Tdi still drawing air

Langers · Sep 2, 2011

So after replacing the fuel sender unit and ensuring no leaks at that end, my 110 200 Tdi is still drawing air into the fuel system. If I loosen the bleed screw on top of the fuel filter housing with the engine running, there is a constant flow of bubbles ejected.

So assuming we can rule out the sender, where else could the air be being drawn in from??

JNOAKES · Sep 2, 2011

Pipeline may be to obvious but you could rig up divert line to the sender outlet line then back to the return pipe with a clear hose of equal length to the filter. In other words a big loop. There with the electric pump running for a short time see if your producing bubbles. That way you can replace the old pipe if necessary.

Langers · Sep 10, 2011

Cheers for the reply. I have now replaced the entire line from tank to lift pump, using new 8mm nylon pipe, compression fitting and union. Problem is still there

So after replacing fuel sender/pickup, fuel line, lift pump, lift pump to filter pipe, and filter itself, I am at a complete loss as to where this air is getting in.

The only thing I can think of is replacing the mechanical lift pump with an electric one, but I don't know if that would do any good.

Also the problem seems to have gotten worse with the new fuel line, engine will idle (slightly lumpy) but when revved it will rev for a couple of seconds then die down and basically stall

landroverjack · Sep 10, 2011

Does it happen more when the tank is full or empty?

landroverjack · Sep 10, 2011

Ive had problems fitting that damn sender unit in mine and it makes a really crap seal. Sometimes the fixing ring can get jolted round i think when off road so double check its all sealed.

pos · Sep 10, 2011

Interesting... I'm sure you'll know about a similar saga that I have been having with my 200tdi. I replaced the pickup pipe, fuel line to lift pump, lift pump, fuel line to filter head, filter head, fuel line to injection pump, injection pump, injector pipes, injectors and the spill rail and I still struggle with the lumpy idle problem every so often (although it is becoming less frequent at the moment). I know that the problem is still air in the fuel, because - like you, I find air in my fuel if I slacken the bleed bolt on top of the filter head but I can make no sense of how the air is getting in. It can only be happening in a few ways:

1) Low fuel in tank, sloshing about, creating bubbles which are drawn into the fuel system.

2) Hole on elbow of new pickup pipe (it's not a hole on the straight length because the fuel level in the tank does not have any effect in my case).

3) Air leak at union between pickup pipe and nylon fuel pipe.

4) Air leak at intake side of lift pump.

Technically speaking, the fuel system is under pressure beyond the lift pump outlet BUT, when the engine is off, there is nothing to say that air will not find its way in if a union is not tight further down the fuel line (after the lift pump pump). It won't necessarily leak fuel out where air is find a way in either. If this was the problem however, you would usually find that engine performance increases after a short while of driving and any air that has crept into the system has been expelled. Does yours get better after a drive? Mine certainly does.

In your case, if there is a constant flow of air at the filter head, even after a drive, it can only be the case that air is finding its way into the system before or at the lift pump. If however your lift pump has failed and the fuel is being drawn up from the tank solely by the injection pump, the air leak could be at any of the joins, or even at the filter head its self (cracked / warped / slack blanking plug or bolt) prior to the injection pump inlet.

I would suggest that you check your new lift pump is pumping (you'll know if diesel is purged from the bleed bolt at the top of the filter head) and perhaps bypass the lift pump to see if it makes any difference with the engine running solely on the injection pump. If there is no improvement, then you know that air is still getting in between the pickup pipe and the lift pump inlet. How is just as much a mystery to you as it is to me when you have replaced and double checked everything. Do you have pictures of your entire fuel setup?

-Tom

Karlos28 · Sep 10, 2011

Try making some kinda bodged swirl pot? Glass jar with 2 holes in the lid, feed to your lift pump to the bottom, from the tank in the top.. Just to see if it helps? You could move it between components to rule them out aswell..

Langers · Sep 10, 2011

landroverjack said:
Does it happen more when the tank is full or empty?

Not sure about that, I don't generally have more than half a tank in her though so it's possible it would go away if I filled it up

If it did I would be annoyed though, seeing as the sender is brand new, it shouldn't be leaking.

pos said:
Interesting... I'm sure you'll know about a similar saga that I have been having with my 200tdi. I replaced the pickup pipe, fuel line to lift pump, lift pump, fuel line to filter head, filter head, fuel line to injection pump, injection pump, injector pipes, injectors and the spill rail and I still struggle with the lumpy idle problem every so often (although it is becoming less frequent at the moment). I know that the problem is still air in the fuel, because - like you, I find air in my fuel if I slacken the bleed bolt on top of the filter head but I can make no sense of how the air is getting in. It can only be happening in a few ways:

1) Low fuel in tank, sloshing about, creating bubbles which are drawn into the fuel system.

