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Re: New Fuel Pump Installed Posted by Gary Stottler [Email]  (#1463) [Profile/Gallery]
(more from Gary Stottler) on Mon, 20 Apr 2026 05:37:09
In Reply to: New Fuel Pump Installed, LJB, Sun, 19 Apr 2026 10:56:52 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Nice work tracking down a part number that will work and adapting it to fit! What we have to do these days to keep 99s running. After all, the 99 is "the forgotten Saab".
Regarding difficulty hot starting:
You are clearly well versed in checking fuel system pressures, so I think that you can easily verify this - there is a rest pressure specification for how much pressure the system should hold 20 minutes after being shut off: 1.0 Bar/14 psi, or 1.5 Bar/21 psi for 1978 and later models.
The hot start problem occurs when the pressure does not hold and the fuel in the 4 injector lines boils, allowing the lines to fill with vapor instead of liquid. There are three main causes of this:
1) Leakage at the injector tips which can occur due to carbon build up.
2) Leakage at the anti-return valve in the pump (you may have already fixed that)
3) Leakage through the Control Pressure Regulator (Warm-up regulator)
Saab/Bosch instituted a service fix which used a special relay to pulse the cold start injector as you suggest - it would start pulsing if the engine didn't start after cranking for a fixed time. They instituted a series of improvements in 1978 which made the problem much less severe (it was a real issue). 1978 had the higher rest pressure, a change to how the CPR is plumbed to prevent that leak path, and a replaceable anti-return valve in the later pumps.
_______________________________________ Gary Stottler
, Mon, 20 Apr 2026 05:37:09 <-- Viewing This Message
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