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Don't laugh but new jag owner here and I'm overwhelmed by the amount of vacuum lines. In all my Chevy's I'd just start unplugging stuff and plugging vacuum holes to simplify. I want to do exactly that with my 88 xj12. Emissions isn't an issue here. If someone can guide me or get me started in the right direction that would be great.
You have an XJS, next forum section down, and V12 info is more readily available in that section, as compared to in here.
Many threads in there about Vac line delete, and the owners in there will certainly give do's and dont's.
Mine runs ONE vac line, RH throttle body to vac advance capsule, thats it for engine running stuff. Obviously other Vac lines for heater, trans etc are as is.
Don't laugh but new jag owner here and I'm overwhelmed by the amount of vacuum lines. In all my Chevy's I'd just start unplugging stuff and plugging vacuum holes to simplify. I want to do exactly that with my 88 xj12. Emissions isn't an issue here. If someone can guide me or get me started in the right direction that would be great.
Welcome to the forum Ivan,
I've moved your question from XJ6 & XJ12 Series I, II & III to XJS forum. This is the place to post technical questions about your model.
Ivan, Welcome to the XJS section. If you have a Lucas ignitioned car then years ago I did as Grant suggested, one vac line to the distributor capsule from the A bank under throttle body tapping, and get rid of the (advance related only) rest. If a Marelli ignition car, I do not know, but someone here will!
Aside from the vac advance I would leave the vacuum lines to and from the distributor cap alone as they draw fresh air into the distributor and prevent the build up of gasses that could ignite and crack the cap.
If you don't have emissions testing, then all that junk can go- including the whole air injection system- just depends on how crazy you want to get about it.
Aside from the vac advance I would leave the vacuum lines to and from the distributor cap alone as they draw fresh air into the distributor and prevent the build up of gasses that could ignite and crack the cap.
If you don't have emissions testing, then all that junk can go- including the whole air injection system- just depends on how crazy you want to get about it.
Okay makes sense. So can I plug the distributor straight into manifold vacuum? What about all the vacuum stuff that goes to the back and front of A manifold? And the front and back of B manifold? What does the things on the manifold that are attached to the fuel rail do? They seem to put fuel into the front part of both manifolds. Is that deal wamp on the back of A manifold the AAV auxillary air valve? I want that to work for sure so it idles up when cold. I would be very happy to get a vacuum diagram for the a manifold.
On one side, the distributor has a hose that runs underneath the B bank manifold and terminates somewhere near the fuse box on the left hand side of the engine bay with what looks like a small lawn mower fuel filter on the end which in reality is an air filter. On the top of the cap is another hose that connects up to the elbow hose connecting the AAV to the left hand air box. It's independent of any other vacuum system so you could leave it alone- but yes it basically sucks air through that filter, into the distributor and then into the manifold.
I made a thread several weeks back about deleting some of the emissions stuff in my car, it's called "Removing vacuum lines" or something and probably only a page or two back on the forum. I posted some diagrams of my findings that you may or may not find useful.
As for all those lines on the back of the A bank manifold- hopefully others chime in. A diagram would be nice if anyone could supply one. I know one of them goes to the blue and white vacuum switch mounted close by which I *believe* is the fuel enrichment switch but someone may correct me on that. And the climate control system gets its vacuum from there too so you would want to leave that.
You can also get rid of the overrun valves on the front of each manifold. I'm slowly doing the same thing you are- deleting and removing all the unnecessary crap and trying to simplify the engine bay. So far, the engine has responded quite positively and is running much better than when I started.
Ecbjag "As for all those lines on the back of the A bank manifold- hopefully others chime in. A diagram would be nice if anyone could supply one. I know one of them goes to the blue and white vacuum switch mounted close by which I *believe* is the fuel enrichment switch but someone may correct me on that. And the climate control system gets its vacuum from there too so you would want to leave that. " Ecbjag
fuel enrichment? Im aware of the wot switch on the throttle pedestal. I will be making my motor move more air someday and would like to add fuel with that air. Is it possible?
Again, I'm not totally sure of this but I think the the microswitch on the throttle pedestal and that blue/white vacuum switch both trigger the same fuel enrichment function on the ECU. It's an On/Off type thing to prevent the engine from leaning out at high RPM's. It's set up so that the enrichment is triggered either by WOT or whatever vacuum level flips that other switch. I'll consult the schematic when I get home tonight.
Ecbjag "As for all those lines on the back of the A bank manifold- hopefully others chime in. A diagram would be nice if anyone could supply one. I know one of them goes to the blue and white vacuum switch mounted close by which I *believe* is the fuel enrichment switch but someone may correct me on that. And the climate control system gets its vacuum from there too so you would want to leave that. " Ecbjag
fuel enrichment? Im aware of the wot switch on the throttle pedestal. I will be making my motor move more air someday and would like to add fuel with that air. Is it possible?
