To all fuel trim/02's questions

[dets]

I've noticed that most of the threads in this forum are about people using either an AFC or MAFT wondering why their 02 levels look so crazy at high rpms.



I think they should be a sticky in this forum that explains the limitations of the narrow band 02 sensor and why wideband 02's are absoultely neccesary for tuning fuel accurately.


I have some information that i could share, but i'd rather pose the questions to the mods first before posting something thats already been made into a faq.


HTH

 

[Jimmy Jr.]

I very much concur. Tuning with a narrowband makes about as much sense as modding a fwd. Zing! Just Kidding. But really, the narrwoband is no good beyond it's intended use which is keeping the closed loop operation as close to stoichiometric as possible.

 

[dets]

After recieving a PM i decided to post a little bit more info,


99% of all ECUs treat the O2 sensor as a switch (don't use any of the remaining 1%). An IDEAL O2 sensor is actually a switch. The only reason it has a curve is because not all molecules in the sensor ceramic switch at the same time. A ECU in closed loop ONLY checks if the O2 voltage is above or below 0.45V. If above, it leans out, if below it richens up. That's where the voltage swings come from, the ECU switches back and forth. No ECU I know of looks at or cares about the O2 sensor curve because it changes with EGT, exhaust pressure and varies from sensor to sensor way too much.

 

[dets]

The advantages of WB as well is that most units allow tuning from a labtop and you can log completely independately from the ECU. Just as a fun test, run your wideband while you are logging with your Palm and compare. You'll see how amazing far off from a schiotic mix you actually are. No DSM link or Piggy back system in the world will help you if you have bad information to begin with. The key to tuning is to actually have a grasp on the components that are functioning in the engine. Without it, its kinda of just adjusting the trims hoping to get lucky.