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Re: Head Scratcher 99 CIS issues Posted by Gary Stottler [Email] ![]() ![]() In Reply to: Re: Head Scratcher 99 CIS issues, Jordan, Thu, 4 Jul 2019 11:12:16 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Jordan,
Yes, the modulating valve should be buzzing all the time. When it's operating it actually reduces the control pressure, so if it stops that pressure goes up and the fuel system gets very lean. The three key components are the controller (under the passenger seat), the modulating valve, and the oxygen sensor. There is also a micro-switch on the throttle body which forces the system richer at full throttle. In addition there is a two-pin connector just above and behind the fuse panel clipped to the inner fender which is the service connection for the test tool. There was a Saab tool for checking "pulse relation", but I think any modern multi-meter can also check a pulse width modulated signal. It's basically the percentage of the time the valve is open from 0 to 100 percent. You should see a steady 60% when the system is running with the O2 sensor disconnected, and it should jump to 80% when the throttle micro-switch is closed. I'm on the road right now so I don't have the wiring diagram handy, but I can get that for you in a few days when I get back. It's also worth confirming that the vacuum advance and centrifugal advance functions in your distributor are working properly, although usually those things are not intermittent.
Best,
Gary
_______________________________________ Gary Stottler
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