i have a 97 dakota cc 4x4 with the 3.9L V6. My fuel guage does not read accurately. It never shows less than a half a tank even when I know that there is less than a quarter tank left. Is this the sending unit or the guage cluster not working properly?

 

It may be the sending unit is not working right. Has the fuel pump been removed or replaced recently or in the past? There are marks on the top of the tank and the pump housing so you can line the pump up in the correct position so the float for the sending unit has the room to travel fully and give an accurate reading no matter what the amount of fuel is in the tank.

It is possible that the fuel gauge may be going bad but this sounds to me like the problem is in the fuel level sending unit. You might try a few doses of Chevron Techron Fuel System Concentrate, it might be able to free up the float if it is stuck. Techron can eliminate sulphur deposits that can form on the sending unit that cause a wrong or erratic reading on the fuel gauge. If that doesn't work, the fuel level sending unit can be replaced separately without replacing the entire fuel pump assembly. It's a messy job and if the fuel pump is original, depending on how many miles are on the truck you might want to just replace the whole pump assembly anyway. I know after replacing my own fuel pump last year that it's a job I sure don't want to have to do again any time soon.

Jimmy

 

Try running a gauge cluster test.

Key off, press the trip odometer button and hold.
Turn the key on, don't start the truck.
Hold the button for about 10 seconds until CHEC appears in the odometer.
Release the button.

It'll test the VFD lights first, then the indicators lights and should end with the gauges sweeping to various points.

 

Not sure if the sending unit has been replaced. I have only owned the truck for 6 months. The truck only has 17000 miles but the under side is extremely rustly. The dealer I bought it from replaced the tank straps and all the brake lines because of rust. I have put Lucas Oil in the tank but that did not help.

 

Lucas won't do anything for the sending unit. Techron Concentrate is the only fuel additive that is known to help with erratic fuel gauges and deposits on the sending unit and float. I have read on other forums that GM even recommends it in their TSB's for erratic fuel gauge operation.

If the dealer replaced the tank straps, maybe they had to remove the tank to do it. It might be worth dropping the tank again to see that the pump is oriented in the right position on the tank. At only 17K the pump itself should be OK but maybe all that sitting without being driven caused something in the sending unit to gum up and now it doesn't read right.

Jimmy

 

My gauge doesnt work right either and hasn't since i bought the truck , according to the previous owner it had sat for a few years with a half a tank of gas in it before i bought it . I dropped the tank ( wow , what a job that was ) and checked the pump and float assembly and i could see where it was " dirty " on the circuit board contacts for the float level , i tried to clean it with an pencil eraser and even some fine scotch brite pads , but it didnt work . I have been running marvel mystery oil with the gas for about 7-8 months now and the gauge needle moves around more but i still dont trust it and go by my trip mileage for a fuel level estimate ,, someday im going to replace the whole pump/float assembly .

 

Thanks guys-I will get some Techtron Concentrate and try that. Living in the Midwest always has its challenges.

 

Make sure you get the Techron Fuel System Concentrate, not the Pro Guard or fuel injector cleaner. The concentrate is the strongest one and is the one that might be able to free up the sending unit and float. The concentrate is in the bigger bottle, I think it says it treats 20 gallons. Sorry to say it but it also the most expensive, around here it's about 10 or 12 bucks a bottle I think. You might have to try 2 or 3 tanks with Techron before you see any results. Maybe Google "GM fuel sending unit Techron TSB" or something like that and there is probably more info out there.

Once you get the gauge problem fixed you might try adding Marvel Mystery Oil at each fuel fill. It lubricates the fuel pump and fuel injectors, maybe that will help keep the sending unit working the way it should. It's a good upper cylinder lube too and it can help increase compression so the truck runs a little better and it can also help increase gas mileage.

Good luck with it.

Jimmy