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AFR Lexus RX300
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drip32 Offline
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AFR Lexus RX300
Hey Mike. Has anyone said yeah or neah on the AFR's. I just installed a smacks system on the Lexus and installed 25ohm pots on each sensor. I set both of them at 16 to start out with. Has anyone had any success at all with AFR's? My testing begins tomorrow. Smile
06-20-2008 06:30 PM
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drip32 Offline
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RE: AFR Lexus RX300
Mike any suggestions on Lexus?
06-20-2008 06:50 PM
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colchiro Offline
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RE: AFR Lexus RX300
Here's a link to Toyota/Lexus sensors: http://rav4world.com/forums/viewtopic.php?t=15537&

You didn't specify a year, but I'm willing to bet you have an air-fuel sensor, which means you can try a 25 ohm pot in series with your sensor wire, but it didn't work for me and I know of only one guy who got limited success with an EFIE and a pot, but that may have been preliminary. I'm guessing you'll get the same mileage or maybe a little worse.

For now I'd try to tune with MAF and other sensors, maybe add an extender and hopefully we'll have a solution soon. Cut the MAF sensor wire and take a 50k linear 1W pot and connect one end of the pot to the output of your MAF sensor, center terminal of the pot to the ECU and the other end of the pot to ground via a 33k (upper left portion of this image). The right side is plans for dual controls, like city, highway. You should just change one thing at a time and check your mileage, tho.

[Image: attachment.php?aid=139]

Someone posted plans for an EFIE last week that might work with air-fuel sensors, but I don't know if anyone has started on it yet. Mike seems to think it's functionally the same as his.Hmm

FWIW, Mike spends most of his time in the EFIE groups.

Rick

Links: Documents / Tuning for Mileage | Toyota Sensors | Autoshop Sensor Tutorials
(This post was last modified: 06-21-2008 08:47 AM by colchiro.)
06-20-2008 09:31 PM
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30firstfuel Offline
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Post: #4
RE: AFR Lexus RX300
drip32 Wrote:Hey Mike. Has anyone said yeah or neah on the AFR's. I just installed a smacks system on the Lexus and installed 25ohm pots on each sensor. I set both of them at 16 to start out with. Has anyone had any success at all with AFR's? My testing begins tomorrow. Smile
the problem with AFR sensor is that 2.5 volts is 14.7:1 anything higher is rich anything lower is lean. So when you add resistance you lower the voltage to the computer making it seem lean. This makes the computer add fuel.
06-21-2008 10:57 AM
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colchiro Offline
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RE: AFR Lexus RX300
Here's what a very intelligent guy I know came up with on an E85 forum:

I don't know how the Toyota's run...the basic O2 sensor circuit for the Acura / Honda is:

[Image: o2sensor.jpg]

The ECU pumps a current to the oxygen sensor via two wires. This current serves to pump oxygen either into or out of the O2 sensor depending on whether it is flowing in a 'forward' or 'reverse' direction from the ECU. Basically, the ECU pumps current to keep the O2 sensor in a balanced state, then looks to see how much current is flowing and in which direction. (this is discussed in detail on the web...google 'wide band o2 sensor nernst cell' for more info) I generated a graph of the sensor response from some datalogs:

[Image: afrsensor.jpg]

From the graph, you can see why resistors failed (in my case) for several reasons. The normal sensor response is shown in blue. When the ECU pumps a current of approximately -5.8 mA (red line), it knows the AFR is approximately 14.7:1 (blue arrow). Adding a resistor in series (ie - "current limiting resistor") with the pump circuit lowers the current the ECU is pumping (pink curve). This is bad for several reasons . The resistor lowers the forward and reverse current which flattens the curve (and can lead to a 'slow sensor response' error code). The resistor has a diminishing effect as the current nears zero. But more importantly, it moves the signal in the wrong direction. With the series resistor, the -5.8mA current, which used to be stoic, is now balanced - the AFR at about 15.7:1. The ECU response to this is 'we're lean, lets dump in some more fuel to get back to stoic'. So that didn't work at all for me.

Adding a resistor in parallel is a slight improvement (yellow curve). The trouble here is that the response curve gets steeper which makes the fuel response awful 'twitchy'. There is also a limit to how steep you can make the curve. In my case, the yellow curve is about the max my ECU could register and it only moved the AFR from 14.7 down to about 14.35ish. So the ECU thinks it needs to pull out about .35 points of fuel which isn't much and because the steep response it overshoots the mark, then richens up again, but overshoots that, too. So what tiny bit of fuel it might have saved is mostly wasted due to the sensitive response imposed by the resistor.

Rick

Links: Documents / Tuning for Mileage | Toyota Sensors | Autoshop Sensor Tutorials
06-21-2008 01:13 PM
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mtthhrs Offline
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Post: #6
RE: AFR Lexus RX300
drip32 Wrote:Hey Mike. Has anyone said yeah or neah on the AFR's. I just installed a smacks system on the Lexus and installed 25ohm pots on each sensor. I set both of them at 16 to start out with. Has anyone had any success at all with AFR's? My testing begins tomorrow. Smile

I think I got it figured out were discussing it on this thread http://www.fuel-saver.org/showthread.php...69&page=3. Post #23 is my solution.
Matt

Matt
06-26-2008 08:27 AM
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