Tdi hard cold starts

My AHU TDI is having trouble starting in the cold. It was about 30 earlier today when I started, which is hardly even cold and it took about 10 seconds of cranking. But every time I start after that first start, it instantly starts. And when it's warm out, like in the summer it starts instantly. I replaced all four glow plugs recently, and put the GPs on their own system with a push button. I held the button for probably about 15 seconds and it helped none at all. Starter is almost brand new. I got the static timing as close as I could with the *stupid* tensioning method for the AHU, and I set the dyamic timing dead on with VCDS. Injection quantity is good, although I wouldn't think that would affect starting. When I replaced the head gasket I checked compression and that seemed to check out fine. What I'm thinking the problem is fueling somewhere. I noticed while it's running, the clear fuel line will have a fairly constant stream of bubbles. I replaced the fuel filter with the new thermostatic part and new o-ring. So maybe I did it wrong. I used an ALH filter which has a different T-stat tee than than the AHU so I wasn't able to get the fuel lines all the way on, so maybe there is air coming in through there? I've also noticed that there's a constant drip of fuel coming from somewhere.. so maybe a bad injection pump seal??

I think that if you put in matching filter/tee, either the '98 version or the later one and fix the leaking seals on the pump your problems with go away.

The fuel system on a diesel must be sealed completely and without air infiltration, so yes there's a problem is you used a ALH filter with an AHU thermo T. They are incompatible.

You have to get the air out otherwise you'll continue to have these starting issues. I would suggest you get the correct filter (MK2 or Mk3) and that will likely solve your problem.

Steve

Steve Addy said:

The fuel system on a diesel must be sealed completely and without air infiltration, so yes there's a problem is you used a ALH filter with an AHU thermo T. They are incompatible.

You have to get the air out otherwise you'll continue to have these starting issues. I would suggest you get the correct filter (MK2 or Mk3) and that will likely solve your problem.

Steve

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Well I used the ALH filter with the ALH Tee, I was pretty sure the ALH filter was compatible, no? I tossed everything from the old filter

The constant fuel drip could cause the IP to lose prime. Cold weather may just be a coincidence.... you may have the same issue even if warm out.

No clue about A4 filter compatibility, but I’ve used A2 filters that don’t have any thermo T, without issue.

-Todd

Bubbles in the fuel line are almost certainly the cause. You need an air-free stream of fuel.

If you continue to have issues, I had an intermittent hard start or extended crank or no start with a bad relay 109.

Denig said:

Well I used the ALH filter with the ALH Tee, I was pretty sure the ALH filter was compatible, no? I tossed everything from the old filter

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That's fine if you used the T from ALH with the filter, no problem there, but if there's a stream of bubbles in the line then air is getting in somehow.

On the AHU thermo T there is no o-ring, that comes with the filter. On the ALH thermo T there needs to be an o-ring because it no longer comes on the filter. VW reversed the setup for some reason I do not know why.

At any rate if you can eliminate your leakage you will be fine. If however as Todd said you have a drip that will also contribute to your hard starting issue.

Good luck!

Steve

garciapiano said:

Bubbles in the fuel line are almost certainly the cause. You need an air-free stream of fuel.

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I very recently replaced the fuel filter on the wagon. I used the correct filter and have a steady stream of bubbles, yet the car starts and drives fine. Just saying....

-Todd

The cold weather certainly contributes to the issues, because it starts up instantly, on the first crank every time, when it's warm. Maybe I should try the A2 filter?

I remember when I first bought the TDI it was still fairly chilly out.. probably about 40 or so and I had no trouble starting, so it's clearly due to the maintenance that I've been doing. I sure hope it's something easy like the fuel filter..

ToddA1 said:

I very recently replaced the fuel filter on the wagon. I used the correct filter and have a steady stream of bubbles, yet the car starts and drives fine. Just saying....
-Todd

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I have bubbles in mine too Todd and I'm using a Mk2 filter currently. I haven't taken time to try and locate the issue but my car is running ok for right now. I think though if it gets bad enough then the problems start.

After Thanksgiving, when the Dakota comes out of the garage for the winter (I hope) I'm going to go through and fix a bunch of little things on the wagon. Then if I feel up to it (or don't go to AZ for Jan-Mar) I'll get started with the maintenance work on the Jetta tdi.

Steve

With the previous filter, I was able to rid of the bubbles with a larger o-ring. I should go back and do this, but since the car runs perfectly, I didn’t bother.

-Todd