Bad Ground?

JasonGrahn · Post by **JasonGrahn** » Thu Aug 07, 2003 5:25 pm

Okay, so i'm out for a spirited drive last night. Pulling up to a stop light, hit the brakes and my radio goes *Blink* off *blink* back on. The radio is an older Sony model if that makes a difference. The lights dimmed as well, both interior and exterior, as well as the idle dropped.

I'm assuming this is related to a bad ground, though i'm not too familiar with wiring concepts except for the occasional "this" goes "there" stuff.

On a potentially related not, i am starting to hear the rev of the engine as a hum through the stereo. I will be replacing the spark plugs and wires this weekend.

Thoughts?

ciper · Post by **ciper** » Thu Aug 07, 2003 7:06 pm

Just to mention, one of my legacy started to hum through the radio recently. Its getting worse slowly.

Your problem almost sounds like you shorted an a large unfused postive lead!

JasonGrahn · Post by **JasonGrahn** » Thu Aug 07, 2003 7:36 pm

If i shorted a positive lead, say i grounded the battery directly, wouldn't that shut the car off completely - an instant-kill?

ciper · Post by **ciper** » Thu Aug 07, 2003 7:48 pm

I dont think it would, the engine would still be turning so once the short was disconnected it would "restart" and continue running.

JasonGrahn · Post by **JasonGrahn** » Thu Aug 07, 2003 7:50 pm

Okay. So any ideas on where to start tracking down the problem? Maybe a small list of wires to check?

ciper · Post by **ciper** » Thu Aug 07, 2003 8:25 pm

Id look at the big wire running to the alternator, it does run close to the ac compressor area.

Post by **Legacy777** » Fri Aug 08, 2003 2:33 pm

Did you notice this only when pressing on the brakes? Is it reproducable by pressing on the brakes?

JasonGrahn · Post by **JasonGrahn** » Fri Aug 08, 2003 4:15 pm

Did you notice this only when pressing on the brakes? Is it reproducable by pressing on the brakes?

ONLY when pressing on the brakes. It was reproducable quite a bit the night it was happening. It seems to have stopped for now. I would still like to track down this gremlin.

vrg3 · Post by **vrg3** » Fri Aug 08, 2003 5:20 pm

Hmm... weird.

Well, the problem is triggered either by deceleration of the car (and weight transfer) or by the brake switch at the top of the pedal. Can you determine which? Try just pressing the brake pedal enough to turn on your brake lights and see if that ever causes problems. Or try closing the throttle at 6000rpm in 1st gear or something to decelerate without the brake.

I can't think off the top of my head what kind of bad ground could cause this kind of problem.

Shorting out an unfused positive circuit could cause the entire electrical system voltage to drop like that... Or even a circuit that has a big fuse.

So might an alternator failure, but I don't see why the brakes would trigger that... It could be the positive terminal post on the alternator as ciper suggests or maybe even a lot of corrosion around its mounting surfaces. Are those areas clean? A bad ground could result in a ground loop that causes alternator noise in your radio too.

Post by **Legacy777** » Fri Aug 08, 2003 6:54 pm

I asked about the brakes.....mainly because of alternator speed is governed by engine speed. If the car is idling and you hit the brakes repeatedly you are taking vacuum away which can cause the engine to run rougher, and could cause alternator rpms to drop and lower output.

Or so it's a thought.......is your alternator original? how many miles. If you take the belt off and spin the alternator shaft....does it spin very freely, or have some resistance to it?

JasonGrahn · Post by **JasonGrahn** » Fri Aug 08, 2003 7:27 pm

Legacy777 wrote:If the car is idling and you hit the brakes repeatedly you are taking vacuum away which can cause the engine to run rougher, and could cause alternator rpms to drop and lower output.

Or so it's a thought.......is your alternator original? how many miles. If you take the belt off and spin the alternator shaft....does it spin very freely, or have some resistance to it?

I wasn't hitting the brakes repeatedly, more of, hehehe, late braking into the turn.

My alternator is not the original, it is a pull-off of a 1991 turbo, it has about 190k miles on it. My other alternator has 200+. They both sprin freely. Maybe time for a rebuild?

Would pulling the vacuum line from the brake booster so it is no longer power assisted be a potential method for troubleshooting?

vrg3 · Post by **vrg3** » Fri Aug 08, 2003 7:34 pm

The amount of vacuum used by the brake booster is pretty small; it shouldn't really affect how the engine runs.

An alternator that spins too freely might be an indication of worn brushes.

Try to figure out if it's the deceleration moving something or if it's the brake light circuit.

eastbaysubaru · Post by **eastbaysubaru** » Fri Aug 08, 2003 7:49 pm

If it spins freely, it's a sign of a dying alternator. When mine went, it would spin freely. The new one took a lot of effort to spin. I'd say it's time for a new one, especially if it's got 190K miles.

-Brian

Post by **Legacy777** » Fri Aug 08, 2003 8:53 pm

yeah...I would probably look at alternator. I wish I had the time to get mine in......

eastbaysubaru · Post by **eastbaysubaru** » Sat Aug 09, 2003 3:16 am

Josh, you're almost as lazy as me. I've had my radiator for two and a half weeks and it's still sitting in the box.

-Brian

Post by **Legacy777** » Mon Aug 11, 2003 2:28 pm

eastbaysubaru wrote:Josh, you're almost as lazy as me. I've had my radiator for two and a half weeks and it's still sitting in the box.

-Brian

hahaha........there's a small amount of laziness......but it's more the fact I want to get the rest of my house organized since I just moved, and the garage has taken a back priority along with the car.

eastbaysubaru · Post by **eastbaysubaru** » Mon Aug 11, 2003 5:40 pm

I hear ya. I was only giving you a hard time. You're among the lucky, garage having, fools now. Good luck with your new place. I'm jealous.

-Brian

Post by **Legacy777** » Mon Aug 11, 2003 6:30 pm

Yeah I know....

I've been waiting a while for the garage. It's nice to finally have one

JasonGrahn · Post by **JasonGrahn** » Wed Aug 13, 2003 7:04 pm

The suggestion to get the alternator looked at/rebuilt/replaced is a good one; but one that will have to wait until i get back from

RALLY SAN REMO in Italy.

Hell yeah baby. I'm going, gotta save the bucks up.

eastbaysubaru · Post by **eastbaysubaru** » Wed Aug 13, 2003 11:41 pm

Damn! Have a great time in Italy. San Remo's crazy as it is. I can't imagine what it's like when the WRC comes to town. Watch out for all the scooter riders. I had an "incident" with one when I was there. I went to the Acropolis rally in 2000. It was AWESOME! Best experience evAr!!!

-Brian

evolutionmovement · Post by **evolutionmovement** » Wed Aug 13, 2003 11:51 pm

I was in Delphi in '99 and made friends with a guy who ran a shop and had an RB5. He picked up on my 555 team hat and we tried to talk for a little. Not terribly successful, but Subaru mania translates well enough. Too bad he wasn't a hot chick (there are other languages that need no translation), but he did give me a faux aged ceramic elephant.

Steve

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Bad Ground?

Bad Ground?