Diesel starting problems, air in fuel line?

[Hembrowr]

Hi, I have a ‘98 (R reg) Diesel 1.9L VW polo that has done around 110K miles.

However I recently changed the fuel filter on it and straight away it started to have problems starting when the car is left for 8hours or so.

The symptoms are when I try to start my car in the morning, I have to hold the key over and stomp on the gas pedal. Eventually, it roars to life with a big cloud of blue smoke out the tailpipe, and then runs fine all day and with each consecutive start.

I have a gut feeling that maybe I have air in the fuel line, but don’t know how to bleed or remove it.

Does anyone know how to do this or have any advice or experience on with a similar problem.

For info in the last 30K I have replaced all 4 glow plugs, starter motor and in last 6 months the air filter so feel it not any of these components.


As an aside last week I bought a fault code reader for it(hoping not to find a problem with the fuel injectors) but cant find where to plug it in, with the Haynes manual (No. 3500) not being any help!

As always members, thanks in advance for your help.

[kenney]

Since the fault started after you replaced the fuel filter .i think the control valve (on top of the filter)has been damaged,or the o-ring on the bottom of the valve is damaged

[Hembrowr]

Hi Kenny,

Thanks for replying to my question.

Didnt think of that and will give it a look, hopefully it will be that simple!

Many Thanks

[Hembrowr]

Just to update other users i checked the o ring on top of the fuel filter and it appears fine.

The independent garage appears to of cured half the problem as I had my diesel injectors replaced and it has stopped the big cloud of blue smoke on start up and now starts ever time no problems. Refurbished injectors cost £50 each with 50quid labour (total bill £257).

However when its cold it still 'chuggs' for the first 5mins of driving then fine all day. Yet to pin down this problem but at least half cured the problem.

Hope the info is of use to other users.

[Scampy]

I had similar problem on my wife's car. Ended up taking it to a diesel specialist who told me he had experienced the same symptoms on a polo, rebuilt the fuel pump, only to find the fault was with the connection on the fuel filter. I believe this part is a "thermostat" which allows the diesel to be heated, but it was letting air in. He supplied me with a different fuel filter and I removed the offending part and joined the fuel hoses together. After that I had no starting problems

If you look at the clear fuel hose near the filter when you do a cold start you might see air bubbles which cause your starting problems

[Hembrowr]

Hi Scampy thanks for replying,

The clear fuel line (after the fuel filter that connects to the fuel injector pump) does have air bubbles when i first start it up but unclear how I am to stop this, could you explain again please.

Many thanks

[Scampy]

Hi Scampy thanks for replying,

The clear fuel line (after the fuel filter that connects to the fuel injector pump) does have air bubbles when i first start it up but unclear how I am to stop this, could you explain again please.

Many thanks

The air in your fuel line will cause your starting problems and needs to be eliminated. I had 2 1.9 AEF diesels but only one was a bad starter and it had air in the fuel from the filter.
I went to a diesel specialist who told me to change the fuel filter to a Volkswagen filter. This I did but still air in the fuel supply. In desperation I went to another specialist (Clwyd Precision Diesels), who knew what the problem was. He had a non starting Polo brought to his premises. He removed the fuel distribution pump and overhauled it, put it back on and had the same starting problem!!
He came to the conclusion that the air was being drawn in from the "white plastic fitting" on top of the filter, even after trying to seal it (the filter is always under vacuum so will draw air in if it can). His answer was to remove this fitting altogether and join the hoses together. This allows the fuel return to go directly to the fuel tank and not be recycled via the filter. You do, however, have to replace the filter with one that has only 2 connections, ie one in and one out. A specialist diesel company should be able to supply a Bosch one readily.
Once this modification had been carried out, I had no air in the fuel and no starting problems.
I also converted the other polo even though it started OK

Hope this helps!!

[Hembrowr]

Thanks for the clarification. On your advice i went to my local autofactors (Mill Autos) in taunton and explained what I required however got blank faces from the staff there.
I'm going to have to do some further research on where to get the fuel filter you mentioned, or even better if you have the part number it would save me lots of work!

Many thanks again

[Scampy]

Thanks for the clarification. On your advice i went to my local autofactors (Mill Autos) in taunton and explained what I required however got blank faces from the staff there.
I'm going to have to do some further research on where to get the fuel filter you mentioned, or even better if you have the part number it would save me lots of work!

Many thanks again

Don't go to an autofactor, go to a diesel expert and explain to him. Bosch make the fuel filter

[kenney]

Why can you not just fit a new valve? it has a function