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RUNNING LEAN & RICH? WHATS IT ALL MEAN? 

 

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 Post subject: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Fri Feb 18, 2005 1:13 am 
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I dont understand how this works. How do you know if ur car is running lean or rich? if youre using say 12.0 on freeway driving is that rich? or what if its only 7l/km on the freeway, is that lean or is that good? sorry i'm just trying to learn all this lean/rich stuff. thanks.

coz i heard you can damage your engine like pistons and stuff and i wanna learn how to tell if my car is running lean or rich.
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Posted: Fri Feb 18, 2005 1:37 am 
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lean and rich is just the air/fuel mix is it not?


if it run to rich u get unburnt petrol? runs lean to much air the the combustion isnt right?

something along that, ill let someknow with actual knowledy explain it :D

 

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Posted: Fri Feb 18, 2005 8:27 am 
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lol, the lean and richness of your engine have nothing to do with your fuel consumption (apart from waht you actually get)... to find out if your running too rich or too lean you need an AIR TO FUEL METER, which measures the AIR TO FUEL RATIO.

Your car running lean, means that its getting less petrol than needed, can be a good thing, but can also be a very bad thing... (nothing ignites when there's no fuel), how ever when it is running rich, it means that the engine is getting too much fuel with the amount of air that its recieving... this is because there is this perfect figure (don't know where from), of I THINK its 13.8 or soemthing rather? anyway if its 13.8 (could be 14.8), then you need 13.8 parts air to every 1 part fuel.

If you are running rich, then more fuels goes in that's not used, = more fuel consumption... so ti relates.. but in no way can we tell if you are running rich or lean.

Cheers - confused?

 

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Posted: Fri Feb 18, 2005 8:41 am 
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14.7:1 is the figure that you're thinking of. This is what's knows as stochiometric (pronounced like stow-kee-o-metric)

Basically what this means is that all the petrol that is going into the cylinder is being burnt (or chemically talking, oxidised) with all the oxygen in the cylinder.

It's easy to remember what's rich and what's lean. A RICH engine uses a lot of fuel to get anywhere so you have to be RICH to run your car.... lean is the opposite.

You don't have to worry about burning out pistons or valves if your engine is stock, or even modified and the ECU hasn't been fiddled with.

An EFI engine will run with an AFR of anything from 9.0:1 to 20:1 (carby is about 10:1 to 18:1) If an engine is tuned properly, it ahould be running between 11.5:1 (best rich torque) to 16.5:1 (best economy)

you only burn valves and pistons when you run a lean mixture (leaner than 14.7:1) at high engine loads, i.e running 16.5:1 AFR @ 5000RPM with 100% throttle. Even 14.7:1 can burn out valves with high engine loads.

Anyway, unless you've got an aftermarket ECU and are responsible for tuning your engine, you don't have to worry about running too lean or too rich. It will only effect your economy, it won't blow up your engine.
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 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Fri Feb 18, 2005 9:36 am 
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GO_HARD_AU wrote:
I dont understand how this works. How do you know if ur car is running lean or rich? if youre using say 12.0 on freeway driving is that rich? or what if its only 7l/km on the freeway, is that lean or is that good? sorry i'm just trying to learn all this lean/rich stuff. thanks.

coz i heard you can damage your engine like pistons and stuff and i wanna learn how to tell if my car is running lean or rich.


It's impossible to tell from fuel consumption if your car is running lean or rich. There are so many things that affect economy.

Tyre pressures, tyre compound, wind, vehicle weight, wheel alignment, even engine oil (though bugger all really)

The only way you can use economy to tell if your engine is running lean or rich is to compare you economy over time. I.e 3 months ago you were using 10l/100km on the freeway, now you're using 11l/100km.

At best this can only tell you that it's time to visit your mechanic though. If the engine was running very rich or very lean, you'd know about it without having to compare economy.

I.e, if your engine suddenly starts running rich, there'll be the tell tale signs of black smoke pouring out the exhaust, sluggish acceleration and possible mis-firing
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Posted: Fri Feb 18, 2005 6:13 pm 
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In addition to the above. The ECU works in 2 modes.


1) Closed loop. The ECU uses the oxygen sensor in the exhaust to measure what air fuel ratio the car is running at. Normal Narrow Band sensors can only tell rich/lean. Rich being greater than 14.7 and lean being less. So during normal driving the ECU controlls the injectors to oscillate rich/lean rich/lean about this point to maintain maximum efficiency.

2) Open Loop. 14.7 is good for efficiency however if you want more power you need more fuel. This is because things in your engine happen very fast. There is not enough time to burn every little drop of fuel, so you need to put extra in to make sure at least all the air is burnt and the excess fuel will go out your exhaust.
When the MAP or throttle is high enough predetermined tables tell the injectors how much fuel to inject at what RPM and Manifold pressure (and throttle too but MAP and RPM are the main ones) There will be an optimum value for air fuel ratio at each RPM / MAP point.

It's important to remember that richer doesn't always = more power and leaner doesn't always = more economy, but to a point that is generally the case.

Generally running too rich will make your car use lots of fuel and run badly but won't damage your engine. However running lean will make your engine run hot and can damage your valves, cylinders etc etc. It can also contribute to detonation.

You can read the output of your 02 sensor with a multimeter or Jaycar/ d**k smith etc have kits. Quite interesting.

Hope that helps!

