Starting problems fuel related (?)

[onesh0t]

Really weird thing. Whenever I fill up with diesel, the engine is literally coming to life after the second crank with absolutely no problems. Just as the fuel gauge passes half, the problems with starting start. It's fine with a warm start, however after leaving the car overnight one of the three happens:
1. The car starts with no problems and cuts off 2 seconds later. Then it takes about 7-10 seconds of cranking to start it, after which it works completely fine.
2. The car tries to start, but is kind of choking and slowly coming back to life, until it fires, after which it is fine.
3. The car starts, but the RPM starts dropping to about 500, sounds a bit dodgy, after which the ECU brings the RPM up to about 1300 for a second or two, drops it to the standart 1000rpm and it works fine.

I have absolutely to other symptoms while driving or after I have started it.

Can this be the fuel pump slowly indicating that it needs changed? The car has been fully serviced about 2.5 months ago, all the filters, oil, v-belt, cambelt. 130k on the clock. 1.9 tdi sport 100 bhp.

 

[coolypops]

You didn't fill up out of a barrel/drum did you?


All the symptoms your describing, other than that they only happen with the tank under half full, sound like a blocked fuel filter, but if it was only changed its doubtful it is...

Never had the fuel tank open in mine so not sure of the setup, but if there was a crack in the pump or somewhere (above halfway up the tank) it could be sucking air instead of fuel.

If you have see through fuel hoses under the bonnet it might be a good idea to get someone to crank/start the car and watch for air bubbles coming through the pipes...

 

[onesh0t]

Lol, BP is the only 'barrel' I use + millers.

The pipes look the same as here unfortunately, so won't be able to see anything:
www dot myturbodiesel.com/images/8p/audia3tdifuelfilter.jpg (sorry, can't post links yet)

Where is the fuel pump located in the mk4?

 

[coolypops]

well the one that I'm talking about is the one in the fuel tank.

As I said before I haven't had the fuel tank apart/out in mine so not sure exactly the setup, but the top of it should be visible from the top of the tank (clearly recognizable by the fuel lines connecting to it).

When did this start happening?

Have you checked for any fault codes?

It could also be that some other liquid got into your tank and is floating on the diesel, thus only causing a problem when under half full...

 

[onesh0t]

Funny you mention that coolypops, cuz i found it harder to start the car after I filled up at the local sainsbury's once (just felt convenient).

Straight after the service there was a similar problem and I gave it back to the garage, they said they've accidentaly got air into the fuel system when changing the filter, but apparently they got rid of that and the car seemed fine for a while.

The way I understand it, if they would have made a dodgy job of changing the cambelt, the problems would not be related to the level of fuel. The engine did squeak a bit after the vbelt and cambelt change, the garage re-lubricated everything for me and it went away after a week or two.

As well, whenever the car is full I don't really hear the pump priming the engine. The emptier it is, the louder the sound after turning the ignition.

I live in Northern Ireland - every time you give your car to a garage you say a prayer.

No, I don't have VAG COM.

 

[coolypops]

When you say you can hear the fuel pump priming the engine, I'm assuming you mean from the boot, yes?

I've never heard the fuel pump in mine...
Probably knackered...

Price a new fuel pump. If its cheap replace it, if not wait until it dies...

If your changing the fuel pump it's a good idea to clamp the fuel line near it before disconnecting it to minimize fuel spillage.


And I wouldn't use any supermarket fuels as they're of a poor quality (no additives and "watered down"/"stretched").
I read either here or on vagDrivers that using them voids some warranties but not sure if this is true though.

 

[onesh0t]

Yeah, the sound comes somewhere from inbetween the rear wheel and front driver seats, it sounds more like fluid is being pushed through a narrow pipe, only lasts around a second. It's definitely not a mechanical sound.

I'll give it a chance, if it will get any worse I'm going to change it. Weird enough, this morning it started absolutely fine with a quarter tank of diesel in it.

Yeah, I think it's Asda and Morrison's fuels that void the warranties on new VAG cars.


By the way, would a dodgy fuel pump give you poor performance/poor mpg? According to an application on my phone I average 48mpg with quite a bit of cold engine town driving, this time I was doing more motorway and have got 400miles to 3/4 of the tank. So mpg looks normal.

 

[coolypops]

If the injection pump (which would be in the engine bay) was knackered, it probably would,
but I don't think the pd engines even have these as the injectors are cam driven (someone correct me if I'm wrong).

But the one pumping fuel from the tank shouldn't.
It'll just die one day and leave you stuck somewhere.

Is the sound a whirring sound, a whooshing sound or a hissing sound?

 

[onesh0t]

I guess it could be described as whirring. It's like sucking on a straw when you're glass is almost empty, but heavily insulated and much lower. I can record it tomorrow and post it in the evening.

 

[coolypops]

Did you get it sorted?

 

[onesh0t]

It sorted itself weirdly enough. I've been purposely driving with low fuel to evaluate. I'll keep a close eye on it though. Someone suggested old fuel lines to me as well. If they're not 100% they can be sucking in air when the car is not running for a while. Apparently quite common in Audis and since Seat is the cheapest of the VAG group I might be inclined to believe they're not using any better parts than in Audis

 

[coolypops]

good to hear.

I'd love to know what was causing it though...