Why are my gauges inaccurate?

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OTTERMATIC
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Why are my gauges inaccurate?

Post by OTTERMATIC »

Hey everyone, I have a 1993 Subaru Legacy L wagon (5 speed manual, AWD, naturally aspirated, completely stock). It’s got a few electrical gremlins that I’ve decided to try and nail down while I’m waiting to get the catalytic converters replaced.

So main question, why are my gauges inaccurate? The speedometer consistently shows 5mph above my actual speed (checked with a radar), and my fuel shows 1/2 when it’s actually 3/4 full, shows 1/4 when it’s actually half. The tachometer and temperature seem to work fine, but I don’t really have a way of testing either one right now to confirm that.

I don’t think these issues are related but they are also electrical so I’m going to just list them all:
Cigarette lighter provides power to charge my phone but doesn’t seem to actually heat the cigarette lighter.
Power mirrors work very rarely, and usually only in one direction at a time.
Half the speakers do not work, and they’ve all died/come back at random points. It’s fun to be driving around and hit a bump that makes a third speaker work, only to have it die again when I open a window.
The air controls USUALLY work but they’ve gotten stuck on me a couple of times.
The rear defroster isn’t connected on one side, appears to have melted the plastic casing around the soldered piece. I pulled the fuse for it just to be safe.

What’re your thoughts? I’m very much not an electrician but I want to learn how to fix this stuff, and I already have a bunch of electrical repair tools. Hopefully there’s some common spots to check for shorts or something. Thanks

Legacy777
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Re: Why are my gauges inaccurate?

Post by Legacy777 »

The first thing I would do is check all your grounds and what your voltage drop is between the battery and power distribution circuits/fuses to see where you are getting voltage drop or other weird issues.

The first thing I would potential ground difference. The stock setup grounds the battery to the chassis (next to the battery) and to the starter bolt on the engine. So all ground points on the chassis have to feedback through those two points. It's possible one or both of those wires have high resistance and that is causing grounding issues. Check the resistance of each ground wire from the battery to were they connect. Sometimes there may be corrosion under the bolt and taking it off and cleaning things may help.

Some people add additional ground points or extra ground wire to the stock ground points to more easily allow the ground system to work. Once you've checked the grounding points from the battery to the chassis and either verified they are good or added ground points I would then move on to checking resistance of the grounds for various things that don't seem to be working right (mirrors, stereo/speakers, etc.) This will take some patience to go through, but is really the best way to attach things.

Regarding the HVAC controls sometimes working, check out this thread.
viewtopic.php?f=10&t=1142

Regarding the fuel gauge being off....it could be a grounding issue or it could be that the fuel senders in the tank could be dying. This is somewhat common. I've had to replace both senders on my car.

For the speedometer, what size tires do you have on the car? This could also be ground related, tire size, or just margin of accuracy of speedometer calibration.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm

OTTERMATIC
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Posts: 14
Joined: Wed Apr 15, 2020 5:32 pm

Re: Why are my gauges inaccurate?

Post by OTTERMATIC »

Thanks for all the input. I’m very much not an electrician so I’m trying to be careful and educated before I start doing stuff to it.

The tires are the stock 14” size, I think something like 185/60? Whatever it suggests in the manual, I made sure to get that size specifically.

Legacy777
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Re: Why are my gauges inaccurate?

Post by Legacy777 »

The stock tire size should be 185/70 R14. Some tires even of the same size can be slightly different in size so that may just be something you need to be mindful of.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

If you need to get a hold of me please email me rather then pm

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