FUEL PRESSURE FALL

**miles** · 19th September 2011, 06:20 PM

My Disco V8 is getting harder and harder to start especially when it is cold.

Sometimes it will start first pop. Other times I can turn the engine over until the battery goes flat. It turns over ok and the engine tries to start but just fails keep firing and burst into life.

I have done most of the common checks. New plugs etc etc . Yes I have spark, and yes the fuel pump is working.

I have checked the fuel pressure with a pressure gauge and the fuel system pressurizes alright.

When I turn the ignition switch to II The ECU turns the fuel pump on for a few seconds and then turns it off as it should do (Priming the system). The pressure comes up to 2.8 bars,but soon as the ECU turns the pump off, the pressure drops quickly to zero (as shown on the gauge). Not even 0.5 is showing.

When I start cranking the engine the pump comes on again and pressurizes the line (the gauge flucturates as it appears the injectors are opening).

From what I have read in the Landrover workshop manual I gather,that when the system is primed (ignition position II), the system should hold that pressure for a period of time after the ECU has turned off the pump.

In various sections of the workshop manual, they warn you about "residual pressure" and depressurizing the system.

If the system is supposed to hold this pressure for period of time, where is this inline pressure going?

My first thoughts is that the system has an injector stuck open?

What do you think?

Cheers

If all fails, jack up the door handles and replace what is underneath.

**PhilipA** · 19th September 2011, 06:42 PM

Maybe or the fuel pressure regulator is leaking or the non return valve in the fuel pump is leaking.
I would guess 2 then 1 then injector.

Pinch the return line with a pair of multigrips and see whether the pressure drops =Fuel pump.
Regards Philip A

**miles** · 21st September 2011, 10:13 AM

Thanks PhilipA for your reply.

I did exactly what you said to do.

Connected up the fuel pressure gauge again, clamped off the fuel return hose and turned the ignition to on.

The gauge shot up to 5.5 bars and stayed there.

Next I removed the clamp and repeated the procedure. This time the gauge went up to 3.0 bars and stayed there, dropping about 0.5 bars per minute.

24 hours later, the system is still holding about 0.5 bars pressure.

What ever it was - a stuck open injector example, it is now closing.

I now have the answer to my question. When the ignition is turned to on, the fuel pump is engaged and primes the system and turns its self off . When the starter is engaged there is still fuel pressure in the line.

So now for me - back to the drawing board.

Cheers

If you first don't succeed - then get a bigger hammer.