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Pull up resistor wattage


Adzn3k
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The old 2 wire "VDO type" pressure sensors are not much good in a modern environment.  I think originally they were probably designed to be powered by gauges with 12V pull ups built in.  Their resistance is very low, something like 0-185ohms.  So if you use say a 1k pull up to 5v your full scale signal output will only be something like 0-0.7V.  To expand that resolution you need a much lower pullup - something like 20ohms will make it output 0-4.5V full scale, but the problem then is when it is at 0ohms that thing is gonna to pull about 250mA of current.  The ECU power supply can only provide about 400mA total and that's got to power all other sensors, TPS, MAP, temps etc so you will be wasting 2/3 of your power on just that one sensor.

You can get genuine Honeywell 3 wire pressure sensors for <USD$40 if you shop around so I would suggest re-thinking this one.  One example: http://www.mouser.com/ProductDetail/Honeywell/PX3AN2BS150PSAAX/?qs=sGAEpiMZZMvhQj7WZhFIAMbIIQV5NoTbL6isqunddabblqqeR%2f4hsw%3d%3d

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  • 2 weeks later...

Are the Brass pressure sensors in the link above any good for fuel pressure when running E85? or should the MLH stainless steel sensor be used?

I have had one used with e85 for many years with no drama yet.  Some will tell you "brass" is susceptible to corrosion with damp E85 but I have never seen any corrosion on all the brass jets etc I see inside carburetors running E85. 

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