AFR only reads the amount of 'burnt' fuel, and I say this because if you have unburnt fuel flowing out the exhaust pipe (non firing spark plug from one cylinder causes this effect, there are other possible causes as well, like valve leak like in my case) the AFR would read lean.
Depending on where you install the AFR meter, it can read the total AFR for 4 pistons (the stock location on most Mugen/DC2 extractor,
or
you can read one cylinder, if you mount it in a location like the old EF's where the o2 sensor is in the 4th piston exhaust port, one inch out on the extractor. Then you'd need four holes and four bungs and switch the 02 sensor position after each test.
Personally, the idea of drilling a bung into my mugen B18C header is definitely not an idea I'd like to use. I'd just rely on having a healthy engine, then tune it.
If you mount AFR sensors on the normal location like the stock o2, you're reading the total AFR of the engine, NOT an INDIVIDUAL cylinder.
That's why if you have issues with the engine, the AFR value absolutely worthless.
Now I posted this before, but this is just proof that if the engine ain't healthy, the AFR reading is totally worthless. Unless of course, I happen to have a 'magic' engine that can idle at 20.8AFR.
