A/F Ratio going lean at high RPM

[MaxPSITalon]

My talon has a stock fuel system and turbo. I have a Autometer A/F ratio gauge in it. I notice that under a heavly load in 3 4 and 5 gear that the A/F ration goes lean, usually around 4500 RPM. I was wondering if anyone else has experienced this or maybe i have a problem with my fuel system. Is this lean mixture triggered by the ECU? or i am i actually running out of fuel? I am running 10 psi. it did the same thing at 6 psi. Thanks in advance for your input on this.

 

[Quasimondo]

A/F gauges are useless, unless they're of the wideband variety that gives you an actual Air/Fuel Ratio instead of a bunch of lights.

What you need is a datalogger. With that, you can tell us if what your timing and injector duty cycle, and oxygen sensor voltage is. Keep in mind that the oxygen sensor voltage, while not as useless as the autometer A/F gauge, is not that useful for tuning or troubleshooting either.

 

[ericbev]

If you are still running the T25 which your profile suggests, then I wouldnt worry at all. Having your narrowband sensor wired up to one of those gauges doesnt really give you any useful information and are commonly reffered to as "blinky light shows". The stock sensor doesnt read very accuratley except around ye ole' 14.7:1. For real A/F numbers, a wideband is the only tool that should be considered.

 

[MaxPSITalon]

I'll have to get a wideband and see what it does. Thanks for your advice.

 

[MaxPSITalon]

Update: i just installed a walbro 190 fuel pump.... and it still goes lean. i understand that my a/f gauge is inaccurate... but why doesnt it stay rich? Is this done intentionally by the ECU for tuning? Has anyone else experienced this? or do i have another problem? thanks for your help.

 

[Gromit]

Update: i just installed a walbro 190 fuel pump.... and it still goes lean. i understand that my a/f gauge is inaccurate... but why doesnt it stay rich? Is this done intentionally by the ECU for tuning? Has anyone else experienced this? or do i have another problem? thanks for your help.

As mentioned in the 1st reply, you really need to get a logger & post up a log in order for anyone to be able to tell you what's going on in your engine. Since the gauge provides no useful info we can't tell you what the problem might be. The lean mixture is not "triggered by the ECU" - the factory maps are slightly rich for these cars to be on the safe side. If you are actually lean you could be causing damage to the motor. At a minimum, a wideband O2 will at least give you some useful info to work with.

 

[LordDigi]

Well, if it's going lean with different boost levels at the same spot ... I would suspect the fuel filter, when was that replaced last?

 

[MaxPSITalon]

not sure. i'll try that and let you know.

 

[LordDigi]

Any luck yet?

 

[MaxPSITalon]

i tried changing it... hard to get to that bottom fitting. i am gong to have it on a hoist next week and i am going to do it then. i did figure out today that it wont go lean in 1st gear, and it doesnt do it at the same RPM. Does anyone know what the stock fuel maps are in these cars??

 

[GVR4592]

Does anyone know what the stock fuel maps are in these cars??

Very rich, like 9.5-10.5:1 at wot. After you replace the fuel filter, save up for the logger or a wideband or both.

 

[LordDigi]

... Does anyone know what the stock fuel maps are in these cars??

Oh, my bad man, I over looked this last time I read it ... GVR4592 is right, and a logger should deffinitly be the next item on your todo list

 

[MaxPSITalon]

i had the fuel filter changed and at the same time i had full 3 inch exaust ran no cat. i hung the rear o2 sensor underneath the car (i read about that in other forums.) Now things are worse. the ratio is so lean that it doesnt read on the gauge. open loop shows the last red LED on the gauge. occassionaly it will spuraticaly jump then go back off the gauge. I am thinking of getting a o2 simulator and see if that helps. i have read though that the rear o2 sensor has nothing to do with the a/f ratio. What do you think is happening?

 

[Bo0O0ostedDSM]

i had the fuel filter changed and at the same time i had full 3 inch exaust ran no cat. i hung the rear o2 sensor underneath the car (i read about that in other forums.) Now things are worse. the ratio is so lean that it doesnt read on the gauge. open loop shows the last red LED on the gauge. occassionaly it will spuraticaly jump then go back off the gauge. I am thinking of getting a o2 simulator and see if that helps. i have read though that the rear o2 sensor has nothing to do with the a/f ratio. What do you think is happening?

Why are you still trying to determine your A/F ratio with the same narrowband gauge when countless people have told you that the gauge is worthless??? You need a wideband O2 and/or a datalogger to properly tune/diagnose your car.

 

[fwdturbobov1996]

Wow can you not read. That guy is virtually useless. Listen to the advice other people have given you.

 

[Mikael]

The only thing a stock O2 sensor will tell you is if you are above or below 14.7:1. It will not tell you how much above or below you are. So you could be at 14.6:1 or 5:1, its all the same to the ecu. You can do some rough tuning by reading the mV output, and should be fine for your car, but any serious mods require a wideband.


For the gauge you have, its a neat light show, stop using it. Your car is not running lean, and an O2 simm will not do anything for you either, except stop a CEL from coming on.


STOP TELLING US WHAT YOUR A/F GAUGE SAYS. IT IS POINTLESS.
STOP TELLING US WHAT YOUR A/F GAUGE SAYS. IT IS POINTLESS.
STOP TELLING US WHAT YOUR A/F GAUGE SAYS. IT IS POINTLESS.
STOP TELLING US WHAT YOUR A/F GAUGE SAYS. IT IS POINTLESS.

 

[MaxPSITalon]

the only reason i said what the a/f ratio was doing to give you an idea of the difference after the exaust was done. i know that the gauge is not accurate, but how the gauge become sparatic rose some questions in my mind. i know the car is not running lean. i would just like to use the gauge as reference until i buy a wideband. i guess i cant do that.