Sean F

I have an 82 SC track only car that I recently dyno'd and saw an AFR of 14:1 at WOT. Obviously, this is too lean for a track car. I've never had working interior lights but never thought anything about it. Looking at the electrical diagram in Bentley, I see that the Lambda unit and the dome lights are on the same circuit. My question is, do I have this right and if that is the case then would the fact that the frequency valve likely isn't working cause the system to run lean at WOT?

psalt

Yes, even thought the system goes open loop after 35% throttle, there is a default duty cycle setting and the frequency valve always needs to be pulsing. The engine will run OK without an 02 sensor, but the FV needs to be working to get the default fuel curve. The way the system works, is that the basic fuel distributor setting is too lean, and the pulsing FV at the default 65% duty cycle, bleeds off lower chamber pressure richening the mixture to the default fuel curve. When the system goes closed loop, if the 02 sensor reads lean, the duty cycle goes up, bleeding off more lower chamber pressure and richening the mixture. If the sensor reads rich, the duty cycle drops, leaning out the mixture.

Replace the fuse, hook up an analog dwell meter to the test plug under the left hand engine compartment cover (green/white wire), If the FV is working, you will see a steady 58 dwell on the meter open loop. Closed loop, the needle should fluctuate between 40-58 dwell. If you are trying to optimize the engine, set the mixture with an allen wrench so that the neddle fluctuates between 30-40 dwell. The stock ignition timing was retarded on your car to run on the Porsche specified 87 CLC octane fuel and limited to 25 BTDC. If you run better fuel, you will make more power out into the 30's BTDC. You should also disconnect and plug the vacuum retard at the back of the distributor. It's only purpose is to meet the curb idle HC test and it raises the engine temperature.

Sean F

Thank you!