Hello. Hoping an expert here can provide some insight. As I understand the 2005 XJR has two fuel pumps. One of which controlled by the REM (activation signal received from ECM) and the other controlled by Fuel Pump 2 Control module (activation signal received from ECM).

My question is do both fuel pumps operate in tandem being activated with the same duty cycle or is one a primary pump of sorts and the other activated only when deemed necessary?

Thank-you!

Brian

 

The way I understand it (And I had a S-Type R with the same setup) is up to 3000 RPM your running on one pump. At 3000 RPM the system commands the second pump to kick in because the fuel the SC engine needs ramps up quickly as the revs and the boost build. You DON'T want to ever starve a blower motor for fuel! That will cause a lean condition and you will roast the engine in seconds. So think of it as a safety system.

I don't know if the REM does this or not?

But Jaguar seems to have built in some kind of protection because we have seen a few cars that don't have any power from 3000 RPM and up when the second pump is not working. Also note only the SC cars have this setup. The NA cars usually use a jet pump which is only used to keep the fuel level on both sides of the fuel tank even. It does NOT feed the engine.

They need 2 fuel pumps because when the car manufacturer's moved the gas tanks up in front of the rear differential they had to fit the tank to that area. This caused the fuel tanks to act as if they had 2 separate compartments because the drive shaft runs thru the middle of the gas tank.

Are you having problems?
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Too add here, when the second fuel pump kicks in you will note fuel pressure rises from 50psi - 55psi to anywhere between 65psi - 75psi.

Another way to tell if your secondary fuel pump is kicking in, if hooked up to a scanner.

 

Thank-you both. I'm having a stumbling coming off idle under heavy load. The fuel pressure is dropping off while monitoring live data with the scan tool. Fuel filter is new and both pumps previously replaced mid 2023 with Amazon specials adapted to fit into the factory pump housings. I was going to replace just the one if they had separate activation points as you've both clarified they do, but have decided to buy a set of higher quality pumps to retrofit into the baskets to (hopefully) avoid future issue.

For further edification would it be safe to say pump 1 as labeled in the repair manual is activated at lower RPM and pump 2 as labeled activated at higher RPM?

 

Amazon specials may be your issue. The OEM pumps for the Supercharged vehicles are higher pressure units; specifically 3.5 - 5.0 bar.

You may be able to find OEM electronic fuel pump units - Pierburg 03T260/7.28177.01 but they are about $200 - $300 each, again if you can find them.

Your better bet may be to find a set of used fuel pump assemblies off of ebay.

Worst thing you want to do is have fuel starvation on a SC engine, which sound to be the problem.

Pump 1 is the main pump driven by REM and Pump 2 is driven by fuel pump module. I believe pump 1 (main) is on passenger side of car.

If you want - feel free to post the Amazon special you purchased. Again, output must be 3.5 - 5.0 bar. If they are any less, your asking for trouble.

Another possibility is your fuel rail is not holding pressure, but - there are no suitable aftermarket high pressure fuel pump unit drop in units available.

Some other part numbers you can look for:

Product Group Fuel Pump 7.22013.02.0

BMW Fuel Pump E39 (eBay auction 16146752368) - the auction is long gone but you may be able to get a part number or just type "BMW E39 Fuel Pump"

Hope the above helps.

 

they’re both being duty cycled

the pids are all in there you can check for yourself

 

Great info abonano! That fuel pressure tip is a good one especially if you don't have an SDD setup. I have seen those numbers on my old S Type but did not realize the higher pressure was telling me the second pump was actually working.

xalty can you tell us which PID's? I just looked at fuel pressure but my problem was the FPR acting up and my fuel pumps were OK. The error codes also pointed to my FPR.
Does a failing second fuel pump set a code?
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Please be aware, when you search for the pumps, that you need the fuel pumps that BMW fitted to the E39 M5. Only these will be able to provide the required pressure.

The pumps fitted to the E39s with smaller engines will not solve your problem, as described in older threads in this forum.

I installed these pumps in my MY2004 Super V8, and they work fine:

Best regards,

Thomas

 

Quick update. The pressure line from the pump located on the right rear (passenger side) which crosses over the span of the tank to the driver side had ruptured creating an internal leak in the tank. I ended up fishing a fuel submersible rated 3/8" line in its place. All seems well again. Thank-you all for the input.

Edit: I wanted to add a TIG filler rod acted as a good way to pull the new line across. The tank bumps up in the center for driveline clearance so pushing the line directly over would not work. I put a slight bend in the TIG filler rod as to angle upwards at the center hump and fed it into the tank from the passenger side until it hit the opposite side where the tank dipped down into the driver's side pump area. At this point I bent the end of the still exposed rod in my hand and used it as leverage to rotate the rod so the upwards facing bend inside the tank would face down. This allowed me to continue pushing it through to the other side. This was initially a trial and error process in which I attempted to use string trimmer line, 12 gauge wire, etc, but found the TIG filler rod to be the ticket.

 

No need for a rod, the openings to access the fuel pumps are big enough to get in with your arm and guide the fuel lines over the "bump" in the middle of the fuel tank.

At least it worked for me when I replaced the fuel pumps, I found it easier to remove the fuel pump assemblies without removing the lines from both units and risk to damage them.

Best regards,

Thomas

 

Whatever works to get the job done. My arms did not fit deep enough into the tank to feed the line over. I also believe the factory lines being more stiff than the line I used probably played a roll in your success.

 

True, you do what works best.