Date: Sun, 29 Aug 1999 13:09:49 -0400
From: "Karlheinz G. Schoenfeld" <kschoenfeldnopsamhlink.net>
Subject: Re: 900 starting problem


Jim, Symptoms seem to point towards a leaking check valve at the fuel pump. What happens is, fuel pressure in the system cannot be maintained and essentially drops to zero over time. When you start from cold (a few hrs. or over night) the initial cranking fuel pressure is just enough for the cold start valve to produce a spray, but not enough yet to crack the fuel injectors, sometimes this is enough to keep the engine going, until the fuel pump has run long enough to bring the fuel pressure in the system up to normal, about 28 psi, I think. Now, if you try to start with an engine not cold enough yet, the thermo switch will not allow the cold start valve to operate, that's why you have to keep cranking for a while until the fuel pressure has built up. It is during this period when the engine wants to die. Also, when warmed up and shut off for just a short time, say a few minutes, there's still sufficient fuel pressure left in the system for the engine to run. As you might imagine, actual times during which your engine will or will not start depend on the severity of the check valve leak. You might try this: Turn the ignition key without actually starting the car. You should hear the fuel pump run for a few seconds. Repeat this several times, to allow the pump to build up pressure, then try starting. Generally, if the problem is with fuel pressure, you should notice an improvement in getting started. Ideally, you'd want to hook up a pressure gage to the fuel system, to make a final determination. Hopefully, this will point you in the right direction. Karl Jim Ashley wrote: > I have a 87 Saab 900 (8V, 4 dr. 180K mi.) I am having trouble starting > it in certain circumstances: > > - When it is difficult to start it cranks for 4-5 seconds then it > catches, idles for 1-2 seconds and dies (the only way to get it going > sometimes is to hit the accelerator during it's catch sequence). > - Mornings it starts fine having sat overnight for 12 hours. (New > England climate) > - Once I try to re-start after a stop I have trouble. (The other morning > I left my house after the first start went for 5 minutes to the gas > station. Shut the car off, filled it up (6-10 mins) and I had trouble > starting it). > > I cleaned the air flow plate and throttle butterfly and adjacent air > ways w/Gumot, replaced the air filter. Then I finally installed some > tune up components (Dist. cap, rotor, Bosch Plat. plugs). > None of these actions improved my original condition of tough starting. > However I can add 2 more observations: > - It will start immediately after it has been shut off (1-2 min.) > - It also seems to start after a minimum rest period of 6 hours. > I think it is probably one of the sensors (cold start valve, thermo time > switch or maybe warm up regulator). > > Please let me know if you think of anything, > Thanks, > Jim

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