AFR disappear when it gest cold

[mark budgen]

Guys,

I'm a non-buick Porsche 993 driver with a supercharger on it. Not pushing anywhere near as much power as you guys but as I've used this site for information so many times I have a question that I hope someone might be able to help me out on. Car runs fine in warm weather O2s around 800 with a 50:50 mix of methanol/distilled water injection. When it gets cooler say below 10C the AFR soars off the scale (weak). I'm not sure if it is a side effect of the methanol/water injection and to be expected or its a real issue. Car runs fine but the AFR tells me something is amiss. Tried lots of things, temperature sensor, fuel pressure, all spot on. So i'm left with this being a side effect of the methanol injection or the Air flow meter. So my question really is would injecting alcohol on a cold day cause the O2 reading to read way to weak when in fact it is ok?

I know this isnt related to buicks but this sites a real eye opener to those who believe in the powers of alcohol injection.

Many thanks for any help you can be, Mark.

 

[Razor]

When you say soars do you mean lean or rich. Water injection tends to make AFR go up since it leans the motor out way more than alcohol. You make a mix and it doesnt lean out as bad. Tho this is part of the tuning process to figure what your particular setup likes best.

Now the air temp sensor can play havoc on the way the computer responds. And if your spraying on it directly. Some vehicles if the air temp sensor goes down, then the computer adds fuel accordingly. Other vehicles with MAF sensors dont respond very happy if the liquid is shot through it.

Is your nozzle pre SC, or in the intake after the SC?

Are the readings using the stock O2 sensor or a wide band sensor? The stock O2 sensors typically respond well, but they are not very accurrate once you get away from stoich.

Maybe describe your nozzle placement in relation to the air temp sensor and air flow meter..

BTW, welcome

 

[mark budgen]

Razor,

the nozzle is after the supercharger, after the air flow and intake temperature sensor. Both AFM and temperature sensors are before the throttle body and supercharger. Im going to try and adjust the mixture to see if that has an effect on AFM which with 50:50 methanol/water goes very weak under full boost (13-14:1). This only happens when its cold.

Another alternative might be an ignition blow out causing the fuel and air not to ignited. But I'm not sure what effect that would have on the AFM. But as I dont get any noticeable power rop off I cant thinks it that.

I have substituted the temperature sensor with various resistor values which equated to the temperature outside and that had no effect.

I'll let you know how I get on.

Thanks for your help, regards, Mark.

 

[Razor]

Well water will make the motor lean out. And when you hit water with cold temps.. your asking for it since it doenst have a chance to flash.

I would tell you to try straight alcohol, and have the engine at running temp, then shoot it after at least a few PSI boost to get the charge air heated up.

Alcohol flashpoint is about 60 degrees. Water is like 180 degrees. Mix them both and you get a middle point in temp. Now if its cold outside, and you run lets say 3-4 PSI, you'd be looking at 30-40 degrees above ambient. At that temp, water doesnt work very well. When its hot outside.. sure.

Spraying through the blower may have made your issue lessen. Since the blades are nice and hot(somewhat).

 

[salvageV6]

How do you know the "weak" reading is okay?

In the winter with cooler/colder air that is more dense you usually make more power requiring a richer mixture, or more alky. if you prefer to add that.

Try a richer engine management scheme if you can, also check for detonation knocking if you can.