This may be a stupid question, but does the X308 have a fuel pressure regulator? I have a 2001 Jaguar XJ8 Vanden Plas. I have low fuel pressure at the schrader valve on the rail and am wanting to test the pressure by removing the vacuum line from the fuel pressure regulator. Would somebody be able to direct me in the right direction?

Thank you!

 

Not sure about the xj8, but on the xjr its on the back of the passenger side head, below the intake tube.

 

As K-man has stated...it's at the rear of 'B' bank head (left) tucked down to the left hand side of throttle body.
make sure the little vacuum hose is not kinked.
I had a strange stumbling during acceleration \that was down to fuel
starvation because th ecac. line had been kinked over shutting it off.
had ort snip a piece of tubing off and good to go.
You should have 41 psi at the Schreader valve at idle.
make sure there are no vacuum leaks.

 

Thank you K-man & xjay.
It's in a fairly hard spot to get to, did you have any trouble removing the vac hose? Maybe I'm just not doing it right.

 

It is in a bit of a tricky spot....I used long nose needle pliers to
manouvre mine around.

 

If you could help me just one last time , which hose is it that I'm wanting to remove? The one heading toward the driver side label, or the one heading toward the windshield label?

The car has been starting very poorly the last couple days. I've been getting restricted performance & engine lights several times.

 

The fuel pressure regulator is on the fuel rail itself at the right rear corner.
The return line is attached to the outlet of the regulator running directly in front of the throttle assy.

There is a single small bolt (8mm hex) holding the regulator retaining clamp to the rail.
There are 3 'O'ring seals in the housing.

bob

 

Thank you motorcarman! I just tested the regulator. Hooked up my fuel pressure tester to the schrader valve, started the car and it was maintaining fuel pressure, I popped off the vacuum line from the regulator and the PSI jumped a bit and there was gasoline dripping out. Does this confirm the regulator is bad?

When I hook up the fuel pressure tester to the car and turn the keys to auxiliary but no start, the pressure will be a little over 40 and quickly drop. Within 5 or so minutes it will be down to 0 or close to it.

I appreciate your help!

 

There should be NO FUEL leaking from the vacuum port.

bob

 

Yes, the diaphragm in the FPR has failed. Not only does this mean that it cannot properly regulate the fuel pressure, it also means that raw, unmetered fuel is being inhaled into the intake manifold, potentially leading to rich running the ECM may not be able to correct.

Cheers,

Don

 

Thank you everybody for your help. It's been a very stressful last couple days and I'm glad to have finally been able to pinpoint the problem.

 

Replaced the fuel pressure regulator and the car starts like a hot damn now! No more cranking it 3 or 4 times only to end up with a weak start. Having said that, immediately after changing it the car started driving very poorly! The first drive with the new regulator, the car would barely move, once I did get it moving there was no acceleration. Wouldn't go faster than 60km. It was driving normal earlier in the day with the original regulator, but hard to start. New regulator, starts like a hot damn and driving extremely poorly. Could it be that the computer needs to be reset? I had been driving it for months with the bad regulator getting all sorts of codes.

 

My first guess would be that a vacuum line or electrical connector was disturbed or was not reconnected, a brittle breather hose was cracked, or some similar issue. It would be worth double-checking everything in the area of the FPR.

Cheers,

Don

 

Now I'm completely perplexed. I did some troubleshooting. This is what I found out. I put the known bad fuel regulator back on the car. This is the regulator that is leaking fuel into the vacuum hose. While running, the bad regulator is reading just over 40 PSI. While running & in park, revving the engine, the engine revs as it should!

Bad fuel regulator, pressure tested while car running, just over 40 PSI

I then took the bad fuel regulator off, put the new one on, no gas leaking into the vacuum hose, car starts perfect, the pressure reading while running is now about 35 PSI. Pop the vacuum hose off and it jumps up to a little over 40 PSI. While the new regulator is on, I have the car running & in park and test the revving. Absolutely horrible. Inconsistent and all over the place! While driving, the car has terrible acceleration and will barely drive.

Any help would be greatly appreciated! I took videos of me revving the engine with both the old & new regulators as well.


New regulator connected and car running, showing about 35 PSI.



New regulator connected, car running, and vacuum hose popped off, showing a little over 40 PSI.

 

I'll also add that when the old, leaking regulator is connected, when the car is turned off the pressure leaks down. When the new regulator is connected, when the car is turned off the pressure stays at 35 PSI.

 

I would be a little suspect of the 'new' regulator, I think the pressure should be higher than what is being shown with every thing connected. Re bad running, could be that the ECU needs to relearn the map. Have you tried disconnecting the battery for a few minutes to reset the ECU? Might be worth a try.

 

I'm going to leave the battery disconnected overnight and check in the morning. Would a low reading indicate a vacuum hose leak?

 

Make sure you do a "hard reset" (touch the battery cables together for a few minutes while the battery is disconnected). The ECU probably learned to "deal" with the old leaky regulator and needs a full hard reset.

 

I left the battery disconnected overnight and did as you recommended, touched the battery cables together for a few minutes. Compared to yesterday, the car is driving far better! However I'm still getting the occasional restricted performance flashing up (no engine light present), but when I hook up the scanner I do have a knock sensor code. I cleared it and went on my way, and again will get restricted performance at random times. I had been getting restricted performance & engine lights (fuel codes & knock sensor) all throughout the time the car had the bad regulator. Could the actual knock sensor be bad? My parts car is arriving today so I may just switch them out and see what happens.

 

A knock sensor WILL trigger 'Restricted Performance'.

The engine won't run bad but it is NOT happy without the KS input. Revs are limited.

bob