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Old 03-06-2007, 11:04 PM   #1
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AFR running extra rich at WOT?

I'm not sure if anyone here has an air-fuel ratio sensor on their car, but hopefully someone knowledgeable can help me with this.

Normally the ratio flicks between rich and lean, from what I understand this is normal, just the ECU's way of improving the catalyser's performance.

But, I was on the highway the other day, in 5th gear, pedal to the metal, crawling along the traffic (), and I was checking my AFR gauge, which was stuck pretty high, at a little under 12:1. When this is the case there is also a slight sulphurous smell pervading the cabin.

So, as my ECU has not been touched, is this rich ratio normal in these situations? From my understanding it should be running maybe a little lean in order to extract maximum power, right? Or could this be a result of a faulty/dirty MAF sensor, or just my AFR gauge being stupid?
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Old 03-07-2007, 05:42 PM   #2
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well ur pedal to the metal right, so throttle wide open, shouldn't the ECU sense a wide open throttle and asume u wants power, rich mixture more juice gives u more power. From my knowledge during wide-open throttle ECU will run with pre-set configurations ignoring couples like MAF and O2.

i can read some articles on EFIs
http://www.autoshop101.com/autoshop15.html
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Old 03-07-2007, 09:39 PM   #3
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Quote:
Originally Posted by Teruyume View Post
well ur pedal to the metal right, so throttle wide open, shouldn't the ECU sense a wide open throttle and asume u wants power, rich mixture more juice gives u more power. From my knowledge during wide-open throttle ECU will run with pre-set configurations ignoring couples like MAF and O2.

i can read some articles on EFIs
http://www.autoshop101.com/autoshop15.html
Yeah but the thing is, contrary to popular belief, a richer mixture does NOT give more power! The main use for an over-rich mixture is to provide a cooler burn of the air-fuel mix, to reduce the chance of knocking, most especially in a turbo application. It also causes a lot of fuel to be unburnt, which results in worse emissions and mileage.

In order to get the most power out of a normal air-fuel combustion, the ration needs to be stoichiometric (14.7:1) or very slightly lean.

Anyway I got some free time today, I'll try to reset my ECU, clean my MAF sensor and see if this helps. Also (doh), I just reread that thread about the TSB for the catalyser linked to the sulphur smell, I don't know if that is an option here but it may solve that part of the problem.
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Old 03-08-2007, 03:19 AM   #4
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Originally Posted by eTiMaGo View Post
Also (doh), I just reread that thread about the TSB for the catalyser linked to the sulphur smell, I don't know if that is an option here but it may solve that part of the problem.
First thing I thought, but its cool we might have just found why it was recalled and why it smelled like that. I want an AFR gauge!

Thomas, do you have a fuel pressure regulator on that thing?
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Old 03-08-2007, 03:35 AM   #5
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First thing I thought, but its cool we might have just found why it was recalled and why it smelled like that. I want an AFR gauge!

Thomas, do you have a fuel pressure regulator on that thing?
An AFR gauge is kinda annoying most of the time as it just goes up and down, as the ECU normally normally switches between lean and rich to maximize the efficiency of the catalyser. But in this case it's kinda handy

No fuel pressure regulator, would it do any good with a stock engine though?
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Old 03-08-2007, 03:46 AM   #6
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Originally Posted by eTiMaGo View Post
An AFR gauge is kinda annoying most of the time as it just goes up and down, as the ECU normally normally switches between lean and rich to maximize the efficiency of the catalyser. But in this case it's kinda handy

No fuel pressure regulator, would it do any good with a stock engine though?
Your engine is stock!?!?! You need to fix that!
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Old 03-08-2007, 03:52 AM   #7
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Originally Posted by ChinoCharles View Post
Your engine is stock!?!?! You need to fix that!
Oh I will, I will....
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Old 03-08-2007, 03:56 AM   #8
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Betty!
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Old 03-08-2007, 04:05 AM   #9
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Quote:
Originally Posted by ChinoCharles View Post
Betty!
Oh I already have a bastardised intake...

