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Jan 26, 2010 | 05:20 PM

#16

subford

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From: Easton,Ks

Quote:

Originally Posted by mike L

OK, so why don't I get a code for the map, egr and tps? if they all have the 1.25 volts problem.

The TPS voltage range input to the computer is from about 0.90 volts to about 4.5 volts so the computer may think it is OK as 1.25 volts is in that range.
The egr sensor is from 0.50 volts to about 4.4 volts so it may think it is OK also.

You are the one reporting the bad voltages so until you get 5.0 volts between the VREF and SIG GND you are going to have problems.

Also I would not bank too much on the codes from a computer that is not putting out the right VREF voltage.

Jan 31, 2010 | 08:00 PM

#17

ri_truck_guy

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From: Suffolk, VA USA

Signal return sends the residual power not used by the sensor back to ground. If you have 5 volts going into a sensor, and the sensor needs to send 3.75 volts to the computer as the sensor reading, the other 1.25 volts has to go somewhere. Thats where signal return comes in. It takes all the residual power not used by the sensors and disposes of it. The numbers you want to concern yourself with are having 5 volts in to the sensors, and a sensor reading within the specified range.

Feb 1, 2010 | 04:50 AM

#18

EPNCSU2006

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From: Concord, NC

Quote:

If you have 5 volts going into a sensor, and the sensor needs to send 3.75 volts to the computer as the sensor reading, the other 1.25 volts has to go somewhere. Thats where signal return comes in. It takes all the residual power not used by the sensors and disposes of it.

I'm not sure I agree with that. In the case of the TPS, the voltage drop between the 5V reference and the signal is a function of the resistance of the TPS, and the power is dissipated in the resistor, not sent over the signal return (0V) wire back through the computer to ground.

Feb 1, 2010 | 06:26 AM

#19

ri_truck_guy

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From: Suffolk, VA USA

This explains how signal retrun works in more detail.

Ford Fuel Injection Sensors

Feb 1, 2010 | 07:01 AM

#20

subford

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From: Easton,Ks

Quote:

Originally Posted by ri_truck_guy

This explains how signal retrun works in more detail.
Ford Fuel Injection Sensors

I do not think that is a very good explanation as it is wrong and misleading.
It is a voltage divider with 5 volts at one end and zero volts at the other.
You have a movable wiper that moves along the resistant part and is hooked to the information wire going back to the computer.
Along this resistant part the voltage is variable from one end to the other, 0 to 5 volts DC.
Where ever the wiper touches the resistant part this is the voltage level it sends back.
You do not send voltage anywhere. Only its potential. The only thing that is sent along a wire is current.
So you do not send any voltage back on the SIG RET wire. It is at ZERO volts.

Feb 1, 2010 | 10:19 AM

#21

ri_truck_guy

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From: Suffolk, VA USA

Bill...not trying to argue, and I'm certainly not claiming to be an expert...all I know is that if you disconnect a ground wire and put a voltmeter in between it and the ground point you will get a voltage reading. Signal return connects to ground. That voltage would indeed be potential until it reaches a ground source and completes the circuit. I'd be looking for a weak or missing ground connection, probably off pins 40 or 60, and rule that out before anything else.

Feb 1, 2010 | 11:36 AM

#22

subford

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From: Easton,Ks

I am not trying to argue either but saying the way it works and that it is stated wrong on that web site.

A bad ground would be putting another resister in series with the resistant part of the TPS.
Then you would be reading the voltage drop of the bad ground if you taking the reading at the SIG RET wire of the TSP. If it were and open ground you would read 5 volts at the SIG RET wire of the TSP.

Until he reads ZERO volts at the GND RET (SIG RET) at all three sensors he will have a problem.
It may be a bad connection at the computer plug (pins pushed in) or a bad ground at G101 (on the fender by the battery).

The computer itself would not cause a voltage reading on the ground wires.