4 to 2 exhaust O2 sensor

[redmt]

4 into 2 means that there are 4 pipes on one bank going into 2 collectors instead of 1. The sampling would come from one of the 2 collectors on each side.

[Gaz64]

Originally Posted by Gaz64

Something to think about.

If your O2 sensors are only looking at one cylinder per bank, and that cylinder misfires intermittently, the O2 sensor reads lean (high oxygen from no combustion).

If the ECU retrims the fuel accordingly from a momentary lean condition, the whole engine will be trimmed in the rich direction.

A permanent miss in that cylinder will have the engine go rich as the ECU trims will allow.

Please reread my post above. "One cylinder per bank" are the key words.

Originally Posted by redmt

4 into 2 means that there are 4 pipes on one bank going into 2 collectors instead of 1. The sampling would come from one of the 2 collectors on each side.

I know what 4 into 2 means. Can't see the point really, especially if a negative pressure wave is not put to use.

Yes, you would fit an O2 sensor in a collector on each bank, or you could fit both sensors in both collectors on the same bank.
Either way, you'll only be sampling half the engine, rather than sampling all of the engine to get mean average A/F ratios.
Any misfire will then "average" higher O2 content, and then the whole engine will richen up momentarily to compensate.

[Luce]

Lopey cams misfire all the time at idle. With megasquirt, you can dictate how much authority it has to adjust the fuel based on O2 readings and how quickly it can make adjustments. I'm not even allowing it to run closed loop, but rather just using the O2 for tuning so I can make sure the data is valid by hand.