Seems like every web site I look at that has anything to do with making modifications to the V12 has the "cap" at the radiator end of both intake manifolds (see photo) removed.

Being a minimalist at heart (I know that conflicts with owning a V12 Jag, but what the heck) I'm more than happy to strip it of anything it doesn't need (no emission inspections here), and I can see where a cap to replace this piece would be easy to fabricate. What are the advantages of doing so?

Thanks!

John
1997 XJS V12, (supposedly) 61,000 miles

 

those are your fuel pressure regulators. you dont want to cap anything. 8p

 

UMMMMM< WRONG.

Those are the "overrun valves", and I am surprised a '97 XJ-S has them at all.

The were originally for extra air on closed throttle overrun, such as down a hill.

If its an '87 as I suspect it may be, the ECU has a fuel cut off feature at closed throttle plate, and overrun revs above 1200rpm.

I removed them from ALL my V12's very early in the ownership.



Mine run NO emission stuff at all, no testing here ever.

 

whups, my bad. i didnt zoom in on the pic.

 

No such thing as a '97 XJS. But on a Lucas HE, there were overrun valves that prevented backfires on deceleration by allowing air into the manifolds. I'm not sure that's what you have in the picture though...I think it's on the other end of the manifold.

Dave
Atlanta

 

I am with Dave.

You say the "front" of the manifold, SO yes they are the overrun caps with the spring loaded valve inside each.

As far as I remember when I was at Jaguar, they were deleted with the Marelli cars in about '89ish.

 

Sorry guys, got fat-fingered with my numbers. It is a 1987 XJS.

Did they prove to be ineffective? Is that why Jaguar removed them?

Is there a reason "to remove or not to remove"? My thought is the less stuff cluttering the engine bay the better...

John

 

Think he might have meant 87 mate.

 

The later cars had the overrun fuel cutoff done in the ECU. The fuel injectors won't fire above ~1200 RPM if the throttles are closed.

You can block them off. I did it on my '83.

Dave