Rapid Fuel Gauge Fluctuation / Drop

[brendanr279]

Hi, guys.  2002 Forester S, 140k miles, automatic

 

SITUATION: My fuel gauge just started intermittently, rapidly dropping from above a half tank to near E.  I get freaked out, pull over, and it will go back up usually.  There is an occasional, short-lived sputtering/hesitation of the engine (not sure if it's directly corresponding to these instances but makes me feel like the engine is going to quit).  As well as the check engine light coming on during these times, but doesn't continuously stay on.  I have not caught the check engine light to read the code yet.  I'm also occasionally getting what I would call crappy MPG (20 mpg highway).  These issues seem to only present with prolonged highway driving. 

 

BACKGROUND: I changed my downstream O2 sensor about a month ago, everything seemed to be fine with that.  I changed my fuel filter about 2 months ago, as well as added some Seaphoam.  During cold winter days I would get the smell of gas coming through the vents, but that doesn't happen above 20 degrees F and I was told I just need to tighten up some clamps (probably around the fuel filter i had recently changed)

 

Any thoughts on whats causing the funky fuel gauge, etc?  Or what I should do for assessment?

 

Thanks.

[1 Lucky Texan]

2-3 things;

 

any other electrical problems or new alternator recently?

 

could be a ground somewhere is intermittent.

 

there are floats on both side of the tank, one of them seems to be sticking (most likely)

 

I suppose there could be an issue with the jet pump - but this would only be true if, when it measures empty, it only takes 6 gallons or so, instead or 12 or w'ever (this seems least likely problem)

[brendanr279]

No electrical issues I can think of, but I did clean off my battery terminals a couple months ago.  Used the baking soda paste method.  Maybe it's the battery, is that what your suggesting?

[1 Lucky Texan]

it really seems like a float or wiring problem.

[brendanr279]

I'll double check my battery terminals just to be sure.  But to check the gas tank floats, do you think I should just use a fuel cleaner additive first?  Or should I actually look at the floats?  Those are attached to fuel sending unit and I can get to it from the trunk/hatch right?  

 

Thanks

[1 Lucky Texan]

if the Forester is like our Outback, you'd go under the rear seat. Pump and it's float is on the right side (US pass.) and the second float is on the left. You can probably find images and youtube videos , if not for thr Forester specifically, for some similar soob model to get an idea of what to watch for,

 

searching for a schematic would be a good place to start - if the problem is an abraded or rodent-chewed wire somewhere, that means you wouldn't need to pull the access off the gas tank.

 

and be careful about fumes. - it wasn't bad when I inspected my fuel pump (for a different reason), just something to be aware of.

 

 

on the smell, most likely thing, Impreza-based models of that vintage have fuel clamps in the engine compartment that leak in the winter - many people have solved the leakage by just tightening them. Other possibility would be a rusted filler neck or evap system problem - but those usually throw a code.

 

when it indicates empty - is it really empty?

Edited April 18, 2017 by 1 Lucky Texan

[brendanr279]

No.  It's not really empty, and it's short-lived.  Goes up on it's own when I pull over or restart the engine, and only happened with the few long distance drives I did this past weekend. I'm going to tinker a bit and monitor.  

 

I've replaced a fuel pump in an older Legacy, so it'll probably be real similar.  Might not get to it until next week.  I'll keep you posted. I appreciate the help.  Thanks.