Cold start mystery

[greg lousy]

I crashed my pick up... My only car for the last 6 years... Frame is gone.

On the upside, I lucked into an 86 golf that I managed to pretty much steal because it had what turned out to be a glow plug wiring problem. The car seems to have been fairly neglected in all ways but the engine feels strong.
What I'm curious about is this... It starts great in cold temps... Maybe 2 second crank at around 20 degrees EXCEPT if the cold start cable is pulled. If it is pulled its either an unhealthily long crank or a straight fail. At idle, you hear marbling when pulled, none when not, which is exactly what you would want to hear AIUI.
So why could this be happening? Right now this is just a curiosity thing, as I'm just happy to be getting from a to b, but may affect future maneuvers and tweaking...
What do you guys think?

[Quantum-man]

Greg , does the car immediately perform as 'normal' [startingwise] if you change your mind and push the cold start back in? Or does the hard-to-start continue?
If it persists, I suspect air getting in through the cold start.
Any diesel coming from the pump or air bubbles appearing when cranking stops?

[greg lousy]

There were a few starts where it fired right up after pushing it back in. I haven't noticed any leakage around cold start seal, but I haven't really looked carefully.

Also, I may be off on my whole line of thought, as I think my glow plugs are burnt and I made the cold start observation when they were in the process of failing. I'll work it out then revisit the cold start cable thing.

[Fatmobile]

Sometimes the preferred method for starting a VW diesel is to crank with the cold start pushed in.
Then pull it after it starts. Especially with the MK2s, not so much with the Rabbits.
Sometimes advancing the timing causes the fuel to spray in before TDC and that pushes the engine backwards.
That's what it's supposed to do so the fuel gets compressed and warmed a little before ignition.

[surfcam]

Bentley has starting instructions. If the engine is warm or above 10C ? I think. The advance is to be pulled out. If it's stone cold and below 10C you leave it in and pull it out when it first catch's. I'm pretty sure this was written before low sulfur diesel so you have to find your own sweet spot. Or play with the little valve springy thing on the front of the pump but that's for more of a summer day.

[greg lousy]

Thanks, i didnt know that about the cold start... Maybe not so much of a mystery. I may have worked out the glow plug situation but it's hard to really tell because it's strangely 50 degrees out. I'll probably experiment with the cold start again once Im sure I have consistent glow plug action.

The mk1/ mk2 difference makes sense as the cold start feels like different specs than the pick up. Is it more of an advance? ..... Feels that way