Huh.....low fuel light on with 1/2 tank fuel....?

[flintknapper]

Just got back from a weeks vacation. Got in my Cruiser this morning and fired it up.

I noticed the Low Fuel Light on the dash was clearly illuminated, but my fuel gauge was (correctly) reading a bit over 1/2 tank of fuel.

I've NEVER seen that light in the 18 yrs. I have owned it. I don't let my tank go below 1/4 tank.

So...I drove to town and filled up. The tank took right at 12 gallons, so the fuel gauge is correct.

During my trip home the Low Fuel Light got progressively dimmer but I can tell it is still on.

Question: What might be the cause of this? (shorted wiring)?

 

[nukegoat]

Head gasket. The low fuel light is based on hydrophilic spectrum mass whereas the gauge is a float. One common cause of the fuel light coming on is a reverse injection of coolant from a blown headgasket into the throttle body through heater bypass tube 3. This will pressurize and destroy your charcoal canister but also pump coolant back into your fuel tank where it eventually is miscible with the gas and leads to poor fuel economy and loss of horsepower.

One way to tell if this theory is true is to open your fuel cap and smell the inside of the cap. If it smells like gas then its probably a blown head gasket because the coolant is heavier than the gas and sinks, leaving the gas free to vaporize at the top of the tank.

It could also be a bad sensor or dash electronics but I doubt that.

 

[Dave 2000]

Depending on year the level and low fuel warning are seperate systems, earlier (circa up to 94?), if light is on, and gauge disagrees, then the level sensor windings are probably toast, low fuel sensor is on a fixed length rod.

Stick a gallon in the boot just in case hntil uou get a few minutes to yourself, checking super easy, remove 2nd row seats, remove oval plate, usual safety thinking and remove the fixings and lift out float assembly.

Try this before the head gasket as it is cheaper.

Regards

Dave

 

[-Spike-]

Head gasket.

He's baaaaack!

 

[Marine7]

Yes, always work from simple to difficult.....auto 101.

 

[flintknapper]

Head gasket. The low fuel light is based on hydrophilic spectrum mass whereas the gauge is a float. One common cause of the fuel light coming on is a reverse injection of coolant from a blown headgasket into the throttle body through heater bypass tube 3. This will pressurize and destroy your charcoal canister but also pump coolant back into your fuel tank where it eventually is miscible with the gas and leads to poor fuel economy and loss of horsepower.

One way to tell if this theory is true is to open your fuel cap and smell the inside of the cap. If it smells like gas then its probably a blown head gasket because the coolant is heavier than the gas and sinks, leaving the gas free to vaporize at the top of the tank.

It could also be a bad sensor or dash electronics but I doubt that.

^^^^^ I'm sure its all this and more.

So all that coolant in my fuel is going out the exhaust system and will probably take out my new muffler bearing too?

Sheeesh...what next. I have a vehicle inspection coming up and already have a blinker that won't work. I'm pretty sure its just low on fluid though.

 

[Dave 2000]

^^^^^ I'm sure its all this and more.

So all that coolant in my fuel is going out the exhaust system and will probably take out my new muffler bearing too?

Sheeesh...what next. I have a vehicle inspection coming up and already have a blinker that won't work. I'm pretty sure its just low on fluid though.

View attachment 1740478

There is no way you can repair that wearing those gloves, you need blue latex not white.......common knowledge.

Regards

Dave

 

[mattimooseprime]

One common cause of the fuel light coming on is a reverse injection of coolant from a blown headgasket into the throttle body through heater bypass tube 3.
.

I don't have a throttle body though? are my muffler bearing bad? is my combobulator debobulating?
the plus side is if i get coolant in my fuel, it will keep it cooler so that's always a plus.

 

[slow95z]

my 93 has a bad sending unit and does stupid things like this. i have been too lazy to swap it out. it will run 100% out of gas when it shows 1/4 tank and the light comes on about 20 miles before that. in other words dont trust your gauge now. if you need a new sending unit i have a couple and its just sad i am willing to pull one to sell to someone and wont get off my rearend and swap mine.

 

[flintknapper]

my 93 has a bad sending unit and does stupid things like this. i have been too lazy to swap it out. it will run 100% out of gas when it shows 1/4 tank and the light comes on about 20 miles before that. in other words dont trust your gauge now. if you need a new sending unit i have a couple and its just sad i am willing to pull one to sell to someone and wont get off my rearend and swap mine.

