PWM Fuel Pump Control with Siemens/VDO Unit

[dmg210]

Hi guys,

I've come up with this wild idea of creating a rising rate fuel system using the Siemens PWM Fuel Pump Controller. 

The part number: 7W83-9D372-AA  (Jaguar XJR V8 - 2018 model)

At the moment the car has a returnless fuel system with an in-tank FPR fixed at 43.5psi. The car was originally NA although i did a turbo conversion about 10 years ago.

To take things to the next level, what I'm planning to do is install a larger fuel pump to overwhelm the stock FPR and then PWM control the pump. This way I can maintain stock fuel pressure during idle / cruise, quieten down the pump and reduce heat etc. During boost I can increase pressure (1:1) by speeding up the pump (in theory anyway). 

My old pump was around 160 Lph, the new pump I’m testing with is a 340 Lph from Deatschwerks.

The new pump has the PRV set at 100psi. With a raising rate FPR this should allow for around 50psi of boost (way more than what my little TD05-20g can handle)... One good thing about these aftermarket pumps they are rated for between 6v and 18v which seems a perfect match for the fuel pump controller I'm testing. I need to do a little more research and check if the 340lph is within spec in terms of max current draw etc. I also need to review the wiring specs (especially on the PWM side).

From initial testing:

Voltage at pump (engine running - FP Speed - Open Loop)
voltage    fuel pressure         duty cycle
4.8v          45psi                    40% (unhappy)
6.1v           47psi                    50% (sounds good, very quiet)
7.4v          48psi                     60%
8.6v          50psi                     70%
9.7v          52psi                     80%
10.7v        68psi                     90%
11.6v        65psi                     100% (loud AF)

Note: The duty cycle is backwards in the screenshot. 70% = low speed (6v at pump), 50% = full blast (12v at pump).

The stock FPR which sits inside the fuel pump housing. It seems to have a tiny little hole in the return line.

Testing base fuel pressure with the PWM output rigged up to the AP:

[dmg210]

Problem 1:

When testing under boost the fuel pressure seems to drop off... I thought at first maybe the fuel pump wasn't large enough so i switched from the Walbro 255lph to the Deatsch 320lph but it hasn't made a difference. I was expecting the larger pump to increase base pressure even further but that wasn't the case, it's still around 65psi with the pump at 100% duty cycle. 

To be honest I haven't seen this done before and i'm unsure if this is going to work... I'm just posting for ideas or advice  

Problem 2: 

I think I possibly have a leak on the fuel pressure regular hose as it sounds like I've installed a jet wash in the fuel tank. I wish i could see inside the tank whilst it's running... It could just be fuel shooting out the tiny hole in the return line that i can hear. I'm just worried it's leaking from the FPR hose clamp and spraying fuel into the electrical connections. To be honest i'm a bit stuck and I can't seem to find an example online of anyone else that has done this.

Questions: 

- What are the downsides of running 43psi base FP with 30psi boost? Can this be done safely? I'm not seeing any drop in fuel pressure.

- Could the stock FPR be completely removed? 

- From a safely aspect is there anything i've overlooked?