Fuel Gauge Calibration

[AndyB.]

‘85 2.8 that I’ve owned since ‘96 (second owner). I replaced the worn out sending unit a few years ago, prior to that full was off the chart and when you first hit E, you were down about 8 gallons (17 gallon tank). I drive it around 1k miles per year, wasn’t sure how close to E I could get before I ran out of gas. Last week I was between 1/8 and E and put in 15 gallons.

Adapting the check method in the service manual, I used a 10 ohm and 75 ohm resistor (I couldn’t find a 73). When hooked up to a 12vdc power supply and an old gauge with the 10 ohm resistor in circuit, I zeroed the trimmer on the instrument voltage regulator until the needle was on F. I then replaced to 10 ohm with the 75 and checked position.

I swapped the IVR in my truck—nailed it. No longer over shooting F by 1/4 of a tank.

 

[ford4wd08]

Nice work, I track miles more than anything when I drove my B2.

 

[AndyB.]

I’ll keep an eye on it for a bit. After two hours of driving today it’s down 1/4 of a tank, before adjustment it would have still been above full. I don’t have a trip odometer, and I drive it infrequently enough that I don’t remember mileage.

I adjusted two IVRs with this setup, both motorcraft made in Mexico parts made in the ‘00s. I don’t know if there was a spec change or just loose QC on these. The original would also read off the scale when full.

 

[ford4wd08]

I’ll keep an eye on it for a bit. After two hours of driving today it’s down 1/4 of a tank, before adjustment it would have still been above full. I don’t have a trip odometer, and I drive it infrequently enough that I don’t remember mileage.

I adjusted two IVRs with this setup, both motorcraft made in Mexico parts made in the ‘00s. I don’t know if there was a spec change or just loose QC on these. The original would also read off the scale when full.

I didn't realize they made a RBV without a trip odometer. That's what I use when tracking mine. Just reset it every time I fill up.

 

[RobbieD]

That is great work. And it's very useful; thanks for posting it.

 

[helpme]

I was always afraid that the gauge would burn out if it was pegged past "F". But fortunately, that didn't happen.

 

[vigness]

Please expand on the method or attach the pdf. I have one that pegs at 3/4 tank, and I constantly forget to zero the trip meter when I fill up. Have to carry a 2.5 gallon can 'just in case'.

 

[AndyB.]

I would start off with this check.

In my case, going through the workflow I would have kept replacing the instrument cluster voltage regulator. I set up a fuel gauge circuit outside of my truck so I could adjust the trimmer on the IVR out of my truck.

 

[vigness]

Ah, that was the part I missed, adjusting the trimmer. Is that fairly simple, or a PITA but worth doing once? Is that the voltage regulator I see in the lower left of the original pic?

 

[AndyB.]

It was fairly simple. This was the third IVR I’d had in the truck, I’d already replaced the sending unit (which was bad) and the gauge (hoping I wouldn’t have to replace the sending unit).

Adjusting it in the car, seems like it would be a pain. One IVR required 3/4 of a turn unscrewed, the other 1.5 turns. If you can test with the resistors to rule out the sending unit, go for it.

 

[AndyB.]

Yes, the IVR is the small metal box in the lower left.

 

[AndyB.]

As a follow up to this, I bought gas today. My gauge said I was down 1/2 a tank, I put 8.661 gallons into a 17 gallon tank. I think that’s close enough.

 

[xr7g428]

You can test pre magnetic style gauges (57 to about 1986 some later) with this $30 shipped:

Gauge Tester GT-Ford-1 | Desert Classic Parts

desertclassicparts.com

 

[AndyB.]

The gauge read a little above E, and I put just over 13 gallons in it (17 gallon tank). I got in and noticed it was just above F.

it’s like having a normal gas gauge in any other car. I’m glad I took the time to calibrate the instrument cluster voltage regulator.

 

[ford4wd08]

The gauge read a little above E, and I put just over 13 gallons in it (17 gallon tank). I got in and noticed it was just above F.

it’s like having a normal gas gauge in any other car. I’m glad I took the time to calibrate the instrument cluster voltage regulator.

Are the other gauges just warning lights? I wasn't aware they made a cluster like that early on.

My 85 B2 has gauges with needles for each.