I was preparing to set my timing so I got everything together and she wouldn't start. This is unusual. I'd just driven her the previous night and everything was fine. Ok. Fine. Look at the fuel pressure gauge. 18psi. Right. There's your problem right there. Pull the gauge. Pop it right on the fuel pump. 22 psi. Ok. Order one up. It comes in I switch it out and bam!19 psi on the rail. Now if I hadn't dead head metered the other pump I'd kick myself for not ordering a regulator instead. But the pump was weak as hell. And I'd straight wired it off the battery for the test. No chance of poor power supply. Battery is good and fully charged.

So, what's up? Too late to do tests on the brand new pump tonight. I have an early day tomorrow. Do I throw a regulator at it and see if that's what it wants this week or am I missing something?

 

Did you consider your fuel gauge is bad?

 

For giggles bypass the RH (inlet) regulator (easy to do) and see if anything changes. If the engine starts it's OK to leave the RH regulator bypassed if you want.

If no change I'd replace the LH regulator

Cheers
DD

 

Yes. But I plugged another gauge into it and they both agreed at 0 psi.

Perhaps a bad gauge. But it's been consistently accurate for me up to now. But I will pick up another.

I looked at both and considered their interchangeability. Since the left is crucial and the right o have no idea the purpose of I was going to swap them. Nope. How is the right easily bypassed? Looks to me like I need to make up a hose with the right fittings.

I'll replace the left with a new unit.

Is the right hand FPR failure mode not to just flow full pressure?

 

If the diaphragm in the LH regulator has failed you will have low fuel pressure.

 

The A bank and B bank FPFs are NOT interchangeable.
The point to measure pressure at is just before the A bank FPR. If the pump is producing more than 3 bars at the fuel pipe just before the A bank FPR, and you have poor pressure at the rail itself, then the B bank FPR is most likely the problem. If there vis insufficient pressure, but plenty at the pump, then it is blocked filters, or blockages in the feed pipes somewhere.
The A bank FPR is there just to damp out pulses from the pump. It can be removed with no noticeable chnages at all. On later V12s Jaguar deleted it.
Greg

 

Diaphragm not leaking. Fuel filter clean and clear. Sump pickup clean and clear. Tank and sump clean. Fuel flow through the system and return to tank all flowing.

Greg, are you saying meter before the first ( Right hand - B bank ) FPR to check pump pressure then if good and rail is low it's the A bank FPR? Makes sense.

Are both FPRs set to the same pressure? And what psi should they be holding with vac attached?

 

NEARLY The RH bank (USA passenger side) is the A bank. I am saying that it will be the B BANK FPR that is the problem (ie the USA driver's side FPR). The B bank is downstream of the rail, and that is the one that controls the rail pressure. I think you have just got the A and B banks mis-identified in your post.

No, the A bank one is lower than the B bank one. The B bank one should show 2.5 BAR (about 38 PSI). I suggest you bypass the A bank FPR.


Greg

 

If indeed you have fuel flowing through the return back to the tank at 19 psi. The FPR has to be shot.

 

Indeed I inverted them above. Thanks for the clarification. I'm going to check the new pump with a new gauge and I've ordered a B bank FPR. Locally I can get the a bank FPR from almost every parts house. They don't even know about the other one.

Edit: one other thing I should mention because it may have some bearing. I heard a unusual noise from somewhere around the middle of the B bank intake when I'd turn on the ignition without starting the motor prior to this issue. I drove it subsequently so it did not kill it. It was a buzz. Almost like the aerial motor lifting. Would sound for about the duration of the fuel pump running. After several instances ( searching for the sound ) it quit happening. This was one day prior to failure to start.

 

Bad regulator could make buzz with fuel rushing through. Sounds more and more like the FPR is your problem.

 

Bad gauge.

Not even able to articulate the feeling.

And then she started. Again, no words.