Leaning fuel mixture and effect on engine temp

[Flatland2D]

I've heard that running a leaner fuel mix will make the engine run hotter because there isn't extra fuel to absorb some of the energy. I am considering making a microprocessor based EFIE-like device that would hijack the O2 sensor signal and scale the signal higher or lower so you can fine tune your mix. I'd also like to add a bar graph of fuel mix for aid in tuning. I have it all designed, it's just a matter of buying some extra parts and piecing it together. My only reservation is this possible rise in engine temps. Should I just keep a close eye on the thermostat, or should I wait till I can rig up a water injection system?

If all goes well with my device I will probably post plans. I don't know if it's really worth the time and effort to get into selling fuel saving devices.

[SVOboy]

Sounds very interesting. From what I have heard there is not so much of an issue like this leaning out your mix but I am not exactly sure. I do know if you lean it out too much you will do lots of wear on the engine, but I dunno about heat increase. I'd say watch your thermostat, and there is always a market for something like that. If you can design it well enough you should talk to matt about selling it on the site with some sort of partnership cuz I figure it'd help the both of you, but I'll research on the heat issue tomorrow night when I have more time I hope.

[Flatland2D]

Thanks in advance for anything you might be able to find out.

As far as selling something like this, I'd have to look into what kind of profit margin there is and factor in my time making them. I'm a 4th year electrical engineering major, so this is the kind of stuff that really turns me on, but consequently I don't have much time for this.

[Matt Timion]

I saw this recently and I instantly thought of you and DieMaster (Diemaster is an electronics guy too). I posted about it here:

http://www.gassavers.org/node/53 (it's the last post in the thread)

They have schematics for electrically controlled water injection system.

Back to your original post, I think that such a device would work, but only to a certain degree. I'd be afraid to lean out a normal engine too much as they are build for a standard 14.7:1 ratio. Then again, my fear might just be paranoia.

I know that with my vtec-e engine air fuel ratios around 20:1 are not uncommon, but then again the engine was built for this.

if you are ever looking for an engine swap (your engine dies, etc.) you might want to look into the 3 stage D15b vtec. It's a japanese engine, but it has vtec-e and normal vtec combined. It can get around 50mpg in "lean mode" and can still get over 130hp at higher RPMs.

You can actually manually lean out your air/fuel ratio using a SAFC. they are typically used for tuning RPM ranges, but we could actually tune it to be super lean during certain RPM ranges. Once again, I'm not sure if this type of thing will eventually damage the engine or not.

[SVOboy]

Well, mainly I got some japanese stuff that was way up there on the phd I don't understand this crap level, but at least it was translated well, however not written strictly for automobile applications. The closest I have come to finding an answer is that carbed engines have the problem of overheating under lean burn conditions, but I still say try it and monitor your heat versus air-fuel ratio and see what you learn.

[diamondlarry]

I found this link regarding fuel mixtures and temperatures. http://www.sdsefi.com/techegt.htm Here is an exerpt:
Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT.

[Flatland2D]

Thanks for posting the article. There are some interesting things discussed in there that are relavent to what I want to do.

I found another website that sells a fuel mixture device. Read this article at <a href="http://better-mileage.com/mixture.html">Better Mileage</a> about it and how the oxygen sensor work to control the air/fuel mix. They make no mention of increasing engine temps on that page, but if you click "Next" at the bottom the first thing they say under "Dangers" on the next page is "Remember a lean condition is potentially damaging..." That would have been nice to know when reading the page that acutally deals with leaning the mixture.

Sounds like having a real-time air/fuel mix display is a useful feature for engine tuning, especially when dealing with efficiency.

[Matt Timion]

Sounds like having a real-time air/fuel mix display is a useful feature for engine tuning, especially when dealing with efficiency.

Of course the downside to this is that you usually need a wideband o2 sensor to accomplish this. They are ridiculously expensive (upwards of $180-300 brand new). I still can't believe i found one for $25.

I'm still weary to attempt to lean out my new engine (once it's installed, of course) at all. From my understanding, the engine/ecu/o2 sensor I will be running can actually safely run 20:1 or leaner air/fuel ratio. Imagine that, an engine actually designed to run super lean.

