Well whilst pondering about my glowplug/relay problem I thought I would change the fuel filter as well.
I do not suspect the filter to be the cause of the hiccupping when driving but one never knows. Now in the past has started up after not too much cranking, not this time. I have filled the filter with diesel and pumped fule from the tank using a pump then quickly reconnected hose. I can crank for ages with no luck. If I disconnect the fuel supply line and turn the engine over should there be fuel coming out? Because there is not. Mind you I thought the filter full of fuel would have run the engine if only for a short time.

The pump in the tank does NOT push fuel to the engine.
The HP fuel pump on the engine includes a lift pump which sucks fuel from the tank up through the fuel filter and then back to the tank.

The JLR recommended method is to insert a hand ballon pump in the line coming up from the tank and attach to the inlet side of the fuel filter. The hand pump then sucks up fuel and pushes it through the filter to the engine and back around to the tank.
This way all the fuel is filtered.

You can hear bubbling in the tank as air is pushed through. The bubbling stops and the balloon goes firm when all the air has been pushed through.

AKAIK if there is any air in the HP lines, then HP pump cannot generate enough pressure and the ECU then wont allow the engine to start. Jules

"Mind you I thought the filter full of fuel would have run the engine if only for a short time."

Not if there is any air in the HP lines - engine is prevented from starting if HP fuel pressure is low Jules

I had done that with the hand pump between tank and filter inlet. Then put it on the outlet to the HP pump and sucked fuel in through the filter. Gave it one more try and she started. Left running for 10 minutes or so then tried again. Started but took time so am assuming air in there and will disappear eventually. Interesting to know that is the HP pump that gets fuel to the engine so assume this mechanical one only does the leveliing of the two sections of the tank. That would account for no fuel
when the pipe from the tank disconnected and cranked over nothing appeared.

The engine lift pump generates a negative pressure and if there is a leak, fuel doesnt leak out but air gets sucked in.

Could this be the cause of your hiccupping ?

There was a thread on this a while back - IIRC someone inserted some clear tubing and observed bubbles entering the fuel line. Jules

Bogart wrote:

I had done that with the hand pump between tank and filter inlet. Then put it on the outlet to the HP pump and sucked fuel in through the filter. Gave it one more try and she started. Left running for 10 minutes or so then tried again. Started but took time so am assuming air in there and will disappear eventually. Interesting to know that is the HP pump that gets fuel to the engine so assume this mechanical one only does the leveliing of the two sections of the tank. That would account for no fuel
when the pipe from the tank disconnected and cranked over nothing appeared.

The information is all in the free JLR manual.

Click image to enlarge

Which I am currently going through

jules wrote:

The engine lift pump generates a negative pressure and if there is a leak, fuel doesnt leak out but air gets sucked in.

Could this be the cause of your hiccupping ?

There was a thread on this a while back - IIRC someone inserted some clear tubing and observed bubbles entering the fuel line.

It could be anywhere on the lines going from tank to HP pump (via the fuel filter) - the lift pump is sucking all the way from the tank. Jules

But its slightly more complicated because a varible amount of the returning fuel (now warm) is recirculated in the fuel filter to preheat the fuel being sucked up from the tank.

pg 1589 Jules

Last edited by jules on 2nd Nov 2024 3:18 pm. Edited 1 time in total

The return line will have a positive pressure though. Jules

Bogart wrote:

jules wrote:

The engine lift pump generates a negative pressure and if there is a leak, fuel doesnt leak out but air gets sucked in.

Could this be the cause of your hiccupping ?

There was a thread on this a while back - IIRC someone inserted some clear tubing and observed bubbles entering the fuel line.

Is this the line from the tank or the return line?

Hi, just my thoughts. The nearest filter inlet to the engine is the one to suck fuel through the engine pipework. I was just remembering, I filled the filter with a syringe first, and checked the drain was closed. The wire controls the heater sensor.
Once running, run at 3000 revs to clear air bubbles. Its in the manual. Power UK have a bit on how to change the filter. You know what its like when one looks at the thing from the front, not the back, its an age thing.

Is there any advantage in always having a full tank?