhere they did not…..?

If not, how does the system operate in comparison to the Aust and US compliant vehicles….?

Advice on this much appreciated

Regards

Darren

 

UK spec cars were not fitted with the micro switch, they were only fitted with the full throttle vacuum switch (the thing bolted onto the top cabin end of the A bank intake manifold) with two wires and one vac tube coming out of it. The two switches were so wired that either if activated would ensure full throttle fuelling.

Greg

 

Hi mate

My 1985 XJS V12 HE has that microswitch.

Mine has been moved from original position I believe and sits on top (see first picture, red circle). My car was bought in South Australia from new so they had them fitted in Oz.

The second picture is from a Jaguar book and it is of a 1981 XJS HE. It has the microswitch mounted underneath the other plate marked with a green circle. I'm pretty sure this is from a British Publication and so I think they were like that in the UK also (somebody can confirm?)

As to further details just hang tight...

I am sure the Great Wizard of Oz Grant Francis and others will be able to fill you in more soon...

EDIT: Wow that was fast Greg. In the time it took me to write the first response you arrived!

 

All is right in the world of the mighty V12.

Locate a switch and mounting plate, attach 2 wires from the 2 wires of that vac switch (splice into them), and plug then into the micro switch. Thats how it was when that 2 switch system was used in the market that required the 2.

Side note: That Blue/White vac switch is adjustable. Pry out that black bung, use a vac gauge, and an OHM meter, and establish where THAT switch is switching. Rotate the screw 1/4 turn clockwise, and renote the readings, etc etc. Bear in mind that vac is used to keep the contacts OPEN. When vac drops the contacts close, and the ECU changes maps. Mess with it a tad, and you will soon grasp the operation principle. Knowing the vac the engine draws whilst cruising helps heaps. I forget the numbers now, but mine was set to change the fuel map not far below the cruise vac, and that made the engine much "snappier". Particularly when overtaking, when you may only want to "squeeze" the throttle, as apposed to "stomping" on it, it is a V12 after all, so "stomping" is really not always needed.

If figures are really needed, let me know, I will have them written somewhere in the library.

 

The second (green circle) pic shows the kickdown microswitch for the gearbox kickdown. Separate matter from the full throttle switching system, which is to prevent too lean a mixture at WOT wrecking the engine by burning holes in the piston crowns!

Greg

 

Greg is right.

Goose has NOT got the kickdown switch, it kicks down just fine without it, as do all TH400 V12 cars. The "mash" of the gas pedal thru the floor to get kickdown is just dumb. The strain on all those components is really huge.

Lots of owners have done all sorts of systems to get kickdown in a more civilised manner. That is one mod for each individual.

I went with the compact, adjustable modulator, and simply played with spring settings via the spigot screw, until it gave what I wanted.

 

whoops! I'm confused

Sorry, don't mean to Hijack the thread

So the Blue Goose (engine bay on the left in my first thread) doesn't have the throttle kick down microswitch? I thought that was what the microswitch was near the capstan circled in red?

The microswitch in the 2nd picture (circled in green) is the same microswitch just mounted in different spot yes?

So we are talking about a different animal then? Does anybody have a picture of where the vaccum switch is mounted?

So when the throttle kickdown for the transmission activates, it will drop down gears almost instantaneously where as the other microswitch we are talking about, when it activates, prevents too lean a mixture @ Wide Open Throttle. It sends a message to the ECU and controls your fuel injection?

Am I close to understanding?

Sorry beginners questions I know

 

On cars so equipped the vacuum operated enrichment switch is mounted at the rear of the RH inlet manifold. In the attached picture it's the blue/white plastic device next to the vacuum balance tube....lower right corner of the picture


Cheers
DD

 

Easiest way to remember is that the kickdown switch is actually mounted on the throttle cable itself. The cable has a square, metal mounting tab....maybe 1.125" x 1.125" in size. The kickdown switch is attached to the underside of the tab

The (electric) enrichment switch is mounted on the throttle turntable itself.

The (vacuum) enrichment switch is mounted on the inlet manifold as seen in the above post





You got it!

Cheers
DD

 

Don't apologize, no need. It gets confusing.

Adding to the confusion is that Jaguar parts catalogs often misidentify various switches.

The generic snap-action micro-switches that we're discussing were originally used and cataloged as "kickdown" switches decades ago. As years went by Jaguar found the same switch/part number (C33509) useful for a variety of functions. Often, when used for another function, it is *still* described in the catalog text as 'kickdown' switch. I've seen this numerous times and to this very day the errors still exist in the JDHT catalogs.

Cheers
DD

 

Thanks for sharing Doug. I think I am on my way to understanding. Appreciate your post.

So..in your picture that I edited...the green circle is the The red circle is the ?

Just having trouble finding the I cant seem to spot it.


I need to go home and poke around my engine bay to see what I got...

 

Look to the right of your green circle. You'll see a light blue/white device. That's the vacuum operated enrichment switch. The white is a bit dull from age.

Cheers
DD

 

Oh I see it! Cheers mate. I appreciate it.

I wonder if Darren (original poster) had some success with his question?

 

Paul,

In YOUR snap, the switch you circled IS the throttle switch (Enrichment switch), and if you look closely at the throttle cable where it crosses the fuel rail, there is a metal angled bracket thingy. That is where the kickdown switch lives.

The Blue/White vac switch is tucked down the RH side of the throttle pedastal (kind of to the backside), it just sits there, it is not attached as such to a bracket.

I simply dont remember if the Goose has the small campact vac modulator on the transmission, or the GMH larger unit. When you guys change the oil, have a look at the RH side of the trans, just alongside the exhaust pipe, and you will easily identify the modulator. The BIG one is about 2+" in diameter, the COMPACT is about 1+".

 

oh...I think I am assed about backwards

So I have the enrichment switch on mine but NOT the throttle kickdown for the transmission?. As you said, you believe it used to place heaps of strain on the system? I can see that bracket your talking about. You can see in the pic of the 1981 HE (green circle first picture on right) it has said micro switch but not the enrichment one as you guys have been saying all along.

Now it is all starting to make sense. Penny has dropped

Cheers Grant yet again