2000 bravada fuel guage

[smeltdan]

It seems that when get low on gas the guage will jump around and give different readings on amount of gas there is. It will jump to half a tank then to full tank,etc. All the other guages are working. Gets difficult knowing how much there really is.

[Joshua M. Smith]

Originally Posted by smeltdan

It seems that when get low on gas the guage will jump around and give different readings on amount of gas there is. It will jump to half a tank then to full tank,etc. All the other guages are working. Gets difficult knowing how much there really is.

It sounds like your sending unit is shot, unless this only happens on starts and stops. Then that's the gas sloshing around.

I'm betting the sending unit is giving false impedence though. You can check this with a multimeter while moving it by hand after removing it from the tank.

Josh <><

[ericn1300]

false impedance would be a fairly consistent problem, showing up thru the whole range, full or low on fuel. same with low voltage or bad grounds. might be a mechanical problem with the float, but i doubt it.

GM's are notorius for fluctuating fuel guages. vacumm and amperage changes from hard acceleration combined with the transfer of fuel to the rear of the tank (sloshing) seem to show up more radicaly with a low tank. most newer vehicles have baffles in the tank to inhibit sloshing fuel.

an old trick my daddy taught me is "it's just as cheap to fill the top half of the tank as the bottom half" as he came to the rescue with a can of gas, and that could actualy save your fuel pump from premature failure. the fuel surrounding the pump acts as a coolant for the pump. check your owners manual to determine the capacity of the tank and never let it get below 2 gallons left. also a full tank is less likely to get water condensation in it since there is less air in it and hence, less humidity in it.

[Joshua M. Smith]

Originally Posted by ericn1300

false impedance would be a fairly consistent problem, showing up thru the whole range, full or low on fuel. same with low voltage or bad grounds. might be a mechanical problem with the float, but i doubt it.

I respectfully disagree.

The sending unit is only a variable resistor. It's not uncommon to have several bad spots in one.

Explain to me, if you have one bad spot that has no resistance, how is it going to show up throught the whole range? As well, a spot beginning to go bad can shoot it to half a tank because of changed impedence in that area. I've got my money on the sending unit.

It's like a bad spot on a starter. As soon as it's moved off that bad spot the starter spins again.

Sending units have been the same since almost the beginning, and will likely remain the same until we stop with liquid fuel.

[ericn1300]

Originally Posted by Joshua M. Smith

I respectfully disagree.

The sending unit is only a variable resistor. It's not uncommon to have several bad spots in one.

You might be right. a variable resitor is the inverse of a variable rehostate which might be subject to bad zones of conductivity from corrosion or wear, which could cause an increase in resitance, but no decrease in current, leading to greater impedance but no lessoning of impedance would occur and no upward swing of the fuel guage. had the same problem with my toaster oven last month. I=C/R

I still think the problem could be mitigated at minimal cost by just filling up the tank.

[Joshua M. Smith]

Dan and Erin,

I guess my first question would be whether this has been happening from the get-go. That'll tell us where to look specifically.

Josh <><

[aeo]

I also suffer from this problem with my 2000. Does seem to happen only when the tank is not completely full. Have had so many problems with this vehicle it's ridiculous. I will be posting separately about the others...

[Chris Stewart]

The stock level sensor has 3 tiny wipers on the pot. My '97 had 2 broken and one bent...hit and miss connection. The new one has 2 wipers and they're a bit larger to last longer my guess. It's still a pretty poor contraption though.