# Am I running rich for an N/A?



## Ninety-Nine SE-L (May 5, 2002)

hey, I was jus taking a look at my old Dyno chart ans I noticed my A/F ratio hangs around 11 throughout most of the run. Is that too rich for an N/A engine? what's a good A/F for an N/A? for a Turbo?


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## himilefrontier (Jan 21, 2003)

Well,you probably won't hurt anything(except maybe the Cat)but it seems a bit rich to me.I think that you would gain some power if you got closer to the stoichiometrically correct ratio of I believe 14.4:1.I think max power is supposed to be around 13.5:1,but can't remember right now(I can't sleep).Hope this helps!


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## hpro123 (Apr 30, 2002)

Car manufacturers and Nissan in particular tend to run rich fuel mixtures at extreme situations (high rpm, high MAF load) in order to assure the longevity and reliability of the engine (rich mixture drops the combustion chamber temps).

They do that to the extreme in Turbo engines that have higher temps.

Your car is fine. I am not familiar with GA16 engines but if SR20s are any indication, you are fine.


N/A SR20s are programmed by the factory for AFR from 11:1 to 10.6:1 at WOT and 6800rpm.

Turbo SR20s are programmed by the factory for AFR from 9.5:1 to 9:1 at WOT and 6800rpm.

Chris


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## Ninety-Nine SE-L (May 5, 2002)

could I benefit by bringing it up to about 12 or 13? Would I gain/lose power? right now, I get terrible gas mileage (around 21-22 mi/gal)


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## hpro123 (Apr 30, 2002)

Your poor gas mileage indicates some other problem and cannot be explained by the factory-set AFR at high loads. There are a thousand things that may lead to low mpg and you sohuld definitely start looking for probable causes.

As for the AFR, how do you plan to bring it to ~ 13:1???

You are definitely going to see gains by going from 11:1 to 12.7:1 (theoretical ideal but may vary slightly with the motor and its configuration). Problem is that if it is not done properly you may handicap the car in the longevity/reliability departmetn.

Chris


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## Ninety-Nine SE-L (May 5, 2002)

hpro123 said:


> *Your poor gas mileage indicates some other problem and cannot be explained by the factory-set AFR at high loads. There are a thousand things that may lead to low mpg and you sohuld definitely start looking for probable causes.
> *


I thought so. I am thinking either my O2 sensor, something wierd with my ECU, or my driving. BTW, that's my highway miles too.


hpro123 said:


> *
> As for the AFR, how do you plan to bring it to ~ 13:1???
> *


 got me, I was just giving the idea. I'm not sure what would make it run at a 13:1 from a 11:1.


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## hpro123 (Apr 30, 2002)

1997 GA16DE said:


> *I thought so. I am thinking either my O2 sensor,
> *


Very probable. Has been known to increase fuel consumption. Change it.


> *
> something wierd with my ECU,
> *


Very unlikely. Usually if it fails you get Check Engine Light and you KNOW something major has gone down.


> *
> or my driving. BTW, that's my highway miles too.
> *


Highway eh? Unless you are full of speeding tickets it is not your driving.

Chris


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## nitestridar (Jun 29, 2002)

I have the same gas problem you do...
I am changing the O2 by the cat this weekend to see if that helps..

I also get a real bad smell from the vents when I go FT.


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## Ninety-Nine SE-L (May 5, 2002)

hpro123 said:


> *Highway eh? Unless you are full of speeding tickets it is not your driving.
> 
> Chris *


well, lets just say I like driving @ WOT . I don't have too many speeding tickets b/c I'm careful, but I usually drive between 80 and 100 on I-4 (that would be at night when it actually moves).


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## Nostrodomas (Jun 15, 2002)

Shifting over 3,000 rpm's, will produce higher mileage. The economical shifting points I believe are between, 2,000 and 3,500 rpm. So driving over the 3,000 rpm mark on the highway will give you a lower mpg.


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## Ninety-Nine SE-L (May 5, 2002)

yea, well of course that's true. you get more mileage when you're engine's turning slower. The problem with that is that I have an auto. That means 4 wide ratio gears and also, my car's not that powerful, unless I drive like a granny, I usually shift above 4k. also, I'm a hard driver. I like to hang onto that WOT.


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## javierb14 (Jul 9, 2002)

u might also want to run a higher octane if u alter the A/F.


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## himilefrontier (Jan 21, 2003)

Do you have headders?And if you do,is there a leak in them before the O2 sensor?if there is it could be causing you to read a false lean making your computer richen the mixture.That fuel mileage is horrible.I had a 98 Sentra Xe/5spd a few years ago that got 32 mpg delivering pizza(in the same general area I see that you live in)-and I drove it HARD!Is the car far from stock? Do you have a turbo or something(larger injectors?)that would increase fuel demand?