OK, rear plate of A Bank Inlet manifold.
4 spigots (mine does).
1= trans modulator
1 = Climate system
1 = Blue White valve.
1 = CAPPED.
USA market may have other stuff on that capped spigot, but I seriously doubt it.
The current ECU, in the boot uses vac signal for fueling, and LESS vac = more fuel, and MORE vac = less fuel. VERY SIMPLISTIC EXPLANATION, THERE IS MORE TO IT OBVIOUSLY.
When either of the enrich switches are activated, the system goes APPROX 15% richer.
Mine all have BIG throttle discs, Cold air ram in, and a STANDARD 16CU in the boot, NO issues at all.
Kind of tough how no one member knows all the cars due to the many iterations. You just kind of learn your own car. I'm going to come back with more questions when certain things don't work. I don't quite get the explanation on the rear a bank setup. But with deductive reasoning I can figure it out.
This RH and LH is ALWAYS referred when sitting IN the car facing forward. It takes the guess work out of "drivers side/passengers side", which is of course depends where the steering wheel is located.
As has been already said Sitting in the Drivers Seat looking through the Windscreen 'A' Bank is on the Right Hand Side Of the Car and 'B' Bank is on the other side (The Same Side as the Oil Filler Cap)
The Vacuum Pipes you were asking about are on the Rear of the Inlet Manifold on 'A' Bank where there are 4 Spigots where one of those is capped off (which now leaves only 3 to be configured)
The Lower one, The Black Tube with the White Stripe goes to the Gearbox Modulator on the T400 Gearbox underneath the Car on my 1989 and 1990 XJS V12's
The Black Tube that is above this goes into a Tee Piece where the Higher one of these Tubes goes into the Round White Switch, where this 'Tee Piece' then sends Vacuum to the Air Con
The Black Tube with the White Stripe is the Vacuum Pipe to the Gearbox Modulator
The Vacuum Pipe above this goes into a 'Tee Piece' as you will see from the following Photo
On the 'Tee Piece' The upper most one of those two pipes goes to the Round White Plastic Switch
Coming off the 'Tee Piece' the upper most Tube goes into the Round White Plastic Switch
Where this 'Tee Piece' sends a Vacuum to the Air Con
That leaves only ONE Spigot (apart from the Blanked OFF one which isn't used in this particular setup)
The Vacuum Pipe from this Last Spigot goes into the Blue Switch
The 3rd Spigot goes to the Blue Switch (see Photo above)
But that's not all, because coming out of the Bottom of this 'Blue Switch' is a Rubber Tube which looks the same as the other Rubber Tubes 'For the first few inches but then reduces to a 'Very Small Diameter Hard Plastic Red Coloured Tube'
And this very small Hard Plastic Tube, goes into the 'Dizzy' Too many 'Gizmos' in the way to try and get a Photo but I think that you will be able to see where that goes
So that's it, Job done for the Rear Vacuum Pipes on 'A' Bank
Now onto 'B' Bank (The Side With the Oil Filler Cap)
On The FRONT this time of the 'B' Bank Inlet Manifold (The one near the Oil Filler Cap) is the Vacuum Pipe for the 'B' Bank FPR (Fuel Pressure Regulator)
This Vacuum Pipe goes from the Front of the 'B' Bank Inlet Manifold to the 'Thermal Fuel Enrichment Switch' and then from the 'Thermal Fuel Enrichment Switch' to the 'B' Bank Fuel Pressure Regulator
This 'Thermal Fuel Enrichment Switch' was giving a problem on my Car, as the Wax inside it Melted and so I cut it out of the Mix
See Photo:
Vacuum Pipe from the Front of the 'B' Bank Inlet Manifold Should go! to the Thermal Fuel Enrichment Switch on the Fuel Rail (That's the switch with the Two Spigots) then from this Thermal Fuel Enrichment Switch to the FPR on 'B' Bank
The Switch on my Car caused a load of Problems, when the Wax Melted Inside it and as I didn't need it in the UK Climate, I cut it right out of the Mix
Last edited by orangeblossom; 04-05-2019 at 01:14 AM.
1. Read the theory, study the manual, after you have learned how the stuff works start cutting and plugging. This method is totally against human nature and nobody uses it. Some nutty geek excluded.
2. Trial and error. This is the popular way. More complicated the system you are messing with is more chances there is to arrive to "aw ****!" result. Nevertheless, this is the method for normal people.
OB
Great write up; just one small point: the tube off the A bank T piece (one side of which goes to the white switch) actually sends vac to the aircon vac reservoir, not to the ECU. The ECU signal comes off the middle of the crosspipe that joins the two inlet manifolds at the rear. I only mention it in case the OP gets in a muddle. You have given the guy a brilliant explanation and the photos are such an important aspect in explaining this sort of thing.
03-26-2019, 11:27 PM
Simplifying and deleting unnecessary vacuum lines
