SC cold start cranking time

[Aurel]

Hi there,

When I go to start my SC in well below freezing temperatures, it usually takes about 5s cranking to start all the six cylinders. If I stop cranking after 1 or 2s, it will only fire on 3 or 4 cylinders, and may stall, or catch up. As soon as it has run, it will restart instantly.
I was curious if others have experienced that, if it is normal behavior or if it indicates something wrong with my freshly rebuilt motor.

[psalt]

Hello,

You have a lean condition at cold start up. If you have CIS it is probably caused by a combination of conditions. The system is designed to have the CSV supply the extra fuel to fire the cold engine and the cold control pressure to supply enough fuel to make it through the transition to cold running. Below freezing you may need a 4.0:1 AFR to make this transition. When new, the system was calibrated so that as soon as the engine fired, the mixture was rich enough to make the transition. Vacuum leaks, pressure drops, compression drops, cam changes, will alter the height of the air flow sensor and throw off the calibration. Your extra cranking is dumping more fuel from the CSV to compensate. The later SC also put in internal airbox plumbing to improve the fuel distribution at cold start and the factory changed the cold start calibration several times in SC production. You can try richening up the mixture a bit and if you have vacuum retard, disconect it, it causes cold start stumbles. On later SCs there is a VW temperature switch that can be substitued for better cold start behaviour. With a non stock engine, you are on your own to find the best compromise settings of timing and mixture for you temps.

[Aurel]

Very interesting, thank you Paul. Next time I start it, I`ll try disonnect the vacuum retard. The engine is mostly stock, except for DC15 cams. I had the mixture adjusted by a pro to pass emissions, and I suspect he set it too lean. Seems like an easy fix.

[Paulporsche]

In addition to psalt's excellent description you should search this, as it is extremely common in CIS cars. Check Jim Williams' website on CIS and/or get the Bentley manual or Probst's book for more CIS info. The Warm Up Regulator on these cars can be adjusted to provide extra richness when needed, and the Auxiliary Air Regulator must be functioning correctly to keep revs up during warmup.