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Join Date: Oct 2009
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86'turbo computer & O2

I bought a 78' euro 930 with a 86' USA 3.3 engine. It does not have the computer or O2 sensor to run the cis. Will the engine perform ok without these inputs. I have asked around and some say it is just a emissions issue for low power, others say I have to have them. I have rebuilt the engine and about to install. If anyone knows the answer please let me know.
Thanks
Old 10-30-2009, 09:01 AM
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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.
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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, 09:37 AM
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Thanks for the info, I only drove the car about 100 miles before engine removal. It was smoking in all phases, during tear down the engine had worn cylinder walls, but did not seem high mileage. It ran ok before if you don't mind a little smoke, but was the wear from a lean mixture?
Old 10-30-2009, 10:35 AM
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The wear was most likely not due to lean mixtures. Worn rings, clogged oil passages, bad valve guides, those sort of things. If overly lean, especially on boost, the symptoms would be broken rings, holes in pistons, those kind of minor details.

Check and see if that frequency valve is still in place, behind and at the base of the fuel head -easy to see with the engine out. If the engine was originally installed in the '78 and ran that way for some time before you got it, then I'm guessing someone already did the needed adjustments to run without the freq valve. To give you a reference point, I once disconnected my freq valve to see if I could tune around it. My AFR's went from 14.4 at idle, to damn near 17, and I had to adjust the screw in a good full turn to get the AFR's down to just over 15....then it would go lean again as soon as going down the road.

I would suggest that before you run it, get your hands on the gauge setup to test the control pressures in your WUR, and set the ignition timing per specs (probably 0 to 2 ATDC at idle with the hoses connected, and 26 BTDC at 4000 rpms). Or if you can get your hands on a CO tester, you can check the mixture at the exhaust pipe...usually runs best at 2 to 3% CO, adjusted at the mixture screw on top of the fuel head.

Excuse me if you already know all this stuff. Good luck, let us know how it all turns out.
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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, 11:02 AM
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