 

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Posted: Fri Feb 18, 2005 8:39 pm 
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Idle and cruise is normally 14.7 - full throttle rower runs around 13.2 - otherwise things have a tendancy of going pop :shock:
Shane

 

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 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Mon Feb 21, 2005 6:13 am 
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GO_HARD_AU wrote:
I dont understand how this works. How do you know if ur car is running lean or rich? if youre using say 12.0 on freeway driving is that rich? or what if its only 7l/km on the freeway, is that lean or is that good? sorry i'm just trying to learn all this lean/rich stuff. thanks.

coz i heard you can damage your engine like pistons and stuff and i wanna learn how to tell if my car is running lean or rich.


Lets put it this way from something I learnt with my car...

My ECU self test was indicating a low signal from my O2 sensor in the exhaust manifold. So, low signal means it thinks that it is running lean according to the ECU so it boosts the fuel/richens it....

Now... my O2 sensor was basically not operating... on a highway trip I would average around 10-12 lts/100km running slightly rich... 400 km out of a 68lt tank...

I replaced my O2 sensor... $86 from Autobarn...

The ECU test says everything a-ok! And on the highway I can average 7-8 lts /100kms... 700 kms p/tank

So a faulty O2 sensor can chew up to 4lts / 100kms of highway driving, imagine if it was just city driving!!!

There is only a certain ammount of fuel which can burn per volume of air... too much fuel is rich, excessive heat, excessive fuel usage, tiny power gain...

on the other hand... too lean, not enough fuel, risk of detonation, loss of power...

 

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Posted: Mon Feb 21, 2005 8:30 am 
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Spork wrote:
2) Open Loop. 14.7 is good for efficiency however if you want more power you need more fuel. This is because things in your engine happen very fast. There is not enough time to burn every little drop of fuel, so you need to put extra in to make sure at least all the air is burnt and the excess fuel will go out your exhaust.
When the MAP or throttle is high enough predetermined tables tell the injectors how much fuel to inject at what RPM and Manifold pressure (and throttle too but MAP and RPM are the main ones) There will be an optimum value for air fuel ratio at each RPM / MAP point.


The extra fuel you need for more power also dies two other things aswell.

1. It helps cool the engine
2. It helps lubricate the engine.

Those two things also contribute to more power from a richer mixture
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Posted: Mon Feb 21, 2005 1:30 pm 
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unclewoja wrote:
Spork wrote:
2) Open Loop. 14.7 is good for efficiency however if you want more power you need more fuel. This is because things in your engine happen very fast. There is not enough time to burn every little drop of fuel, so you need to put extra in to make sure at least all the air is burnt and the excess fuel will go out your exhaust.
When the MAP or throttle is high enough predetermined tables tell the injectors how much fuel to inject at what RPM and Manifold pressure (and throttle too but MAP and RPM are the main ones) There will be an optimum value for air fuel ratio at each RPM / MAP point.


The extra fuel you need for more power also dies two other things aswell.

1. It helps cool the engine
2. It helps lubricate the engine.

Those two things also contribute to more power from a richer mixture


Diesel is called a lubricator, but petrol is an abrasive. I cant exactly see it helping too much :D

 

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Posted: Mon Feb 21, 2005 1:55 pm 
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Rich certainly does not equate to power gains. The leaner the better. Take a stock falcon and lean it slightly via fuel pressure and watch kw increase on dyno.... very cool.

Too much fuel basically chokes the combustion process and hurts power. Richer fuel mixtures at WOT more a matter of safety... as shane mentioned... lean engine condition is conducive to detonation under high load... high load + detonation = broken engines. But of course, air/fuel cannot (shouldnt?) be considered in isolation of spark timing....

 

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Posted: Mon Feb 21, 2005 2:02 pm 
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@ decell = 16.3-15.5
@ idle = 14.4-14.7
@ cruise = 15.5-16
@ accel = 14.2-13.8
@ WOT = 13.3-12.8

this is a general estimate that i found works quite well.

these are form the general revs that the style is used.
ie, cruise=1200-2500 rpm
accell= 2500-4000 rpm at a medium map pressure

ect...

 

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 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Mon Feb 21, 2005 2:26 pm 
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Lukieman wrote:
... too much fuel is rich, excessive heat, excessive fuel usage, tiny power gain...

on the other hand... too lean, not enough fuel, risk of detonation, loss of power...


Close, but not quite right. Too rich actually keeps the cylinder and valves cooler. Once the oxygen in the cylinder is burnt, the rest of fuel cannot be burnt. This evaporates and flows out the exhaust. Evaporation = cooling (evaporative airconditioners for example). As an experiment poor some fuel on your skin, don't smoke at this time. As the fuel evaporates your skin cools.

In piston aircraft we use exhaust gas temperature (EGT) as an indicator of mixture, becuase we control our mixture manually. High EGT = too lean. Add more fuel, EGT goes down.

The risk of detonation from running too lean is PARTLY because the valves and plugs are glowing white hot. This lights the fuel before the plug has a chance to fire.

Anyway thats enough of my Physics lecture, I am sure you get the picture.

 

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 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Mon Feb 21, 2005 2:28 pm 
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Posted: Mon Feb 21, 2005 6:17 pm 
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4.9 EF Futura wrote:
Rich certainly does not equate to power gains. The leaner the better.
.


Um no.

Rich is anything greater than stociometric (spelling!) or 14.7:1
As explained in my post richer that this point will generate more power untill a certain point, then power goes down.

Falcons run a little rich so leaning them out gives more power. There is an optimum point for max power (say 12.5:1) and another for max efficiency (say 16:1) and these will be different for each car and with different mods and at different RPM/ throttle.

 

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