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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Just some educational crap to confuse things even more: The less O2 that the sensor sees, the lower it's millivolt output will be to the computer. When the computer sees the voltage dropping it will change the duty cycle on the frequency valve to lean things out (if I recall, said valve bridges the upper and lower chambers of the fuel distributor and - depending on it's duty cycle - has more or less of an effect on fuel pressures, thus changing the fuel/air mixture and AFR's). If you unplug the frequency valve, your car will go instantly very lean.

If you unplug the O2 sensor, the frequency valve will default to open loop at a fixed duty cycle of something like 50%. That's how I always ran mine because I didn't have to worry about smog testing and didn't have a CAT anyway. Makes it easier to tune in my opinion.

As Oilonly mentioned, that black relay is what sends power to the heating element internal to the O2 sensor. Without it the sensor takes too long to heat up or may not heat up enough to work correctly. Also, make sure you have the correct sensor for these cars. What came with your AFR gauge isn't necessarly what your Lambda system needs.

This is all from memory; I should pull out the ol' Bosch K Jetronic manual to refresh myself so I don't send conflicting info.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 11-03-2014, 11:14 AM
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