Doc302
Active member
- Joined
- Aug 19, 2018
- Messages
- 36
- Reaction score
- 2
- Location
- Florida
- My Car
- 1973 Mach1 Q code 351 replaced with 1968 “429 thunder jet”
[url=https://ibb.co/dQW99z][img]https://preview.ibb.co/bEMnwe/Mach_1_front_side_up.jpg[/img][/url]
I am attempting to get a somewhat functional fuel gauge in my 73 Mach 1.
Current problem ( no pun intended): When I turn on ignition , gauge goes from E to about 1/2 tank with tank full as fuel is consumed it moves down some but never to E ( even when I ran out of gas recently. ) except when ignition is off battery disconnected etc never reads E
if I short yellow wire to ground needle sweeps to a bit above 1/2 ( should go to full as I understand it )
ground is good - ground wire to tank 0 ohms ground wire to rear bumper or leaf spring ( rust scrapped off ) or neg battery all 0ohms - Ground is always my first suspect but here I think it is ok.
sending unit tank full reads 14ohms ( I also have the common full is not full premature fuel shut off so a bit Hi is expected, full is not full)
resistance empty 73 Ohms
When I check the potential at the yellow wire pulled off the sending unit my ( very high quality ) analog potentiometer sweeps from zero to 5 volts at about two sweeps per second. It is my understanding that the OEM Instrument Panel Voltage Regulator puts out 5 volts and works by rapidly opening a closing a circuit in response to thermal heating on the 12v side of the regulator, but this should happen too fast for meter to see it happening.
It seems that I should see a constant 5v or if I can see the opening and closing of the internal circuit of the Instrument Panel Voltage Regulator
shouldn't I see a sweep from 0-10 basically a slow always positive a/c source ( RMS voltage=5 much like -120 to + 120 has RMS of 120 )
Should I suspect the Instrument Panel Voltage Regulator or the gauge itself ?
if it helps Oil pressure nor temp ever hit H either, but I do not think these parameters have ever been abnormal and have not tested further
should the wiring harness be considered suspect ( I know it always is to some extent in these cars ) or is the fact that the yellow wire is hot (even of at wrong potential ) probably enough to looks elsewhere first.
Current problem ( no pun intended): When I turn on ignition , gauge goes from E to about 1/2 tank with tank full as fuel is consumed it moves down some but never to E ( even when I ran out of gas recently. ) except when ignition is off battery disconnected etc never reads E
if I short yellow wire to ground needle sweeps to a bit above 1/2 ( should go to full as I understand it )
ground is good - ground wire to tank 0 ohms ground wire to rear bumper or leaf spring ( rust scrapped off ) or neg battery all 0ohms - Ground is always my first suspect but here I think it is ok.
sending unit tank full reads 14ohms ( I also have the common full is not full premature fuel shut off so a bit Hi is expected, full is not full)
resistance empty 73 Ohms
When I check the potential at the yellow wire pulled off the sending unit my ( very high quality ) analog potentiometer sweeps from zero to 5 volts at about two sweeps per second. It is my understanding that the OEM Instrument Panel Voltage Regulator puts out 5 volts and works by rapidly opening a closing a circuit in response to thermal heating on the 12v side of the regulator, but this should happen too fast for meter to see it happening.
It seems that I should see a constant 5v or if I can see the opening and closing of the internal circuit of the Instrument Panel Voltage Regulator
shouldn't I see a sweep from 0-10 basically a slow always positive a/c source ( RMS voltage=5 much like -120 to + 120 has RMS of 120 )
Should I suspect the Instrument Panel Voltage Regulator or the gauge itself ?
if it helps Oil pressure nor temp ever hit H either, but I do not think these parameters have ever been abnormal and have not tested further
should the wiring harness be considered suspect ( I know it always is to some extent in these cars ) or is the fact that the yellow wire is hot (even of at wrong potential ) probably enough to looks elsewhere first.