Diesel fuel filter

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TCubed

Active Member
Posts
991
Location
Surrey
Hi chaps,

Part of 96k service is to replace fuel filter - it looks like an easy job according to rave, apart from one bit:

Refit
4. Ensure mating faces are clean.
5. Lubricate seal on new filter with clean diesel fuel.
6. Fit filter to filter head. Tighten securely by hand.
7. Remove container.
8. Slacken fuel feed union at fuel injection pump
using LRT-12-117.
NOTE: Position cloth over feed union to
catch any fuel spillage.
9. Reconnect battery negative lead.
10. With assistance, turn on ignition switch to
operate fuel lift pump.
11. When all air is bled from filter, secure feed pipe
at injection pump. Tighten to 14 Nm (10 lbf.ft)

What does that red bit mean? Can someone give me the confidence to do this, I'm nervous about ending up with air in the system and having to bleed...
Thanks :)
 
It's an injection pipe special extended C obstruction socket. Like an extended crows foot. A spanner does much the same job. Remember engine must be cold with glow plugs operative to enable fuel pump to run. It will only run whilst glow lamps are lit. Filling the new filter with fuel prior to fitting negates the need to bleed in most instances.
 
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OK, so use a spanner :) why are we slackening though? Do you just have to turn ignition on and off again to get the plugs and pump to run, or will the pump run until it's ready to start? When cranked should it take any longer to start than normal? Sorry for all the questions! :p
 
TCubed said:
OK, so use a spanner :) why are we slackening though? Do you just have to turn ignition on and off again to get the plugs and pump to run, or will the pump run until it's ready to start? When cranked should it take any longer to start than normal? Sorry for all the questions! :p
Click to expand...

You are slackening to allow the air inside the filter to be expelled, when air stops coming out nip up the union. There is fuel in the injection pump it should start but may peter out if you don't fill the filter with fuel. If you fill the filter with fuel the pump should self bleed. But it won't self bleed if the filter is empty. There is an HP pump inside the injection pump that supplies pre-injection high pressure fuel to the pump body controlled by a pressure relief valve. Any air inside the pump will be expelled through the relief valve and back to the tank via the spill return pipe. Contrary to what some people think spill fuel from the spill off pipes does not go back inside the injection pump it returns to the tank along the same line as the injection pump excess spill fuel. If you fill the filter with fuel then start and run at 2000 RPM for a couple of minutes it will self bleed.
 
wammers said:
You are slackening to allow the air inside the filter to be expelled, when air stops coming out nip up the union. There is fuel in the injection pump it should start but may peter out if you don't fill the filter with fuel. If you fill the filter with fuel the pump should self bleed. But it won't self bleed if the filter is empty. There is an HP pump inside the injection pump that supplies pre-injection high pressure fuel to the pump body controlled by a pressure relief valve. Any air inside the pump will be expelled through the relief valve and back to the tank via the spill return pipe. Contrary to what some people think spill fuel from the spill off pipes does not go back inside the injection pump it returns to the tank along the same line as the injection pump excess spill fuel. If you fill the filter with fuel then start and run at 2000 RPM for a couple of minutes it will self bleed.
Click to expand...

Excellent info, I will do this tomorrow :) There may be an argument at the petrol station fillling a jug with diesel though!

I take it from the 2000 rpm bit that it will start happily with the fuel already in/near the engine, and then you're bleeding to make sure it keeps starting?
 
TCubed said:
Excellent info, I will do this tomorrow :) There may be an argument at the petrol station fillling a jug with diesel though!

I take it from the 2000 rpm bit that it will start happily with the fuel already in/near the engine, and then you're bleeding to make sure it keeps starting?
Click to expand...

There should be no need to bleed if you fill the new filter with fuel. Any trapped air should be expelled with the engine at 2000 RPM for few minutes.
 
Done :)
Filled filter with diesel, and she started right up - ran her at 2000rpm for a minute or so. Then put the remainder of the diesel in the tank - quite a bit of air came out when I opened the filler cap, so was that the air that was bled from the system?
 
TCubed said:
Done :)
Filled filter with diesel, and she started right up - ran her at 2000rpm for a minute or so. Then put the remainder of the diesel in the tank - quite a bit of air came out when I opened the filler cap, so was that the air that was bled from the system?
Click to expand...

Nope, there should not be any pressure in diesel tank. Make sure the breather is clear.
 
Datatek said:
Always a small hiss when I undo mine, I though that was due to the vapour trap required by emission regs. MR2 does it too.:)
Click to expand...

Maybe wrong Keith but don't think there is a vapour trap on the diesel. Petrols definitely. I have never noticed any air efflux on mine. But maybe there is a one way vent and mine is duff. Don't know for sure.
 
wammers said:
Maybe wrong Keith but don't think there is a vapour trap on the diesel. Petrols definitely. I have never noticed any air efflux on mine. But maybe there is a one way vent and mine is duff. Don't know for sure.
Click to expand...
Maybe it's an model year thing? Mine runs fine so it's not a vacuum in the tank.
 
TCubed said:
Mine's 2001 if that adds anything
Click to expand...
It won't be anything you have done on the service. I don't know where the breather is on the P38, on many cars is on the filler pipe.
I wouldn't worry about it as long as it runs OK. Oh mines a late 200o model so will likely be the same as yours.:)
 
Datatek said:
Maybe it's an model year thing? Mine runs fine so it's not a vacuum in the tank.
Click to expand...

There is a filling breather that comes off the fuel pump that goes up to the filler neck. There has to be some way that air can get into the tank or usage would cause a vacuum. Diesel does not give off vapour to the same extent as unleaded petrol, which is notorious for that. So the only thing i can think of is that the air vent is a one way affair allowing air into but not out of the tank. When running the engine, fuel is constantly being circulated back to the tank from the injection pump and will heat, causing it to expand. Maybe this is the reason for the gush of air when the cap is released. But as i say never noticed mine doing it.
 
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