2) Hole on elbow of new pickup pipe (it's not a hole on the straight length because the fuel level in the tank does not have any effect in my case).

3) Air leak at union between pickup pipe and nylon fuel pipe.

4) Air leak at intake side of lift pump.

Technically speaking, the fuel system is under pressure beyond the lift pump outlet BUT, when the engine is off, there is nothing to say that air will not find its way in if a union is not tight further down the fuel line (after the lift pump pump). It won't necessarily leak fuel out where air is find a way in either. If this was the problem however, you would usually find that engine performance increases after a short while of driving and any air that has crept into the system has been expelled. Does yours get better after a drive? Mine certainly does.

In your case, if there is a constant flow of air at the filter head, even after a drive, it can only be the case that air is finding its way into the system before or at the lift pump. If however your lift pump has failed and the fuel is being drawn up from the tank solely by the injection pump, the air leak could be at any of the joins, or even at the filter head its self (cracked / warped / slack blanking plug or bolt) prior to the injection pump inlet.

I would suggest that you check your new lift pump is pumping (you'll know if diesel is purged from the bleed bolt at the top of the filter head) and perhaps bypass the lift pump to see if it makes any difference with the engine running solely on the injection pump. If there is no improvement, then you know that air is still getting in between the pickup pipe and the lift pump inlet. How is just as much a mystery to you as it is to me when you have replaced and double checked everything. Do you have pictures of your entire fuel setup?

-Tom

Hi Tom, cheers for that, lots to go through there. I have seen you post about your problem before, and indeed I found SSL Diesel parts from one of them.

I know for certain that my lift pump is good, plenty of pressure there.

My problem is characterised by power loss across the rev range, but particularly at high revs where it becomes jerky and reluctant. No difference before or after driving, always get the same amount of air coming out of the bleed screw.

I will post pictures tomorrow, but there's not a lot to see.

pos · Sep 10, 2011

Langers said:
Not sure about that, I don't generally have more than half a tank in her though so it's possible it would go away if I filled it up If it did I would be annoyed though, seeing as the sender is brand new, it shouldn't be leaking.

Hi Tom, cheers for that, lots to go through there. I have seen you post about your problem before, and indeed I found SSL Diesel parts from one of them.

I know for certain that my lift pump is good, plenty of pressure there.

My problem is characterised by power loss across the rev range, but particularly at high revs where it becomes jerky and reluctant. No difference before or after driving, always get the same amount of air coming out of the bleed screw.

I will post pictures tomorrow, but there's not a lot to see.

Right then - you may have just opened up the potential for something else. Have you had a really good look at the inside of your fuel tank? I removed the pickup pipe (I know your setup is a little different) and used a bright torch and a magnetic extension to pickup bits of rust and ****e from the bottom of the tank - there was actually quite a lot. If it just so happens that there is something being sucked into or across the opening of the pickup pipe, the lift pump will simply draw air in from the weakest part of your system such as a fuel hose join or a union for example. That will instantly create a drop in vacuum below the air leak and an adequate flow of fuel will not be drawn up from the tank because it is easier to draw air in from somewhere else. It might be a good idea to try a bottle of diesel on a short length of pipe (no more than 30cm) directly feeding the lift pump or the fuel filter head.

-Tom

jamesmartin · Sep 10, 2011

i use a snap on suction pump with clear bowl and tapered rubber nozzle to push into pipes and test by sucking fuel through,working forward ,maybe you could make or borrow similar,have you just two pipes on filter lift pump to filter and filter to injection pump

Langers · Sep 13, 2011

pos said:
Right then - you may have just opened up the potential for something else. Have you had a really good look at the inside of your fuel tank? I removed the pickup pipe (I know your setup is a little different) and used a bright torch and a magnetic extension to pickup bits of rust and ****e from the bottom of the tank - there was actually quite a lot. If it just so happens that there is something being sucked into or across the opening of the pickup pipe, the lift pump will simply draw air in from the weakest part of your system such as a fuel hose join or a union for example. That will instantly create a drop in vacuum below the air leak and an adequate flow of fuel will not be drawn up from the tank because it is easier to draw air in from somewhere else. It might be a good idea to try a bottle of diesel on a short length of pipe (no more than 30cm) directly feeding the lift pump or the fuel filter head.

-Tom

Definitely going to try out your bottle/short pipe idea tomorrow. Luckily I have lots of 8mm nylon pipe left over. Should help me narrow it down a bit. Determined to beat this problem! Will update as I go...

pos · Sep 13, 2011

Langers said:
Definitely going to try out your bottle/short pipe idea tomorrow. Luckily I have lots of 8mm nylon pipe left over. Should help me narrow it down a bit. Determined to beat this problem! Will update as I go...

Let me know how you get on. I am getting a lot of air in my fuel at the moment, which is particularly annoying on hills

pos · Sep 14, 2011

Made any progress?

Tdi still drawing air

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