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What EXACTLY does the 2003 Jaguar XK8 X100 Fuel Pump Control Module do?
I have a 2003 XK8 and the mechanic has determined that they put the wrong Fuel Pump Module on my car and they claim that this is why I have no fuel pressure on the Fuel Rail (for the record, I disagree. I believe it is due to a bad Check Valve in the Fuel Pump).
I believe that the Fuel Pump Control Module for the 2003 - 06 XK8 Jaguar's just controls when to kick the Fuel Pump on..... I informed them that the corrrect 03-06 Jaguar XK8 X100 Fuel Pump Control Module 3W839D372AB OEM.
Does anyone know what is all of the functions of the Fuel Pump Control Module is?
The correct Jaguar part # for the fuel pump control module is C2N1503. It may or may not be the same as 3W839D372AB which appears to be a Land Rover part.
How does it work?
Basically, it controls the amount of power supplied to the fuel pump based on the instructions it receives from the ECM.
How it achieves that is rather less straightforward, and the ECM can instruct the FPM to turn off the pump.
This snippet from the 2003 MODEL YEAR XK SERVICE TRAINING TECHNICAL GUIDE gives a taster:
" To support the installation of the 4.2-liter engines and continuing the drive for fuel
consumption benefits, a new fuel system including fuel tank, fuel pump, pipes, breather
pipes has been installed.
The XK now benefits from the use of the return-less fuel delivery system very similar to the
X-Type and S-TYPE models.
One major change on supercharged (S/C) variants is the use of only one fuel pump instead
of the usual two as used on all previous S/C models (XJR, XKR and S-TYPE R).
The fuel pump uses the same principle of operation as the on the X-TYPE where the ECM
monitors differential pressure across the fuel injectors and the injector pulse width and
duration to accurately calculate the fuel quantity being delivered to the cylinders. It uses
this to demand a specific fuel flow rate, which it communicates to a fuel pump driver
module located in the right hand side rear wheel arch.
The ECM use a frequency of 150 Hz (PWM) signal during average conditions, varying its
duty cycle between 4 and 50% to control fuel delivery rate or turning it to 75% to turn off
the pump.
"
I presume that the car was running OK at some point. What happened before this issue arose?
I can't really testify to what was going on prior to, because I just purchased the car a few months ago. I found out that this particular mechanic stated that they replaced the fuel pump and really just kind of fuel pump control module about 300 miles ago. However, although when it's running it runs good, it has a long crank start and doesn't retain any pressure on the fuel rail once the car is turned off. There is a warranty of two years for parts and service from the mechanic, but he's upset that he is in this predicament and refuses to believe that the fuel pump is bad.
Some research indicates the FPRV* could definitely be defective. This a part of the Pump Module Assembly, a mechanical device. Several owners have experienced this situation. Long crank time after car is shut off usually occurs overnight or extended periods of shut down. The defective FPRV allows the fuel to drain back to tank and the fuel pump has to supply line and rails with fuel to allow car to crank. Possibly the Scharder valve would be an indication if there was 0 fuel when depressed after extended parking, Most time there is a tiny bit of fuel that will dribble from it even after parked overnight. *FPRV=Fuel Pressure Relief Valve.
Throwing parts at it is going to be an expensive way of troubleshooting. That module is showing at around $190 on the Jaguar Heritage site.
If the tech did indeed replace the fuel pump recently with a kosher Jaguar part (around $800 and nobody has yet found a reasonable-price alternative, AFAIK) then he may be correct. There has been a small number of issues with the wiring around the pump also. Unfortunately Jaguar didn't make access easy - especially on the convertible
It might be worth dropping member JayJagJay a pm as he's been through this and may have some pointers.
edit: picking up on ksteveusa's post, I believe Jay also found an issue with the FPRV where an 'O' ring was displaced during reassembly.
On the 2003-06 Jaguar XK-8, the FPCM is electronic only. It's my understanding that Jaguar stopped using mechanical FPCM in 2002. They also went to a single Fuel Supply line with no Return line. The one way check valve is in the tank with the actual fuel pump.
Smokey59
The FPRV is built in mechanical device and operates independent of the Driver module (separate). The driver module tells pump when to run and shut down. It is built into the housing assembly at top. This is the way i understand the operation of the fuel pump module. Jay maybe can explain it more clearly?
Below are some parts of the pump assembly (missing the canister, level sender and some other bits from the picture). The drain back check valve is A (not much to it) The spring is supposed to push the rubber stopper against the hole in B. The over pressure limiter is C, just a mechanical spring loaded check valve to ensure the highest pressure that can happen is ~70psi. Too much pressure can prevent the fuel injectors from opening.
When assembled fuel flows out to the right though the hose with the metal clamp. The extra bit past B with the elbow nipple at the end is the bypass recirculate path to make sure the pump is always submerged. It flows back into the bottom of the canister the pump is suspended in.
The control module outputs a variable drive signal to control the speed of the fuel pump based on the input signal from the ECU.
As stated above the signal operates at 150hz. Imagine 150 pulses per second where each of those can be either 12V or 0V. The duty cycle is the fraction of those that are “on”. At 50% duty cycle there will be 75 on pulses and 75 off, and the pump will run at half speed (more or less).
Control the speed of the pump, control the flow of fuel into the injector rail. If flow into rail from pump is greater than flow out through the injectors, pressure goes up. If flow into the rail is less than the injectors use, then pressure goes down.
The ECU watches the pressure sensor on the rail and speeds up or slows down the pump to control pressure.
I've had this problem and even replaced the VDO Driver....but it still didn't work!!!! I visited with Charlie by email and as I told you earlier...I tightened all the contacts around the Gas Tank including the VDO Modul and dropped a drop of Solder on each connection.....Charlie said that vibration apparently loosened the connection over time......I've not had any problems in over a year with the same set-up that wouldn't run a year ago....As Charlie said, it would have to be the connections....
By doing this...I believe that nothing has been wrong with any of the (4) $650.00 to $700.00 Fuel Pumps that I bought over the years.....It is apparently the connections vibrating loose! It worked for me! Ask Charlie.............
I just went out to the Garage and She started right up!!! This works!
Billy Clyde @ Cinco Ranch
Last edited by bcprice36; Mar 6, 2022 at 10:45 AM.
The way that work is not so complicated. They sit in the boot on the RH side. They take a signal from the fuel pressure sensor on the rail via the ECU and use a pulse width modulation (PWM) signal to run the pump a certain percentage of the time,,, tapping it with 12v for a 55, 65, 75 etc % run rate according to the sensor signal trying achieve and maintain a certain pressure at the rail. If you need one, I would grab one for 40 or 50bucks from these folks. I find them to be a great outfit!
Last edited by JayJagJay; Mar 6, 2022 at 12:34 PM.
I misunderstood your situation. Thought the car ran, but after shutting it down, became difficult to restart. Seems you are indicating the fuel pump is not pumping fuel to the rails at all. The module functions as noted above telling fuel pump to push fuel to the filter and then to the engine. There is a fuse in the trunk (#5) that could be defective and prevent the module from getting power. If filter is clear and fuel pump does not activate, either the fuse, module or pump is defective unless as BCP notes, the connectors or wiring is defective. Advise what the wiring and connector test reveals please?
What EXACTLY does the 2003 Jaguar XK8 X100 Fuel Pump Control Module do?
