air in the diesel line

[jameslibra]

Ive got a UK spec 2.5 diesel D22 and the filter top manual pump just keeps pumping. It does not "stiffen up". When driving it stutters and farts mainly in third thruought the rev range, but seems ok in all other gears. Please help!

 

[Old.Tony]

I'm not sure there's a great deal of difference in the fuel systems between the recent 2.5L diesels - both being common rail, their pumps, filters etc should all be very similar.

That being said, I was strongly warned about removing the air from the fuel lines if I ever ran out of fuel. I was told to pump - for considerable amounts of time if need be - the primer bulb until it was very hard to press and then keep going a few pumps more to be certain I'd gotten the fuel up and through to the return lines.

I've honestly never done it so I can only give you the advice given to me. I was advised that air in the fuel system was harmful to the motor and that I should not drive it until I had removed "as much of that as possible". The problem is that air compresses much more readily than fuel, and can cause the pump to run dry (it's not a cheap pump!).

Here's the instructions from the D40 manual, which covers your exact problem:

Air Bleeding GBS000E2
After fuel filter is replaced and after fuel system components are removed/installed, bleed air from fuel line as follows:

Move priming pump (1) up and down to bleed air from fuel path.
When air is bled, pumping of priming pump becomes heavy stop
operation at that time.

Crank engine until it starts. Do not crank engine for more than 30 seconds.

If engine does not start, stop cranking and repeat step 1 above.

If engine does not operate smoothly after it has started, race it two or three times.

If air cannot be bled easily (pumping of priming pump does not become heavy), disconnect feed-side of hose between fuel filter and electronically controlled fuel pump. After that, operate priming pump and confirm that fuel comes out.

CAUTION:
Prepare a tray to collect fuel. Prevent fuel from adhering to rubber parts, especially the engine mounting insulator.

My next attempt on yours would be to give the primer a few more goes then give the engine some decent revs.

 

[Dave]

If I remember correctly James's Navara is a YD25DDTI non CRD motor.

Anyway replace the primer or put in a electric pump and do away with the primer.

Dave.

 

[nismo4x4]

i replaced me fuel filter today...and yes the pump kept pumping away...went hard then soft then hard then soft etc...after 2min pumping i thought surely thats enough and drove and seemed all ok...

 

[tweak'e]

i replaced me fuel filter today...and yes the pump kept pumping away...went hard then soft then hard then soft etc...after 2min pumping i thought surely thats enough and drove and seemed all ok...

not a good way to do it. as per the thread on how to change filters....remove fuel hose and pump primer till it pours out out the hose. that way you don't go filling the whole injection pump with air.

 

[jameslibra]

Found outwhere the air is getting in. It was obvious when is saw the pool of diesel under the tank. I need a new fuel sender.

 

[nismo4x4]

not a good way to do it. as per the thread on how to change filters....remove fuel hose and pump primer till it pours out out the hose. that way you don't go filling the whole injection pump with air.

hmmmm shit ayy...if i did have air would the motor start to miss? we drove about 100km on the weekend and seemed ok...hopefully in future

 

[tweak'e]

hmmmm shit ayy...if i did have air would the motor start to miss? we drove about 100km on the weekend and seemed ok...hopefully in future

once its running it should be fine but can take a while for it all to go.

the main problems of having air in the injection pump is these pumps are built to fine tolerances and require fuel for lube. when your trying to start it and its full of air it runs dry and wears rapidly.
also the pump ecu is on top of the injection pump, any air means the fuel dosn't cool the electronics and they soon cook. even air bubbles will do that.
what can compound it is if you do fuel filter change on a hot motor. the pump is hot and gets hotter from heat soak and you remove the fuel which is the only thing cooling it.

try to have as little air as possible go through the injection pump. these are NOT as forgiving as the old VE pumps.

 

[Old.Tony]

There is another good reason for not having air in the system, particularly with these high-pressure common-rail diesels that run much higher pressures than petrol engine, is that the air will compress much more than the fuel and when it releases its pressure, occupies a much greater volume. This can cause problems with fuel delivery.

Remember how letting the combustion chamber flood with fuel is bad, because of hydraulic lock? That happens because the fuel won't compress as well. Letting air into the fuel system where it's expected to be pure fuel is the opposite, and obviously negative, effect. Your brakes work the same: air in the lines will compress much more, meaning your pedal will travel much further in to achieve the same result.