Am planning to take a fuel pressure reading this coming weekend. Doug generously provided advice as to how to attach the fuel pressure gauge. If pressure is high (above 40psi) are the regulators adjustable? If so, which regulator should be adjusted, the right or left side?, or both. Also, how do I tell if the fuel return line is "blocked" causing high fuel pressure? Do I read fuel pressure only at idle, or at another specified rpm?
Thanks.

Rodd Leeds
1988 XJ-S Cabriolet 5.3

Submitted by dougdwyer@adel… on Tue, 06/06/2006 - 09:17

Roger Bywater of AJ6 Engineering recently posted this on Jag-Lovers which I found interesting:

"The exact purpose of the incoming regulator has never been made
clear. For a long time I assumed that it was there to prevent pump
noise transmitting through the car and also to prevent vapour lock
occurring in the fuel feed line. With further thought I suspect
that it also works as a sort of fire door, isolating the fuel rail
from the feed pipe so that any seepage that might take place would
be limited to the contents of the rail and not added to by
vapourisation in the feed pipe. It should be remembered that fuel
temperatures can easily exceed 60C on a hot day with a near empty
tank."

Cheers

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe

Submitted by dougdwyer@adel… on Wed, 05/31/2006 - 09:24

Dick is right. On the V12 the manual specifies a f/p while the engine is at idle. I was thinking of the 4.2, which, for reasons not known by me, Jaguar specifies the f/p be checked while the engine is cranking.

As far as the right regulator goes I had read, on the AJ6 site, I think, that, its only purpose was to dampen noise. In any case the car will certainly run fine without it....if mine is any example...although I'll admit I never thought of the boiling issue, nor have I experienced it.

I might add that correcting errors and/or adding more information is not stepping on toes but your politeness is appreciated :-) :-)

Cheers

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe

Submitted by dougdwyer@adel… on Tue, 05/30/2006 - 22:14

No adjustment.

The left side would be the one to replace. In fact, the right hand regulator is superfluous.....you can eliminate it if you want to.

As I recall the pressure test is performed while cranking the engine on the starter.

How to check for a blocked return ? Hmmm. My first thought is to use compressed air....regulatd down to 20 psi or so. But I'll try to divine another way ..under the assumption you don't have a compressor.

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe