1.4 Tdi Struggling to start..

[DaveySprocket]

I got everything hooked up and found a break in the rain to give it a go. I meant to take a video, but apparently I didn't

Not the best setup maybe but I couldn't find many hose clamps the right size. Anyway, there was no fuel coming through at all

So I had a look at the filter housing, and it was weeping slightly.. I'm pretty sure the sender is good, so I will take out the filter and see what is going on. @rotifer looks like you might be right about the drain plug doh


Anyway very conveniently my hose clamps just arrived. I don't care much for US Pro tools, but these were the best I could find for a reasonable price.

It'll be slightly embarrassing if this is a problem I have created, but what the heck, I will be highly delighted to get to the bottom of it.

Many thanks for all the input from everyone, it is much appreciated

 

[DaveySprocket]

I took the filter off and it is clean as, I would have replaced it anyway if I had a spare one, but don't yet. I decided to have another go at the drain plug situation. I drilled out the centre of the original plug to 10mm, so I could put a bolt through it, and then put an o ring on the bolt. This seems like a much better solution, so will see.

I've just realised I could have put an o ring under the bolt head as well.. I'll maybe do that.

I'm not going to get too excited about this being the cure, but at least now with the clear hoses in place I can see straight away what is going on.

I won't do anything else until tomorrow now, but be sure to stay tuned for the next instalment

 

[CrispyEdd]

No fuel coming through to the pump?! worth looking at the pipe from the tank see if it actually leaks any diesel inot the filter at all, thus working the problem backwards toward the tank? Im sure you have the diagram form on here for the correct pipe to choose from the pile of pipes under there !

 

[DaveySprocket]

No fuel coming through to the pump?! worth looking at the pipe from the tank see if it actually leaks any diesel inot the filter at all, thus working the problem backwards toward the tank? Im sure you have the diagram form on here for the correct pipe to choose from the pile of pipes under there !

There was fuel in the filter, but that doesn't mean too much really.. It could still be a few different things, the tandem pump has maybe given up completely, or the sender is blocked again, or a pipe is blocked.

Oh I forgot to mention, I saw the battery was fully charged, so couldn't resist putting it back in and trying again. Still no fuel at all getting to the tandem pump..

I will hook up VCDS Lite later and see if I am getting any codes on that.

 

[DaveySprocket]

I tried scanning the fuel pump and got this message..

I didn't really know what I was doing though (as usual), so I will do a VCDS Tutorial later to try and educate myself..

Hmmm maybe this is because the pump is entirely mechanical..

 

[CrispyEdd]

I tried scanning the fuel pump and got this message..
View attachment 120547
I didn't really know what I was doing though (as usual), so I will do a VCDS Tutorial later to try and educate myself..

Hmmm maybe this is because the pump is entirely mechanical..

Correct pump has no electrical connection. It doe however run a vacuum o if you take pipe off back and run it maybe you'll have your finger sucked to prove its working.

I have no idea if this is sensible so don't blame me if it sucks the car inside out

 

[DaveySprocket]

Correct pump has no electrical connection. It doe however run a vacuum o if you take pipe off back and run it maybe you'll have your finger sucked to prove its working.

I have no idea if this is sensible so don't blame me if it sucks the car inside out

I've never been too worried about "sensible" Edd

I was just thinking that I have a vacuum pump, so I can try sucking the fuel up from the pipe into the tandem pump, to see if that works..

 

[CrispyEdd]

I've never been too worried about "sensible" Edd

I was just thinking that I have a vacuum pump, so I can try sucking the fuel up from the pipe into the tandem pump, to see if that works..

There you go, we've muddled yet another option between us

 

[George Hogg]

Or you can feed the fuel pump from a little jar of diesel beside the engine….

 

[TAABVW]

The clear pipe on the feed pipe has introduced lots of air. You will need to bleed the injectors before it will run.

 

[DaveySprocket]

Well what a lovely warm Southerly breeze we have here today, bloomin marvellous!

Today I decided that seeing as I have had trouble with the sender in the grey car, I would swap them over, to try and eliminate that from the equation. I wasn't expecting the sender in the blue car to be so filthy though, it was as bad as the grey one was when I first took it out.



There was a big blob of gunk in the bottom of this one as well.

You can see how blocked the mesh on the bottom of the pickup was

So I cleaned it all up and put it in the grey car. I dropped some Marine 16 into the tank of the blue car and put the other sender back in there.

I tried starting the blue car and it fired up immediately, so nothing much wrong with the sender.

So back to the grey car, I hooked up my vacuum pump to the fuel feed, and once I realised I had forgotten the rubber seal in the container cap , it pulled fuel through, but with loads of air as well. The container is only small so I had to do it a few times to get a steady flow of fuel through, but there always seemed to be some air in there too.

