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Old 05-05-2009, 10:02 AM   #1
generalee69
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Default Some questions about lean fuel conditions on the track

I haven't had any problems yet (knock on wood).. but I am curious about if I prepared to catch a problem before it happens.

There are 2 issues that concern me a little. One is fuel starvation on high load right hand corners. The second is oil in the intake system. Both of these would cause a lean condition inside the combustion chamber correct?

If that is an accurate statement, would my A/FR gauge alert me to these problems?

My fuel system is all stock (I KNOW I need a surge tank at some point - until then I just make sure I am going out on track with a full tank of gas). For a 30 minute race I burn just barely over a half tank of gas.

Also, I have not put catch cans on the car yet. But I am in the middle of fabricating them, and I should have them on the car prior to the next race. I'm going to go with the dual can setup (one from the breathers and one from the crankcase). Both lines will be 1/2" ID hoses, and I am going to mount them where the battery used to be. I took the intercooler off before the last race and it had a couple of ounces of oil puddle up in it, kind of freaked me out. But that was after 140 minutes of track time. Still even with that oil in the intercooler, I was seeing AFR's in the 10.9-11.0 range in dry low 60's weather conditions.

I probably need an EGT gauge at some point. But while I'm still running an OTS Cobb Stage 2 map on the stock turbo, I don't know if it is necessary yet.
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Old 05-05-2009, 10:47 AM   #2
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An air/oil separator and a surge tank are two things that you definitely need if you are racing an STi. Enough oil blowby will increase the chances of detonation without question. And before my surge tank, I was getting stumbling at anything below half a tank. With the surge tank I can literally run the tank down to empty without issue. A couple weekends ago I ran the fuel so low I was afraid I wouldn't make it back to my paddock spot and I didn't get a single hiccup.
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Old 05-05-2009, 10:50 AM   #3
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Originally Posted by boost junkie View Post
An air/oil separator and a surge tank are two things that you definitely need if you are racing an STi. Enough oil blowby will increase the chances of detonation without question. And before my surge tank, I was getting stumbling at anything below half a tank. With the surge tank I can literally run the tank down to empty without issue. A couple weekends ago I ran the fuel so low I was afraid I wouldn't make it back to my paddock spot and I didn't get a single hiccup.
I know everyone is going to say that. However, I have run my STi out of gas on the track before and never had a stumble while it was getting low. Granted that was on a track with high load left hand corners so the fuel is pushing towards the pump.

Too much of back and fourth about the AOS. People either love 'em or hate em. I don't see any downside to just running catch cans, other than checking them fairly regularly and topping off the oil if necessary.

My question is -- will my AFR alrert me to either of those conditions (fuel starve or oil in the intake)?
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Old 05-05-2009, 11:36 AM   #4
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the cobb ots maps are dangerous, IMO, for real duty. i wouldn't run that map for high speed/high load stuff; and definitely not track time. but that's just me.
that said, your AFR isn't bad (steady?), but without a real log you dont know where you are through the whole range. see if you can video your afr meter with your RPMs in the shot, and try to pinpoint where you are at peak torque, peak HP, etc. of course you can knock from too much fuel, too, which the ots maps used to be notorious for.

as you said, an EGT gauge is a good next step. i'd have the car tuned while you're at it. if you're not OCD like me, just keep putting good gas in it, and you should be alright.
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Old 05-05-2009, 11:42 AM   #5
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to take a shot at that question above:

your wideband O2 measures after combustion, so it's a direct reading of what the mixture was, at whatever resolution, 10x/sec. any change in fuel supply, or in the contents of the mixture would show up on your meter. id think the oil would richen the mixture, but definitely affect ignition temp, causing pre-ignition that way.
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Old 05-05-2009, 11:45 AM   #6
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Quote:
Originally Posted by midnite_wrex View Post
to take a shot at that question above:

your wideband O2 measures after combustion, so it's a direct reading of what the mixture was, at whatever resolution, 10x/sec. any change in fuel supply, or in the contents of the mixture would show up on your meter. id think the oil would richen the mixture, but definitely affect ignition temp, causing pre-ignition that way.
That was my thought on the purpose of the AFR also. BUT what I have been reading about catch cans and the ill effects of oil in the intake is extreme lean condition.. not rich.
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Old 05-05-2009, 12:08 PM   #7
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Oil in the intake causes detonation because it reduces effective octane. At least thats how I understand it. I don't think it affects AFR's though. Why do you think it would lean out the mixture? The ECU pumps in fuel based on the airflow through the MAF. In open loop, I don't believe it's looking at the 02 sensor. The stock 02 sensor won't read that low so, I'm almost certain of it.

