Staffan

Spend a day on the track a couple of weeks ago and found that my car didn't feel as strong as it usually does, didn't have that extra power compared to the NA cars at the long straight that I am used to.

Anyway today I spend the whole day trying to figure out if something was wrong. After trying to be very scientific I gave up and just turned the mixture **** a little bit more rich and disconnected the o2 sensor.

Wow what an improvement, the car was more responsive and accelerated much harder than before. Looks like it managed to detune it self.
Tomorrow I will check my CO level and fine tune the mixture.

CIS is a bit scary, glad I checked this.

turbosport

What are your mixture ***** set too?

Staffan

Don't know yet, but I am going to tune it to 3% CO at idle with o2 sensor unplugged, that's what recommended with these cars. Not very good for the catalytic converter but you only live ones.

fc-racer

Staffan,

My car does this as well. The mixture drifts lean over time. I keep an allen wrench in my car and can set the mixture pretty close by a bunch of variables, even without a CO meter.

I wonder what causes this???

Staffan

Farzaan, Interesting that this happens to you to and on a regular basis I gather ?
How do you set it without measuring CO ?

I went to the viechle inspection center today and borrowed their CO meter.
When I was fiddeling with the mixture I realized that I was using their CO meter in order to make my car illegal, kind of funny.

Anyway, it turned out that my car still was running to lean, I dialed it in on 3.1% CO. I think that's probably on the rich side for me since I am running stock boost, I might turn it down a bit. There is a rich smell from the car now which means that it's time to remove the cat. Perhaps I should connect the o2 sensor and just have it disconnected at track events ?

Farzaan, do you have a cat testpipe on your car ?

Well the moral of the story I guess is that you can't check your mixture to often, especially if you are running your car with the o2 sensor disconnected.

fc-racer

I tried 3% but found that my top end power suffered. I would say that 3% is good for response, but it may be too rich for ultimate power. I run 2% or thereabouts and it gives a good compromise. I also still run my cat (although it's coming off soon) and don't want to kill it with a 3% mixture.

Staffan

Yeah, I think I should lean it out a little bit, 2% is probably more in line with my stock boost and that the cat is still there.

Vince5

Had the mixture checked while I did a 20 000km service last week and it was way to lean as well. I didn't notice better response afterwards but much better top end power. Thanks for the tip

BTW the rumble sound of the engine when lifting your foot from the gaz pedal is much less pronouced now the mixture is set right. I remember there was a post on this sound a while ago, that may be a good clue the engine is running lean


PS - Staffan I noticed my car was not really faster than yours on the straight at Mantorp (before my left tires gave up ) so I guessed I had the same issue

Staffan

Vince, good stuff!
I still suspect you had more power than me on Mantorp.

Are going to the track event this weekend ?

Vince5

I sure had a lot of fun on saturday and it felt like the mixture change made a huge difference

KP

Hi guys
From what I know, the mixture should be 2% at idle with the air pump disconnected, tube plugged and O2 sensor disconnected.
Another way to do it is by checking the duty cycle of the valve through a 2 pole diagnostic connector located behind the plastic cover on the left side of the engine compartment. It should be set at 45% duty cycle as I know.

Staffan

Hi KP
Thanks for your input!
Doesn't CIS go into "limb home mode" when the o2 sensor is disconnected ? Thought it goes into 50% duty cycle.

I will check my car for the diagnostic plug though, tried to use the one on the passanger side with little sucess, didn't know there was one in the engine compartment!

Thanks

KP

Hi Staffan,
That's right. Duty cycle can also be checked by porsche handheld tester at the diagnostic plug. Another way is to use a dwell meter at the engine compartment plug.

Ian964

I have not checked my fuel mixture ever. I think I should just to be safe. What kind of things do I need to do this? Can I take it to a regular garage?

Staffan

Ian, better safe than sorry, makes a lot of sense checking your mixture since you are running 1 bar boost.

The easy test would be to check you CO at idle, I think a regular garage should be able to take care of this without a problem.

The best thing would be to take the car to a dyno and do a run and check A/F ratio at the same time. Then you would know for sure what your mixture is like during full boost.