how lean is too lean?

[talon187]

ok right now im running a maf pro. Its totally diffrent then the maft translator. Im running it as speed density. I use the program turner pro rt to tune my car.For those that have used this program know it has many features. You also know gas is at an all time high its 465 here for 93 octane. This program has part thorttle tracking cruise a/f it also has part thorttle tracking lean a/f ratio. So ive ben told if this is set correctly it will stay at the desired a/f ratio on driving around town. Not under boost and yes i know it should be some where around 11.5-10.9ish depending on who you ask. but im wondering on the lean curise whats the safest leanest a/f i could run without hurting anything ? thanks for the input guys

 

[1stGenTSi]

For cruising you can run a little on the lean side of stoich, about 15 to 1. I don't think you wanna go any leaner that that though.

 

[turboglenn]

14.7-15.5:1 is what i normally run on pump fuels during cruise... 11:1 is for wide open, you don't want to cruise that rich or you'll be filling your tank daily.

I set mine (full EMS though) to where when cruising teh 02 (AEM UEGO) oscilates between 14.7 and 15.5... ON ethanol i run a bit leaner(16.2:1), but alcohol is a little more friendly to lean tunes than regulat petrolium gas.

 

[talon187]

I was about to program 15.5 into the program but 15 should be ok.

 

[pneumo]

How lean you can go depends on how much airflow (grams per rev) is going through the motor. At light load you can go very lean without fear. As airflow goes up the A/F ratio should gradually get richer until around 5 in/hg vacuum where it should be around stoich.

From my experience the limit to how lean you can go will be misifires. If the motor misfires, it's too lean. Bigger plug gaps helps to reduce lean misfires, but you'll have to balance that against WOT misfires if the gap is too big. I've been able to run slightly leaner than 18:1 at very light throttle.

I also found that my motor doesn't have a smooth idle and it stalls easily if the A/F ratio goes leaner than around 16.0:1. So I've set my rolling idle A/F ratio at 16.0, then it goes to 18.0 just off idle, and gradually richens.

A side effect of running leaner than stoich is that the mixture burns slower, so knock is less likely, but the engine needs more timing to keep power levels from dropping, so I've also added one or two degrees of timing in the same parts of the map that are very lean. It's working very well!

Here's some good info. Scroll down to the bottom, there's a little chart that shows mixture burn speed at different A/F ratios. It'll give you an idea of timing changes needed for leaner A/F ratios. The whole page is good, too. I forget who posted up that page, it's a good find. www.max-boost.co.uk/max-boost/ignition_deeper.htm

And for proof of concept, here's my daily driver. www.gassavers.org/garage/view/207

 

[wishihadatalon]

I just logged 24mpg with a 2g awd with plenty of spirited sprints up to and past the speed limit. With my fiance driving it I have no doubt it will go 30mpg. I have afr tracking off boost via MS2 set up and it is 14.5 pretty much across the whole bottom of my map under my boost curve. I intend to lean out the map a little more after I get 1 oil change on the motor. I am really hoping to see 30+ mpg out of the car with not too much effort.

 

[JayRolla]

How lean you can go depends on how much airflow (grams per rev) is going through the motor. At light load you can go very lean without fear. As airflow goes up the A/F ratio should gradually get richer until around 5 in/hg vacuum where it should be around stoich.

From my experience the limit to how lean you can go will be misifires. If the motor misfires, it's too lean. Bigger plug gaps helps to reduce lean misfires, but you'll have to balance that against WOT misfires if the gap is too big. I've been able to run slightly leaner than 18:1 at very light throttle.

I also found that my motor doesn't have a smooth idle and it stalls easily if the A/F ratio goes leaner than around 16.0:1. So I've set my rolling idle A/F ratio at 16.0, then it goes to 18.0 just off idle, and gradually richens.

A side effect of running leaner than stoich is that the mixture burns slower, so knock is less likely, but the engine needs more timing to keep power levels from dropping, so I've also added one or two degrees of timing in the same parts of the map that are very lean. It's working very well!