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## BORNGEARHEAD (Apr 30, 2002)

You can adjust your throttle position sensor to get a little richer or leaner.


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## Ninety-Nine SE-L (May 5, 2002)

to answer,
-I already run 93 octane b/c of my advanced timing. This is why I'm so ticked, at 21mpg, GAS IS EXPENSIVE!!!
-No header, all stock around both O2 sensors.
-Not sure how to adjust the TPS.

I think I'm gonna start with my first O2 sensor and go from there.


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## nitestridar (Jun 29, 2002)

1997 GA16DE said:


> *to answer,
> -I already run 93 octane b/c of my advanced timing. This is why I'm so ticked, at 21mpg, GAS IS EXPENSIVE!!!
> -No header, all stock around both O2 sensors.
> -Not sure how to adjust the TPS.
> ...


are you getting a rotten smell like my car gives at FT...?


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## Ninety-Nine SE-L (May 5, 2002)

Hmmm, I'm wondering if this could have anything to do with this. Does anyone remember Jeff's Breather gizmo? I got one of those on my car. I'm not sure if a small crank case breather would help/hurt the fuel economy or mixture.


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## Ninety-Nine SE-L (May 5, 2002)

selrider99 said:


> *are you getting a rotten smell like my car gives at FT...? *


 whaa?
you mean like a heavy, heavy exhaust smell or what?


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## nitestridar (Jun 29, 2002)

no like a real bad gas smell coming out of the vents....

I don't think it's the gas becuase no matter what station I go to it happens...
People have told me its the o2 and I get really crap mpg maybe 15.... I guess I will buy the o2 and let you know...


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## Ninety-Nine SE-L (May 5, 2002)

no bad smell from the vents. how many miles do you get from a tank?


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## nitestridar (Jun 29, 2002)

I fill up and at the end of the week I am left with 1/4 tank 
with about a clocked 120-130 miles... and I do drive about 50 miles hwy a week... I think my car should be getting like 27mpg

whats up with that?


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## togenji (Oct 10, 2002)

1997 GA16DE said:


> *well, lets just say I like driving @ WOT . I don't have too many speeding tickets b/c I'm careful, but I usually drive between 80 and 100 on I-4 (that would be at night when it actually moves). *


Really? I've been shifting at the low rpm's thinking i get better mileage. Even though I'm already getting like 35-38 mpg, I just curious.


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## togenji (Oct 10, 2002)

oh i hit the wrong quote button. first time i ever used it.


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## himilefrontier (Jan 21, 2003)

[
*are you getting a rotten smell like my car gives at FT...? *[/QUOTE] 

If it's a rotten egg smell it could be due to a bad catalytic convertor.


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## dookie (May 21, 2002)

*check EVAP system*

my haynes manual mentioned something about checking the EVAP system if you smell gasoline in your cabin. i'm not exactly sure what the evap system does, but it does have something to do with the fuel tank. there is a canister in your engine bay that you can check or replace. i'm not exactly sure what all of this shit means but i'm sure someone here knows what i'm talking about.


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## hpro123 (Apr 30, 2002)

Start with the O2 sensor.

Chris


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## nitestridar (Jun 29, 2002)

I guess it is the 02 sensor on the manifold... but when I test the ecu I get a all clear... 5,5....


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## johnnykomac (Jan 30, 2003)

you could get a slightly leaner mixture by removing the intake temperature sensor and letting in hang inside your engine bay. This will trick the computer into thinking you have less oxygen in your air and will lean out the mixture. This could work pretty well in conjunction with a CAI.


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## nitestridar (Jun 29, 2002)

yeah but wouldn't you have a CEL on all the time?


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## Ninety-Nine SE-L (May 5, 2002)

on that little thing, the CEL won't go on so long as the AIT sensor stays plugged into the wire. I took mine out of the stock intake but I still left the sensor in tact with the wire. CEL never came on. Right now, it's zip-tied to the other wires going into the fender area.I wouldn't want it in the engine bay b/c even though it may make the fuel run leaner, it might also retard the timing as well b/c of the higher temp reading.


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## hpro123 (Apr 30, 2002)

DO not trick the car into supplying leaner mixtures.
I doubt that a 30% decrease in mileage could be attributed to and corrected by leaning the mixture.

Find the real problem.

Chris


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## Equivocal (Sep 6, 2002)

I think I get around 30 mpg. I have a question. From my expirence with filling up on E, It seems like the gas tank is 11.5 gallons. is that right?


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## Ninety-Nine SE-L (May 5, 2002)

it's 13, but the fuel light seems to come on around 11.5


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## Equivocal (Sep 6, 2002)

13? wow. Ive never actually seen the fuel light. But Ive drove till it was past E basically. It just seems like when I fill up that the pump stops at 11.5, So I stop too. Interesting, thanks.


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