lean burn: now i have a 1k pot on my MAF sensor - Fuel Economy, Hypermiling, EcoModding News and Forum

modmonster · 01-20-2009, 06:13 AM

through trial and error i have found that about a 0.1-0.2 volt subtraction from the MAF sensor signal leans out the engine nicly.

i noticed that when my MAF sensor broke (lost calibration by 0.5v) i was actually getting slightly better milage on short trips than when i replaced it. altough milage (and power!) was slightly worse on highway journeys -i assume that was because it was too lean.

i've just put a 1k pot on my MAF sensor and i should see higher mpg numbers soon. noticed engine warm up takes much longer because the mixture is not rich.

Daox · 01-20-2009, 08:00 AM

Do you have any provisions for cleaning up the additional NOx you are now creating more of?

tasdrouille · 01-20-2009, 08:33 AM

Quote:

Originally Posted by Daox

Do you have any provisions for cleaning up the additional NOx you are now creating more of?

I know NOx skyrockets as you lean out the mixture, but what I'd like to know is how much more NOx am I putting out for various lambda values. I don't play with the AFR on my gasser, but I think such information could help people make more informed decisions on whether or not they should tamper with their AFR.

Also, if someone was to lean an engine, and wanted to keep the same NOx output level, how should they go about it? Are there special aftermarket NOx traps available?

Funny · 01-20-2009, 09:01 AM

If you plan to continue leaning out the mixture, you'll want to get an A/F meter to check to see how close to stoich you are. It is likely that if you don't, you'll cook your valves and cause brown deposits on your spark plugs. More instrumentation is required when modding a car than just a butt-o-meter. The other posters are correct, if you go too far away from stoichiometric mix, you create exponentially more NOx.

modmonster · 01-20-2009, 09:44 AM

why does lean burn cook stuff in the engine where as a rich mix is used to warm up the engine? surely one extreme has to be colder right?

its only experimental at the moment. i've probably killed my cat already driving round on the broken MAF sensor for 3 months.

i agree with trasdrouille about the need for a NOx graph. we may be worriying about nothing or it could be super bad.

Ryland · 01-20-2009, 10:45 AM

when your engine is cold not all of your fuel is turning in to vapor, so it's not all burning, but once your engine is warmed up all the fuel is burning the fuel then also has a cooling affect in the engine as it evaporates so it can be burnt, and the air is getting hot as the fuel burns as well making it less stable so any left over oxygen is going to look for something to bond to so it can oxidize it (burn it), so it will start to bond with the nitrogen in the air creating NOx and getting even hotter and given the chance it will bod with the metal of the engine, burning holes and bending valves.

IndyIan · 01-20-2009, 11:22 AM

I guess what you need to "play safe" is an exhaust gas thermometer.
You sound pretty handy though so a budget thermocouple on the manifold and a voltmeter might be all you need. Drive for a few miles at full throttle with stock settings to get your max safe temp, and then don't go over it with your lean burn fun.
Basically you are trading CO2 emmisions in for NOx which, if your area is having good air quality isn't a big deal. On bad air days leave it stock.
Ian

tasdrouille · 01-20-2009, 11:24 AM

It should be noted that temps go up as you lean the mixture, but past a certain ratio, they start to go back down again.

IndyIan · 01-20-2009, 11:42 AM

Quote:

Originally Posted by tasdrouille

It should be noted that temps go up as you lean the mixture, but past a certain ratio, they start to go back down again.

So I guess the issues with the NOx bonding with engine parts goes away?
I imagine since he's not fooling with spark timing that he can't get to this point though. You must need some big advance numbers to get the engine to run that way.
Ian

wagonman76 · 01-20-2009, 01:28 PM

Quote:

through trial and error i have found that about a 0.1-0.2 volt subtraction from the MAF sensor signal leans out the engine nicly.

My Celebrity does not have a MAF. But I built a device to adjust the voltage to the MAP sensor. I found that subtracting 100-150 mv from the stock signal gave it just a hint more power under light load. I did this early last summer, before I joined here. Back then it did not contribute anything to my mpg. But since ecodriving, it might be helping some.