How lean is too lean?

[Melbowski]

Long story short while cruising around 55ish my car is running a bit on the lean side (noted via my wideband). It breaks down as such: 20% of the time between 14.7-15.1 70% between 15.2-15.6 (tends more towards 15.5, makes me uncomfortable) and abour 10% between 15.7-16.1 (scares the shit out of me!). Idle is rich (bout 13.6 or so) and WOT is good and rich (bout 11). The car still runs great and I don't feel any feedback constituting problems. Bluntly however, I fear for my engine's life, but I don't specifically know if this is dangerous or not.

I did some searching and all I found was people with narrowbands, or people using EGT, neither of which specifically help me. I guess all I really want to know is how lean is too lean? What is normal for idle/cruising/WOT and what is dangerous to the engine at idle/cruise/WOT? I appreciate any help, and thank you in advance.

 

[haswesley]

Your numbers are right where they should be. Cruising down the highway should be 15.0 - 16.5. As soon as you give it a little gas, it should richen up to 13's and 14's. If you step down all the way, it should richen into the 10's and 11's. Idle should be 13.0 - 13.5. WOT should be 10's and 11's. I've been running my car like this for 2 years without incident. The 15's during cruising helps save gas.

 

[Melbowski]

Wow, you have no idea how happy this makes me! I've been stressing hella-bad for a couple days thinking my rebuilt engine is going to burn up my valves!

Ever since I bought the car it had O2 problems and ran in open-loop, so i never really knew what it should be at. Now I finally get the O2 problems sorted out and I'm scared shitless cause I have no clue what A:F is pushing into the danger zone. Thank you very much, I'll finally be able to quit staring at my wideband.

 

[jdm98gsx]

Your numbers are right where they should be. Cruising down the highway should be 15.0 - 16.5. As soon as you give it a little gas, it should richen up to 13's and 14's. If you step down all the way, it should richen into the 10's and 11's. Idle should be 13.0 - 13.5. WOT should be 10's and 11's. I've been running my car like this for 2 years without incident. The 15's during cruising helps save gas.

I'd have to disagree. Wide open should NOT be in the 10's thats way too rich. You should be in low 12's to be safe running wide open.

 

[2gGSXEclipse]

I run 11:1 WOT. Never had a problem...found that to be the sweet spot.

 

[beniger]

how much knock do you see at 12 afr? whats the temp like where you're from?

 

[EagleTSIawd]

You are running a little lean, idle and cruise should stay at 14.7 AFR with maybe the ".7" changing a little. Your high readings could mean you have an exhaust leak.

An example of mine, I have my WB Sensor on my rear O2 and one of my downpipe gaskets blew and a little exhaust gas started to leak from there. My air fuel readings went up to 15 or 16, i fixed the leak and now it always stays at 14.7 in closedloop

 

[Melbowski]

You are running a little lean, idle and cruise should stay at 14.7 AFR with maybe the ".7" changing a little. Your high readings could mean you have an exhaust leak.

An example of mine, I have my WB Sensor on my rear O2 and one of my downpipe gaskets blew and a little exhaust gas started to leak from there. My air fuel readings went up to 15 or 16, i fixed the leak and now it always stays at 14.7 in closedloop

I see, I thought the ECU aimed for 14.7 all the time, but I'm still relieved that others have had it a bit lean for years without damage. I'm pretty sure my exhaust manifold is warped with a small leak (previous owner). Been looking/saving for an Evo 3 manifold to replace it. I also have a few minor leaks up front, working on fixing those. My wideband was the best thing I ever bought for my car, but the worst thing I ever bought for my peace of mind. At least it's helping to keep my car running properly by not letting me be lazy. I apreciate all the responses, thanks guys.

 

[Calan]

I'd have to disagree. Wide open should NOT be in the 10's thats way too rich. You should be in low 12's to be safe running wide open.

For most people on pump gas, 12's at WOT is probably a little lean. Something like 10.5:1 to 11:5 would be more reasonable.

I see, I thought the ECU aimed for 14.7 all the time...

Here is the factory 2G table that the ECU uses to initially look up a target AFR, depending on RPM and engine load. As you can see, it covers quite a wide range, and the higher loads/RPMs from the factory are very conservatively rich at 9.5:1. It doesn't make much power, but it provides a large safety margin.

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14.7:1 is the stoichmetric or ideal AFR for a complete burn of gasoline. But the ECU only targets that under certain conditions, normally while cruising at low engine loads. Most of the time it is varying depending on the driving conditions and engine requirements.

Something else to note is that higher AFR's will normally be seen when the injectors aren't firing or when under extremely low loads like coasting or going down a hill.

 

[BigBeans]

My car likes 10.8-11.0 for WOT on pump fuel.

12+ just isnt safe at with 93 octane and decent boost. The timing you have to pull will cost you power.

 

[GSXeclipsePSI]

Im at 10.8-11.2 on my car with 93 and any leaner and I can't run more then 15psi on my setup. I got meth/water injection installed this week so 11.5 been fine with 11-13 timing @18-19 seems faster then 21psi right now.