air fuel ratio on crack

4gotn · Post by **4gotn** » August 3rd, 2007, 10:05 pm

ok im not sure what is causing this to happen, probly just bad ecu programing, but my af ratio seems to spike from lean(sometimes off the scale) to norm.... and when i put my foot into it ill go more twords rich(obvious) but sometimes runs almost full rich
its driving me nuts lately because ive got a brand new t3 in my garage and ive held off on any future mods simlpy because i dont want to overboost and not have enough fuel in there
the only ideas i have are the idle air bypass and the fact that there is an autotranny ecu instead of manual (no speed sensor may cause issues)
there are no vaccume leaks, timing is 100% (new belt, tensioners are good, etc), and the car runs perfectly fine except for the surging
any ideas ?
thx

ModMX3 - (Carmaster2005) · August 3rd, 2007, 10:34 pm

What your Air/Fuel gauge has gone Lindsay .....

J/k. Maybe check your TPS as most 94+ are varible resistor type. Not sure of the differences between the auto vs. mannie ecus but i do have an extra 94 manual transmission ecu if you find that to be at fault. Just im me. maybe spark plug wires or temp sensor could be the cause. But im guessing you have a turboed setup now which if so have any boost leaks ?

mr1in6billion · Post by **mr1in6billion** » August 3rd, 2007, 11:03 pm

You are using a wide band sensor and not just a guage, right?

4gotn · Post by **4gotn** » August 4th, 2007, 12:28 am

no im not bosting yet but i still have my old ecu..i got the autotranny for diagnosis... thought the other was bad... as for the tps sensor it went bad and i spent about a week ordering from my store till i found one that wasnt 300$..came from a toyota... it works fine and its denso and everything...shouldnt be the problem...as for the coolant temp sensor it should be good...its fairly new..did blow a head gasket after i bought it though...

as for my sensor
its a short band, just a guage...i know its not going to be completely acurate but the thing seriously looks like its on crack the way it jumps arround so its making me nervous about the boost
know where i could get a wide band for less then out the a$$?

Yoda · Post by **Yoda** » August 4th, 2007, 1:43 am

Sounds like your A/F meter is working 100% to me. The output of the OE O2 sensor in a square wave not a sine wave so all you would get is a series of on/off (or rich/ lean) pulses which increase or decrease with engine rpm. So waht you are seeing is normal. Now if the signal was a sine wave then your meter will display a smooth lean to rich display as the voltage from the O2 ramps up and down. Any A/F that works with a narrow band O2 sensor is just for show anyway. The reaction time is so slow that by the time that meter show you a reading what the engine is actually doing has shot past what the display is showing and has on real value for serious tuning purposes. By the time the the meter show you have a dangerous reading it is to late. To be of any real value you will have to uses a Wide Band set-up. Since a wide band sensor cannot supply a signal to the cars ECU you will need to weld in a seperate fitting for the wide band O2 sensor. The only low cost alternative is to read the exhaust gas temp if you know what to do and understand the science. To make the explansion simple is the exhast gases are to hot it too lean and if to cold it is running rich.

4gotn · Post by **4gotn** » August 4th, 2007, 3:19 pm

that makes sense
but the car does tend to surge...any ideas on that?... is it just mazda tuning?

Skuce · Post by **Skuce** » August 11th, 2007, 2:42 am

Some wide bands have a 0-1v analog output too that you can use inplace of your stock 02.

Anyways. Have you changed the ignition timing at all? cause that will effect your A/F's. Sometimes substantially.

4gotn · Post by **4gotn** » August 11th, 2007, 1:34 pm

yea i have but its just advanced a few deg.
im off today so maby ill tinker with it and see if i get any results