Fuel Gauge Troubleshooting: 1985 5.0L EFI

[mat in tn]

Just wanted to touch base again ... Filled up our 2009 Ford Escape and noticed that the gauge read exactly Full when it was full. Also, and interesting note: the fuel gauge dial almost has the same swing angle from F > E on the Escape as on the F-150.

Have not checked out what the Escape gauge shows at empty (and don't want to) but planned to take a picture of it as it was around the 1/4-tank reading just to find out how many gallons would be there, to see if the gauge was liner or non-linear.

Based on a 1,034.8 miles and three tank fills, where the starting tank fill and the ending tank fill was as close to exactly the same (filling it up to near the neck), it took 30.368 gallons. Calculating, that is 34.08 mpg and at the local price works out to ~ 14¢/mile.

Planning to do something similar with the pickup but probably won't happen this year because I don't drive it that much. Based on what others have reported for their rigs, maybe I don't want to find out! (Don't ask the question if you don't want to hear the answer).

i like the thought process even though you may still be comparing apples to bananas

[Nemesis F150]

i like the thought process even though you may still be comparing apples to bananas

The main reason I posted about the Escape fuel gauge was becasue it was very similar to the one in the 150. The Escape needle swing is within a few degrees of that on the 150. While there are many years between the two vehicles, sometimes parts don’t change that much between models, and sometimes parts change within a model year. The thought was about how one could re-purpose the guts of the Escape gauge into the 150. Just a thought.

A little background: as a kid, we lived in a neighborhood that had an abandoned auto wrecking yard nearby. This was after WWII and there were lots of, by today’s standards, very old vehicles (almost all were pre-war, some even pre WWI). There were interesting things for kids to take apart, like instrument gauges, gas gauges being one of them because they had small coils of very fine copper wire. The gauges were individual self-contained vice todays 1985 printed circuit types.

Now, still thinking …. What if one could cannibalize the part of the Escape instrument printed circuit that controls the gauge then apply that to the 150 panel with some possible tweaks in the circuit to work with the tank sending unit?

At this point I’m outa time…. Decided to just calibrate the existing gauge by keeping track of how many gallons are in the tank at the various quarter-fill marks then note where the 100% full and Empty needle locations are then call it good. With two tanks the hope is to keep the engine running when the tank empties then just switch tanks. Done this before (switching tanks, long time ago) and that much works.

Going forward, noting the gallons at various key pints will be good enough. Have a lot of other things with higher priority to work on, one of which, at the moment, is what fuel additive(s) for low vehicle use during the winter months.

[Gary Lewis]

The main reason I posted about the Escape fuel gauge was becasue it was very similar to the one in the 150. The Escape needle swing is within a few degrees of that on the 150. While there are many years between the two vehicles, sometimes parts don’t change that much between models, and sometimes parts change within a model year. The thought was about how one could re-purpose the guts of the Escape gauge into the 150. Just a thought.

A little background: as a kid, we lived in a neighborhood that had an abandoned auto wrecking yard nearby. This was after WWII and there were lots of, by today’s standards, very old vehicles (almost all were pre-war, some even pre WWI). There were interesting things for kids to take apart, like instrument gauges, gas gauges being one of them because they had small coils of very fine copper wire. The gauges were individual self-contained vice todays 1985 printed circuit types.

Now, still thinking …. What if one could cannibalize the part of the Escape instrument printed circuit that controls the gauge then apply that to the 150 panel with some possible tweaks in the circuit to work with the tank sending unit?

At this point I’m outa time…. Decided to just calibrate the existing gauge by keeping track of how many gallons are in the tank at the various quarter-fill marks then note where the 100% full and Empty needle locations are then call it good. With two tanks the hope is to keep the engine running when the tank empties then just switch tanks. Done this before (switching tanks, long time ago) and that much works.

Going forward, noting the gallons at various key pints will be good enough. Have a lot of other things with higher priority to work on, one of which, at the moment, is what fuel additive(s) for low vehicle use during the winter months.

I got lost in this process as it appeared the gauge wasn't working with either tank, but I think you are now saying that it is but isn't calibrated correctly. So let me explain how the gauge works and suggest a couple of possible solutions.

First the fuel level, coolant temp, and oil pressure gauges for the Bullnose trucks are thermometers. Yep. There's a heating coil in the gauge that is right below a bi-metal spring that is wrapped around the shaft of the gauge, and as the temp goes higher so does the gauge.

And the heat is generated by the current going though the sending unit - more current means more heat. But the gauges were designed for a 6V system, and when the industry changed to 12V Ford just reduced the voltage to the gauges. However, they did it with a device that is called the Instrument Cluster Voltage Regulator (ICVR), which is really only a chopper - the voltage sent to the sending unit and thence to the gauge is a series of spikes, and the average of the spikes over time gets the wattage down to what it would have been with a 6V system.

But the ICVR's are known to fail or go wonky. And that changes the reading of all three gauges, but since the fuel gauge is the only one that usually goes to full scale, that's the one that is the most impacted.

So here are my suggestions:

• Test: The way to test if your system is working is to ground the wire to the sending units. (Plural as you can do this for both tanks and for the coolant and oil pressure sending units.) The gauge should swing to full scale and probably more pretty quickly, so don't leave it grounded for a long time.

• ICVR: If the gauges don't go to full scale then replace the ICVR with a true voltage regulator. We have a how-to at Documentation/Electrical/ICVR, but some of the vendors are now selling a plug-and-play unit. If you go with the adjustable regulator you can fill one tank FULL and tweak the voltage so it reads right on Full.

• MeterMatch: If you find that you still can't get the fuel gauge to read how you want it to read then consider a MeterMatch. Jim and I are using them to interface the later sending units, whose resistance ranges are backwards awa different to the Bullnose units, to the Bullnose gauges. But they can be used to simply calibrate a gauge as you can use them to calibrate Empty, Full, and two other points in the range.