Cold Start Valve & Electrical Explanation
 

As of September 22, 2003 I became a proud owner of a 1981 Porsche 911 SC (factory Sahara Beige). I have two questions that I hope the experts here can help me with an answer.

My car averages 17.90 MPG (smooth highway driving) and I was under the impression that beginning in 1980 that these cars were rated at 29 MPG for the highway. I am using Chevron Premium fuel (91 octane). I have just replaced the Oxygen Sensor with no improvement. My first question is: what is the likelihood of the cold start valve leaking during normal operation / has anyone else found their valve to be leaking? I certainly do not wish to remove the valve unless there is a strong possibility that this could be at fault. The car starts well both warm and cold.

Second question concerns the Bentley 911 SC Service Manual: when looking at the wiring diagram, the letters "NCA" is listed connecting to the Oxygen Sensor. These same letters are used in many different areas of the electrical diagrams and I can find no reference to this in the legend. What does "NCA" represent?

:confused: :confused:

i hate acronyms so i cant help you there.

but my book list three possible causes of bad gas mileage:
leaking injectors, leaking cold start valve, and improperly adjusted air fuel mixture.

so line up the easiest first and work down the list. but i get crappy gas mileage, because i drive like a fool.

oh yea, i think you are supposed to post some pictures. hurry before the picture police show up.

Check your plugs. If the cold start valve is leaking, you most probably are running rich and your plugs will show this (dark and soory). Remember, a rich mixture will is not only caused by a leaking cold start valve, idle CO% and incorrect system and control CIS pressures will also cause a rich mix.

Sorry, don't know what NCA is either.

I think you can check the cold start valve for leakage the same way you test the injectors for the correct spray pattern. But I also read there are some worse symptoms caused by a leaky cold start valve than bad mileage. I'm not quite sure if I have experience with that or not though because checking mine for leaks is still on the to-do list. If i get motivated I'll look at the CIS trouble shoot book in a little while and post back. or hopefully someone with practical experience will post and teach us both something