Gas gauge not working 1990 Legacy

[Kenneth1948]

Gas gauge not working.

I plan to check the tank sender unit(s) I understand there are two.

• Are there any other likely causes on these older cars?

Thanks, any advice and information is appreciated, John aka Kenneth

 

[johnceggleston]

there are 2 on AWD cars.

only one on FWD cars.

 

does it move at all when you turn on the car?

has the gauge ever worked while you have owned it?

how long have you had the car?

 

you might try a bottle of ''techron'' fuel system cleaner.

it brought the fuel gauge back to life in my 95 lego after sitting for a year+.

you can get it at most auto parts stores.

 

one bottle in a tank of gas, improved it, got it to move.

a second bottle and tank of gas got it to work mostly well.

these gauges tend to read lower / emptier than actual amount left when they get old.

at least the 95 - 99 cars do.

i'm not sure about the 90 - 94 cars.

 

you can get it at most auto parts stores.

[heartless]

my 90 Lego fuel guage only works when it wants to - seems dependant on ambient temps and humidity levels, leading me to think there are wiring issues...

 

I have tried the Techron additive, pulled both sending units & cleaned them manually (AWD version), even replaced one of them - it is still very intermittent as to when it works/doesnt work.

 

I have given up on having a properly working fuel guage. Whenever I fill up, i make sure to reset the trip odo, and go by that - when I hit 280 - 300 miles on that, I know it is about time for a fill up.

 

your mileage may vary....

[Kenneth1948]

Have not owned the car long. Had not been driven for a while. Now running well but we're still fixing a few things like the A/c and the gas gauge.

As far as I know it doesn't work at all (daughter's car) and has not since whe have owned the car.

 

I like and use Techron too although have not put it in this car. When cars are not used for a while they seem to be prone to corrosion problems in the gas tank.

 

I have just completed somewhat similar project on an old BMW. I removed the tank, it's easy on the BMW. Hope I don't have to do this on the Subaru!

 

I soaked the sender unit in Kano Kroil for about a week. I know there are lots of opinions about penetrating oils but I think Kroil seems to have some ability to remove or dissolve or somehow deal with rust which causes problems with items like tank senders & fuel pumps. 

 

I plan to try this with the Subaru. It's AWD so I will do both senders and post the results.

 

Thanks for the input. I think we're on the right track. John aka Kenneth

[johnceggleston]

removing the gas tank is a real pain.

i hope that is not necessary, ever.

 

but you do not have to remove it to get to the sending units.

there are 2 access panels under the carpet in the cargo area / trunk just behind the rear seat back.

remove a bunch of small bolts and expose the top of the tank, fuel lines and wiring connectors.

open the tank and remove the fuel pump / sending unit assembly.

 

good luck.

[heartless]

Please do post back with the results of the kroil treatment - interested to know if makes any difference at all.

 

and johnc is very right - pulling the fuel tank on an AWD Subaru would be a major pain in the backside! Pretty much the entire rear drive assembly would have to be removed to get that tank out - not something you want to do if you dont have to - especially if there is rust involved!

 

That said - I live in northern Wisconsin - major rust belt here - and I have never had a problem with a Subaru fuel tank rusting out/thru - so far...(knocks on wood! lol)

 

If your kroil trick doesnt work, just fall back to the old failsafe trip odo method - I have only run out of gas once in this old car - and that was right after I got it - guage wasnt working then either! LOL

 

Fill the tank, reset the trip odometer, and drive - when it gets around, oh, say 275 miles or so on that trip meter, put a 5 gallon can of gas in the back and run it till it quits - make note of the mileage, put in your five gallons, and go on your merry way to the gas station - fill er up, reset the trip meter, and repeat - just make sure to pay attention to the number of miles driven since last fillup.

 

With everything at optimums (tire pressures, fresh tuneup, etc) I can squeeze nearly 30 mpg out of my AWD wagon - as an average, I get around 27-28 mpg in the summer - about 25 in the winter.

 

these cars have a 14 gal tank ...14 x 27 = 378 miles, give or take (winter = 14 x 25 = 350 mi)

 

I dont typically let mine run real low - i usually fill up around the 300 mile mark on the trip meter, just because.

[Kenneth1948]

New information:

Pulled the sender from left (driver's side) Resistance changed smoothly until about the middle of the range where the quadrant was visibly worn. I tried cleaning and even sanding it very carefully with wife's emery board but to no avail, gauge works with full tank (daughter's car, she didn't tell me this) but stops working as the fuel level drops which is consistent with the resistance readings.

 

• Does anyone have a source for the quadrant part that wears? this seems to be the problem.

• Also, how do the two senders work on the AWD cars? if one is working and the other not, what does the gauge read?

