Petrol Guage

7173Mustangs.com

Help Support 7173Mustangs.com:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Helicopter

Well-known member
Joined
Jan 26, 2017
Messages
97
Reaction score
1
Location
USA
My Car
1973 Mustang, 351 Cleveland 2bbl. vinyl roof.


1973 Mustang

Code H

I went out for a short jaunt tonight and noticed the fuel gauge read very slightly above peg-low.  Stopped and got petrol and there was no measurable change in gauge reading. 

When I got home I checked voltage to the fuel tank sending unit.  It was PULSING !  About 1.5 Hz with peak voltage around 7 or 8 Volts D.C.

This CAN'T be normal !!!

Any ideas?

 
Last edited by a moderator:
Pulsing is normal. The voltage is from the instrument voltage regulator, which reduces the voltage in the gauge circuits to around 8 volts. It has a bimetal contact in it that opens and closes to regulate the voltage. There are aftermarket replacements that are solid state and eliminate the pulsing, and are adjustable.

Ground the wire you checked the voltage on, see is that moves the needle on the gauge. The gauge receives voltage from the voltage regulator on the positive side of the gauge, the negative side connects to a variable resistor in the fuel sending unit. It sounds like your sending unit float may not be floating.

 
Last edited by a moderator:
Pulsing is normal. The voltage is from the instrument voltage regulator, which reduces the voltage in the gauge circuits to around 8 volts. It has a bimetal contact in it that opens and closes to regulate the voltage. There are aftermarket replacements that are solid state and eliminate the pulsing, and are adjustable.

Ground the wire you checked the voltage on, see is that moves the needle on the gauge. The gauge receives voltage from the voltage regulator on the positive side of the gauge, the negative side connects to a variable resistor in the fuel sending unit. It sounds like your sending unit float may not be floating.
Thanks.   As old as this old Tang is I am surprised the pulse mechanism still works. 

This is a relatively new float (installed August 2018) but it sounds like what the Prob is.

TNX

 
The reproduction fuel sending units have a hit and miss reputation, like most reproduction parts. The one in My Mach 1 has been fine. I've gone through 2 in my Cougar in 4 years. Always bench test them be fore installation, I had one bad out of the box. Chuck

 
Back
Top