Re: Hot Start Kit project - Saab Saab Model 99 Bulletin Board - Saabnet.com
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Re: Hot Start Kit project
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Posted by Gary Stottler [Email] (#1463) [Profile/Gallery] (more from Gary Stottler) on Sat, 27 Mar 2021 05:02:37 Share Post by Email
In Reply to: Re: Hot Start Kit project, LJB, Fri, 26 Mar 2021 17:54:44
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75-77 cars had basically a "Mark 1" set of CIS hardware. 78 and later had "Mark 2" which fixed a number of weaknesses. Those changes included a larger accumulator, a replaceable check valve, and a check valve in the Control Pressure circuit. Those changes were all intended to prevent the system losing pressure after it is turned off which at the end of the day is the culprit on the hot start problem - as the pressure in the system falls, the heat from the engine causes the liquid fuel in the 4 injector lines to boil which fills the lines with vapor instead of liquid. Since the injection system works by volume, the next attempt to start it results in injecting a fixed volume of vapor to each cylinder instead of the same volume of liquid fuel - of course that's not enough fuel to start the engine, and it takes a long time to fill the lines with liquid again. You could chase this problem around for a long time and unless all the leak paths were pretty much perfect you would have hot start problems. The hot start kit was a result of Saab acknowledging that customers were unhappy about multiple attempts/big bills to replace all the expensive Bosch components that could be causing the problem. Injectors that are leaky can also be a factor although unless all of them are leaking down you will generally be able to start, just on fewer than 4 cylinders. The last go-around I had with this was in my '77 EMS - I ended up putting the larger accumulator in and that improved although did not completely eliminate it. I think ethanol gets more of a bad rap than it deserves, I've always run it in my cars and never seen any problems that I would attribute to that. But if it evaporates/boils at a lower temperature than gasoline I suppose it could make this problem worth. I don't think it's the underlying cause though.

_______________________________________ Gary Stottler


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