 

Thanks for helpful posts, I will continue my quest and post further results

[heartless]

yup, your findings sound about right - works when full, then quits at about 3/4...might possibly start working again around 1/4 to the "empty" mark... does the little "low fuel level" light work in this one (mine does not - found out the hard way)

 

it has been a while, but if I remember correctly, the main sender (passenger side, oval opening) reads primarily from full to 3/4 and then again from 1/4 to empty - the secondary (drivers side, round opening) is mostly responsible for the 3/4 to 1/4 readings...or something along those lines...kind of a goofy system, but there you have it.

 

as far as "sourcing" parts - yeah, good luck with that one. the 1990 is 23 years old - you are more than likely not going to find "new" sending units for these cars (i tried several years ago with no success - even tried to source the entire assembly as "new" - nada). Pumps and strainers are easy to come by, but sending units? sorry, but not likely...

 

You could try finding a decent used assembly, but chances are it will have the same problems as your current one, or will develope them soon after installation (ethanol eating away at the element? i dunno).

 

I have used the trip meter method I outlined above for several years now and have not run the car out of gas yet - not since I first got it and discovered the guage only worked when it wanted to (first time I drove it!). As I said before, I tried replacing the assemblies with used in better condition, and the guage sort of worked for a while, but eventually they, too, failed.

[Kenneth1948]

Yes the little "Low fuel" light on the dash does work and daughter is managing quite well managing the mileage. 

You're right, this cars is 23 years old but don't think the left access had ever been opened. 

I will try to figure out a fix and publish it if I ever do,

Thanks for the advice and info in all the posts.

 

BTW Kano Kroil didn't help this problem. It did solve the sender problem on the '84 BMW.

Also, the OEM Bosch fuel pumps are $180 + and are very susceptible to rust in the tank despite the screen on the intake.

The pump simply stops working (at speed on the Interstate - ask me how I know)

I tried to clean and re-start several pumps but never could get one to work.

I put a good shot of Kroil in each end of a couple of stuck pumps, put them in a ziploc bag and left them for several weeks, don't remember how long, actually forgot about them! When I did take them out, both worked and was able to drive the car with one installed. I don't know how reliable yet as I took the tank off the car, cleaned and etched to remove the rust and haven't re-assembled and driven the car again. No affiliation and it is expensive but I think its good stuff..  

[johnceggleston]

i would assume that the gas gauge reads the resistance of the sending units, and that the units are wired in series.

so if one reads full and the other reads half, the gauge would show 3/4.

just a guess, but it makes sense.

 

if only one sending unit is worn, what would happen if you left the driver side unit ''pegged'' in the full position?

would it run out of fuel at 3/4 tank?

or maybe ''peg'' it at 1/h, or just above where it stops ''sending''.

that way it would never read full or empty but be accurate in the middle.

 

but my guess is that both units are worn and both have a dead or weak spots.

[Kenneth1948]

Don't mean to perpetuate this string indefinately but I do have more questions.

I have not had time to pull the other sender yet, the one with the fuel pump.

I agree, it's probably in similar condition.

Questions:

• Are the later model AWD Subarus the same or similar?
• Would it be possible to substitute or adapt a later model part?

Thanks, Kenneth

[1 Lucky Texan]

Dunno about just the quadrant but, junkyard part, ebay part might be a less expensive option. I THINK both Bosch and Airtex makes replacement parts, not certain though.

[rxleone]

I've had this problem on my 89 sedan Legacy, gauge would be erratic on long trips. Pulled right hand (US passenger side) sender and tested continuity with a multimeter. Several dead spots. Went to the junkyard armed with the multimeter, pulled sender units until I found one that went the whole range with no breaks. Installed in my car, no problems in two years.

[Kenneth1948]

Is your car AWD?

Does it have 2 - senders?

Was the other sender OK?

 

Point I'm getting to is - Will one good sender resolve the problem or does it take two good senders?

 

Thanks, John aka Kenneth

BTW I was born in Otaki

[heartless]

Don't mean to perpetuate this string indefinately but I do have more questions.

I have not had time to pull the other sender yet, the one with the fuel pump.

I agree, it's probably in similar condition.

Questions:

• Are the later model AWD Subarus the same or similar?
• Would it be possible to substitute or adapt a later model part?

Thanks, Kenneth

 

 

Hmmm - interesting question...

 

just for grins, I went and looked up the wiring diagram for a newer model (97 legacy, chosen at random), and it does in fact show two sending units for the fuel guage - wiring diagram is laid out slightly different, but it "might" be possible to make a newer version work...

 

'>1997 fuel guage system diagram  (may need to scroll down to pg 50 of 92)

 

1990 fuel guage (pg 44 of 82)

 

Would take a little more digging to determine resistance values (values for the 1990 are listed a couple of pages further in on the posted pdf, 1997 model has no trouble shooting in that particular pdf), but it just might be possible...

 

If you want to do a little digging of your own - look here: http://jdmfsm.info/Auto/Japan/Subaru/

Edited July 12, 2013 by heartless