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[TRS300]

May be simple question but not obvious to me...

Why can a car operate on one O2 sensor controlling 3 to 4 pistons / injectors.

But a Harley cannot use a single O2 sensor to control 2 cylinders?

In other words, why cannot the blended O2 reading be monitored and the same signal fed back to both cylinders?

Regards

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[windjammer]

Many cars have multiple o2 sensors usually before and after the CAT Harley uses one for each cylinder before the CAT.

[GregKhougaz]

Why? Using two sensors, one for each cylinder, is more precise. If you were to use one, both cylinders would receive the same AFR adjustments. In Harley's V-Twin, the rear cylinder typically runs hotter because of its placement. The different temperatures between the two cylinders alone justify different settings.

[TRS300]

Why? Using two sensors, one for each cylinder, is more precise. If you were to use one, both cylinders would receive the same AFR adjustments. In Harley's V-Twin, the rear cylinder typically runs hotter because of its placement. The different temperatures between the two cylinders alone justify different settings.

Well... the 4 cylinders in one half of a V8 receive the same AFR adjustments also based on one sensor in the blended exhaust...

You raise a good point about the difference in temperature of each cylinder...  And yes for sure you will get more precise control for sure.

But the narrowband sensor is a on/off switch trying to maintain 4.7 AFR regardless of cylinder temperature. It doesn't care about temp in regard to trying to maintain 1.0 lamda (14.7 AFR).  So?

The only thing I can think is that one cylinder might run rich and the other lean and the two would result in a 4.7 O2 measure when blended.  But again I would expect it would be the same for the 4 cylinders that share a common meter in a car?

Now that I think of this more I think it has to do with the fuel injection.  On a car all the cylinders are at the adjustment of a single throttle body, to O2 feedback adjusts the mixture of the single EFI throttle body.  Whereas Harley controls injection to each cylinder independently (unlike carbs of the old days). so if each cylinder sees it's own injector that injector needs to be controlled by it's own O2 feedback loop.

I'm assuming the Harley has independent injection for each cylinder when I say this...  I'll have to check.  If not, I'm still confused.

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[grc]

Depends on the type of fuel injection system.  Sequential port injection is what Harley uses, but considering the very short distance from each cylinder's intake port to the other cylinder's port and the uneven timing arrangement, some fuel can wind up in the other cylinder.  Automotive systems can be sequential port systems, or direct injection systems.  Direct injection systems are the most precise of course.

As for why Harley doesn't use one sensor at the inlet end of the collector, it may be due to the fact that non-touring models don't use a collector exhaust system and they want one system that will work on all models, or it may be due to the fact that the collector also houses the catalyst in very close proximity which could affect the sensor.  It could also be due to the fact that the Harley injection system is imprecise and a blended AFR would not be accurate enough for best overall operation.  Hard to tell why Harley does many of the things they do.

Jerry

[Doc 1]

Each cylinder does its own work, each cylinder breathes differently, so each cylinder has to report the the ECM so the Adaptive Fuel Values can make small adjustments to maintain the Fuel Request in the Fuel Table. One sensor in a neutral area would not be accurate fuel delivery for both cylinders.