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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,267
CIS oxygen sensor question

My car is an '87 930 with CIS.
Is the oxygen sensor in the loop doing it's thing at all times accept at full throttle?
The way I understand it the full throttle position switch on the throttle body turns off or bypasses the oxygen sensor lambda system at full throttle so you get a richer mixture on boost, but it is working at all other throttle positions monitoring the CO in the exhaust and changing the pulse frequency of the frequency valve on the fuel head to keep the fuel mixture about as lean as possible to lower emissions at all other throttle positions.

My car has a K27 7200, 1 bar spring, B&B headers with heat and single out muffler.
It also has a Garretson half bay intercooler with stock recirculating valve with new seals in it, and it has powerhaus high lift cams.
All this stuff was on the car when i bought it and the previous owner didn't remember which powerhaus cams he had installed when I talked to him once.
The boost comes on around 4500rpm so I think they are timed pretty late.

Anyway, it has a little miss at idle and mild lean surging on slow accelerations around town.
If I disconnect the oxygen sensor it idles absolutely perfectly smooth with no miss at all.
Only thing is it is too rich at times during warm up from a cold start and it oscillates up and down at idle because it is a little too rich and if you blip the throttle in nuetral it will drop below normal idle speed and then come back up to normal idle speed. That is how a slightly rich mixture with fuel injection behaves at idle speed.

I am thinking the best thing to do is just leave the oxygen sensor disconnected and then lean out the CO adjustment on the fuel distributer till it idles smooth without the rich mixture symptoms.
Or is there a way to keep the lambda system operating as it should without idle and low speed running being a little too lean?

Any thoughts?
...thanks in advance,
Jim
Old 09-27-2007, 10:25 PM
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