Fuel gauge inaccurate

[slowmo]

There is only one way to find this out and I found out yesterday. Is it possible to recalibrate the fuel gauge?

On a funny note, I installed a new generator because the old one wasn't creating gen. Apparently I have a broken wire somewhere (or a bad regulator) because yesterday the battery died at the grocery store. I got a helpful lad to give me a jump and 10 seconds after the truck started it died again. He hooked back up and then it wouldn't even fire. Going into my broken truck algorithm the easiest and first thing to check first is fuel flow. Disconnected at the carb and pumped the fuel pump...no gas. That's right. That is when I ran out of gas. I wouldn't have been surprised if a meteor struck the truck at that point.

[superstator]

Check your voltage regulator for the gauges. If it's not doing 10v anymore that will throw off the level reading.

[slowmo]

Hmmm. Good idea. As an engineer I don't believe in coincidence until proven to be such. The battery being dead and running out of gas at the same time is plain weird. Your idea puts the regulator as a potential common denominator which I hadn't considered at all. I'll check that tonight.

I still have a mechanical fuel pump BTW. What is the standard fuel capacity of 1970 Series IIa 88 anywho?

edit - found it. 12 gallons US. I put between 11 and 12 into it so I was indeed out of gas. The gauge indicated between 1/2 and 1/4 so it is definitely not calibrated. I suppose it could be the sender. I assume it is a resistive type of sender and I could remove it and measure the resistance. Guess if the regulator is OK that is what I'll do.

Could be the regulator is shot, and that is leading to my problem with the generator as well.

Other ideas?

[slowmo]

http://www.spritespot.com/Video/Polarizing_the_Generator.htm

Great link for troubleshooting the charging system.

[lumpydog]

I ran through getting my gauge to work correctly a few months ago. I had several issues that were contributing to a faulty reading.

1) There is a voltage stabilizer behind the instrument panel. It's usually screwed (and grounded) to the bulked - or in later 2as and SIIIs its screwed to the back of the speedo. The voltage stabilizer has a power supply going into it (usually to a post marked "B") and then 2 wires coming out of it (from posts marked "I") that go to the fuel and temp gauges. Use a multimeter to make sure that the power supply going into the voltage stabilizer is 12-13v. Use a multimeter to check the average power reading going out to the gauges, from the voltage stabilizer, is 10v. The stabilizer pulses to an average output of 10v - which is what the gauges are calibrated to. Note, you will need an analog multimeter. A digital one can't read the voltage from the constantly pulsing stabilizer. My voltage stabilizer was putting out low voltage.

2) Is your fuel tank/sender properly grounded? Take a wire and touch one end to a good ground and another end to the top of the sender. See if the needle climbs. The sender grounds to the fuel tank. Fuel tanks sometimes are not properly grounded. This was part of my problem. I ran a ground wire from one of the sender fixing screws, directly into the chassis.

3) Is the sender providing the right level of resistance - if you search my old post/question on this topic, Safeairone posted a chart that shows the resistance readings that your sender should be registering at different fuel levels.

I've read that the traditional voltage stabilizers typically fail over time. If you don't want to purchase a traditional voltage stabilizer replacement from our hosts (link provided earlier), Moss motors sells a replica voltage stabilizer that is "solid state" and converts the power source to a constant 10v - it's part number 131-555. They have some trouble shooting instructions that are helpful too.

Also, given you are trouble shooting your voltage regulator, here is a guide that may help.

[slowmo]

Excellent! Thanks lumpy. It would appear my charging circuit has a problem which I need to sort out first. It is not working. If I still have the fuel gauge issue I'll tackle that next.