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Can we maybe sticky some proper advice....
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abently Offline

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Joined: Nov 2010
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Wink Can we maybe sticky some proper advice....
I've read a lot of threads where people have no idea about what they are doing or why, so its no surprise that success is a 50/50 hit or miss.

You can not modify a sensor, and expect success, unless you know how that sensor operates and how its operation effects fuel/timing etc.

From my own research it seems that most post 98 vehicles have more advanced ECU's where it will spit a 'check Engine' light upon the tiniest modification and get stuck in 'Fail-safe or Open loop mode' till its reset.

You only have to read the 2004 Toyota Corolla Workshop manual to see how the ECU will determine if a sensor is starting to fail and I suspect other auto makers systems are similarly sophisticated.

The positive side of this, is that once you know how the ECU actually operates and under which conditions it will throw and error, you can then get a 100% success rate on any modification you make.

A tip I would like people to remember for IAT and Water temp sensors, is does the resistance reduce or increase with increased temperature? If it reduces, then adding a resistor inline will make the ECU think the temp is higher and therefore for coolant, generally reduce your 'Cold-start enrichment' increasing fuel economy. If the resistance increases, then add a resistor in series.

I have a 680K resistor parallel on my Water Sensor, OBD I Toyota, (practically eliminating enrichment) which does make my idle hunt for about 10 secs during very cold starts, but netted me a 7% gain overall in MPG.

Additionally I know this Toyota, going from the autoshop101 articles, has a +/- 20% adjustment range, ie correction factor it can apply to fueling before it will throw an error. So making sure the correction factor is positive, ie adding fuel, means I can then lean it out 20+% without any Error being thrown. In fact if I wanted to lean it out 40% I could, I just have to make sure its adding 20% more fuel than the base value.

How can you get a vehicle to add more fuel? Well the simplest way is to swap in smaller injectors. And for fine adjustment to get it right to the edge, add a FPR and reduce it by a couple psi. (though this does affect atomization a little)

To be fair to most of the fail stories, I would hate to have to try and manipulate the newer vehicles which have all sorts of 'checking' codes to trip an error.

For those that want to modify a Voltage based 5V MAP sensor, read this article and download the attachment.

Be aware that the spreadsheet is only designed for the Toyota OBD I 5V MAP but gives you an idea of how to set the Pot resistors and its affect.

You can play around with the file and alter it to fit the characteristics of your particular MAP sensor, once you get the baseline diagram from presumably the workshop manual.

I almost think we should have a dedicated thread with links to workshop manuals because the success of any modification is always going to be dependent upon your ability to let the ECU think everything is OK / normal.

11-15-2010 07:58 PM
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