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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
Posts: 3,776
1st question: Was it running while in your '78 car when you bought it, and you're rebuilding it just because? If it ran fine prior to the rebuild, then you've got nothing to worry about.

Yes, on cars equipped with the Lambda system, you can (many of us do) run without the O2 sensor connected and simply tune your idle mixture around it. But the control electronics (which reside under the drivers seat) will still function in an open loop to control the frequency valve at the back/bottom side of the fuel distributor...which in turn normally reacts to the O2 sensor by leaning out the mixture under certain conditions. Without the O2 sensor connected, that freq valve stays at a fixed duty cycle of something like 50%.

Now, if you unplug that freq valve, your mixture will go waaayyy lean and you can't easily tune around it (it can be done, though, via adjusting each of the 6 fuel plungers in the fuel head to deliver less fuel and balancing the flow to each injector). Depending on how your engine is setup and if it was originally designed to operate with the Lambda system components, then it may act as though you just unplugged the freq valve.

What I've just described is how the system works in a car with all the correct bits and pieces. Your engine either (a) won't run worth a crap because it came out of a chassis complete with the lambca control unit, and thus the fuel head is designed to work with the frequency valve operating, or (b) someone has already deleted the freq valve (unplugged or removed it) and adjusted the fuel head accordingly. But as I said at the start of this long-winded explanation, if it ran fine before, then you're good to go. Just tune your AFR's and/or CO% at idle with the adjusting screw, and forget it.
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 10-30-2009, 10:37 AM
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