What exactly does the "cold start" pull out do on my MK1?

[Pre95]

I understand that it attaches to the injection pump, and causes something inside to make the car run a hell of a lot better then normal, without adding smoke. Whats it do? I noticed today cruising the highway it allowed me to peg the needle on the rabbit which it was unable to do with the cold start pushed in.

[burn_your_money]

It advances the timing. It only has an effect up to about 2000 RPM (depending on your pump and it's condition)

It will have NO effect at cruising speeds

[lovinthedeez]

omfg .  cold start is actually german for "fast mode"

[Rabbit on Roids]

has no affect at cruising speed? if i leave it pulled and i drive around after its warmed up, it takes a little longer for the turbo to light and it seems like it takes some of the quick away.

[Vincent Waldon]

has no affect at cruising speed?

Correct.  The cold start handle moves the timing piston slightly, but by around 2000 RPM the piston is already moving on its own (due to increased internal pump pressure... aka "dynamic" advance) past where the cold start lever has pushed it.

[rabbitman]

has no affect at cruising speed?

Correct.  The cold start handle moves the timing piston slightly, but by around 2000 RPM the piston is already moving on its own (due to increased internal pump pressure... aka "dynamic" advance) past where the cold start lever has pushed it.

Makes perfect sense once you see the inside of a pump.

[Pre95]

has no affect at cruising speed?

Correct.  The cold start handle moves the timing piston slightly, but by around 2000 RPM the piston is already moving on its own (due to increased internal pump pressure... aka "dynamic" advance) past where the cold start lever has pushed it.

Makes perfect sense once you see the inside of a pump.

Hmmmm... this has me thinking my dynamic advance isn't functioning properly? Or possibly my pump timing is off a bit?

[lord_verminaard]

.. Or possibly my pump timing is off a bit?

Ding!  Winner. 

Brendan

[Pre95]

.. Or possibly my pump timing is off a bit?

Ding!  Winner.  

Brendan

Well SOB... I just had the timing belt & tensioner done but I am sure they locked in the timing where it stood instead of checking if it was all proper. Well, at least I know where the fault is....  Any easy way of setting the pump timing (not involving going full TDC on the motor, removing the valve cover, using a dial indicator, etc etc etc)?

[rabbitman]

has no affect at cruising speed?

Correct.  The cold start handle moves the timing piston slightly, but by around 2000 RPM the piston is already moving on its own (due to increased internal pump pressure... aka "dynamic" advance) past where the cold start lever has pushed it.

Makes perfect sense once you see the inside of a pump.

Hmmmm... this has me thinking my dynamic advance isn't functioning properly? Or possibly my pump timing is off a bit?

If your dynamic advance was far enough out of wack for the knob to affect it cruising it would run really bad, the cold start knob only changes the timing at idle and slightly above idle. If you have zero internal pressure at all rpm then the knob would change the timing at all rpm.

[Rabbit TD]

As rabbitman just mentioned, IF your cold start does affect the performance at cruising RPMs then it points to either internal pump problems or poor adjustment.  On the upside, when properly functioning and adjusted, there should be significant gains in both performance and economy.  I would start by checking and adjusting internal pump pressure.


Andrew

How do you actualy check and adjust the internal pump pressure anyway.  I know there is a pressure regulator in there but have no idea how it works or is adjusted or even if it's possible.  Or is this one of those things that has to be done on the expensive test stand?

[Vincent Waldon]

When www.vwdieselparts.com is back up have a peek there... there's an entire thread on internal pump pressure... you measure it with an oil pressure gauge and adjust it with a hammer.

I'd post the link but the site is down at the moment... usually comes back quick.

EDIT: here's the link: http://www.vwdieselparts.com/forum/viewtopic.php?t=5936&sid=76b741e42d5a2e19b2a8d6df2c2b9976

[Pre95]

Ok well after some tooling around and test driving I guess it really doesnt effect much @ cruising speed. It does seem to handle the up-hill struggles a little better but for now she is tuned at a comfortable level, with minimal smoke. For now I will leave well enough alone, I am not going to put much of anything else in to the 1.6 N/A as I have gotten the green light from the misses to start sourcing a 1Z TDI swap. More on that later...