MicroSquirt.com read only forum (Jan.15,2018)

I took the new engine for its first drive today, using the tune for my old engine. According to the LM-1, I was running at about 15:1 AFR. Good, good. But the engine starting bucking like it was way too rich and fouling the plugs. I datalogged, ran it through MegaTweak, and modified my VE map, which made it much leaner. The engine now ran great but ... the LM-1 now says 18:1 AFR during cruise. That can't be right, can it? The engine wouldn't run very well, it at all, if it were that lean, would it?

I think it must read leaner than it actually is. The sensor is reading the end of my 3" turbine exhaust (nowhere else to put it).

The LM-1 was calibrated correctly.

This is very common..

If there is a miss, the raw air and fuel gets dumped into the exhaust. The wideband O2 sensor reads this as being very lean as there is alot of unburnt oxygen.

This is very common..

If there is a miss, the raw air and fuel gets dumped into the exhaust. The wideband O2 sensor reads this as being very lean as there is alot of unburnt oxygen.

That's what I'm thinking.

Drove it around some today and it was saying around 15:1, then it started running choppy and saying 18:1, so I richened the map. It didn't help so we brought it home and pulled two plugs. One of them was wet and fouled and the other was pure white.

Got some investigating to do ...

Aha! One of the injector wires was pulled out of the relay board and continuously grounding against the case. Screwed it back down and it all works now.