How dangerous is lean burn ?
 

I asked this question in forum topic: "Tricking your O2 sensor": https://www.gassavers.org/forum_topic/tricking_your_02_sensor.html
I suggest you first read that topic.

And i want to ask it in new forum topic:

Yes, How dangerous is lean burn ?
Does it really causes expensive damage to the combustion chamber elements ? or is it an urban myth ?
And also i must mention that my car has a "knock control" mechanism. Does having "knock control" feature reduces the risks of lean burn ?
Do you have experiences concerning lean burn and its effects ?

Lean burn is dangerous
 

Lean burn is dangerous depending on how lean/which engine. Matt's new engine, for example, can burn extremely lean. Anything more than 10% lean of stoich (14.7 air to fuel ratio), I would say is dangerous, especially under acceleration and high load situations. Stay away from lean unless you can do things precisely.

Knock control has to do with ignition timing, not fuel mixture. When knock is detected your knock control mechanism will retard timing to compensate, killing power and mpgs.

Re: Lean burn is dangerous
 

But saving expensive powertrain components.

If you want to see what lean conditions do, go to the Honda-Tech Forced Induction board and look around. You'll see melted pistons, destroyed combustion chambers, and split cylinder walls. More power [and I suppose, more economy if lean burning is the route you're going] and the death of your engine walk a VERY fine line.

Lean burn
 

Is lean burn dangerous? It depends on what you mean by "dangerous":

1) Your engine isn't going to "explode" from lean burn so it's not "dangerous" to you.

2)Lean burn may create internal damage due to detonation, so it's "dangerous" to your engine. If you also retard the ignition timing, you can avoid detonation. Ignition timing used to be easy to change in the days of points, vacuum and centrifugal advance distributors. Ingition and fuel controls are programmed into chips now, so that it's hard to change timing without a degree in electronics.

2) If you artificially lean out the mixture by fooling the oxygen sensor, it will run lean all of the time. Most modern engine pollution controls are designed to use three-way catalysts that require "stoichiometric" (neither lean nor rich) mixtures. Fooling the oxygen sensor will prevent the catalyst from destroying oxides of nitrogen ("NOx"), a major air pollutant (the catalyst will still control carbon monoxide and hydrocarbon emissions). So, operating lean is "dangerous" to the environment.

Leaning out your engine may
 

Leaning out your engine may or may not be dangerous depending on how you do it. I use an EFIE from Eagle Research to step up voltage from the O2 sensor causing it to run lean in closed loop. Once the load on the engine reaces a certain point the ECU just ignores the O2 signal and goes into closed loop with the engine saving, too-rich stored fuel maps. This has been the case on the two vehicles on which I've used this - '89 Nissan 240SX and 2006 Mazda B2300 (ford ranger).

The net effect is that you get the best of both worlds, fuel efficient lean burning at lower throttle settings and maximum safe power as mapped by the computer at high load throttle. The cat will burn up the excess unburned fuel exiting the engine.

Now if you re-map your fuel to be lean at full throttle when you're generating maximum heat, could cause some serious damage as mentioned before. Excess fuel cools and dampens combustion and is safe for lots of conditions, running on the hairy mixture edge at full throttle will give you max power but can also melt parts if not done perfectly. I don't use maximum power very much so I prefer the safe too rich high load settings for now.

Re: Leaning out your engine may
 

I was just reading about the EIFE from Eagle Research. Does it really work? Have you been able to measure an increase in fuel efficiency?

There is no reason it
 

There is no reason it shouldn't work, but I would not use it because the 02 output is not linear and should not be leaned in all cases.

I have used it before and it
 

I have used it before and it does work. But, like SVOboy says, it's not perfect. I do know that if you try to go too high with the voltage, the ECU will go into open loop and ignore the O2 sensor. Right now I'm only using my IAT sensor mod. It seems to be near the limit that the ECU will accept and when I try to run even a small amount of voltage through the EFIE the ECU thinks something is wrong and goes to open loop. That irritating thing is that the IAT mod only costs about $.40 and the EFIE costs $50+ shipping. :-(

Re: I have used it before and it
 

OK, so how do you do the IAT mod? Does the IAT play a large role like the coolant temp when it comes to injector duration?

Re: I have used it before and it
 

On my car it seems to make a significant difference. But I think that some cars are set up differently. What I did was, I unplugged the IAT from the sensor and took two 220 ohm resistors and tied them together-this combination equals 110 ohms- then I shoved the ends of the resistors into the holes in the sensor plug. This makes my ECU think that the intake air temp is 242-247 degrees F.