Hi everyone,

I have a 1998 Jaguar XJR with two fuel pumps. I think the second pump is for the supercharger. I'm planning to add another fuel pump for both the supercharger and the regular fuel pump.

I'm considering:

- Using Denso fuel pumps.

- Connecting the new pump with a T fitting to the existing system.



I need advice on:

1. Will the T fitting work for this setup?

2. Do I need to upgrade anything else for this to work properly?

Has anyone done something similar? Any tips would be great. Thanks!

 

You can only force so much fuel through the stock line. If you’re adding 1 or 2 additional pumps into the already 2 pump setup, you’ll have a 3 or 4 way battle between the pumps trying to cram all that fuel into the stock pipe and nowhere to go. Not only that, you’ll heat up the fuel much quicker and you’ll have evap codes having to run more wire into the tank that you can’t stop from leaking fuel vapors.

I replaced the Mickey Mouse (no name) fuel pumps the previous owner installed in my car with 2 Walboro 340 pumps. I replaced the stock fuel hose with the correct submersible ($$$) and a brass 3 way tee to connect the 2 pumps to the factory fuel feed pipe. I have no issues with fuel starvation running my mods.

 

Okay that makes sense what’s the best budget friend performance fuel pump I can run.

 

Fuel pump delivery is limited by the fuel pressure regulator ( 43 to 47 PSI on throttle up vacuum pressure ) and the pulse width ( open time ) of the injectors regulated by the ECU and the O2 sensors to keep the fuel trim ( mixture ) at target 0.0 %

Too much fuel delivery detected by O2 sensors ( too low O2 unburnt combustion gasses , yep some O2 needed for the Cats ) cuts back pulse width

The ideal mixture is 14.7 mass ratio, but the engine design regulation is different than that

This graph not the easiest to follow

Your 2nd fuel pump does not come on until 4000 RPM and drops out as it goes back through and off at 3200 RPM

 

The second pump is not really a "supercharger pump" but just an additional pump to cover increased fuel demand by the engine. When activated, it runs in parallel with the first pump in order to provide additional fuel flow (on hard acceleration, high speeds etc.). At other times, only the first pump runs. Adding another (third) pump to a system which already has an additional pump makes no sense as the two existing pumps are designed to well cover the maximum flow that the engine can require and have a very good margin above that. If the third pump is installed, and wired to run in parallel with the first pump, it would only cause additional return fuel flow from the pressure regulator (FPR) and may even cause the FPR to be overwhelmed causing increased fuel pressure on the injectors = engine running rich. The same would happen if the third pump is wired to run together with the second pump at the times when the second pump is "instructed" by the ECU to run.

Running sequences of the 2 pumps on SC engines:

1. At ignition "on" - Second Pump will run briefly (1-2 seconds) to prime the system.
2. During cranking and subsequent engine running - First Pump will run and continue to run alone until higher fuel flow is demanded
3. On higher fuel flow demand (hard acceleration, high speeds etc.) - First & Second Pump will run as long as the higher fuel demand is present (revert to First Pump thereafter)

 

98xjr, may I ask why you need more fuel pumps? What modification(s) have you performed or are going to perform?

I will say that if your fuel pumps are original or you aren’t sure what you have, I would definitely recommend Denso pumps with new pickup screens that fit the bottom of those pumps and a fuel filter.

 

Ok thanks