[Diy_efi] Fuel circuit

Fri Feb 21 06:07:31 GMT 2003

hey bill,

the tank is metal, and the sending unit is metal, and the gasket is present, 
but the bolts that hold it to the tank might be making the ground connection 
??? what do you think?
there definitely is not a third connection, at least not through a conductor 
(wire) .
i will perform said tests below, tomorrow evening, and let you know what i 
come up with, i'll also test continuity between one of the screws that holds 
the sending unit in place, and a ground on the car

-j

From: Bill Washington <bill.washington at nec.com.au>
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>To: diy_efi at diy-efi.org
>Subject: [Diy_efi] Fuel circuit
>Date: Fri, 21 Feb 2003 09:50:32 +1100
>
>J, Matt,
>    See my comments inserted below
>
>>------------------------------
>>
>>Date: Wed, 19 Feb 2003 19:37:12 EST
>>From: fuelogic at ihug.com.au
>>To: diy_efi at diy-efi.org
>>Subject: [Diy_efi] re: circuit
>>Message-ID: <E18lei8-0001fi-00 at grunt23.ihug.com.au>
>>Precedence: list
>>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>>Message: 3
>>
>>Hey Circuit guy,
>>
>>Just to add my two cents worth...u are using the wrong symbol for a pnp 
>>transistor in circuit 5...and the wrong pin configuration. I should be 
>>emitter to 12V, base to R4 and collector to the relay coil positive. 
>>Otherwise I like the circuit.
>>
>>Matt
>>
>>
>No! It should be an NPN as drawn!
>
>>------------------------------
>>
>>Date: Thu, 20 Feb 2003 02:01:12 -0500
>>From: "Toyota Supra" <turbosupramk3 at hotmail.com>
>>To: diy_efi at diy-efi.org
>>Subject: [Diy_efi] Sending unit confusion
>>Message-ID: <BAY2-F1482mFqF7PsgS00036b1e at hotmail.com>
>>Content-Type: text/plain; format=flowed
>>MIME-Version: 1.0
>>Precedence: list
>>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>>Message: 5
>>
>>hi all :)
>>
>>in my never ending quest to conquer this circuit, i have encountered 
>>something very strange. when i removed the fuel level sending unit to try 
>>and test my circuit, i found that i am not able to simulate its electrical 
>>function.
>>the sending unit has 2 wires, a yellow and a brown w/ black tracer. when 
>>the sending unit is not plugged into the body harness, the yellow wire has 
>>+12vDC (or whatever battery voltage may be) on the body harness side of 
>>the connector, and the brown w/ black tracer has approximately 15k of 
>>resistance to ground, or 35mV of positive voltage.
>>
>>when the connectors are plugged in, the yellow wire will have anywhere 
>>from 0 to 3.5vDC, dependent on the position of the "float". the variable 
>>resistor will have resistance ranging from 0k to 55k.
>>
>>now, my problem is, i can't simulate the variable voltage outside of the 
>>vehicle, to test my circuit. if i put 12vDC into the yellow wire, the 
>>brown w/ black tracer will also have 12vDC, so what could that wire 
>>possibly be doing, or connected to, that would make the circuit and unit 
>>work properly?
>>
>>i have enclosed some scans of what the factory manual diagrams it out to 
>>be, and some pictures of the sending unit, with descriptions
>>
>>here is a description of the sending unit, and pics of its resistor
>>http://68.7.7.84:8080/schematics/sendingunit1.jpg
>>
>>http://68.7.7.84:8080/schematics/sendingunit3.jpg
>>
>>
>>
>My best guess is that the Yellow wire may be fed from a current source and 
>the voltage sensed to indicate the fuel level.
>The schematic by itself, is, in this case not very helpful in understanding 
>how it is intended to function.
>
>Now I assume that the tank is plastic, and that the top of the fuel sender 
>unit is plastic(it appears so in the photo), is that correct?
>If so there needs to be an earth connection, probably the other wire, 
>unless there is a third connection which has not previously been mentioned.
>Even if they are metal there should be an earth connection, because there 
>will be a gasket between the sender and the tank which will insulate the 
>sender from vehicle earth(chassis).
>If there is a separate earth connection, the other wire may still be a 
>return/reference wire for the sender because  it may be designed to operate 
>isolated from earth.
>
>To test:
>1. connect up in vehicle (out of tank, sitting on rubber mat or cardboard 
>to isolate from vehicle) and confirm normal operation, ie fuel guage goes 
>up and down with float position.
>2. If there is a third (earth) connection disconnect it only. does the 
>guage still operate normally?
>3. disconnect only the second wire (black?). The gauge should indicate 
>empty (possibly full, but failsafe operation requires empty indication) 
>regardless of float position, reconnect.
>4. disconnect only the yellow wire. The gauge should indicate empty 
>(possibly full, but failsafe operation requires empty indication) 
>regardless of float position.
>
>If behaviour follows this pattern, that combined with your previous 
>evidence of full voltage on the mating spade to the yellow when 
>disconnected suggests that my guess above may be correct.
>
>
>Regards
>Bill
>
>
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