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What Afratio Is Safe To Run?

kristafa

By kristafa,
in Engines & Forced Induction

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kristafa Proficient

kristafa

Posted
Posted

Just bought a new autometer Air/Fuel Ratio gauge and installed it into my rb20det bmw. The gauge shows that i'm running stoich when the car is warm, but it's about 2 led's away from running lean.. Should my car be running in the middle of stoich (12 o'clock)?? When i rev the car, it seems to stay around that same area, it never really enters the lean section, or rich section (though the car has only been running with this new engine for a week, drove it for the first time last night)..

I'm scared even though it's showing stoich, that it's a bit to close to the lean area.

any help appreciated, thanks.

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fr0st Experienced

fr0st

Posted
Posted

Your still only using a narrowband oxygen sensor so you will only ever be able to tell if its running lean or rich, not the actual AFRs. I think you'll find it will run around stoich < 3000 rpm because its using the oxygen sensor to stay at stoich (closed loop). If you give it some revs it should drop into the rich section since your running open loop and the stock ECU is very rich. If not your O2 sensor may be screwed.

Sydneykid Grand Master

Sydneykid

Posted
Posted

The standard slow and narrow lambda sensor only sees A/F ratios around stoich. It is too slow and too narrow to record A/F ratios outside that area.

Well buying a useless gauge was a waste of money, wasn't it?

;) cheers :D

RB30-POWER Mentor

RB30-POWER

Posted
Posted

you should see the guage bouncing back and forth from rich to lean when in closed loop mode as its aiming to acheive an average afr of 14.7:1.

when you are under high load or wot, it should go into the rich zone and when the de-accelerate it should go lean or off altogether as the injectors are cut off.

MerlinTheHapyPig Mentor

MerlinTheHapyPig

Posted
Posted

the afr gauges are pretty useless, for reasons suggested above.

The stock o2 sensor is pretty useless, the stock ecu uses it when cruising to gradurally lean out the mixture safely, but it's too slow to rely on the readings when doing anything else other than cruising!

If you had a wideband o2........

As far as turbo's go, most tuners aim for 12:1 or 12.5:1, N/a cars can be tuned leaner than that 13:1 - 15:1

i don't recommend tuning it yourself unless you have the equipment and you know what you're doing!!

a turbo car running 14.7:1 on boost is bad news! it is too lean (hot) and you will burn out valves...

rob82 Mentor

rob82

Posted
Posted
the afr gauges are pretty useless, for reasons suggested above.

The stock o2 sensor is pretty useless, the stock ecu uses it when cruising to gradurally lean out the mixture safely, but it's too slow to rely on the readings when doing anything else other than cruising!

If you had a wideband o2........

As far as turbo's go, most tuners aim for 12:1 or 12.5:1, N/a cars can be tuned leaner than that 13:1 - 15:1

i don't recommend tuning it yourself unless you have the equipment and you know what you're doing!!

a turbo car running 14.7:1 on boost is bad news! it is too lean (hot) and you will burn out valves...

Some WRX's hold closed loop until around 8Psi of boost from the factory. And alot of modern cars are now coming out with wideband 02 sensor factory.

kristafa Proficient

kristafa

Posted
  • Author
Posted
The standard slow and narrow lambda sensor only sees A/F ratios around stoich. It is too slow and too narrow to record A/F ratios outside that area.

Well buying a useless gauge was a waste of money, wasn't it?

:( cheers ;)

i find it hard to believe that autometer marks these gauges as "not for use with wideband oxygen sensors" and sells them knowing that they aren't useful. If the 02 sensors output voltage drops to 0 volts, i would see that it's running lean, right? so it would be doing its job in that sense...

Adriano Grand Master

Adriano

Posted
Posted

They aren't anywhere as accurate as their display would suggest, they should just have three led's rich' lean and stioch, but then they wouldn't sell very many. Neither would they if they made it a proper kit with a wide band sensor and sold it for $800

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