Here's some good info. Scroll down to the bottom, there's a little chart that shows mixture burn speed at different A/F ratios. It'll give you an idea of timing changes needed for leaner A/F ratios. The whole page is good, too. I forget who posted up that page, it's a good find. Tuning the LET

And for proof of concept, here's my daily driver. 90 Laser

Here is a post ive been looking for. Im having issues tuning my lo and mid throttle. At any load I hit 14.7 but that causes mid throttle to be way rich. If I tune everything below 5 in/hg vacuum a lot leaner and make sure I hit 14.7 at 5 vacuum, I think my tune will be a lot better. I was scared to run leaner than 14.7 at any load but after this info I think I will be fine. Dont want to burn another valve, so Ive been running rich to be safe.

 

[Black_Bullet]

Interesting post.
And what happened when you burned a valve, or how did it happen.
What type of AFR were you seeing then?

Right now im running 14-15.5ish idle and cruise, and it eventually makes its way down to 11.1-11.2 at WOT... I been wanting to set up a nice lean burn for gas milage, but I also have extended closed loop set in my chip and if I start coming onto boost to quick w/ this quick spooling setup, it will trigger some nasty knock if the ecu doesnt switch to open loop before that happens, and i dont want the issue to be worse if I set the tune even leaner.

 

[JayRolla]

Actually I did not have a wbo2 at the time. But I believe I was running real rich. When the head was torn down though it looked as if the valve burnt from running lean. I think it burnt up when I was tuning and I must have ran it lean for a bit that burnt it. Thats what I get for tuning off of a logger.

 

[pneumo]

Interesting post.
And what happened when you burned a valve, or how did it happen.
What type of AFR were you seeing then?

Right now im running 14-15.5ish idle and cruise, and it eventually makes its way down to 11.1-11.2 at WOT... I been wanting to set up a nice lean burn for gas milage, but I also have extended closed loop set in my chip and if I start coming onto boost to quick w/ this quick spooling setup, it will trigger some nasty knock if the ecu doesnt switch to open loop before that happens, and i dont want the issue to be worse if I set the tune even leaner.

I was also seeing a knock spike when quickly coming out of lean burn mode and going WOT. I backed off the extended closed loop settings in the TPS map so it would go into open loop a little quicker. The TPS map will give you a quicker reaction.

 

[xxShaneOmac]

Im at 14.7 ish area give or take .5 at any time.


But why when I lift off to shift does my afr goto the high 11's low 12's every single time i shift.

Thats got to be killing me.

 

[JaxTalonTSi]

Busted ringlands
Melted Pistons
blown headgasket
warped cylinder head
maxed out knock sensor
max retard ignition timing

If you have any of the above applies to you, you may have ran too lean

 

[pneumo]

Im at 14.7 ish area give or take .5 at any time.


But why when I lift off to shift does my afr goto the high 11's low 12's every single time i shift.

Thats got to be killing me.

It's called 'decel enrichment' and richens the A/F mixture when you lift off the throttle quickly.
Or it could be a BOV vented to atmosphere.

 

[xxShaneOmac]

BOV is recirc.

So its soposed to do that. Should I let off slower?
I hate that i bet its a huge waste.

 

[turboglenn]

It's called 'decel enrichment' and richens the A/F mixture when you lift off the throttle quickly.
Or it could be a BOV vented to atmosphere.

The richness is most likely from the "throttle pump" enrichment feature that prevents lean spots when the throttle opens suddenly (when gassing it after a shift) the decel feature you're talking about is actually backwards from that it's called "decel cut-off" and cuts fuel completely above around 2k RPM's when you're at 0% throttle to save on gas during engine braking.

Now if for some weird ass reason Mitsubishi put a decel enrichment in their ECU it will be the first I've heard of and so some one please correct me if so.

It's not that big of a waste since it's only for a split second... now if yours is doing it for longer periods of time i am confused and would need to see some data-logs to help you any further

 

[wishihadatalon]

I was wondering about that too. I have never noticed my 1g doing a decel fuel saving trick. I have my megasquirt setup to do it and I like it. It makes throttle tip in a little weird and wideband readings go crazy for a sec, but other than that, not too bad.

 

[turboglenn]

If there's something you need help with or are just wondering about on the decel cut off and tip-in enrichment or anythign like that on a stand alone, just PM me or post it in the tuning section so that the info can be there for future use or found during some one's search and i'll do my best to help you understand it, not to mention there's several other people on here with a vast amount of knowledge to help get you going

 

[JayRolla]

Every dsm Ive seen a wbo2 and a stock ecu would run rich when dropping the throttle. I always thought it was normal.

