So I was reading about EFIE devices, and...

[t vago]

I have a question about them, but I'll get to it at the end.

O2 sensors are used by the engine computer to sense the amount of oxygen needed to completely combust the remaining hydrocarbons in the exhaust stream. Rich exhaust causes oxygen to flow from outside into the exhaust stream, and lean exhaust causes this flow to slow or even stop.



Standard O2 sensors can detect AFRs between 14:1 and 15:1 (much simplified explanation for the sake of brevity), but they don't do a very accurate job of it because they'll go to an equilibrium oxygen flow, which will cause the O2 sensor signal to become slightly inaccurate. Such inaccuracy may be tolerated with post-cat O2 sensors, where their primary job is to monitor the cat's efficiency, but this inaccuracy is unacceptable for AFR control. This is typically why engine computers continuously vary their fuel output between slightly rich and slightly lean, in order to keep the O2 sensor signal from going to equilibrium.



Now, my question is - If an EFIE device is supposed to trick the engine computer into running leaner than before, by modifying the O2 sensor signal to make it appear that the engine's running more richly than it really is, how can you maintain control of the air fuel mixture if the O2 sensor output only goes to 15:1? Because it seems to me that if you're going to go beyond 15:1 (where real fuel economy gains would be realized), you're going to need something other than a device that merely changes the signal coming from a sensor that is limited to 15:1 on the lean end. Otherwise, you have no idea what the AFR is, and you'll eventually end up burning something up inside the engine due to an unanticipated over-lean condition.

[redneck]

A wideband LAFtype O2 sensor will read up to a 22:1 A/F ratio.

Here's an idea.

You may be able to install one in addition to the one your trying to trick.
Then monitor voltage separately to get a idea of how lean your running.


Honda uses these type O2 sensors in their lean burn engines.

>

[ECONORAM]

Redneck beat me to it. Yes, you will need a wideband in order to accurately monitor the AFR outside the typical "narrow" band range. Something like this one from Dynojet: AirRam - Cold Air Induction System

[t vago]

Last summer, I installed an ancient old PLX M-250, and it takes the place of the pre-cat O2 sensor. It has a wideband output suitable for an aftermarket engine computer or a gauge, and a narrowband output suitable for the stock engine computer. It enables me to determine when my truck goes out of closed loop operation when I accelerate, and is pretty neat to watch.

I could build a circuit that could take the wideband output, and generate a narrowband output in the desired AFR range, and that would only take effect at 20% throttle opening or less. Above 20%, the circuit would revert back to an unmodified signal. I'd still have to replace the post-cat O2 sensor with my other M-250 that I have sitting around, and have this circuit modify that signal as well, so as to successfully fool the stock engine computer.

However, that is something that we would do. I imagine that most people who buy these EFIE things do not actually take the effort to ensure an accurate AFR by buying a $300 or so wideband O2 sensor to monitor their output. What do they do, instead?

[mwebb]

Originally Posted by t vago

However, that is something that we would do. I imagine that most people who buy these EFIE things do not actually take the effort to ensure an accurate AFR by buying a $300 or so wideband O2 sensor to monitor their output. What do they do, instead?

"most" of those sell their mistakes on craigslist
with a statement like
"i do not have time to complete my project"
which really means
" i screwed everything up and i have no clue how to make it work right again"

google a plot of a graph for 5 gas emissions , look where NOX peaks
at about 16 or 17 to 1
Knowing that NOX forms at very high combustion temperature s , you should not operate at "slightly lean" ....
at conditions leaner than "slightly lean " combustion temperatures DECREASE.
as marked by the NOX graph in the 5 gas graph

most people should not tamper with this

[EdKiefer]

Standard narrowband O2 can detect wider than 14-15 AFR . while that range is were it is most accurate I have seen it able to output values wider than that graph (something like low-mid 13's for 0.9v and probably same on high end,close to around 16 AFR but i never checked that end )

As above poster running lean has many side affects , I wouldn't do it alone .

[cfg83]

mwebb -

Originally Posted by mwebb

...

google a plot of a graph for 5 gas emissions , look where NOX peaks
at about 16 or 17 to 1
Knowing that NOX forms at very high combustion temperature s , you should not operate at "slightly lean" ....
at conditions leaner than "slightly lean " combustion temperatures DECREASE.
as marked by the NOX graph in the 5 gas graph

most people should not tamper with this

Does this agree with your statement? :

Automotive electronics handbook - Google Books


CarloSW2

[mwebb]

[QUOTE=t vago;218060]I have a question about them, but I'll get to it at the end.






QUOTE]THIS LOW RESOLUTION 02 SENSOR WAVEFORM
is showing pronounced consistant MISFIRE
====================
yes
that NOX graph agrees with my SWAG
but
it is true that combustion temperatures are HIGH during hi load with slightly rich conditions , when NOX output is very low, perhaps because there is no 02 availible to combine with the N
to form
NOX , during rich condition.

[t vago]

This is the book (rather, two-volume set) that I reference whenever I start researching something or other about gasoline engines

It would appear that my question was answered. I think it would be a good idea to put up a sticky on the potential drawbacks of using an EFIE (particularly EFIEs that only rely on the stock narrowband O2 sensor), perhaps as part of listing the potential drawbacks of running lean.

[arcosine]

So how much less O2 is there after the catalytic converter? Can this sensor be used to trick the ECU into running leaner?