Land Rover Repair: 98 Disco startup, vise grips, max pressure

Question
John,

So, check this out - I put a pair of vise grips on the return hose, and with my gauge in place, turned the key on. The gauge showed nothing for a moment, then moved right up to 50 psi, held for a moment, then dropped to 5 psi. This is with the key "on" I then started the engine - it took a couple of tried - and it ran a bit rough, but was again showing 50 psi. As soon as I shut off the engine, it again dropped to 5 psi. So, this indicated the pressure is being lost on the pump/filter side - thoughts?

Thanks,
Michael

Answer
Hi Michael,

As mentioned if pressure builds with the return clamped off its the fuel pump regulator.  

Fuel is going somewhere.  Drop in pressure is too fast.  Check valve may be gone in pump.

Here's one final test:  

With the Return line clamped, turn key on and pressurize the fuel system.

When the max pressure is reached, quickly clamp the fuel supply line. Fuel system should be completely closed.  IF the pressure drops - it's an injector(s).

IF no change - has to be fuel pump (maybe a check valve).  Did you check/monitor voltage at pump?

Regards,
JohnMc