So next I tried putting the tandem pump feed line into a little jar of diesel, and the pump drew the diesel up okay.

Realising that I hadn't really proved anything conclusively, as there could either be air getting into the lines somewhere, or the tandem pump could be down on power, with a flat battery, rain starting, and other duties calling, I gave up for the day.

The clear pipe on the feed pipe has introduced lots of air. You will need to bleed the injectors before it will run.

Doh

I don't doubt you are correct, but how is it you can take out senders and fuel filters, which must surely introduce air into the system, and the car will still start okay?

 

[DaveySprocket]

I've been having a read of some other threads, and it seems like I should reconnect the feed pipe to the tandem pump, then use the vacuum pump on the return line to the tank, to draw fuel all the way through. I'll try that tomorrow and see if it does the trick. If I can't get a clean flow of fuel coming through, then it will probably be time to start looking for a leak somewhere.

 

[Goddas]

Hello.
I can only assume that the tandem pump has failed internally as the reason for your fuel tank to be black inside. It has to be engine oil. This design of pump is rather weak in terms of the seal arrangement and the cover plate flexing/distorting. Often they leak fuel or oil externally too, I have replaced many on A4's that I have owned in the past. On the A4, from 2004 they got a different pump design which is a direct replacement and has a cast alloy cover rather than the shabby steel plate on our ones. The updated pump will fit perfectly on any 1.9 or 1.4 PD engine as far as I am aware.
My new A2 is running ok but the tandem pump is leaking so I will be replacing it with a used one of the newer style pretty soon.
For example, I'll be buying one on ebay part no 038 145 209 Q, it looks like this

Note that the cover is completely different when searching for one, I expect that the Q at the end is the key but there will likely be other letters for this style so the part number above is not definitive.

IIRC correctly, oil can also get into the fuel system from the injector seals but I think we should cross that bridge if it comes to it! Tandem pump is no1 suspect at this point.

Apologies if I have covered old ground here, all the best...Dan

 

[TAABVW]

Well what a lovely warm Southerly breeze we have here today, bloomin marvellous!

Today I decided that seeing as I have had trouble with the sender in the grey car, I would swap them over, to try and eliminate that from the equation. I wasn't expecting the sender in the blue car to be so filthy though, it was as bad as the grey one was when I first took it out.
View attachment 120599

View attachment 120600
There was a big blob of gunk in the bottom of this one as well.
View attachment 120602
You can see how blocked the mesh on the bottom of the pickup was
View attachment 120603
So I cleaned it all up and put it in the grey car. I dropped some Marine 16 into the tank of the blue car and put the other sender back in there.

I tried starting the blue car and it fired up immediately, so nothing much wrong with the sender.

So back to the grey car, I hooked up my vacuum pump to the fuel feed, and once I realised I had forgotten the rubber seal in the container cap , it pulled fuel through, but with loads of air as well. The container is only small so I had to do it a few times to get a steady flow of fuel through, but there always seemed to be some air in there too.
View attachment 120601
So next I tried putting the tandem pump feed line into a little jar of diesel, and the pump drew the diesel up okay.

Realising that I hadn't really proved anything conclusively, as there could either be air getting into the lines somewhere, or the tandem pump could be down on power, with a flat battery, rain starting, and other duties calling, I gave up for the day.













Doh

I don't doubt you are correct, but how is it you can take out senders and fuel filters, which must surely introduce air into the system, and the car will still start okay?

Because the air hasn't reached the injectors.

The tandem pump will bleed air out of the fuel feed line (into the fuel return line) quite effectively (but not infinitely) when the engine is running. By doing this it keeps air out of the injectors. So when you introduce air into the system at the tank there is plenty of air free fuel in the feed pipe and filter to start the car. Once started the tandem pump bleeds out the air as it should.
If any air is at the tandem pump when attempting to start, this gets into the injectors and will result in either a non start (requiring suction bleeding) or a very difficult start as the tandem pump tries (and often fails) to bleed out the air while starting.

 

[DaveySprocket]

Hello.
I can only assume that the tandem pump has failed internally as the reason for your fuel tank to be black inside. It has to be engine oil. This design of pump is rather weak in terms of the seal arrangement and the cover plate flexing/distorting. Often they leak fuel or oil externally too, I have replaced many on A4's that I have owned in the past. On the A4, from 2004 they got a different pump design which is a direct replacement and has a cast alloy cover rather than the shabby steel plate on our ones. The updated pump will fit perfectly on any 1.9 or 1.4 PD engine as far as I am aware.
My new A2 is running ok but the tandem pump is leaking so I will be replacing it with a used one of the newer style pretty soon.
For example, I'll be buying one on ebay part no 038 145 209 Q, it looks like this

View attachment 120607


Note that the cover is completely different when searching for one, I expect that the Q at the end is the key but there will likely be other letters for this style so the part number above is not definitive.

