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My U.S. 1989 900 Turbo has a cold start injector plug included in the wiring harness, so adding a fifth injector is simplified. Other years may be similarly equipped but, if not, you can easily tap into the injector harness -- there is sufficient power for a fifth injector.
For power, you need to access the ECU wiring plug, ground the 5th injector wire (see your Bentley manual), and add an adjustable pressure switch to the circuit so the injector only runs at high boost. The switch can be found on LH2.2 Saab 900 Turbos, and is located under the dash (refer to Bentley for specific location -- it's the boost overpressure switch). You can also buy a Hobbs switch at the parts store.
To supply fuel to the injector, go to the boneyard and grab a double banjo bolt from a CIS Audi or Volkswagen; you'll also want to grab a braided stainless steel fuel line from the same car; be sure it's long enough to reach the intercooler from the front end of the fuel rail. The banjo bolt will fit right on the Saab fuel rail and allows you to easily supply the injector. The follow photo diagrams the fuel line set-up at the fuel rail:
http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTI1MDc0NDZzNDEzZGZkMzF5NTQx.jpg
Mount the fifth injector at the intercooler outlet. You can do this by poking a very small hole in the rubber coupling, then forcing the fifth injector nose through the hole. It's a tight fight (as it should be), so take your time. Once installed, secure the injector with a couple hose clamps. Do not mount the injector in the throttle - the 4th cylinder will receive insufficient fuel and run lean.
The following photo shows the installed injector:
http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTI1MDc0NTZzNDEzZGZkMzF5NTQx.jpg
Using a 100ml graduated cylinder, I carefully measured the flow of a number of Bosch cold start injectors (average of three times sprays). The largest one came from a 5-cylinder Audi. Presumably, larger CIS-equipped engines, such as V6 Volvos or V8 Mercedes will flow more.
Some data: Saab CIS cold start injector at ~9.2 lb/hr (89 cc/min), Audi 5000 at 11.6 lb/hr (113 cc/min). Tested in car, while running, with 3 bar FPR, healthy fuel pump, and nearly 43 psi on pressure gauge.
posted by 67.183.22...
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