but, as I mentioned in your thread, the only reason mine is not shorter is because of that breather tube, I did not want to remove that first piece of tubing... But now I might just try it
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Old 03-08-2007, 06:44 AM   #10
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http://en.wikipedia.org/wiki/Air_fuel_ratio

Oh well, this explains a lot, looks like it does not only affect forced induction situations, and I guess I'll just shut up now
Now, I wonder if this rich mixture is affected by the actual engine's knock sensor, or if it is a pre-mapped setting... Time to try some higher octane fuel (less chance of knock) next time and see what happens

Quote:
A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel air mixture. Due to the high temperatures at this mixture, detonation of the fuel air mix shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinging). Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence stoichiometric mixtures are only used under light load conditions with more fuel added for acceleration and high load condition to prevent detonation and to cool down the combustion gasses.
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Old 03-08-2007, 08:59 AM   #11
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wideband afr guage would work on our cars better.
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Old 03-08-2007, 10:17 AM   #12
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A narrow band AFR guage is useless. Get a wideband for a more accurate picture of what is going on.

Higher octane will not change your AFR. the car will run 14.7:1 in closed loop while putting around, but in WOT situations the car needs more fuel to keep EGTs down. This is a scenario where it is not practical to run the theoretical limit because you will harm the engine. This is typical in ALL cars, and more pronounced in FI applications.

Your intake could very well be contributing to this issue. While I wouldn't call just below 12:1 too rich, but it could probably be leaned out a bit safely. Generally intakes make power by leaning the car out a bit, but yours has a tight 180 degree turn right before the MAF that could be throwing things off a bit.

Ashley
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Old 03-08-2007, 11:56 AM   #13
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A narrow band AFR guage is useless. Get a wideband for a more accurate picture of what is going on.

Higher octane will not change your AFR. the car will run 14.7:1 in closed loop while putting around, but in WOT situations the car needs more fuel to keep EGTs down. This is a scenario where it is not practical to run the theoretical limit because you will harm the engine. This is typical in ALL cars, and more pronounced in FI applications.

Your intake could very well be contributing to this issue. While I wouldn't call just below 12:1 too rich, but it could probably be leaned out a bit safely. Generally intakes make power by leaning the car out a bit, but yours has a tight 180 degree turn right before the MAF that could be throwing things off a bit.

Ashley


This is very true. The stock ECU should have you running somewhere in the 12.5 range at WOT and 14.7 at part throttle. This is what we typically see out of toyota ECUS. The Rich reading on a narrow band ecu is about as useful as that one buddy who always wants to help but breaks the parts he attempts to install.

I would put the thing on a dyno with a sniffer and get a better idea. I am not sure that I would be that worried about it if all you have modded is an intake. I am confident the car is safe.
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Old 03-08-2007, 12:18 PM   #14
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Ashley, could you suggest a wideband that would work well for a Yaris?
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Old 03-08-2007, 01:39 PM   #15
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Quote:
Originally Posted by ZPIracing View Post
The Rich reading on a narrow band ecu is about as useful as that one buddy who always wants to help but breaks the parts he attempts to install.
Hey that sounds like me

I'm not actually sure if my meter is narrowband or wideband, it's an analog one with a range from 10 to 17, or am I barking up the wrong tree?

So, this extra cooling capacity is meant mainly as a protection against engine overheating, not knock?

Anyway thanks for the input guys, largeorangefont, I never really liked that bend in the tube there, I'll see what I can do about shortening/straightening it, probably have to get one of chinocharles' bouncing bettys or similar
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Old 03-10-2007, 12:10 PM   #16
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Ashley, could you suggest a wideband that would work well for a Yaris?
Sorry I missed this.

http://www.rpmoutlet.com/aemgauge.htm

That is the AEM wideband. $279 is about the best I have seen.


If you don't want a round guage, Dynotune has the Innovate wideband with a small digital display. You can get it with a red or green readout. This is $279 as well.
This is the wideband I run in my Mustang, just with the Innovative round display as opposed to the square display


You can find it here
http://www.dynotunenitrous.com/store...?idproduct=150


Also, Autometer just came out with their own wideband that will match your tach. $349 from Summit.


Ashley
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