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Super Moderator (Actually a SuperSpy)
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Discussion Starter · #1 ·
Hi everyone,

2002 WRX.

I had unstable voltage, ranging from 12.5 to 15.0 or so and varying a lot while driving. I changed the alternator thinking it was the voltage regulator. The problem went away for about 3 weeks. Now it's back, and worse -- voltage goes above 15 and below 12, and I got random lights on the dash that are indicative of a charging failure.

However, I've got a new alternator in there...

I also changed the small harness connector that comes off the main + loom on top of the alternator because I found those wires frayed.

So now I'm thinking:
1. That harness I changed is actually bad or loose.
2. Some other connection is loose.
3. The new alternator is failing.

Any advice?

Thanks!
 

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It has been my experience with electrical systems in all types of vehicles (cars, tractors, lawn mowers) that the battery is most often the culprit. I have had more than 1 battery go bad internally, and make it look like the charging system is at fault. Also, battery 'connections' at the batt and at the engine ground and start solenoid give me problems either getting loose or corroded. :dontknow:
 

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You are reading the spikes with a tool or the cars dash?
 

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Legitimately n00b question, but is the VR integrated in the Alternator?

My Buell had voltage spikes that were solved with changing the VR. Not even 1 riding season later, the stator failed. Replacing that fixed both problems... for the 2 weeks up until my accident totaled the bike.
 

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Discussion Starter · #5 ·
It has been my experience with electrical systems in all types of vehicles (cars, tractors, lawn mowers) that the battery is most often the culprit.
It's never happened to me but I've considered it and still am. First time around, before the current alternator was swapped in and the loom wire replaced, I grabbed a Snap-On tester and threw it on there and the only abnormality that I could detect (the problem at the time was intermittent) was a 115% stated charge status for the battery. It's a gel type and I don't know what failure mode cells of that nature generate.

You are reading the spikes with a tool or the cars dash?
The lights flicker inside and out, the radio reboots, the dash gives the classic "alternator" Xmas lights (battery and brake lights on momentarily) and/or random lights (ABS on momentarily) and I stuck a V meter into the ashtray so I can watch and drive simultaneously -- that's when I saw the spikes and oscillations.

Legitimately n00b question, but is the VR integrated in the Alternator?
Almost invariably, particularly in our "Denso-style" alternators, yes.
 

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Almost sounds like an ignition switch cycling. But of course that would shut engine off too. Can "part" of the switch go bad and just cause the lights/radio/ABS to cycle and not engine management functions?? Or a relay feeding those things (vs. engine) going bad?? Just thinking out loud....
 

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Discussion Starter · #7 ·
I'd not considered that, thanks. I'll look at that too! I've had an ignition switch go bad in a Z car, but that lead to the inability to turn off the engine (fun times). I'm saving the weekend to sort this out because I'd like the Impreza back, it's my daily. Thanks everyone and I'm welcome to any/all/additional suggestions any time!
 

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Discussion Starter · #8 ·
Changed the battery too. So now I've got a new alternator, loom over the alternator, battery. Of course the behaviour was normal before I did anything at all today, and I can't fix something that works. I'm having someone take a look with an oscilloscope to see the diodes in the alternator are actually OK even though it's a replacement unit.
 

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Changed the battery too. So now I've got a new alternator, loom over the alternator, battery. Of course the behaviour was normal before I did anything at all today, and I can't fix something that works. I'm having someone take a look with an oscilloscope to see the diodes in the alternator are actually OK even though it's a replacement unit.
Who made the alternator?
 

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Discussion Starter · #10 ·
Best guess is Denso, I've dropped the car at the place with the oscilloscope so can't check but I'm fairly certain.
 

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Discussion Starter · #11 ·
So, I've changed the alternator twice, installed a new battery... I still have the same problem. It's intermittent though. Invariably the car scopes clean when I have it hooked up to check on the oscilloscope, then I drive a few days and the same issue comes up. Today it stalled -- the engine actually cut out. Usually the voltage oscillates and spikes, then drops.
 

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Honestly outside of the alternator or battery I can't imagine anything that could feed back voltage into the system. Unless something is making a heavy draw then suddenly stopping. That would likely cause a spike.

You don't seem like the decibel drag race type of guy, so i can't think of anything that could do it besides maybe the ignition.
 

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Ignition!! Exactly what I was going to post XJ. The obvious suspect is Coils. But plug or coil wires could do it also. If any one of them was shorting to the chassis, that could cause voltage spikes at the battery!

I had a coil slowly go in my GMC van and the only symptom was hard to start. Couldn't figure it out until I happened to see sparks (!) from the coil to its housing (where the potting had burned through.)

I should have thought of this sooner :(
 

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Discussion Starter · #17 ·
The suggestion on ignition was made and I appreciated it but I could find no loose wiring -- I'll look again, thanks!

I kinda wish I had a CEL to go with, but I don't, and I suspect ignition might generate one.

I'll look at ignition too. Thanks!
 

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Is the alternator the right amperage? I know a lot of times aftermarket replacement units can be far off of the oem rating. For example the 220a alternator on my truck is nearly impossible to find and you've got to get it from the dealership or order one to spec.

I'm not an electrical guru but that's the only other thing that comes to my mind as a possibility. Nothing should feed back into the system so it's got to be at what creates the power.
 

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Discussion Starter · #19 · (Edited)
I think a lot of electrics is actually magic.

I measure a 0.5V drop at the lighter socket in the dash compared to across the terminals with the engine at idle. That in itself is actually OK I think, it's to be expected.

When I pull up on the window switches and the windows are already all the way up, the voltage drops from 13.5-14.0V to as low as 12.5V and then it oscillates a bit (up/down from 12.5V to 14.0V with rapid changes).

I can't find any faults in the (second replacement) diodes in the alternator. I'm looking at all th earth leads and am also looking at the loom to the alternator and starter.

I think the solution is to buy an Alfa Romeo Giulia QV with the 505HP V6, aluminium wings and bonnet, leather interior, and carbon fibre driveshaft and roof. I went by the dealer last weekend.

Hm.

Any suggestions about the Impreza always welcome! Thanks!
 

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Have you tried adding more grounds to the system? I know it sounds stupid, I did this on my first car ('69 Cadillac) when I converted to electronic ignition and was having crazy voltage changes. It worked like a dream.

I know it is a long shot, but like you said....magic.
 
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