Replacement fuel gauge died too

[richw46]

1995 Merc 115 and Ranger R72 boat. Last year the fuel gauge quit registering any fuel. I took the boat in for something else and had them replace the gauge. I checked it when I got home and the new gauge was showing fuel; that was last fall. I went out to the boat yesterday, still sitting in my garage, turned the key and now this gauge is dead too.

The boat hasn't been anywhere. I occassionally plug in the charger (3 bank Pro charger) and all my batteries were fully charged. Yes, there is fuel in the tank Is it possible that something is blowing the gauge? What readings should I see on a voltmeter or resistance check?

Thanks,
Rich

 

[Silvertip]

Re: Replacement fuel gauge died too

Mistake #1: Telling the dealer to replace the gauge. That is exactly what they apparently did.
Mistake #2: Not telling them to actually "diagnose WHY the fuel gauge doesn't work".

The fuel gauge receives a signal from a variable resistance sender located in the fuel tank. when the tank is full, the resistance of the sender should measure about 33 ohms. At half full it should measure about 109 ohms. At empty it should measure about 240 ohms. So, siince there is a wire running from the sender to the "S" terminal on the gauge, there is a ground wire on the gauge, there is a +12 volt terminal on the gauge, there is a ground terminal on the sender which means there are lots of places for loose or corroded connections. There is also the possibility of the sender itself hanging up or not reading correctly. So when a gauge doesn't work, it is seldom a gauge issue. Always diagnose why something doesn't work before replacing expensive parts. Here is a diagram of a fuel gauge system.

 

[richw46]

Re: Replacement fuel gauge died too

In fairness to the dealer, I was having other problems. The tachometer wasn't working which I assumed was the voltage regulator. The trim tilt has been bouncing and the fuel gauge quit. Since the alternator was sending 16.5 volts to everything I just thought it burned up the fuel gauge. When I picked it up, it was working. Now, sitting there all winter, I guess the problem is somewhere else.

Excellent diagram, I sincerely thank you for taking the time to respond. They gave me my old gauge back so I can experiment with it to see if it's bad. I've had good service from this dealership. Lesson learned, though :redface:

 

[Silvertip]

Re: Replacement fuel gauge died too

Since you have other gauges that are dancing around, that says there are wiring issues somewhere. Those same wiring issues may be the reason charging voltage is spiking. For example the connections for the voltage regulator may be loose.

 

[richw46]

Re: Replacement fuel gauge died too

Well, they replaced the voltage regulator so that should resolve the voltage issue. When the trim gauge quit working I found that if I ran a jumper between the engine mount and the drive unit, the gauge would work (it had quit) but when I was running down the lake it would bounce from one extreme to the other. In the garage it used to be steady but now it's bouncing even when on the trailer. I suspect the sending unit on the motor is bad and should be replaced. When it gets warmer I'll see if I can spray some tuner cleaner in it to make a better contact. Not sure what to do with the grounding issue or even why I have one. The engine sits on motor mounts (rubber probably) and that would isolate it but why wasn't it an issue before now? Still may have something to do with the sending unit.

But the tilt indicator is not a big deal. I know the motor and where the trim needs to be. If I get the fuel gauge working I'll be happy.

 

[seabob4]

Re: Replacement fuel gauge died too

Not sure what to do with the grounding issue or even why I have one. The engine sits on motor mounts (rubber probably) and that would isolate it but why wasn't it an issue before now?

Put a meter on your engine zinc and you batt ground terminal, check for continuity. You'll find out that your engine is an integral part of your boats grounding path...

 

[Silvertip]

Re: Replacement fuel gauge died too

Every symptom you point to says "bad connections" including the one regarding the voltage regulator. I'm not a betting man but all of the other glitches point to grounding or connection issues so the regulator is certainly part of those issues as well. I think you really need to spend some time looking at grounding and bonding issues starting with the integrity of the ground cable, the cleanliness and tightness at the battery AND the engine (looking is not good enough). Disassemble, clean, install and tighten securely at both ends. There are many grounds on the engine which are usually bolts directly into the engine block. Check them. Check the ground bus at the console.

 

[richw46]

Re: Replacement fuel gauge died too

Sitting at the office today so I don't have access to test it right now. The boat is garage kept and I'm pretty fussy about it. I guarantee that the battery connections are all very clean and tight. The choke operates OK and that's mounted on the engine carbs. Power trim is OK too, no problems with it. All cable connections on the motor are clean, like factory, and tight. With two depth finders showing the same voltage, no jumps or jitters, with a steady increase or decrease with the engine revs, I feel good about saying it's all OK.

At the engine mount is where the trim sending unit is located. On each side of the drive shaft housing, as I recall, there are places where there is a shock absorber. When I ran a wire from that area to the engine, the trim gauge started working. Since this was a temporary solution I suspect that perhaps there is corrosion there and that's why the gauge is bouncing again. I'll have to clean that area to be sure.

The fuel gauge, however, gets power and ground from the battery through the bus at the console. It's very clean and no other connection indicates any problems there. As I recall from your diagram, the negative wire comes from the battery to the fuel sending unit with variable resistance to the gauge. No direct link to the motor. So a bad ground on the motor wouldn't have any impact on the fuel gauge, would it? Maybe some pictures would help

 

[Silvertip]

Re: Replacement fuel gauge died too

The instruments are all powered through the engine harness, not the boat harness. Remember, gauges are activated when the key is turned on. The harness from the battery to the console feeds the fuse panel and any accessories so you are correct -- that system would not have a bearing on any engine related functions. The "A" (accessory) terminal on the ignition switch feeds 12 volts to the gauges. So +12 volt wiring can impact things just as easily as ground connections. If you look at the sticky for the generic boat wiring diagram at the very top of this forum you will see that +12 volts and ground jumper from one gauge to the next. A loose connection will affect any gauge(s) after that point.

 

[richw46]

Re: Replacement fuel gauge died too

I had a chance to test the gauge they took out as "bad" and it tests OK. I put a 12v line on the I and L posts, a ground on the G post (light comes on) and a resistor between the S and G and the gauge showed 1/8 of a tank.

The light on the one in the boat comes on so I know it's getting ground and 12v+. When I returned from the boat dealer it was working so there must be an issue with the sending unit in the tank. Connections under the dash are all clean, it's a garage kept boat. It's rare that wiring goes bad so that leaves the sending unit.

On the Ranger R72 the tank is located under the bench seat. The instructions show I have to pry up the flap on the back of the seat in order to get to it. I tried this when the boat was new and couldn't get it to open. Maybe it's looser now.

Rich

 

[richw46]

Re: Replacement fuel gauge died too

Guess what? The gauge in the boat is working today.

 

[seabob4]

Re: Replacement fuel gauge died too

Guess what? The gauge in the boat is working today.

Ain't electricity wonderful?

Still something loose. Just because it works today doesn't mean it's going to work tomorrow...