Engine air/fuel tuning

Are your O2 sensors in good shape? I have the same read out on my gauge because I have a faulty O2 sensor that I used to relay to my Air/fuel meter.

air/fuel tuning

Whats the best way to get an accurate air/fuel ratio reading? I have air/fuel gauge which usually reads lean but I don't trust it to be accurate at all. My auto class has a wideband o2 sensor thing, will that get me an accurate reading? I would like to figure mine out since I have many airflow mods but not extra fuel. Also 14.7:1 is normal correct?

14.7:1 is stoichiometric but its pretty lean..... i think optimum sits right above 12:1 afr

and yes, a wideband is the only way to accurately read your afr

14.7 is optimal for cruising, actually slightly leaner than that (around 15:1) - b/c you don't need a lot of power for just cruising @ light throttle and you want to save gas. 12:1 is rich and is best for power and idle, but you don't want a mix of 12:1 constantly - only with heavy throttle or idle. Rich all the time will dilute the oil and that's not good.

Trav

Thanks guys that helps a lot, I will take my car into auto class this week and figure it out. If I am lean as I suspect, will bigger fuel injectors and pump help alone or will I need something to program my ecu such as a apex s-afc?

the afc will do, no way your injectors are even near maxed out without some forced induction

Yeah - the '93 models had the MAP sensors, so a vacuum leak causing a lean mixture is out of the question. Check exhaust gas temps. Anything over 1800ºF @ WOT is most likely a lean mixture or MAY be the EGR valve/modulator crapping out.

Trav

You can buy an UEGO wideband O2 sensor for your ride, they run about $400 though.

Used the wideband o2 thing in class today. The readings jumped around a lot and made me question how good the thing really was, my teacher said it usually doesnt do that. Maybe my air/fuel gauge that is in my car is reading right? Either way I'm going to get a new o2 sensor. For anyone who has put a new one in, do they come with the flange already on them? Or how do you install one?

My readings at idle were between 15.5:1 and 17:1, obviously lean. Then at 3000rpm it was reading between 15:1 and 16:1, still lean. Is this normal at all? I will probably end up buying a s-afc becuase I would like it for future projects anyway, does anyone have experience with one on a 93-97?

very lean

The only thing I can really think is that you are 1) lean but 2) perhaps not AS lean as you're thinking. I mean, you gotta think, if you're at full throttle, then 16 or 17:1 would detonate and kill something. But, if you're holding @ 3000rpms, then the throttle plate isn't open very far (what...maybe around 10º if even that). I guarentee that if you were somehow able to hold 3000rpms @ WOT, then the mixture would most likely richen up somewhat - you know, extra fuel b/c it's in open loop @ WOT. Probably not enough though becaue the idle mixture is definitely too lean. The fact that you're lean @ idle means there's a problem. You normally should run rich @ idle - like around 13.5:1 or so.

Things I would check. All the auxiliary systems...EVAP and PCV systems - they do provide extra fuel into the intake system. If one stops working, then you are loosing fuel to the mixture. The ECU determines pulse width based on A LOT of variables - one is that these systems are functioning properly.

Since you have an OBD-I engine, check the learned value (Vf). You can check your long-term fuel trim by the voltage output of the Vf terminal on the diagnostic port. Search on the internet for info on Vf for the TCCS - can't remember, but I believe it's with ignition on and the TE1 and E1 terminals bridged. The Vf terminal will also give you a digital read-out of the O2 sensor function depending on the idle contacts on the TPS and the TE1 and E1 being bridged or not bridged - I don't remember exactly, but it can be done somehow.

Check your MAP sensor. They shouldn't wig out like MAF sensors do when you install an aftermarket intake - of if you had a vacuum leak somewhere because the computer just thinks you've got your foot on the gas pedal.

Trav

Thanks for the response guys. I don't really think my car has a vacuum leak or anything because its been running this way for a while, I will go check the MAP sensor though. I'm gonna put in a new o2 sensor this weekend and see what it does. Does anyone know if when you buy a new one it includes the flange? I'm also going to check my whole exhaust for leaks this weekend, I've had a suspision that the flex pipe on my header is leaking for a while. If I am loosing back pressure there, could it cause me to run that lean? Well I'll just have to take a look when I get time.

hate to jump in on your topic, but since its along the same lines..

Aren't backfires from a richer a:f, and is deceleration really rich? Cuz with the cutout open, during deceleration (and just a tad on the gas pedal) I can get it to fart continously and sometimes it backfires. Sounds badass lol, but I should stop with it >_>

my mr2 backfired when i had a turbo 4age map in my megasquirt and still had the cat on there (running way rich)..... it was to the extent to where the cat was getting red hot on the outside.... got a new exhaust on there and removed the cat..... no more backfiring..... at least with this car, the reason it backfired was the excess fuel in the air mixture getting passed through a ridiculously hot/clogged cat causing the fuel to ignite in the cat (and was shooting a constant "fire" out the tailpipe when i cut the original muffler off)....

and unless you're using a WB o2 sensor or a split second a/f gauge, then the reading is nothing more than a lightshow.... a real time narrowband output will not be accurate at anything over 1500 rpm's or so

So do you think my exhaust could be causing me to run that lean? I just have a short ram intake, header, no cat, full cat back 2.5" exhaust. I replaced my o2 sensor but havn't driven it yet to see if it helped anything. I was going to put my old cat on and see if it would make it richer but that thing was so rusted I can't even get it off my old pipes without it just shattering into dust.

If I get a s-afc, can I tune it with the wideband o2 set up I have in auto class? Or would it be something that has to be done by a professional? I'm pretty much against it if I can't do it myself.

Do you guys think that a the complete straight through exhuast and a intake could be causing my car to run that lean? In addition I think I have a exhaust leak in my header flex pipe which could cause a loss of even more back pressure.

Is the s-afc something that has to be tuned by a professional or can I do it myself with the wideband o2 sensor.

could i'd bet....get the AFC and tune it with that wideband like you want to, you should gain some throttle respose and a little hp