fuel gauge on dash

[Stan Simpson]

We took a 600 mile trip this past weekend, filled up with fuel about 100 miles out, and suddenly the fuel gauge started bouncing all over the dial. When we stopped for breaks, it seemed to be showing the correct fuel level based on my best guess. On the way home, the gauge still bounced all over, and sometimes for miles it would just stay at the far right (way past full) on the dial.

I'm guessing a sensor of some sort in the fuel tank is the culprit. Or perhaps a faulty gauge.

Any ideas would be appreciated.

Stan

[Gerald Farris]

Stan,
there is no way to tell what is wrong with you fuel gauge without troubleshooting the circuit. A simple way to troubleshoot the circuit was discussed in a previous thread; http://forum.bacrallies.com/m-1302658733

The problem that you are having is intermittent (is not a consistent failure) so diagnosing it is more complicated. A hard failure is much easier to diagnose than one that comes and goes as you drive. The problem is that you can not tell were the malfunction is as long as it is working properly when you are checking the system.

Gerald    

[Stan Simpson]

Thank you for the help, Gerald. I'm troubleshooting this weekend, I read the archived post. Lots of good information.

Stan

[charlie drake]

WE HAD A SIMILAR PROBLEM--BOUGHT NEW GAUGES, SENDING UNIT.   COME TO FIND OUT ALL IT WAS --TURNED OUT TO BE A GROUND WIRE.  CHECK THAT FIRST. CHARLIE DRAKE

[Stan Simpson]

Troubleshooting the fuel gauge problem. I'm guessing this is the sending unit. Could someone confirm that? I'm no mechanic for sure. I raised the front of the coach with the air leveling system in order to get a good look at it. Is it safe to crawl under there while the coach is raised by the air? I want to check those connections to make sure they are secure.

If this is the sending unit, does anyone have an idea which of the three wires is the ground?

I feel stupid asking these questions, but I'm cognizant of Charlie's post above.

Thank you.

Stan

[Gerald Farris]

Stan,
Yes that looks like the fuel sending unit from what I can see in the picture.

About your question in regards to working under the coach when the coach is raised with the air leveling system only, the answer is NO, although I have done it before. To be safe you need to have the coach supported by safety stands in case you happen to accidently do something that would cause the coach to drop, like damaging an air line.

As for telling you which wire goes where, I can not.  However that will be easily sorted out with a good DVOM (digital volt/ohm meter).

Gerald

[Stan Simpson]

Gerald,

I suspected as much regarding crawling under there. I have a digital volt meter. I will sort it out. Thank you for your reply.

Stan

[Edward Buker]

I was a little surprised to see three wires here. Usually there is only the need for a "wiper" lead from the rheostat and an end lead that is usually grounded.  I noticed this was an aluminum tank and there may be issues with the grounding and bonding of the aluminum that requires an extra lead.....not sure. Out of curiosity I thought I would raise the quuestion as to what the three wires are doing so we would hopefully all know. Anyone looked at one of these?

In the marine industry with an aluminum tank you are concerned with both bonding and grounding. Grounding is meant to assure the flow of electricity so that if a potential is raised and it should not be, it will go harmlessly to ground. The filler neck and tank are usually grounded to the boats ground system. Bonding is meant to assure that electricity will not flow and that components involved will maintain the same potential. This is usually done to prevent electrolysis which is a concern with aluminum tanks. So they are also bonded. Not sure how the RV industry treats aluminum fuel tanks and if any of these wires are involved here with grounding or bonding.

Later Ed

[Stan Simpson]

Its raining today, but as soon as I can get under there with a DVM, I'll post the results.

Thanks,

Stan

[Dick Simonis]

I was a little surprised to see three wires here. Usually there is only the need for a "wiper" lead from the rheostat and an end lead that is usually grounded.  I noticed this was an aluminum tank and there may be issues with the grounding and bonding of the aluminum that requires an extra lead.....not sure. Out of curiosity I thought I would raise the quuestion as to what the three wires are doing so we would hopefully all know. Anyone looked at one of these?

In the marine industry with an aluminum tank you are concerned with both bonding and grounding. Grounding is meant to assure the flow of electricity so that if a potential is raised and it should not be, it will go harmlessly to ground. The filler neck and tank are usually grounded to the boats ground system. Bonding is meant to assure that electricity will not flow and that components involved will maintain the same potential. This is usually done to prevent electrolysis which is a concern with aluminum tanks. So they are also bonded. Not sure how the RV industry treats aluminum fuel tanks and if any of these wires are involved here with grounding or bonding.

Later Ed

Ed, it might be set up as a potentiometer vs. a reostat.  Not common, but not unheard of either.  One lead probably goes to ground instead of trying to using the tank and internal ground.

[Edward Buker]

Dick,

I'm guessing that is probably right given all the leads are built into that plastic head of the sending unit. If grounding is involved here it is internal to the tank or a wire externally tied to the tank somewhere else.

Later Ed