Pulldown resistors for TPS MAP

[goflo at pacbell.net]

Bruce Plecan wrote:
 
> >This is the most likely, and will give 0 to nearly 5V adj
> >
> >        5V   ______
> >                   |
> >                   /  5K pot, linear taper
> >                   \
> >                   /<------ Variable voltage to ECU input
> >                   \
> >                   /
> >                   |                   |
> >                   |
> >                 Ground
> 
> This is what I have..
> >
> >                          /*  less likely  */
> >
> >5V pull-down  _____
> >voltage from       |
> >ECU                |
> >                   /  5K linear taper pot
> >                   \
> >                   /<---------/\/\/\-------- Ground
> >                   \            1K
> >                   /
> >                   |
> >                   |
> >               No connection
> 
> Where is the ecm connected?.  Or in this version just thru the 5K.

MAP connector is 5V, GND, & Signal so use schematic #1. You should be
able to ID the connections at the ECU - One will be 5V, one GND, and
the odd one out will be the signal input. Put the 5V to one side of 
the pot, GND to the other, and connect the pot wiper to the signal 
input.

My guess is TPS is the same deal.

 
> The Coolant temp sensor, and Intake Air Temp have two terminal
> connectors...

Hook one end of the pot to one & the wiper to the other. What 
Mr Hergen says about a log taper pot makes sense. If you have the
actual sensors try reading sensor resistance at ambient & at 212 F
(boiling water) with an ohmmeter. This'll give you an idea of what
range is required, independent of possible internal switching of
shunt resistances. Murphy being my constant companion, I'd freeze 
the damn sensors, measure resistance, and then put that value
resistance in series with the pot as a current-limiting precaution.
Or heat them and do likewise, if the tempco is negative. In other 
words whatever the lowest sensor resistance you can produce by
heating or cooling it. The series resistance does'nt need to be
exact.

> and the TPS, MAP have three terminal.  I verified that
> there is 5v to them, a ground, and the sensor signal to ecm (unk)
> Cheers
> Bruce
> >
> >This will give approx 1V to 5V adj. If you need less than 1V
> >( say .9V ) use a smaller current limiting resistor, but at
> >least 500 ohms or so. This resistor prevents shorting the 5V
> >input to ground at the high end of the pots travel ... If the
> >ECU uses this scheme the current is probably internally limited
> >but we dont need to find out the hard way that it is'nt. It is
> >Monday, after all.
> >
> >If this doesnt make sense describe the connections as fully as
> >possible and we'll beat on it some more.
> >
> >Regards, Jack
> >