1700 XFlow AFR setup

[redursidae]

On 9/14/2025 at 10:18 PM, IamScotticus said:

Still a lot of questions here.

If Mudder puts in a logging AFR, it only shows his O2s based on what?  An AFR meter doesn't know what test of fuel, altitude, compression ratio,  blah blah blah...Murder needs to know what his ideal AFR should be based on his variables first, and it may not be the perfect stoichiometric ratio of 14.7:1. So Mud needs to determine his Stoich point before an AFR is useful. 

hey, I say if you're blowing smoke, that's good 

 

This is a common misconception about oxygen sensors and gauges. Oxygen sensors don't read AFR, they read Lambda. Lambda doesn't change with the type of fuel, and Lambda 1 is always stoichiometric regardless of fuel. The gauge converts the Lambda reading to AFR based on a user configurable setting which is a multiplier of stoich AFR * Lambda. By default this setting tends to be 14.7AFR = Lambda 1 for the gasoline scale we are used to. As a result, an engine idling with an AFR reading of 14.7 but running E85 doesn't actually have a 14.7:1 ratio in the exhaust, but instead 9.8:1 . The sensor is reading Lambda=1 (9.8:1 for E85), but the gauge has converted it to the gasoline scale. This of course changes if you modify the scale in your gauge.

 

@Mudder The AEM X series gauges are good and reliable. Install the oxygen sensor behind the collector of your 4-1 header. It's also a good idea to wire the controller in such a way that it doesn't heat the sensor until the engine is running to prevent condensation from damaging the sensor.

 

[JohnCh]

54 minutes ago, redursidae said:

@Mudder The AEM X series gauges are good and reliable. Install the oxygen sensor behind the collector of your 4-1 header. It's also a good idea to wire the controller in such a way that it doesn't heat the sensor until the engine is running to prevent condensation from damaging the sensor.

 

Piling onto this comment, another place where people go wrong -- including Caterham -- is the sensor mounting orientation. Sensor manufacturers recommend positioning it at least 10 degrees above horizontal to minimize the condensation pooling on the tip.