The problem with the AFR gauge is like the problem with an oil idiot light. By the time you notice there's a problem, it's probably already too late. Maybe you need some kind of buzzer. It would go off every time you get off the gas though, AFR's on my car go to 20:1+ when the throttle closes (probably the limit of the wideband).

Quote:
if you're not OCD like me, just keep putting good gas in it, and you should be alright.
I run 100 octane on track on a 93 octane tune. Gas is cheaper than a new motor.
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Old 05-05-2009, 12:15 PM   #8
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Quote:
Originally Posted by MasterKwan View Post
Oil in the intake causes detonation because it reduces effective octane. At least thats how I understand it. I don't think it affects AFR's though. Why do you think it would lean out the mixture? The ECU pumps in fuel based on the airflow through the MAF. In open loop, I don't believe it's looking at the 02 sensor. The stock 02 sensor won't read that low so, I'm almost certain of it.

The problem with the AFR gauge is like the problem with an oil idiot light. By the time you notice there's a problem, it's probably already too late. Maybe you need some kind of buzzer. It would go off every time you get off the gas though, AFR's on my car go to 20:1+ when the throttle closes (probably the limit of the wideband).

Ok, now we are getting to my question. That's I guess what I didn't understand. I thought that detonation would be picked up by a lean reading on the AFR... sounds like a yes, but by the time it detects it is too late.

I misunderstood, I thought that reducing the effective octane level was equal to a lean mixture.

Mine goes to 22.4 on closed throttle, I was told this is perfectly normal.

Most of the way through the RPM the AFR's are in the mid to low 11's. And they appear to decrease (11.4, 11.3, 11.2, 11.1) all the way through the RPM range. Then again if it is only read 10x/sec there may be some fluttering between readings that the gauge just doesn't display.

I sounds like EGT is the way to read detonation then? Is that a correct statement or am I misunderstanding the purpose of the EGT also?
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Old 05-05-2009, 03:15 PM   #9
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If you want to know if it's detonating, get a tactrix cable and use the "Learning View" tool which lets you see a map of where your ECU is pulling timing. Your ECU knows when you detonate and reduces timing to protect the motor automatically. These engines are pretty robust as long as you don't tune the ECU in such a way that you disable the features that protect the motor.

You probably want to compare your AFR readings to the fuel maps in the ECU. If you're driving along, engine load of 2.75 at 5500 RPM, you look in the fuel map and it tells you what your AFR should be. If what you measure doesn't match what the fuel map says, you have a problem. Either you need to remap the MAF sensor or maybe you're running out of injector or the fuel pressure is dropping out.

I throw a laptop under the floor mat, connected to my wideband and tactrix cable and log my sessions. I can then review them after the fact and see what the car's doing. It's pretty neat, you can look at the logs and tell where you are on the track, what your speeds were, engine load, engine temp and the like.
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Old 05-05-2009, 03:19 PM   #10
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Thank you for the helpful information.

So -- Now the next question is. Will the datalogger on the AP tell me the same info? Or I guess since the wideband is a seperate loop on it's own, I won't be comparing the same info will I.

No floor mats (...or seats, or carpet for that matter) But I get what you are saying.
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Old 05-05-2009, 05:00 PM   #11
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My wideband has a serial interface and RomRaider has a logger that integrates with the wideband and the tractrix. I plug both into the laptop and can log. I don't much see the point of an AFR gauge because I don't think I'd notice it while driving. I'm planning for an EGT and oil temp gauge for my car.

I don't know anything about your EM so, I can't really answer and questions about it.
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Old 05-05-2009, 05:25 PM   #12
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Quote:
Originally Posted by midnite_wrex View Post
the cobb ots maps are dangerous, IMO, for real duty. i wouldn't run that map for high speed/high load stuff; and definitely not track time. but that's just me.
that said, your AFR isn't bad (steady?), but without a real log you dont know where you are through the whole range. see if you can video your afr meter with your RPMs in the shot, and try to pinpoint where you are at peak torque, peak HP, etc. of course you can knock from too much fuel, too, which the ots maps used to be notorious for.

as you said, an EGT gauge is a good next step. i'd have the car tuned while you're at it. if you're not OCD like me, just keep putting good gas in it, and you should be alright.
What makes them so dangerous?
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Old 05-05-2009, 06:29 PM   #13
generalee69
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Quote:
Originally Posted by MasterKwan View Post
My wideband has a serial interface and RomRaider has a logger that integrates with the wideband and the tractrix. I plug both into the laptop and can log. I don't much see the point of an AFR gauge because I don't think I'd notice it while driving. I'm planning for an EGT and oil temp gauge for my car.

I don't know anything about your EM so, I can't really answer and questions about it.

