Re: AKA modulator valve - Saab Saab Model 99 Bulletin Board - Saabnet.com
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Saab Model 99 Bulletin Board
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Re: AKA modulator valve
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Posted by Andy in PDX (more from Andy in PDX) on Sat, 11 Jun 2005 21:04:25 Share Post by Email
In Reply to: AKA modulator valve, David S., Sat, 11 Jun 2005 20:04:34
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You're talking about what Bosch calls the "control plunger," which is the valve that controls the amount of fuel that gets through to the injector lines. In a static pressure test the top of the plunger should be the same pressure as the line in pressure, but when running, pressure on top of that plunger is modulated by the bleed-off of the warm-up regulator; when cold the regulator bleeds off more pressure than when warm. You don't want the cold start valve hooked up to the control pressure circuit outlet because the cold start won't function properly, and neither will the pressure control circuit. You won't get proper modulation of the fuel pressure on the top side of plunger.

Theoretically pressure is equal throughout a hydraulic system, but it can be controlled by orifice sizes and bleed-off. Just upstream from the pressure control valve is a small orifice into the slightly larger control pressure circuit. The larger bore inside this passage leads directly to the warm-up regulator, and there is another small orifice from the chamber where the regulator hose connects and the top of the plunger. A friend of mine had this passage clog up on his '78 99 EMS and you couldn't lift the air flow sensor plate with the fuel pump hot-wired. The fuel pressure was holding the plunger closed all the time and the air flow couldn't lift the sensor plate.

I would connect everything back to the proper ports as different ports serve different functions and you won't get proper pressure control inside the distributor with things connected to the wrong ports.

posted by 209.102.12...

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