Hello all, I'm new to the Jag world. I just picked up a 2001 XJ8 Vanden Plas in remarkably good shape mechanically, it has some cosmetic problems and a Salvage Title but I was able to insure it and get it on the road.

Being a former (and still on-the-side occasionally) automotive technician, I know my way around an engine, but I have very little experience with Jaguars. I'm going to restore this car as much as I can...

My main issue, mechanically, is in the fuel system. With a fuel pressure gauge connected, at idle, the pressure flutters around 34psi. With the vacuum removed from the FPR, it leaps to 42psi and holds steady. When starting the car, it has an excessive cranking time and my suspicions were confirmed when I found that the fuel system is not maintaining pressure. As soon as you turn the key off, fuel pressure drops to zero IMMEDIATELY.

I was unable to find a diagram of the fuel system in my AllData software at the shop, so my conclusion is that the fuel pump is faulty. My question is...am I correct in this assumption, or is there a check-valve somewhere on the return-side of the fuel system?

Symptoms are a hard start, stumble and misfire 1-2 seconds after starting which then goes away, abrupt loss of power at wide open throttle and a light misfire that only appears under load and gets worse as load increases. I smoke-tested the intake manifold and found a few runners were leaking at the gaskets but it was very minor. Hoping the forum can help me because I'd hate to replace the fuel pump only to find there is another problem. LOVE this car though.

 

EDIT: Because it was unclear, I *am* going to replace the intake manifold gaskets, I just need to know if I need a fuel pump additionally.

 

I do not know how you have determined the fuel pump is bad... The pressures are about right, but you need to test under load and road conditions. I use an extended tube on my gauge and tape the pressure gauge to the ouside of the windscreen, then go for a drive.

 

The fuel pump itself seems to be operating nominally. The issue is the fuel system will not maintain pressure, it's constantly recirculating back to the tank. When I turn the key to On, attempting to prime the fuel system, it builds 0 psi. When cranking, the fuel pressure gradually increases until the engine starts and stumbles hard until it reaches normal pressure. When shutting the engine down, fuel pressure drops to 0psi within 2 seconds flat.

Hence my question, is there a check-valve in the system that is stuck, or another issue. I'm unfamiliar with the fuel system on this car, other than knowing that this behavior is abnormal.

 

Hi, there are two tank located fuel pumps. One for starting and the 2nd joins in later. There is a fuel filter in the system too.

https://www.jaguarforums.com/forum/x...e-help-103070/

https://www.jaguarforums.com/forum/x...s-103772/Allan

 

Fuel pressure regulator...?
Also, if you have the normally aspirated engine there is only 1 fuel pump I believe.

 

Yeah, the fuel pressure does stay up (about 15 psi, I THINK) on mine after it shuts down. The pump does not run more than a second or two with the key on - until you crank or tghe engine is running.
To test if it is the regulator or the pump check valve, you could clamp off the return line...

 

- correct - unless it is supercharged, you have only one fuel pump, there has been a substantial problem with the check valve, which is on the discharge side of the pump, on pumps manufactured in 2009 - 2010. Search here or google it. Good luck removing the fuel tank. I bet you cant do it without swearing. Other than that you might want to test your reg with a mityvac, other than stains on the ground it is probably one of those 2

 

in summary, the correct information as to number of fuel pumps:

naturally aspirated, 1 fuel pump
supercharged, 2 fuel pumps

they are conventional pumps, not the pump in a module as found in later cars.

there are two mechanisms responsible for maintaining the fuel pressure when the car is not running. the fuel pressure regulator and a check valve in each of the fuel pumps as applicable.

one other reported trouble spot is the outlet hose on the fuel pump popping off at the outlet. this hose runs from the pump to the tank outlet hard line. certain brands are prone to this because they use a slide in hose nipple.

 

Thanks for the information, folks... I'm not exactly a "veteran" technician, but I've been working in auto shops continuously for 10 years now and as a technician of some sort on and off for nearly half of that...

After testing the fuel pressure, I removed vacuum from the regulator and it performed as it should and increased fuel pressure around 7-10 psi..when vacuum was reapplied, it dropped to where it was prior. I've got no EVAP codes, and no fuel vapor smell whatsoever, therefore I'm led to believe the problem is in the pump's check valve, which means I need to replace the pump.

Dropping a fuel tank sucks, but I've done it many times...granted never on a Jaguar. I'm hoping it has no unusual, Jag-specific quick-connect type of fittings that require special tools other than standard Quick-Release tools, which I own... I'll just wait til a slow day, schedule myself off, and change it myself on our split lift using a transmission jack.

Thanks for the help.

 

You will probably find that a piece of 1/2 or so hard metal tubing (conduit?) about 8" long split lengthwise to slip over the gas lines will help push in the release tool. If you have fat, arthritic hands like me you will find it is easier to loosen the rear end subframe on the front and lower the back end down to allow access to the ports where the fuel line and return connect to the bottom of the tank.
Good luck!

 

Sparken, thanks for the tips! I've found a few different fuel pump options on RockAuto, I think I'll probably go with the full kit, Carter I believe makes it...it's the most expensive pump on their site but it's OE electrical connections, hoses, gaskets, strainer, etc. Some of the cheaper pumps like Airtex or AC Delco are missing bits or require wiring in a different connector, which I'm not going to do because I only want to do this job once.

And my arms and hands are long and thin, so I can get them into just about anything anywhere, but I have a bad back and both of my hands are getting either arthritic already or it's carpal tunnel. I left a Technician job for Sales for those reasons, so I'll still be able to function still in another ten years lol...

 

Well, I have disconnected the pipes without disconnecting the rear end on my X-300, but dropping the rear subframe only added about 15 minutes to the job and prevented skinned knuckles and bad language. 10-4 on the bad back. I finally broke down and bought a lift for that reason!

 

My shop data program, AllData, doesn't have a step-by-step for this car, all it says is "Step one, remove fuel tank. Step two, disconnect hoses and electrical connectors." Thanks for the hot tip, Quincy....

One more question, did you just lower the subframe down to the last few bolt threads and sneak it out, or did you drop it entirely? It would make so much more sense to just provide an access point under the rear bench, but that would mean we wouldn't need to take it to the dealer... Can't have that now...

 

just behind your rear jacking points - there is a bracket on either side, 190mm and 17mm heads, take them off. I use a 24 inch tyre lever to pull the front of the sub frame down - only needs to come down an inch for my fat hands