1981 SC enrichment

[mikemdd]

For what it's worth (which may not be much). There are many opinions floating around regarding the impact of the lambda control system and its affect on the idle mixture vs. the full rpm range. Some have said it mainly affects only the idle and others have said it affects the entire range. Anyway, i hooked up my new LM1 to my 1981 SC and took readings with and without the O2 sensor connected. As background, the CO level is about 0.8% (O2 sensor disconnected) and the test was done with no load.

With O2 sensor connected:
- idle: AFR = 14.9
- 4000rpm: AFR 15.0 +/- 0.3 (some oscillation)

With O2 sensor disconnected:
- idle: AFR = 14.6
- 4000 rpm: AFR = 13.1

Clearly, the lambda system was working throughout the range. This explains why my gas mileage really sucks with the O2 sensor nut disconnected (but it also runs much stronger).

I know this is not new news to anyone, but it was fun to test it. I'm going to check the affect of changing the idle mixture on AFR throughout the rpm range, but I can't get the RPM converter to work. Maybe later.
Cheers

Mike
1981 SC
1987 930

[clevy70911T]

My 81 has a WUR with vaccuum enrichment and the lamda of course. I'm still unclear as to what was stock as WUR frequently get switched out over the years. At any rate, I found this cross section of a WUR with the vaccum port. Basically vaccuum to the WUR lowers the fuel pressure (richens mixture) indepentdent of the bi-metal heating strip. Hope I got that correct.