I've got a small problem and i hope you can show me a way to fix that.

Till today i was only driving around with my RX7 at daytime but today i needed to get home at night. I turned the lights on and drove home and whenever i had to stop for more than round about 5 seconds the engine started to get some light missfiring. I checked the wideband gauge and it showed a very lean mixture.

I have to say i'm using an electric fan which was on at that time. First thing i tried was turning the lights off and the idle and AFR went back to normal instantly. I guess the fan is drawing too much power so the alternator is working harder but shouldn't the ecu recognize that and adjust the injector timing a bit?

My car never had an air condition. How do engines with it manage not to run lean while it's on? Is there any signal the air condtion unit sends to the ecu while on which i could use to fix my problem with the fan maybe?

 

How about measuring the output voltage of the alternator during like conditions.

 

Do you think the old alternator could be too small with the electric fan?

 

Measuring the output voltage under the same circumstances will tell you.