Just removed the RH in tank pump to fit a replacement using the existing frame… The pump was not working , despite 12v at the pumps terminal. Electric change over switch working for pump and fuel guage.
Surprised when removed old pump to discover only half of the internal rubber connection hose from pump to support frame out tube was intact, but quickly disintegrated on touching. So would not have worked any way.
Clean the one way valve in the outflow fuel line, and the bottom of tank rust / debris etc
There is very little info in the Jaguar repair manual cover the in tank pumps used on the late series 2 cars therefore my question:
Does the pump run continuously once the IGN is switched on.If not how does the pump stop pumping if car does not need fuel at carbs. The carb float will shut off fuel however does the pump
still pump ,or is there a check valve within pump to shut down based on fuel pressure setting?
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A fuel pump safety relay is fitted, Al - usually oil pressure controlled; the pump will not run unless engine is running and producing oil pressure, or with the key to ‘crank’. However, the pumps themselves are made for continuous running…
External pumps are usually pressure regulated; they stop pumping when the needle valve closes and fuel pressure rise to a preset level. There are also check-valves to prevent pressure from the running pump feeding into the other. However, there are varieties - and, as you say; submerged pumps are inadequately covered in the manuals…
Thanks Frank for your reply and advice. Seems to make sense there needs to some sort of fuel cut off if the engine does not run. I can hear the fuel pump start when you your turn the key to crank the engine. I will look into a oil pressure feed into the fuel pump safety/cut off relay. The electrical schematic for the in tank fuel pumps is rather limited ,so i will try and trace the actual wiring in the car from the fuel relays.
Still curious how the system works to control the amount of fuel required at idle to that required at open road speed given there are no pressure regulators.
Al
A pressure switch is mounted to the bloc, Al - nominally a green/yellow wire…
The carb needle valves are usually perfectly adequate to maintain float levels against fuel pump pressure, which is the all important factor - with correct fuel levels carbs vary the fueling as required…
The main difference between ‘pressure cut-of’ pumps and plain ‘continuous’ pumps is that the latter run all the time - but both are equally dependent on properly functioning needle valves for proper engine behavior at all speeds.
It may be added that pumps used with carbs runs at unnecessarily high pressures, sometimes forcing the needle valves. Some 5 psi pump pressure is generally adequate, while 15 psi is not unusual for ex factory pumps…