How lean in cruise?

[LumpyVR4]

Near the top of my to get list is an EMClink V3. At the moment I get mild knock past 5.5k which means that I can't use my engine where it's at its best. I was thinking once that is sorted, I could get a logging wideband o2 gauge and fine tune my mixture.

With the ability to see exactly what is going on mixture wise I figure I can set the low load low throttle areas fairly lean i.e. not actually lean, but with no "saftey fuel". The idea is to come up with really good highway numbers. Now to the point of all this blurb. How lean is too lean in a cruise 12.5:1, 13:1, 14:1?

 

[croket]

I get 14.7 - 14.6 cruising and get massive fuel economy ,my car was already tuned to that and never had a problem. Get basicly 100km - 10 litres on highway cruising ,
but punch the pedal and its at 10.4 then it drinks it hahaha

 

[4piknup]

14.7 is only the mixture required for the cat to work its best. You will get better economy if you are leaner still

 

[croket]

14.7 is only the mixture required for the cat to work its best. You will get better economy if you are leaner still

Ive got no cat sshhhh !!! How lean would to lean be though ?

I reckon 100km to 10 litres not bad , but i like to be safe

 

[4piknup]

I gotta try it in mine, but carbys we used to go lean until they miss then slightly richer till the miss stopped.

A bit of google research wont go astray here

I had the crossover wrong in ecmlink for the wideband. It was offset and targeting 15.3 for cruise. I never noticed any issues with that lean. I have fixed the crossover point now and the ecmlink log of wb and the display on gauge are the same now

 

[p055um5]

I run 15.7 cruise (runs great) and down to 10.7 wide open

 

[bazeng]

I go as lean as possible. As soon as it starts to jerk and buckle, that's when you know it is too lean.

 

[LumpyVR4]

Done some Googling. I didn't find too much on 4G's, but there are forums dedicated to using aftermarket ecu's to get engines running as economically i.e. lean as possible. There was even a post about a Honda engine running 22:1 in cruise. I suspect that this was an NA engine though. As I said I didn't find anything about 4G's specifically. A couple of concerns I have are, how lean can you go before you start burning valves, and what happens if you are on the highway running in your lean closed loop and you go back a couple of gears and stomp on it? Is the ECU going to keep up or will the engine go really lean for a moment?

 

[4piknup]

There is some stuff for dsm lean cruise. Ignore any posters that say 14.7

The ecu will keep up no worries. Faster than you can jab your foot down

 

[evo-gsr]

Please explain why you say to ignore the 14.7 ?

 

[4piknup]

14.7 is the required mix for the cat converter to work best. Its not the most fuel efficient mixture. Its another emissions push.
14.7 isnt the wrong answer, its just not a informed answer when it comes to max economy.

 

[4piknup]

http://en.wikipedia.org/wiki/Lean_burn

Wikipedia entry. Interesting to see a version the mitsi 4g15 runs 25:1 for a 20% increase in economy. I dont think any of us could get that lean without a miss. But im sure the g15 wouldn't have any special anti burn valves or seats.
Its similar to egr where part of the exhaust is used to make up the intake charge of a lean burn.

 

[croket]

Im running no cat so think i might retune closed loop for better economy , thats good to know i can go leaner

 

[evo-gsr]

Right...thanks for clarifying Jack.

 

[4piknup]

Here is my old mate julian edgar and his thoughts:
http://www.autospeed.com/cms/A_1595/article.html

He suggests 15-16:1 or leaner until egt reads around 600*c

And more julian. Interesting read about the commodore picking up 10% economy from a Injector change, running it at 15.9- 16.5:1
http://www.autospeed.com/cms/A_110767/article.html

 

[4piknup]

I am a member of dsm-ecu yahoo group. There was a chat about lean running that I would like bring here. The member there is deedubya.
First is the reply, then the question. You will work it out:

You would benefit from adding a few degrees of timing in the same cellswhere it runs leanest since the burn rate of fuel slows down when it goesleaner than approx 15.7 AFR.Monitoring knock would be difficult since the code does not look at theknock sensor at light load. Knock is ignored while running in the first 3load rows. Phantom knock code ignores the knock sensor up to higher loads.Dave W.

> I have done some reading on here and I am going to run my 1g DSM in open> loop and then implement lean burn at light loads (and of course where> there is no chance of boosting).>> I'd like to know if I'd benefit by adding timing advance at the lower> load levels as well or do you just leave the factory timing curve in> place? I can of course check for knock counts, but I'd like to see if you> all would bother advancing timing at all under light loads or do you just> leave it alone.>> Thanks in advance.

 

[4piknup]

Deedubya continues:
2 Degrees is a good start depending on how lean your car can run. Like Isaid, the burn rate begins to decrease leaner than around 15.7AFR, so ifyou're running right at 15.5 the car might only benefit from one moredegree. From what I've seen most cars still run smoothly at 17.0 with noissues but some DSM's are really old now so lean it out gradually and makesure it still runs smoothly. Pay attention to the sound and feel of thecar as well as the datalogs. If it runs good at 18.0 or leaner add 3degrees.Dave W

.> Dave,> Do you have any idea how much timing to add? Maybe add 2 degrees across> the board for those load rows?> Is there another way to quantify knock? My ears maybe? EGT?> Thanks

 

[4piknup]

Deedubya replies to my question:
Running lean should improve fuel economy by 3 to 5 MPG. I combined manyfuel economy mods to get my FWD turbo Laser up to 53mpg once, 702 miles ona single tank.There is some danger in running consistently around 15.5 to 16.0 AFR'swhich is where EGT and NOx emissions reach their peak. Avoid that range.Best fuel economy is between 16.0 to 16.5 AFR if nothing else has beenchanged. If you do some mods like add timing and open up the spark pluggap to around .032 to .036" you should be able to push off lean misfiresbeyond 18.0. The 1990's Honda Civic VX was tuned from the factory to runas lean as 22.0, and was responsible for coining the term 'lean lag'. Beaware that the car may not like running that lean at very light load, andit should be richer as power goes up. I found the leanest load range wasaround load level 3 on standard range maps. Above and below that loadlevel needed to be richer. Do not try to run super lean in boost- youwon't save gas and you won't make power.HTHDave W.

>  We were discussing this just the other week at4gtuner.com My internet> buddies were worried that 16:1 would melt pistons, I suggested that the> load is low and the cylinders are not stuffed full of air and fuel so> there is not the intensity in the power stroke. Any thoughts? >  I am yet to try it but I suggested to lean it out until the lean miss> limit then add a little back in till smooth. I am interested in that> figure being as high as 18:1.> Do you have any dsm specific economy improvement figures from this lean> running? >> Regards jack

 

[Benzo4gT]

Awesome info Jack :thumbsup: