As part of my ongoing stalling issue research, I decided to replace my 22 year old fuel pumps and fuel pressure regulator as preventive maintenance.

In addition to that, I decided to add two check valves to supplement the existing check valve(s) that already exist since that also is known age related failure point.

I have an XJR which has two fuel pumps, and the description of the Denso fuel pumps is that they have a check valve in the nose/nipple of the pump itself. And when I disassembled one of my old pumps, I confirmed this is true.

So I assumed that the check valve function for the fuel system was the check valve(s) in the fuel pump. So when I added secondary/backup check valves, I did so by placing the secondary/backup check valves in the fuel line immediately past the pump(s) outlet inside the fuel tank.

However I've now seen a few posts that suggest the check valve may be somewhere else on the fuel injection supply line. I've heard that the check valve is on the evaporative cap/flange, or maybe up under the tank, or?

I can say for certain that there is no check valve in the evaporative cap/flange on top of the fuel tank as that only has a pass-through for the fuel pump wiring, and an evaporative (vapor) fitting which does not pass any liquid fuel. And all fuel lines enter/exit at the bottom of the tank anyway.

So, my question is: Can anyone confirm where the fuel supply check (backflow preventing) valve is located?

I'd like to make sure I've placed my secondary/backup check valves in a place where they actually help. But honestly, even if there is another failed valve downstream from the pumps and my new check valves, the location I've got the new valves would work too since the only upstream outlet on the line are the pumps themselves.

Thanks.

 

Since the fuel pumps have NOTHING to do with the EVAP flange I would suggest that the check valves are indeed in the pumps themselves!!!!!!!!!!!!!!!!!!!!


bob

 

I'm glad you found my post so exciting

But yes, that's my initial conclusion as well, but thought I'd check.

BTW, this is some additional information on the Denso fuel pumps, noting their integrated check valve:

Products | Fuel Pumps

 

Al,

All the countless hours Bob spent uploading Jaguar documents and he didn't even mention that the answer to your question is in one of them! See pdf pages 60 and 61 in the manual at this link:

Jaguar Engine Management Systems Self-Study Training Course 801S

Yes, the fuel pumps have a check valve in their outlets:



But there is also a check valve where the fuel return line enters the tank to prevent reverse flow and help the jet pump keep the surge pot full so the fuel pumps don't suck air when the fuel level is low
:


And here's a close-up diagram of the return line check valve:



Cheers,

Don

 

Thanks Don, great documentation.

What's interesting is that the only "check valve" called out in the diagram is a different check valve than what I'm referring to. The check valve called out in the diagram on the return line as it enters the tank wasn't even one I was aware of, but I assume is there to keep fuel from leaking from the tank if the return line is disconnected.

But the documentation about the pump(s) does mention their check valve(s) in the their description for the supply line, so I feel good about the placement of my backup/secondary check valves in that location to help maintain fuel pressure when the engine is off.

.