IIRC correctly, oil can also get into the fuel system from the injector seals but I think we should cross that bridge if it comes to it! Tandem pump is no1 suspect at this point.

Apologies if I have covered old ground here, all the best...Dan

Hi Dan, that's all very interesting indeed. It seemed strange having all that black stuff in the tank, and up until now I was working on the theory that it was diesel bug related, but the fuel itself does seem clean enough. Curiously both my A2's have the same black stuff in the tank, one has done 125,000 miles and the other 175,000.

Please report back when you have confirmed that the newer type of fuel pump will defintiely work on these engines, as I am sure plenty of folks will be interested.

Thank you for your input, it is very helphul to hear from an experienced professional, I myself have just enough knowledge to be dangerous

Cheers, Dave

 

[DaveySprocket]

Because the air hasn't reached the injectors.

The tandem pump will bleed air out of the fuel feed line (into the fuel return line) quite effectively (but not infinitely) when the engine is running. By doing this it keeps air out of the injectors. So when you introduce air into the system at the tank there is plenty of air free fuel in the feed pipe and filter to start the car. Once started the tandem pump bleeds out the air as it should.
If any air is at the tandem pump when attempting to start, this gets into the injectors and will result in either a non start (requiring suction bleeding) or a very difficult start as the tandem pump tries (and often fails) to bleed out the air while starting.

Okay understood, thanks for explaining

 

[TAABVW]

I have been inside the fuel sender on 8 or 9 TDI's and every one of them had a black coating inside. It is entirely possible that all of them had a bit of oil seepage past the injectors but all of them did many tens of thousands of trouble free miles afterwards. Whatever the reason for the black coating I think it is a red herring when it comes to non starting.

There is an excellent thread on here where someone took apart a tandem pump (with photos) and iirc concluded it was unlikely/impossible for oil to contaminate fuel by pump/seal failure.

 

[Deleted member 20348]

@Little Dog has done a write up on this subject

1.4 Tdi LUK 038145209E tandem fuel pump rebuild.

While addressing a starting issue recently I noticed my fuel pump had leaked. I couldn’t find the exact source of the leak but coolant pipes under the pump smelt of diesel and were softening and ballooning. I have bought a comprehensive seal kit but have no instructions for fitting. Could...

www.a2oc.net

 

[Little Dog]

@Little Dog has done a write up on this subject

1.4 Tdi LUK 038145209E tandem fuel pump rebuild.

While addressing a starting issue recently I noticed my fuel pump had leaked. I couldn’t find the exact source of the leak but coolant pipes under the pump smelt of diesel and were softening and ballooning. I have bought a comprehensive seal kit but have no instructions for fitting. Could...

www.a2oc.net

If you take this approach check the black pressed steel cover for flatness and signs of wear. If there are any issues don’t rebuild; it will leak again as mine did.
Edit, the second failure may not have been due to the cover and its gasket failing https://www.a2oc.net/community/index.php?threads/how-does-a-tandem-pump-work.51970/page-2
Also the pump to head gasket in the thread is the type not to use. There are no blobs of blue silicone, it leaked oil.
I have used genuine Audi gaskets with a Bosch pump and I have had no diesel nor oil leaks. Elring also produce a gasket recommended by other members but I have no experience.

 

[Deleted member 20348]

I took the filter off and it is clean as, I would have replaced it anyway if I had a spare one, but don't yet. I decided to have another go at the drain plug situation. I drilled out the centre of the original plug to 10mm, so I could put a bolt through it, and then put an o ring on the bolt. This seems like a much better solution, so will see.
View attachment 120542View attachment 120540View attachment 120541
I've just realised I could have put an o ring under the bolt head as well.. I'll maybe do that.

I'm not going to get too excited about this being the cure, but at least now with the clear hoses in place I can see straight away what is going on.

I won't do anything else until tomorrow now, but be sure to stay tuned for the next instalment

Jumping back a bit the following information may help those of you who are considering doing your own diesel filter (with the plastic housing) service in the near future.

In 2018 purchased @depronman fuel filter housing drain plug for its functionality and long service life. In essence it's one of the cheapest fixes when diagnosing and repairing a 1.4 TDI thats struggling to start ., I am a fan of no cost, low cost repairs

The link below begins with the FSI filter but further into the thread they discuss the Tdi filter housing.

fuel filter how to change

my 1.6 fsi has a small inline umbrella fuel filter on the off side engine bay next to the brake fluid reservoir i was thinking it might be a aftermarket additon does anyone else have this on there car, i think i will replace it or remove it any thoughts?

www.a2oc.net

As always, good luck!