A guy I know swapped this engine into a 88 CRX HF. He says his curb weight is down to 1600lbs after weight reduction. He claims to get high 50's/low 60's MPG. I see no reason that isn't obtainable with more weight (my car should be around 2100-2200 pounds) and a few other modifications.

[Flatland2D]

I'd thought about getting a wideband O2 sensor, but that article that diamondlarry posted says they might not be as accurate as the narrowband sensors. If the signal is flucuating too much I can implement a moving average filter in the microprocessor to dampen out the oscillation. It's the same way your fuel guage works. Even though the fuel is sloshing around in the tank, a good fuel gauge reads a constant fuel level.

[Matt Timion]

Does this mean you can fix Honda's horrible fuel gauges?

Anyone?

Buehler?

[Flatland2D]

I really like Honda's fuel gauges. The fuel gauge in my last car was all over the place. It would also fall slowly until the last few gallons then drop dramatically. In my Del Sol it takes a few minutes to get a full tank reading after filling up. This is because the low fuel readings are getting kicked out of the average by the new ones, and the average slowly works its way up. Have you have bad experiences with Honda fuel gauges?

[SVOboy]

I really like Honda's fuel gauges. The fuel gauge in my last car was all over the place. It would also fall slowly until the last few gallons then drop dramatically. In my Del Sol it takes a few minutes to get a full tank reading after filling up. This is because the low fuel readings are getting kicked out of the average by the new ones, and the average slowly works its way up. Have you have bad experiences with Honda fuel gauges?

Haha, good fuel gauges must be a 92+ thing. If I take a hard turn (90 degree at 35 or 40 mph) it'll go from 3/8s tank to empty. Damn I hate that thing.

[Matt Timion]

I've never had a bad experience with the EF fuel gauges, but i've heard enough bad things from other EF owners to know it's a problem.

Actually, my fiance's 87 CRX has a problem where it takes around 200+ miles to get to the 1/2 mark on the gauge. it then empties in the next 100-150 miles.

[SVOboy]

80 miles: Leaves full
220: Half tank
300: Empty

[dfoxengr]

a good idea for leaning out your fuel for daily driving would be something like a piggyback tuning unit that is universal, and an egt.

basically

apexi S-AFC
autometer EGT gauge
roughly costing about 200$ when purchased used. and universal on any FI car.

then just experiment with what gives you some gas mileage increase, and doesnt run too hot.
also may want to retard timing some with this idea.

[SVOboy]

then just experiment with what gives you some gas mileage increase, and doesnt run too hot.
also may want to retard timing some with this idea.

What is the effect of retarding the timing?

[dfoxengr]

to reduce knocking/pinging.

[SVOboy]

Okee, that makes sense.

[chuckster]

I've heard that running a leaner fuel mix will make the engine run hotter because there isn't extra fuel to absorb some of the energy. I am considering making a microprocessor based EFIE-like device that would hijack the O2 sensor signal and scale the signal higher or lower so you can fine tune your mix. I'd also like to add a bar graph of fuel mix for aid in tuning. I have it all designed, it's just a matter of buying some extra parts and piecing it together. My only reservation is this possible rise in engine temps. Should I just keep a close eye on the thermostat, or should I wait till I can rig up a water injection system?

If all goes well with my device I will probably post plans. I don't know if it's really worth the time and effort to get into selling fuel saving devices.


I had the exact same idea!! If you can intercept the signal and "Skew" the voltage..you can acheive a higher AFR and still tell the PCM everyting is Kosher.. I guess you need to tell the O2 to give a higher voltage to make the PCM "THINK" it's Richer... then when the PCM pulls fuel to get it to normal you are actually leaning it out.. I'd like to hear more on this..I really do not think water injection is needed..As long as you don't go crazy..
There is a mode in some PCMS called Lean Cruise Mode.. They actually change the target AFR to like 15.X or so... Usually good for a few more MPGs... Illegal in the US because it causes higher NOX in the Air..
LEan Cruise kicks in when the car has a low Throttle position and maintaining a constant cruise speed...

Lean Cruise is used in Austrailia