I think I know what the problem is and I think I know how to fix it. But before I start wrecking my car, I thought I would check first!

2004 MkI 1.9TDI ALH

Symptoms are sometimes there is a lack of power somwhere over 2k (if I put my foot down not a great deal happens, but acceleration lower in the rev range seems OK). Also starting when cold can be a bit difficult.

I think both of these issues are due to air in the fuel line. When the car is running I not only see air bubbles, but at times nearly half the width of the pipe seems to be air not fuel. I recently changed the fuel filter and am now thinking to have a look at the strainer in the tank.

Any other suggestions?

Did you have the problem before you changed the fuel filter?

A common problem (especially with aftermarket fuel filters) is poorly fitting o-rings on the valve on the top of the fuel filter. Also, sometimes the o-rings don't get replaced when the filter is replaced.

My car has always had some air in the clear bit of pipe on one of the fuel lines.

mine too, i think your problem lies elsewhere. Maf, sticky turbo veins, n75, Coolant temp sensor

Doubt that air is the problem

Thanks for replies. I know some air is normal - I'm wondering if my amount is excessive. When it is running there are what look like completely fuel free areas of the fuel line, not just some bubbles. I will check VCDS for codes again. I've heard of the MAF giving similar sorts of problems so may poke about with that. In the meantime are there any quick checks for air leaks and such that anyone would recommend?

if there was i would imagine poor starting would be when warm too.

The clear pipe should be free of air. Anything much more than small bubbles are a problem. OP states that 'When the car is running I not only see air bubbles, but at times nearly half the width of the pipe seems to be air not fuel'. If this is correct, then a piston stroke may be compressing nothing but air.

maybe then bleeding at the injectors by cracking the top nuts?

maybe then bleeding at the injectors by cracking the top nuts?

It won't help as the injection pump will be forcing more air into the hard pipes to the injectors

The way I usually tackle air in the fuel line problems, is to insert a piece of clear tube on the input to the fuel filter. If there are no bubbles entering the fuel filter, there should be no bubbles leaving it.

If there are no bubbles coming from the tank, I just go ahead and replace the o-rings for the valve on the filter with genuine ones and replace the hose clips with 13-15mm JUBILEE FUEL LINE HOSE CLIPS see http://www.ebay.co.u...=item3c9cf2709b

It's very rare that it doesn't fix the problem

An error code to add to the mix:

1 Fault Found:

17965 - Charge Pressure Control: Positive Deviation

p1557 - 35 10 - - - Intermittent

I will have a Google and see if I can find out what that means. I will get some clear tubing leading into the filter as well - nice tip!

That is an overboost fault - sticky vanes in the turbo are the common cause for this. Although n75, MAF, CTS and vacuum issues can also cause this (and maybe to a less degree the MAP sensor). Once the car does this, it will drive in limp home mode until the ignition is cycled. Like this it will struggle to get over 2.25k and drive like a piece of a junk. I find the best way to induce the the fault is to accelerate hard up a hill in 2rd or 3rd gear. Generally you will feel a slight stutter and the car will hold back (and then maybe keep pulling to the next gear change and then it will have no performance and need the ignition turning off and back on again (us pros get used to do this when moving - don't engage the steering lock, otherwise you might crash though!)

Quick test is to disconnect the vacuum pipe between the n75 and the actuator on the turbo and suck on it. If you can get the actuator on the turbo to move smoothly then the vanes and control ring are probably ok. If sticky, you might find Lofty's Mr Muscle trick works, otherwise the turbo might need to come off and be cleaned (time consuming rather than taxing).

In that case I go back to sticky vanes being PART of the issue causing limp mode!

Search Mr muscle vnt turbo treatment. Costs a few quid and has sorted many a sticky turbo.

Overboost! Could be sticky vanes in the turbo. Look on the Ross tech wiki for more info on that fault.

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I think I can rule out the sticky vanes problem as the car has a new (reconditioned) turbo. Also, I don't think the car gets into limp mode (I had that problem before I changed the turbo), rather there is a noticable lack of power at a certain rev range. Given that there is a turbo fault, then I will check all the hoses - hopefully that will fix things.

I'm thinking that this error is a separate issue from the air in the fuel line, so I have two things to play with now. What fun.

Try pushing the turbo actuator and see if it moves freely, just to check its not sticky vanes.

I think I know what the problem is and I think I know how to fix it. But before I start wrecking my car, I thought I would check first!

2004 MkI 1.9TDI ALH

Symptoms are sometimes there is a lack of power somwhere over 2k (if I put my foot down not a great deal happens, but acceleration lower in the rev range seems OK). Also starting when cold can be a bit difficult.

I think both of these issues are due to air in the fuel line. When the car is running I not only see air bubbles, but at times nearly half the width of the pipe seems to be air not fuel. I recently changed the fuel filter and am now thinking to have a look at the strainer in the tank.

Any other suggestions?

if it's a non pd egine and there is no in tank pump there is a "strainer/pick-up" mod on Fred's if all else fails

if it's a non pd egine and there is no in tank pump there is a "strainer/pick-up" mod on Fred's if all else fails

Fred's? Um...

It is a non pd engine.

dodgy MAF maybe if you think your turbo is ok......

forums.tdiclub.com I think it was Andy pandy's sender mod

forums.tdiclub.com I think it was Andy pandy's sender mod

I think this is the one:

http://forums.tdiclub.com/showthread.php?p=647602

A cheap fix that seems to work. I wil take a look.

I think that you need to ascertain what the turbo is boosting at compared to what it should be boosting at and see if it the power loss occurs immediately after an over boost. Logging block 011 on a test drive with VCDS should give you information.

Thanks - I will definately log block 011.

Progress! I've just had a look at the turbo. Despite this being a recently replaced refurb, I can barely move the actuator. It doesn't feel lumpy or gritty, but is very, very stiff. If I disconnect the hose from the N75 and suck very hard it barely moves.

When I changed the turbo I cleaned out the EGR, intake manifold and intercooler. Once I put everything back together tremendous amounts of smoke and oil were being dumped out of the exhaust. This cleared pretty quickly but I'm wondering whether it was enough to clog up the new turbo.

So I'm going to give the Mr Muscle treatment a go.