Hi thanks for any help you can send my way. Have a 1999 XK8 high milage. the other day was driving a friend to the shop was running fine made a quick stop when went to restart would turn over but seemed to not be getting gas.
After sitting for a while would sputter a bit but would not start. Just finished a long trip of over three hundred miles ran fine but ran the gas low but still ran well. Thought I might have a plugged fuel filter so replaced. Think it may be the fuel pump before I dig into that any thought or suggestions.

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The fuel cools the pump, so running below a quarter tank could be risky. Check the fuel pressure by depressing the tip of the Schrader valve on the fuel rail. It should give a good squirt. Use a rag to prevent spraying too much.

 

Autozone rents a fuel pressure gauge. Or they're available on Amazon for about $25. I believe fuel pressure at the rail should be in the neighborhood of 60 PSI. Somebody can correct this if I'm mistaken. What you're describing sounds like a fuel pump leaving the chat.

 

Running the fuel low should not cause a problem but a failing fuel pump is not uncommon on the X100. A fuel pressure test will help to determine. If someone listens in the boot can they hear the pump running? An ODB2 reader might be a quick way to diagnose fuel pressure issues.

Richard

 

AFAIK the X100 doesn't have a fuel pressure sensor. I haven't seen it in the four different scan tools I've used on my 2000. Maybe they did on later years?

 

I'm sure it has the same fuel pressure sensor/regulator as the 4.2 variant of the X100 engine in the X150. I've just changed mine on the X150.
The ECU will certainly be measuring the pressure in the fuel line but whether it transmits that data over the canbus is another question. It certainly does on the X150 as that's how I knew mine needed replacement but it could well be the case that the X100 ECU does not make that information available as it is an older ODB2 system so the pressure would need to be checked using the Schrader valve. In fact, the Schrader valve was removed on the 4.2 X150 which might be relevant.

 

When I pressed down on the Schrader Valve some gas came out but not a big spray.

 

Turn the ignition on for a couple of seconds, then off and repeat three or four times. Check the output at the valve again. It is likely the pump is failing. There should be 45-55 psi which would give a good sqiurt.

 

Fuel pressure isn't available via OBD prior to the 4.2L.

 

If anybody knows where the sensor is, could they post it here? I've been under the hood of my X100, replacing every sensor, hose, and gasket I could find. I haven't seen it. The reason I don't think it has one, besides not being able to find those measurements in the various scan tools I have access to, is that my contemporaneous BMWs, which are electronically far more sophisticated than the Jag, don't have a FPS. The later generations, like E90 and E60, do have pressure sensors and, IIRC, no Schrader valve. Like the X150s. IIRC both the X150s and the E90/E60 (and up) are direct injected. Hence the critical nature of fuel pressure and the lack of a Schrader valve. You don't want to be pressing on that valve when there's 1500 PSI behind it. LOL

 

As stated, cycle key a few times, waiting several seconds between cycles. Then check again. It sure sounds like a weak fuel pump. Good luck!

 

There isn't one on the 4.0L - fuel pressure is managed by the fuel pressure regulator at the rear of the RHS fuel rail.
Excess fuel is returned to the fuel tank.

 

I think we may be talking at cross-purposes. The fuel pressure sensor on the 4.2 engines is actually a fuel pressure sensor and regulator and is therefore connected to the inlet manifold. It sends the fuel pressure data across the canbus so it can be read via a suitable scanner.

The fuel pressure regulator on the 4.0 regulates the fuel pressure but, as advised, does not send the information across the canbus. I've never changed the pressure regulator on my 4.0 but I think that on the 4.2 the fuel pressure temperature sensor is fitted in that location and the sensor/regulator is moved along the rail close to the front of the engine. It is a different part.