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I have written in a couple of times before requesting help with a cold start problem on cold days. Here is what I have written before:
"I would appreciate advice on a problem I have had for the last 3 winters. When I try to start my '94 940 (Bosch ignition) on a cold morning (<32F here in Texas), it requires extensive cranking, sometimes 5-10 minutes, before the engine runs on its own on all cylinders. Once it reaches this point, it runs flawlessly - never missing. Prior to this point, it stumbles and misses while cranking until it finally dies. This never happens in warmer weather. The fuel pressure appears to be fine and I replaced the fuel pressure regulator thinking that this might solve my problem - but it didn't. The crank sensor was replaced a couple of years ago when I had a problem with the car missing under idling and driving conditions so I don't suspect this. New wires and plugs at 95K, new distributor cap and rotor at 126K, car currently has 150K. I replaced the I checked the Maintenance FAQs but didn't find a lot of information specifically associated with this phenomena. Any advice would be appreciated!"
It was suggested by a couple of folks that this problem could be associated with vacuum. (Recently I have had a problem where the air flow from the upper registers of the AC system diverts to the lower registers and defrost registers upon accelerating which lends credence to the vacuum problem theory.)
What I would like to know is this:
1. How does an inadequate vacuum (e.g. vacuum leak) lead to a starting problem? Does this impact the fuel flow to the injectors perhaps through the fuel pressure regulator? I don't get a lot of excess fuel odor from the exhaust when cranking the engine.
2. (Naive question) Where in the engine is the vacuum generated and where is the main vacuum line from this vacuum source located?
3. Where are the most likely sources of vacuum leak if this is my basic problem? (I have been pointed to the lines leading to and from the vapor cannister as a potential culprit.)
4. Where does the vacuum line which influences the air flow in the AC/heater blower penetrate the firewall into the passenger compartment? (My idea is that after locating this line, I would pinch it off in case a vacuum leak in the passenger area is causing the cold start problem.)
Thanks to all in advance,
Ron
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