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Re: Saab 99 turbo fuel pressure issue at injectors Posted by Gary Stottler [Email]  (#1463) [Profile/Gallery]
(more from Gary Stottler) on Mon, 17 Mar 2014 07:26:06
In Reply to: Saab 99 turbo fuel pressure issue at injectors, Justin, Sat, 15 Mar 2014 12:28:00 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Justin,
The easy part - the order of the injectors doesn't matter; they all spray all the time.
The harder part - fuel pressure and volume to the injectors is controlled in two ways.
First is the system pressure, it is controlled by the pressure regulator in the Fuel Distributor which is right at the fitting where the return line leaves the Fuel Distributor. Sufficient system pressure is required to open the 4 fuel injector poppet valves. Fuel flows from the pump, through the filter, into the fuel distributor where it is "bled off" through the pressure regulator, and then back through the return line to the tank. The most likely problem that can arise in the supply side is a blockage of the fuel pickup in the tank or of the fuel filter. These could result in low fuel pressure being delivered to the fuel distributor. In this case, the pressure regulator would never open and no fuel would return to the tank and you might not have enough pressure to open the injector poppets. You can diagnose system pressure with the Service Pressure gauges.
The second pressure item is the control pressure provided by the Control Pressure Regulator (also called the Warm-up regulator). This is really responsible for the volume of fuel that flows to the injectors. In general, Control pressure is at spec when the engine is warm, and it is low when the engine is cold. This seems counterintuitive, but the fuel distibutor works based on the resistance to the control pressure on the top of the plunger, so if the control pressure is low, the plunger can move higher, sending more fuel to the injectors. So, likely your problem is not low control pressure. High control pressure can prevent the plunger from rising and therefore make the engine run lean. I point this out, because if the system pressure is too high (possible caused by a restricted return line from the Fuel Distributor to the tank), then the control pressure will also be too high, and the fuel flow to the injectors will actually be reduced.
All that said, it sounds like you have low system pressure based on your observation that if you raise the airflow plate (and with it the metering rod) fuel does flow through the injector lines, but does not have enough pressure to open the injector poppet valves. I would suggest first looking at the fuel pickup in the tank to make sure it is not clogged. If everything looks clean in there and all the rubber parts are in good condition (make sure the small hose from the plastic fuel pickup to the intake of the pump is not swollen - could restrict the insided diameter of the hose, then try a new filter. If that is known good (can you easily blow through the filter?), then I would suspect the pump. I can't say that I have ever seen the system pressure regulator go bad on one of these.
I hope that helps. Feel free to contact me off-line if you want to discuss in more detail. I have a set of pressure gauges I can lend you if you need them.
Good Luck!
Gary
_______________________________________ Gary Stottler
, Mon, 17 Mar 2014 07:26:06 <-- Viewing This Message
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