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Re: fuel mixture on 8 valve turbo
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Posted by MS (more from MS) on Thu, 4 Oct 2007 13:21:15 Share Post by Email
In Reply to: fuel mixture on 8 valve turbo, Jay, Thu, 4 Oct 2007 09:46:27
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It would be helpful to know why you need to do this. Once that feature is factory set, there's little reason to change it. But, if you're rebuilding from a teardown, disassembly and thorough cleaning, then I can understand the need. Assuming your engine is in good tuned condition to begin with (plugs, cap, wires, air filter, O2 sensor), and all the CIS fuel components and engine electronics are in working order, you can establish a general working fuel air setting without special metering equipment.

Basically, what you want is for the (warmed up) engine to idle, with the modulating valve shuttling back and forth between it's frequency cylces. You can tell just by listening to the valve. If you're starting from a too rich setting, as you decrease the fuel mix, the idle will drop, so you'll have to adjust the idle screw to raise the RPM's. The opposite is true if too lean, although if too lean, it's usually obvious because of the difficulty the engine has to simply idle. In either extreme, the O2 sensor will instruct the modulating valve to stay on a set frequency (either rich or lean) and will not shuttle between cycles.

Once you have the general idle and fuel mix (an established mod valve shuttle, normal idle RPM), you can fine tune by dropping the fuel mix to a lean setting until you hear the mod valve lock on it's compensating rich setting, then rotate the set screw clockwise maybe 35-45 degrees.

posted by 72.67....

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