I mounted my AFR right between my dash clock cluster and the main cluster. It is right in my line of sight most of the time.
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Old 05-05-2009, 07:06 PM   #14
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Quote:
Originally Posted by MasterKwan View Post
My wideband has a serial interface and RomRaider has a logger that integrates with the wideband and the tractrix. I plug both into the laptop and can log. I don't much see the point of an AFR gauge because I don't think I'd notice it while driving. I'm planning for an EGT and oil temp gauge for my car.

I don't know anything about your EM so, I can't really answer and questions about it.
If it's a matter of space, I'd choose a fuel pressure gauge over the EGT. EGT's should be fine as long as your tune is decent. Fuel Pressure can tell you all sorts of things at the track, like if your regulator or pump is going (Information I could have used at the last track event. )

-Duncan
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Old 05-05-2009, 10:49 PM   #15
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Quote:
Originally Posted by generalee69 View Post
That was my thought on the purpose of the AFR also. BUT what I have been reading about catch cans and the ill effects of oil in the intake is extreme lean condition.. not rich.
As MasterKwan said, oil causes knock by reducing effective octane. AFR is just that, air:fuel ratio. Oil doesnt really factor into that calculation unless youre dumping ounces of oil in your chamber.

Quote:
Originally Posted by MasterKwan View Post
AFR's on my car go to 20:1+ when the throttle closes (probably the limit of the wideband).
Quote:
Originally Posted by generalee69 View Post
Mine goes to 22.4 on closed throttle, I was told this is perfectly normal.
The reason this happens is because you let off the gas, and your air fuel ratio is now effectively pure air. Injectors dont fire once you let off.

Quote:
Originally Posted by MasterKwan View Post

You probably want to compare your AFR readings to the fuel maps in the ECU. If you're driving along, engine load of 2.75 at 5500 RPM, you look in the fuel map and it tells you what your AFR should be. If what you measure doesn't match what the fuel map says, you have a problem. Either you need to remap the MAF sensor or maybe you're running out of injector or the fuel pressure is dropping out.
One other thing Ill mention is concerning the bolded portion: Not necessarily. I have thousands of logs where my AFR tables dont match the logs, and that was with a properly scaled MAF and injectors. Now granted, it wasnt 0.5 off either, but its never exact. Too many other factors go into that for it to be that precise.

Random sidenote: Stock O2 sensors are accurate between 13.5 and 14.7. Anything less than 13.5 is considerably off, so its not even worth logging if you have a wideband.

generalee, if knock is that big of a concern to you, Ill offer you two bits of advice:
1. Structure your timing advance map so that the ECU has plenty of timing to work with. For example, dont set your base timing at 13 degrees and give it 2 degrees of advance at peak torque. Something like 9+6 would be better. Since total timing=base+advance*IAM, and you have a 32 bit ECU, if your IAM is at 1, youll get full timing. In my experience, it takes a considerable amount of knock to get the 32 bit ECUs to start dropping IAM.
2. Buy a knocklite. They are cheap and effective. Unfortunately, the knock sensors on our cars tend to be a bit, shall we say, overactive. This is one of the cases where you have to work with what youve got.

I would also look into getting a tune as well.
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Old 05-06-2009, 09:56 AM   #16
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Originally Posted by cucamelsmd15 View Post
I would also look into getting a tune as well.
Thanks for the help.

A more focused/application specific tune is something that will happen sooner rather than later. BUT I also have a FP Green sitting on my work bench at home that I am debating whether to install or not.

Too many options, soo little money and time
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Old 05-06-2009, 11:18 AM   #17
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Quote:
Originally Posted by MasterKwan View Post
My wideband has a serial interface and RomRaider has a logger that integrates with the wideband and the tractrix. I plug both into the laptop and can log. I don't much see the point of an AFR gauge because I don't think I'd notice it while driving. I'm planning for an EGT and oil temp gauge for my car.

I don't know anything about your EM so, I can't really answer and questions about it.
What wideband? I have a PLX M-300 and RomRaider doesn't cooperate with it so I haven't installed it yet.
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Old 05-06-2009, 12:23 PM   #18
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I have the LC-1. It's sometimes touchy and I have to reselect the serial port from time to time. My laptop has a built-in serial port so, I'm not going through USB for it.
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Old 05-06-2009, 12:25 PM   #19
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Quote:
Originally Posted by MasterKwan View Post
I have the LC-1. It's sometimes touchy and I have to reselect the serial port from time to time. My laptop has a built-in serial port so, I'm not going through USB for it.
That's another thing. When I fooled with Hondas the WB went into the ECU and I could log it through my laptop (via serial) to the ECU and log everything the ECU saw including WB02. It was great b/c my software would plot the AFR's against the maps so it was extremely easy to tune for. Not so easy on a Subaru.
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