Hi guys,
I have a bad fuel mileage about 12mpg in all city driving. no more 171/174 error codes after sealing the check valve of a brake booster hose. I guess that my jag has a bad fuel pressure regulator because there was a random misfire at idle speed after engine warmed up. in the morning, in cold start, the engine rpm does not run to 1500. it goes to 1000-1100 only and feeling the car is shaking for a while, then 700rpm the car becomes stable and good.
is there a fuel pressure regulator? where?
2003 jaguar x-type 2.5 automatic 110k
thanks in advance for helpful info.

Thank thermo a lot.
I took the plastic cover away. Unplug the electronic plug which is on the lower side of the fuel pressure nozzle. Cleaned it and plug it back. turned on the key and started the engine. wow it is going on well. rpm goes to 1500 and 1100 and 700 in stable status.
no shaking. hopefully it keeps on this good running.

 

Sienlee, before you start tearing the car apart to get to the fuel pressure regulator, first check to see what the fuel pressure is. There is a Schrader valve under the hood that you can test the fuel pressure with. It should be in the range of 40-50 psi with the engine not running and 30-40 psi with the engine running.

With our cars, the normal issue isn't the fuel pressure regulator, but the fuel pump in the rear of the car not output sufficient pressure. Keep in mind that you have a pump that feeds the motor and a second fuel pump that transfers fuel from the passenger side to the driver's side. So, make sure you replace the correct pump if you end up going this route.

 

Thanks a lot to Thermo.
This last Sunday my car finally lost power on freeway and moved to one exit ramp. after cranking the engine and dying for about 10 times, I called the towing company. At home I checked the Schrader valve for fuel pressure. there's no fuel coming out even though I turned the key to the "on" position. I changed its fuel filter 6 months ago. Inertia switch is down. All fuels are fine including F81 and F92. Fuel gauge works well (that means power is applied on the fuel pump module, right?). I tried jump cable starting my jag but it did not work. I couldn't hear the working sound "humm" of the fuel pump when turning the key to "on". The crankshaft rotated when I turned on the starter.

one month ago I added 2 boxes of cleaner of CF5 BG. it looked good. no more p0171 and p0174 but it died.

I think I have to get a good fuel pump assembly.
what do you think?