Hello all.

I recently got my car dynoed, and it included a air/fuel ratio readout. At about 2250 RPMs, the ratio was roughly 17. Then it dropped down to a little under 14 when it got to 2600 RPMs. My question is, why is it so rich at 2250-2600? The stochiometric ratio is about 14:1, right? So at those lower RPMs, it's putting in a lot more gas than it can burn. Is the ratio lower at higher RPMs because you have less burn time, so you couldn't burn all that gas anyway? But if that's the case, why does it stay pretty constant (13.7) all the way up to redline? Thanks!

 

I believe 14:1 is correct, so at 17:1 , you have 17 parts air per 1 part fuel .

See an old post of mine:

http://web.camaross.com/forums/showt...threadid=46644

My car started off O.K., but richened up.

My only theory - which so far I have been unable to confirm - is that due to my free ram air, the computer has "learned" that I get more air at speed and thus need more fuel.

Could be total hogwash - ?

All I can says is that these PCM's seem to have minds of their own !!


Britt

 

Actually, most tuners aim for 13:1 A/F when doing a dynotune. 14:1 to me seems a little lean, however, if your car was tuned for it, that could just be where it makes the best numbers. As for the high ratio at low RPMs, its normal for a car to start off lean and then richen up as the RPMs climb. As long as youre not pinging, I wouldnt worry about it.

 

Ok, I'm dumb. 17:1 would be LEANER, not richer. Sorry!

So at lower throttle the engine runs leaner to reduce emissions and fuel consumption, but when ya step on it, you get the richer mixture for more power.

Do most people's A/F curves stay pretty flat after a certain point? For example, once mine got to about 2600 it stayed at about 13.7.

Now just one more thing, you get knock if you have pre-ignition due to low ocatne/high compression or hot spots. What's ping cause by?

Thanks again all!!!

 

I think this is why its giving that kind reading, the o2 sensors read the exhaust and if it gets its rich reading it leans it out, it does this over and over (for lower emmissions) until you hit WOT or mabey 80% then it takes a programed timeing map from the computer for the best A/F for best performace on a stock car