2000 Beetle TDI Randomly Dies

[maxfax]

I'm an IDI guy so I haven't really versed myself on these new fangled devil machines yet..

The car in question is a 2000 Beetle TDI sporting about 168K belonging to a buddy of mine..  He had it to a pretty reputable TDI guy with no luck so far..  Of course it never gave trouble when he was working with it.. Here's the poop..

Runs excellent when it runs..  But every few weeks is dies.. No warning, just looses power like it's outta fuel and dies.. Already addressed relay 109...

The first time it did this it was 50 degree F weather. I went and towed it to my place..  Got a P1248 out of it.. Pulled the return off the pump and cranked, no fuel..  Disconnected the inlet to the pump and put air pressure to the tank, slow trickle of fuel..  Pulled the line off before the filter, air to the tank, slow trickle of fuel.. Pulled the sender out of the tank and the screen had a bunch of crap in it..  Cleaned that out, inspected the pickup, blew out the line, replaced the filter and she ran for about a month.. I *think* it had around a half tank in it at this time..

The second time (4 weeks later) it did this is was -10 degrees F and 3 in the morn  .. Had the P1248 again. Went and got it, put in in the garage (heated) and dealt with it the next day.. Pulled the return line and cranked no fuel, pulled the inlet to the pump and put air to it, got fuel gushing out in a few seconds..  We chalked this one up the the fuel gelling..  And he started running I think the Power Serve stuff.. It had about a quarter tank of fuel..  

Third time, (3? weeks later) also around 0 degrees F, about a half tank of fuel,I towed it to the TDI guy. He replaced the filter, primed it and it ran fine..  Had the P1248 again. He drove it for 2 weeks with no issue.. And gave it back..

Here we are again, a couple weeks later, all the same symptoms, bled the fuel system, it runs great. I can't see anything floating about in the tank, I'm wondering if there could be random issue with the float on the bottom of the in tank unit, the one for the "anti slosh" not the gauge. Possibly after a bumpy trailer ride it rattles back up and all works?? I'm pretty sure the fuel gauge is reasonably accurate, I pulled the sender out and had a look down in there a bit ago..
 

[Quantum TD]

Are you sure your sending unit is good? Occasionally, the check valve inside them fails. Fuel runs back to the tank. On Jetta/Golf, you can see the air bubbles through the clear input line. Unfortunately, Beetle lacks that.

Since you've already had problems at that point, I'd keep looking there.

Otherwise, N108 valve as recommended by Ross Tech Wiki. But I'm not sure if it's available apart from the pump.

[745 turbogreasel]

I could see a 14 year old oring  having some shrinkage when its freezing and letting air in.

[maxfax]

745, Are you referring to the o-rings in the little "quick" connectors? Anything special about those? I was considering changing those for the heck of it as they are a few years old.. Although 3 weeks of subzero should have make them show themselves sooner and more frequently I would have though...

Quantum, I'm not sure if the sending unit is alright, that is sort of where I have been placing the blame as of late.. When I had it out to clean it I took the thing apart and looked it over (which means nothing some days) and even tried dunking it in and out of water to see of that valve on the bottom works.. (I dried it thoroughly before reinstalling!) Seemed to work fine every time, but then again it is at least working for 3 weeks out of the month..  

I wish I would have payed closer attention to the fuel level, but I'm pretty sure it has been at a half tank or less every time.. I'm trying to think what the terrain was like where it died, or rather just before..

I really wish these had the clear line to see what's going on, preferably running though the dash! I may have to do some rigging tomorrow. I know the other guy we took it to did have something rigged to the inlet looking for air and saw nothing, but I'd bet it sat in his warm shop all night too..

[Toby]

You have a biological problem. Nothing short of pulling the tank and cleaning ALL of the slime out of everything and then running Biobor or another biocide will keep the slime from coming back. It takes only a couple of tablespoons of the gunk to clog the sock and then you get no fuel. Often times the slime will sink back to the bottom of the tank when the engine quits allowing fuel to flow again so you can prime it and drive away until it clogs again.

In order to cure this "infection" you will need to pull the tank, drain it and pressure wash or preferably steam clean the inside and the pick-up.

I bought a really nice, very low miles Olds Cutlas Ciera with the last of the V6 diesels (which were very good engines) for a song because it was possessed by the devil. Ever since it was new it would starve for fuel and end up along side of the road. It had multiple IPs, GPs, filters, pickups, and 2 engines in its brief life before it was abandoned in its well to do owners garage with another bad motor. (Due to trying to get it fire with ether.) I built a motor for it and it did the same thing. I finally figured out that it was an intermittently clogged sock. I pulled that tank expecting to fine a bunch of goo...

I thought I had mis-diagnosed the problem because I only got 2 tablespoons of a black slimy goo off the bottom. I steam cleaned the inside of the tank and the pick up and dumped in some Biobor and all was well.

These can be a *** to figure out, so just drop the tank and clean it out COMPLETELY, then take it to the the car wash and hose out the inside with engine degreaser. Dump some Biobor in the first takful and you will be home free.

If you do not get all of it and use Biobor to keep it in check it will come back just like the moss does on your roof.

[maxfax]

Algae has been on my list of things to consider on this thing too.. I had a hell of a time with that on my Cutlass.. GM used a MUCH finer screen in the tank than VW did but I could still see it wreaking havoc.

However George and I got to talking today and discussing the time frame and fuel level.. It'd get going again, he'd fuel it up the next morn on his way to work and it would be fine till the next time it got below a half tank..  I ordered a sender so I guess we'll see what happens..  I think I still may drop the tank and give it a wash, pissy poor positioning of the fill spout on these things, would't be hard to get all sorts of crap in the tank (like snow  ) 

[Toby]

That is exactly what happens with a partially plugged sock. When the fuel level is high, they run fine. Get below 1/2 a tank and the sock gets plugged up. Is this because the concentration of algae is twice as high at 1/2 a tank or the fact that you have pulled 1/2 a tank of fuel through the sock already mostly plugging it up. I haven't a clue, I just know this is common with algae infestations.