Hi, I was wondering if any one could help me out. I have a 78' 280z and it is running extremely rich. I have tried a lot of things but I keep wondering about the AFM. I tried replacing it with one from a 77’ parts car and it seemed to work. It ran pretty good until I replaced the battery and alternator, so now it has been really rich. It does not idol or rev well, it is just kind of popy and not smooth. Its so rich that black smoke comes out the back and you can smell it a lot. Well any help would be great. Thanks so much.

Have you checked the timing?

Have you adjusted the idle screw?

Have you adjusted the AFM at all?

I have tried ajusting the timing and the idle screw but I have not adjusted the AFM at all because I heard you shouldn't have to. Is it alright to turn the AFM a couple clicks around?

Adjusting the AFM is a good idea for fine tuning, but if there are other probs, those need to be addressed first.

Check all the sensor connections, mainly the head temp sensor & AFM. Make sure they don't have corrosion on them. Use a lil bit of di-electric grease on each connection. I also suggest pulling all the spark plugs to see if they all look the same. If one is miscolored, you know there is a prob w/ that cylinder.

The AFM is not 100% electronic (no moving parts). It has moving parts which means it will wear. These cars are REALLY old and so some of the parts that have made it this far are likely to need some sort of adjustment/refreshment. The swiper arm inside the AFM in particular can dig a path into it's carbon track and give erratic readings. The flapper door tension spring is likely to loose tension after all these years.

Is there any way to by-pass tha AFM at all? Because that would be really nice. I also put in a new temp sensor and cleaned the connections not to long ago so I dont think its that. Also how do you know how to adjust the AFM or throttle valve switch? Because I have palyed with that too.

Not without extensive ecu overhauling. Or you can buy a VPC (vein pressure converter).

This is J's how to adjust & modify the AFM:
https://www.zdriver.com/forums/240z-280zxt-s30-s130-tech-tips-275/js-how-rebuild-your-afm-15277/