Hello, my 2012 Jaguar XJL has a low fuel rail pressure issue that im trying to figure out the car runs perfectly at idle and drives. . . . **in performance Restricted mode**
im looking for fuel pressure specs but mainly what the voltages are supposed to be both at the pump outlet(low pressure) and at the fuel rail (high pressure)

so far. . . . low pressure is 3.24v key on engine off, vs. 2.33 key on engine running

and high pressure in 1.35v key on engine off and 0.61 engine running
anyone have the proper specifications?

 

Cello, hopefully this will give you something to play with. Looking at the references that I have, the fuel rail has a high and low setting that it is looking for the car to be between. This would be bounded by the fuel rail being between 0.11V (50 KPa, or 7.25 psig) and 4.95V (1000 KPa or 145 psig). Granted, I have to question this as I thought at one time I saw much higher numbers because of our cars being direct injection. This is why you see all the fuel lines being metal as the pressures could get up near 25,000 psig.

Looking up code P0087, it is saying that it is caused by a few different things. The first being that ideal fuel pressure and actual fuel pressure need to be within 1000 KPa of each other and the fuel pump has to be "on angle" ("on angle" is a calculated number that relates the engine RPM and how much fuel that is being admitted to the engine; an angle of 31 is relating to 5 mg of fuel admission and tops out at 122.5 for 160 mg of fuel (max allowed fuel introduction)).

Now, with all this being said, it would appear that there are some secondary stuff that it is looking for to that could trigger it. Those would be as follows:
-The computer seeing the motor not starting
-Seeing the car start and seeing the above paragraph occur after 1 second of the motor running
-The computer seeing the injectors injecting less than 160 mg of fuel (ie, the fuel system is functioniing properly)
-The fuel pump in its START MODE for more than 1 second (ie, the car is getting the fuel rail up to pressure)
-Fuel cutoff not active for atleast 3 seconds (ie, the car does not think that it has been in a wreck and is therefore telling the car not to energize the fuel pump)
-Fuel pressure not changing more than 300 KPa in an 80 ms time frame over a 10 second period (ie, rapidly fluctuating fuel pressures).

Hopefully this gives you something to play with. Worst case, let me know and I will connect up my reader and see if I can find where the reader I have will show me both voltage and pressure together so I can give you a few numbers to play with to ratio out what pressures you are seeing.

 

Thanks for the reply Thermo well this is what ive got.

The main issue is at start up. If the codes have been cleared it'll crank for an extended period- as it watches for fuel pressure (to start up). It wont because one of the numbers is inaccurate. It has two pressure sensors one for low pressure (at the fuel pump outlet for the in tank pump pressure) and one for high pressure at the rear passenger side of the engine (for the high pressure cam driven pump.) Whats happening is one of these figures is wrong and the computer knows it. the code is directly tied to the high pressure pump values. the very first thing jaguar recommends to do is replace the high pressure sensor at the rear passengers side of the head to ensure sensor accuracy. Im about 70% sure that the sensor is the issue because immediatly after the PCM triggers the code and "performance restricted mode" it completely ignores adjustments and runs a base limp in mode. the engine starts right up after that without any hesitation. so with that im assuming fuel pressure is perfect, just the computer doesnt like being lied to and is avoiding engine damage. oh. and i forgot my scan tool also shows sub-codes it explains that this is only during cranking so im assuming that one of the sensors is only inaccurate. not brain dead. so what im looking for if you have the time.

turn the key on and write down the voltage readings at rest. then wait to crank and write down the values after the engine has idled down on its own usually about a minute or two. sometimes it helps a little too to write down the values as it is idled up so you can compare the values to calm idle vs. intentionally raised by the computer. then after that a quick snap throttle to see what max voltage is during acceleration. im sort of making a "parameters chart" of sorts so that i can compare what its doing as to what its supposed to be. thanks man any help would be awesome. hopefully we can clear up fuel issues for everyone here ill try to give a clear explanation.

 

I will do this tomorrow morning.

 

Not sure if this will be of help but its is a link to the AJ133 5.0L training manual AJ133 5.0L engine

 

Cello, looking at my car, all that it gives me is a single fuel rail pressure. I don't see where I can look at a high and low value. But, this is the information that I obtained under a few different situations:

Engine off: 4000 KPA (580 psig)
Idle (1300 RPM, engine just started): 15000 KPa (2175 psig)
Idle (800 RPM, engine just dropped in speed): 3320 KPa (480 psig)
Idle (600 RPM): 2900 KPa (420 psig)
2000 RPM (stepping on gas to raise the speed): 6390 KPa (925 psig)

Keep in mind that all of these were taken before the engine reached normal operating temperature. So, if your motor is warm, you may see slightly different pressures. But, they shouldn't be too different. If you are getting similar numbers under the same conditions, then that would be looking like you have a low pressure sensor problem. If you are getting different numbers, then that would confirm the high pressure sensor issue.

 

There must be a range of fuel pressures because I have been data logging my 2014 XJR and see a range of values like Chris did above.

Usually 800 psi at idle or low engine speeds with it building as I accelerate to around 2500 psi. Now I am still looking at it because DI engines are claimed to run as high as 4,000 psi!
Just getting a feel for what is normal for my car.
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