D90 Fuel pump stays on - Defender Source
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Old January 23rd, 2014, 09:46 PM
Status: Offline
Jack Armstrong
1995 LR Defender D90
Join Date: Oct 2013
Location: Los Angeles, CA
Posts: 1
D90 Fuel pump stays on

Greetings from a new member! I have a client with a 1995 Defender D90
3.9L and after letting it sit for a few months, it won't start. All the dash lights work,
and no malfunctions are indicated. I checked for spark by pulling a plug wire and connecting to a screwdriver while gapping it to ground and cranking the engine...
ZAP.... yep spark is good!

Checked for fuel pressure, and there is no schrader valve on the rail, only an input, 4 driver side injectors, a sensor with 2 wires, the 4 passenger side injectors, and the fuel pressure regulator at the end of the rail. I connected my Fuel Pressure guage to the fuel return hose (thinking it was the supply line from the pump) and I discovered fuel coming out of the regulator, so I cleaned up the mess, and I put the Fuel Pressure guage on the output (overpressure) side of the regulator to find 72psi fuel pressure, when the fuel pump is on.

I thought, this looks TOO EASY.....just replace the fuel pressure regulator which is OBVIOUSLY BAD (lol) and allowing all my fuel to go back to the tank, without ever pressurizing the rail, and this 'ol D90 should be running again!......not this time!

After replacing the OBVIOUSLY BAD fuel pressure regulator twice with the same results, I'm stumped, and a little baffled, frankly!

So, please correct me if I'm wrong here, but when you turn the key to the "ON" position, the fuel pump is supposed to come on, pressurize the fuel rail to 33-36psi (within a few seconds...) and then once there is sufficient fuel pressure, is stops making the wirring noise (actually running) and it goes idle untill you turn the key from "ON" to "START" at which point the rail is pressurized, the ECM fires the correct injector while the mechanical distributor supplies the spark, and the cylinder fires, and you then need more fuel, so the pump delivers again etc, etc, etc, untill highway speed, at which point the pump runs almost constant, you just don't hear it with the road noise of a running vehicle!

When you turn the key to the "ON" position for this D90, the fuel pump NEVER stops running! The fuel is being sucked up from the tank going thru the pump, the fuel filter, going to the rail, going straight thru the fuel pressure regulator, and back to the gas tank!

As crazy as this sounds, I decided to contact tech support at "InterMotor Import Parts", the manufacturer of the fuel pressure regulator for Land Rover, to find out how it is supposed to work, and this is what they said:

This style of rail mounted regulator is designed to keep fuel pressure between 33-36psi on average(temp of fuel, engine, and overall heat may cause the varience). When connected to a vacuum source, in this case the plenum vaccum, during acceleration, depending on vacuum draw, fuel pressue can be increased 3-6psi, untill load returns to normal. Fuel at pressures above this, will be returned to the tank via the return line.

Since the engine never starts, (for lack of fuel pressure behind the injectors...) the only thing it looks like, is that when this D90 sat around for 3 months, somehow, the fuel pump became more powerfull(unlikely!) and is delivering soooooo much pressure, that it exceeds the capacity for the regulator, and the only thing it can do is to send the overpressure fuel back to the tank! Is there ANY other component to test here, or have I about got it covered? Does anybody have any suggestions besides, drop the tank, and replace the working (too well) fuel pump?
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