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92 Legacy fuel sending unit trouble


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10 replies to this topic

#1 4FOR4

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Posted 14 March 2004 - 10:54 PM

The fuel gauge on the Legacy I just picked up only went down from full to 3/4 after 200 miles. I put 9 gallons in so it should have been almost empty, at least to 1/4.

When vacuuming the car I noticed wires coming inside from under a oval cover in the trunk, passenger side just behind the seat. I took the cover off and found that the original 5 wires to the sending unit plug in connector had been cut and new ones were attached. There has obviously been a problem with this before.

Finding another cover at the other side of the car (driver's side) I took that one off too and found a 2 wire connector that wasn't plugged in to some other fuel tank sensor.

Can anyone tell me the relationship between the 2 sensor? Could the 2 wire not being connected throw off the reading on the gauge? I guess I'll find out after emptying the tank again but wondered if anyone has played with this before. Thanks

#2 Tiny Clark

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Posted 15 March 2004 - 05:10 AM

I'm pretty sure it uses two sensors to keep the fule averaged out when in turns. Not sure, since I don't have my account at alldata anymore. Hook it up and see what happens.

#3 lmdew

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Posted 15 March 2004 - 08:53 PM

The passenger side has the pump and sending unit. The drivers side has a sending unit and a fuel pickup to transfer the fuel over the hump in the tank. Both sides are used for proper fuel gauge readings.

If you need the units, I have both from a spare car we parted for my son's auto to manual trans swap. Lmdew@hotmail.com

#4 4FOR4

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Posted 18 March 2004 - 05:20 PM

I've run 6 or 7 tanks through now and it still does the same thing; top it off it goes past the full mark, run it for 250 miles (about 11 gallons) it fluctuates around the 3/4 line.

Plugging the driver side connector back in, didn't seem to have any effect.

Could it be a couple of wires are swapped? Does anyone know where to get wiring diagrams for this?

#5 Cougar

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Posted 20 March 2004 - 11:41 AM

You should be able to order a factory service manual that covers the wiring on your car. Considering the age of the car, getting a wiring manual would be a good investment.

It sounds to me that the drivers side sensor has a open connection to it. Checking the resisitance of the sensor with an ohmmeter will tell you if that is so. This is a fairly common problem with these cars.

#6 4FOR4

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Posted 20 March 2004 - 12:01 PM

Thanks Glen, I was thinking the same thing. My son got a diagram from the shop he works at and it seemed to me that if both reastats weren't operational it would only travel half way. I'll check as soon as its warmer and stops raining.

By the way the low fuel light will still work if the gage doesn't. I let it get low so I could check and even though the gage was better than half, the light came on.

Do you know what ranges the resistance should be in?

#7 Cougar

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Posted 20 March 2004 - 12:36 PM

Your wecome for the help.

As far as the resistance goes, I am not sure but I seem to remember something like around 5k ohms possibly. I have heard that just cleaning the contacts sometimes will get them working again.

#8 Legacy777

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Posted 22 March 2004 - 08:59 AM

you can d/l a pdf version from the fsm of some of the engine electrical from me

http://www.main.expe...ru_manual_scans

#9 4FOR4

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Posted 30 March 2004 - 11:14 AM

WE finally had a warm dry day here so I was able to dig in to the fuel gage problem. The way I see it whenever the original problem occurred they didn't go far enough in the diagnosis, causing the repair to make things worse not better.

In the Turbo there are two sending units, main and sub. I found the sub unit unplugged at the connector (2 wire resisitor, blue in green out). I think this was the original problem. Whoever tried to fix it only went to the main, 5 wire connector (pump and fuel indidcator) and thought there was a bad wire. The cut out the section that went under the car (from under the rear, passenger side seat it leaves the inside of car and travels to top of fuel tank) and spliced in 5 new wires.
By doing this they removed the part of the curcuit that included the sub unit connection, which is a series connection into the main unit resistor. I wired the sub unit back in and the fuel gage works correctly once again, or maybe for the first time as I would suspect the unplugged connector was a factory miss.
Josh, I have a very clear wiring schematic of this that I would like to scan and send to you for posting on your site.
Thanks for the help gang, keep off the path!

#10 Legacy777

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Posted 30 March 2004 - 12:40 PM

Cool,

yeah send it over when you get it scanned and I'll put it on there!

thanks

#11 lmdew

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Posted 11 June 2007 - 04:47 PM

Yep, I have the complete setup. I found the other half today. My PayPal is Lmdew@hotmail.com

Please use a business address and include a phone # for the FedEx shipping. Larry




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