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Air to fuel ration

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Old 06-21-2014, 10:06 PM   #1
yurizx6r
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Default Air to fuel ration

Hey guys, I just put in an air/fuel gauge wide band in my 93 5.0. I am new at air to fuel ratio's, but after driving it for 5 miles (after unplugging the battery) I noticed that if I drive it normal the a/f ratio goes between 14.5-15. This is shifting at about 2800 RPM's. When I put the petal to the metal (WOT) my higest number goes up to 17 and my lowest number was 11.3...........problem? When you mash the gas and shift it at 5,000 it seems to be running lean. I know for turbo cars you don't want that number any higher than 11.5, but I don't know about our cars/naturally aspirated engines. Thoughts?
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Old 06-21-2014, 10:09 PM   #2
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In case this makes any difference here are my mod's worth mentioning to the motor: bama chip with EGR delete, BBK CAI, C&L 73mm MAF, 70mm TB, Trick Flow Track heat intake, stock injectors, and a full exhaust with long tube headers and off road H-pipe.
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Old 06-22-2014, 06:53 AM   #3
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Stupid question for you ,but that C&L MAF housing doesn't have a sample tube set up for larger injectors does it?
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Old 06-22-2014, 07:55 AM   #4
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No. It's set up for 19lbl injectors, and I even checked with C&L what the dimensions were. They were measured with a pair of calipers, so I know for sure it's good.
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Old 06-22-2014, 08:26 AM   #5
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when are you seeing 17 and when are you seeing the 11.3? where is it at were you think it is lean?
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Old 06-22-2014, 09:16 AM   #6
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Ok let me start over. What are the normal ranges for a naturally aspirated car like ours? What numbers should I see and when? I am thinking new that maybe I should give the computer some more time to learn the tunes after unplugging the batter, and the fact that I kept switching tunes on my Bama chip probably didn't give it enough time either.

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Old 06-22-2014, 10:18 AM   #7
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To answer your most recent question, those "numbers" are all in the "normal-ish" range. At 2k rpm steady my car was around 17 on the dyno. When matted it dropped to 13-ish and pretty much stayed right there all the way though the pull up to 5500rpm. That's with a stock fuel system, stock A9L, and an SN-95 MAF housing.

If you see 17 during WOT, something is WRONG. A number like 11 as soon as you step off the gas is normal but it should clean up quick.
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Old 06-22-2014, 12:26 PM   #8
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Just cruising, it should be roughly 14.7 (controlled by the O2 sensors). For wide open throttle, for NA, it should be roughly 13.0:1.
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Old 06-22-2014, 03:46 PM   #9
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Ok so during WOT it would go down to 11.3, but as soon as I let off the throttle and went to idle it went to 17 then went back down to 14. Is this normal? For a naturally aspirated car should I ever hit 17 or is that too lean? Like I said, it stays almost perfect at 14.5-15 if I don't drive it like I stole it.
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Old 06-22-2014, 04:29 PM   #10
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It sounds fine maybe a bit rich but it is ok there.
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Old 06-23-2014, 08:38 AM   #11
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At WOT, does it stay at 11.3 the whole time? As stated above, at initial wot, mine may drop to 11.5 - 11.8, but then quickly recover and hold 12.8-12.9 the whole pull.

Everything else about your setup sounds right.
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Old 06-23-2014, 10:16 AM   #12
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My lowest reading was 11.3 with the "race" tune. I still need to do more pulls with the car and stick with a tune. Once I take my foot of the gas it will go up to 17 and then go back down to 14.5-15. I was wondering if that was normal or too lean. From what I am gathering, it seems 11.3 is a little too rich since it's a naturally aspirated car. I was also told that if it goes to 17 after a pull not to worry as long as it goes back down because the fuel injectors shut off temporary until it stables out at idle. What I am going to do is put it back on the regular (close to stock) tune, drive it for a few miles, and then gather what it's doing. The regular tune runs smooth, the "performance" tune runs a little rougher, and the "race" tune I can smell gas.

I also found this, "
A/F Characteristics
Ratio
5 Rich burn limit. Combustion is weak and/or erratic.
6-9 Extremely rich. Black smoke and low power.
10-11 Very rich. Some supercharged engines run in this range at full power as
a means of controlling detonation.
12-13 Rich. Best power A/F for normally aspirated WOT.
14-15 Chemically ideal. At 14.6 the A/F is at the theoretical ideal ratio
with no excess fuel or oxygen after combustion. Good A/F target for part
throttle cruise and light to moderate acceleration.
16-17 Lean. Best fuel economy A/F ratio. Borderline for part throttle
drivability (worse than borderline if EGR is used).
18-19 Very lean. Usual lean limit (Driveability).
20-25 Lean burn limit. Varies with engine."

Would this be a good table to go by?
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Old 06-23-2014, 01:05 PM   #13
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Yeah, that description of A/F ratios is what I've always gone by.

And your plan for your car sounds good. Let the computer relearn parameters and then start tinkering with a tune. Remember though………baby steps lol.
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Old 06-23-2014, 01:25 PM   #14
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Yeah you're right. This is my first experience with an air/fuel gauge, so I didn't know what to expect. I decided to buy it because I just put in pretty much every bolt on you can do besides heads and forced induction with the stock injectors, so I wanted to see if the car was running too lean or anything like that. Besides, it's a great tuning tool to have for the future. I will do a few more pulls and see what results I get, but now I know what to look for at least.
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Old 07-11-2014, 07:43 AM   #15
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Ok, so after some setbacks and life events I finally got a chance to drive it and do some more pulls. I put it back to the "stock" tune over the very rich running "race" tune. During WOT it usually goes down to 13.3, but the lowest I saw was 12.6. As soon as I take my foot of the gas it will go to 17, but stabilize between 14.5-15.2. If I drive it normally, it stays between 14.5-15.2 also. I am guessing this is chemically ideal, and I shouldn't have to touch it?
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Old 07-12-2014, 06:48 AM   #16
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Yep, thats a good setup. Maybe alittle lean at WOT, but since your na, I wouldn't change a thing.
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Old 07-15-2014, 06:49 AM   #17
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Sweeeet. Looks like I've got this figured out then. Thanks!
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Old 07-17-2014, 03:58 PM   #18
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13.0 is pretty good for an N/A car. I recently was having issues not mphing like the car should for making 1300 hp on motor, bought a set of 02 sensors for my racepak, we were getting 14.1 going down track. Made a 7 jet up switch to add a lot more fuel (Q16) dropped the air fuel down to 11.9-12.1 going down track, car sounded horrible in the burn out but picked up 2 mph. I went back 3 jet sizes and got the Air fuel to read around 12.5 to 12.7 and it picked up another .5. Just give the car what it wants, every engine will want different amounts of fuel.
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Old 07-17-2014, 03:58 PM
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