On a side not I retuned my lo throttle and used the info pneumo suggested. Its amazing how much power I was robbing in the low rpms running so rich. Decel is at 20-25 vacuum. At 15 in/hg I see 18 afr flat. 10 in/hg I see 15-15.3 afr and at 5 in/hg Im at 14.7 and any thing above is ok. Mid is a lot better now. Does this sound safe?

 

[turboglenn]

WOW! 18:1 AFR???/ How are you setting up the closed loop to run 2 different AFRs? Are you re-mapping a stock ECU with it's AFR targets, or are you just leaning it out to where the closed loop can't compensate enough to get it back up in teh 14.7 range?

18 is a tad l;ean but under really light load you should be able to get away with it. I've gotten away with 17 - 19:1 on long highway stretches, but i had to have the laptop on hand to dial in the timing and a fe other things so the car would run smoothly at that lean of an AFR... It tends to start missing at about 18:1 wheni start playing with the same things.

 

[pneumo]

Every dsm Ive seen a wbo2 and a stock ecu would run rich when dropping the throttle. I always thought it was normal.

On a side not I retuned my lo throttle and used the info pneumo suggested. Its amazing how much power I was robbing in the low rpms running so rich. Decel is at 20-25 vacuum. At 15 in/hg I see 18 afr flat. 10 in/hg I see 15-15.3 afr and at 5 in/hg Im at 14.7 and any thing above is ok. Mid is a lot better now. Does this sound safe?

That's almost exactly the same tune I've been using on my car.

Decel enrichment is used when you chop the throttle, or when the throttle is backed off rapidly but not closed all the way. Decel fuel cutoff takes over after the throttle is closed for 3/4ths of a second. That slight delay is built in to smooth out the transition into engine braking. Leaning out these settings doesn't save much gas since it happens for a very short time. Decel enrichment is also useful to reduce what I call 'lift throttle knock', which is a little blip of knock that sometimes happens just as you start to lift off the throttle. Anyone else notice that?

 

[turboglenn]

pneumo, thanksfor the detailed explanation of the decel enrichment , that's honestly something I've never seen in a car, but it's something like what we dial in on track bikes so they don't have hard hitting on and off syndrome coming out of the apex of a turn when transitioning from off throttle to on throttle

 

[Black_Bullet]

Hmm...... maybe i should tune a tad leaner in the lo throttle areas. Doesnt running leaner like that help clean the combustion chamber of carbon depsites.. Long as i dont knock id def perfer e leaner tune on this old motor with all its blowby and what not.

 

[JayRolla]

WOW! 18:1 AFR???/ How are you setting up the closed loop to run 2 different AFRs? Are you re-mapping a stock ECU with it's AFR targets, or are you just leaning it out to where the closed loop can't compensate enough to get it back up in teh 14.7 range?

18 is a tad l;ean but under really light load you should be able to get away with it. I've gotten away with 17 - 19:1 on long highway stretches, but i had to have the laptop on hand to dial in the timing and a fe other things so the car would run smoothly at that lean of an AFR... It tends to start missing at about 18:1 wheni start playing with the same things.

Well this might be another issue. I have the stock o2 replaced with my wbo2. I wired it into the ecu but it must have come loose because I have a CEL and Ive been to lazy to rewire it up. So if the ecu does not see an o2 sensor would that leave me in closed loop?

 

[wishihadatalon]

If there's something you need help with or are just wondering about on the decel cut off and tip-in enrichment or anythign like that on a stand alone, just PM me or post it in the tuning section so that the info can be there for future use or found during some one's search and i'll do my best to help you understand it, not to mention there's several other people on here with a vast amount of knowledge to help get you going

You should come to Michigan and help I know I can make it a smooth transition, I just haven't had the time to mess with it. I don't feel it at all when driving, it just annoys me when I am watching the laptop.

 

[yokotabrat]

Well this might be another issue. I have the stock o2 replaced with my wbo2. I wired it into the ecu but it must have come loose because I have a CEL and Ive been to lazy to rewire it up. So if the ecu does not see an o2 sensor would that leave me in closed loop?

With no O2 sensor feedback, the ecu should stay in open loop and run off the fuel maps.