So far...my sending unit and gauge seem to be accurate. When I pulled up to the pump my gauge showed right at 1/2 tank (just a tad over). The tank only took 12.5 gallons. The gauge then showed full (as it should).

So all that is left to do...is to drive it, let it get down to 1/4 tank (per the gauge)....then fill it up and see if that amount corresponds to the tank capacity. IF it does...then I don't have a gauge or sending unit issue. It will be something to do with the with low fuel circuit or gauge cluster.

Currently the light appears to be on but is very, very dim. You have to really look to see it. Tank is full.

 

[SmokingRocks]

looks like you converted your cluster to LED lights... Did you put an LED in the fuel light?

If so and without the correct resistors it will remain lit... all... of... the... time.... Ask me how I know.

 

[flintknapper]

looks like you converted your cluster to LED lights... Did you put an LED in the fuel light?

If so and without the correct resistors it will remain lit... all... of... the... time.... Ask me how I know.

I did recently install LED cluster lights, but only the four main bulbs and the 'D' (trans position) bulb.

I did not replace any other bulbs and as far as I can tell...it isn't 'spill over' light from the LED's. It was clearly illuminated yesterday...but not now.

 

[MoJ]

I have the same problem and was planning to replace the sender assembly pictured below ($125).

I made the assumption, perhaps incorrectly, that the float was responsible for the indicated fuel level and the other circled gizmo was a sensor for the low fuel light. Can anyone confirm or deny this is the case?

 

[flintknapper]

I have the same problem and was planning to replace the sender assembly pictured below ($125).

I made the assumption, perhaps incorrectly, that the float was responsible for the indicated fuel level and the other circled gizmo was a sensor for the low fuel light. Can anyone confirm or deny this is the case?

That would sure make sense (separate units). I've never had mine out...so I can't confirm. I'm still running the original fuel pump and sending unit (300K miles, 21 years old).

Presently, mine is not fully illuminated...but it was just a few days ago. Never had that light come on ever...because I don't let my tank get below 1/4 full. So...unless my sending unit or fuel gauge on the dash become inaccurate...I will probably just ignore it. One of those things I will fix way down the line.

Didn't know if anyone else had experienced this and perhaps knew what the issue might be.

 

[ppc]

I seem to recall someone a few years back having the same problem. The cause being the in tank wiring where the insulation was worn on the wire to the low level sensor, shorting out against the brackets that support the fuel pump. This is an excellent time to pull the assembly from the tank, check things out and replace the filter sock on the pump pickup.

 

[Tools R Us]

The low fuel light is on the bracket with the fuel pump and gauge, they share a ground, other than that totally separate circuit. When the fuel is low, the sensor sends ground to the light turning it on. My guess would be an intermittent short to ground somewhere in the circuit, would start by unplugging at the tank and see if the light changes, goes out.

 

[inkpot]

Did you go wheeling and crush the bottom of the tank, so maybe it only holds 13 gallons total now?

 

[flintknapper]

Did you go wheeling and crush the bottom of the tank, so maybe it only holds 13 gallons total now?

Negative.

 

[flintknapper]

Hah,

Driving to town a couple of days ago...I ran over some 'rumble strips' on the highway (road work going on) and the low fuel light went off. Stayed off for two days and then mysteriously reappeared overnight.

So...looks like I'm going to have to pull the unit and have a look.

It isn't a big deal to me..as I NEVER let my fuel get below 1/4 tank and the sending unit and dash gauge are accurate. Just don't like that amber light being on at the dash and prefer for everything to be working correctly on my Cruiser.

 

[Tools R Us]

Hah,

Driving to town a couple of days ago...I ran over some 'rumble strips' on the highway (road work going on) and the low fuel light went off. Stayed off for two days and then mysteriously reappeared overnight.

So...looks like I'm going to have to pull the unit and have a look.

It isn't a big deal to me..as I NEVER let my fuel get below 1/4 tank and the sending unit and dash gauge are accurate. Just don't like that amber light being on at the dash and prefer for everything to be working correctly on my Cruiser.

Bumps causing the light, with plenty of fuel, is more likely to be a ground fault in the circuit than a sensor problem?