Pulsing idle, voltage drop. Bad alt? W/ video

[Black88GTA]

Hi all, I have a bit of a strange one. The idle "pulses." When it's running, the idle drops momentarily, dash lights dim, and voltage (taken at battery terminals) drops at the same time. This occurs evenly (not erratic). I took a crappy cell phone video of it, but you can't hear the idle all that well . You can, however, see the DVOM that I attached to the battery, and you can see the voltage drop.

Video: http://www.youtube.com/watch?v=ZlQs6gleXV0

Does anyone know what this is? I'm going on a long road trip on wednesday, and I don't want to get stuck. Could this be caused by a failing alternator / voltage regulator, or is the voltage drop a side effect of the alt turning at lower RPMs during the dips in idle? In other words, is the voltage thing causing this, or an effect of it?

I think whatever this is, it fried my stereo amp too It now refuses to come out of "protection mode"

Sorry if this is a bit incoherent, my fingers are numb from being outside, and I'm a little bit frustrated. Any help is appreciated.

[Sean486]

My previous SVX did that. It turned out to be a bad alternator.

[Black88GTA]

Originally Posted by Sean486

My previous SVX did that. It turned out to be a bad alternator.

Sigh. I was kind of afraid of that. If that is indeed it, at least it's a relatively easy (if expensive) fix. Are our alternators specific to the SVX, or do other Subarus use the same part? Trying to gauge my chances of finding a new one tomorrow. Hopefully the local dealer has one in stock...

[Sean486]

New? Why not get a rebuilt one at advance auto or autozone?

[SoCal LS-L]

Usually when alternators go, the field will collapse entirely and wont come back into a charging state until maybe the next start.

What you can do, this trick has worked for me many times, is if the alternator DOES go and your battery light comes on, strike the alternator with a hard blunt object, like a hammer, which resets the brushes and will give you some more life out of it........... great for emergency situations or if you just cant afford a new one at the moment.

The voltage drop can ALSO be a short, the fans kicking on, or some other weird electrical gremlin.... I wouldnt condemn your alt just yet.

[Black88GTA]

Originally Posted by Sean486

New? Why not get a rebuilt one at advance auto or autozone?

Both Advance and Autozone near me are showing it as a special order part. This is no good, since I need it tomorrow. Wednesday at the VERY latest. The dealer is my last hope. It'll be $$, but at least it's an OEM part and not a questionable reman.

Originally Posted by SoCal LS-L

Usually when alternators go, the field will collapse entirely and wont come back into a charging state until maybe the next start.

What you can do, this trick has worked for me many times, is if the alternator DOES go and your battery light comes on, strike the alternator with a hard blunt object, like a hammer, which resets the brushes and will give you some more life out of it........... great for emergency situations or if you just cant afford a new one at the moment.

The voltage drop can ALSO be a short, the fans kicking on, or some other weird electrical gremlin.... I wouldnt condemn your alt just yet.

Thanks for the tips on resurrecting it if it dies. Hopefully it'll be replaced before that becomes necessary though.

While this is happening, the battery light isn't coming on at all. The dash appears normal, aside from dimming when the voltage dips. But I'm afraid the weird voltage spikes will get worse and start to ruin more things if I run it too long like that. I'm not sure how well it's charging either. I'm hoping I can resurrect my speaker amp once this is sorted out, but not going to hold my breath on that. It's definitely not the fans - in fact, the problem is most obvious when the car is first started when cold and the fans aren't running.

You are right though, it could be some short somewhere. I doubt that it's a frayed wire though, since the pulsing seems timed - it's very even, not erratic at all. I just can't think of anything that would be constantly pulsing like that that would cause this.

[SoCal LS-L]

Originally Posted by Black88GTA

Both Advance and Autozone near me are showing it as a special order part. This is no good, since I need it tomorrow. Wednesday at the VERY latest. The dealer is my last hope. It'll be $$, but at least it's an OEM part and not a questionable reman.



Thanks for the tips on resurrecting it if it dies. Hopefully it'll be replaced before that becomes necessary though.

While this is happening, the battery light isn't coming on at all. The dash appears normal, aside from dimming when the voltage dips. But I'm afraid the weird voltage spikes will get worse and start to ruin more things if I run it too long like that. I'm not sure how well it's charging either. I'm hoping I can resurrect my speaker amp once this is sorted out, but not going to hold my breath on that. It's definitely not the fans - in fact, the problem is most obvious when the car is first started when cold and the fans aren't running.

You are right though, it could be some short somewhere. I doubt that it's a frayed wire though, since the pulsing seems timed - it's very even, not erratic at all. I just can't think of anything that would be constantly pulsing like that that would cause this.

If there IS a short somewhere, it would have to be somewhere thru one of your relays to pull that much amperage from the system. Take a flat blade screw driver and hold the tip on the relays while you have your ear on the handle and see if you can hear any one of them engage when this happens.

I would just eliminate your stereo setup and any weird electrical issues before dropping major coin on a dealer alternator, which might not solve the problem and also may be non-returnable.

[Trevor]

“The Idle drops momentarily,” I gather the engine normal RPM at idle drops, but the engine only hesitates rather than stalls. Simultaneously the voltage drops from 13.8 volts to battery voltage, when the engine is runs below idle speed.

This is what one would expect of a normal charging system. In fact a 13.8 volts at idle would indicate a well functioning alternator. At less than idle speed, the alternator can not be expected to produce charging current.

”I think whatever this is, it fried my stereo amp too It now refuses to come out of "protection mode". This appears to be the crucial clue.

The Amp. output i.e. speakers or wiring could be shorting, or some other internal fault result in the amp. drawing excess current. As a result the protective circuitry would be shutting down the amp, but immediately restoring the circuit as soon as the current becomes reduced. This sort of cycling is not that unusual and would as you have observed, have a fixed time ratio.

The excessive load pulsing on/off would dim the dash lights and could upset the ECU. An intermittent load would also be applied to the alternator. Either could be causing the engine to surge in sequence with the applied electrical load.

First off, disconnect the supply to amp. and see what happens. You may not need an alternator. Happy Christmas.

[Black88GTA]

Originally Posted by SoCal LS-L

If there IS a short somewhere, it would have to be somewhere thru one of your relays to pull that much amperage from the system. Take a flat blade screw driver and hold the tip on the relays while you have your ear on the handle and see if you can hear any one of them engage when this happens.

I would just eliminate your stereo setup and any weird electrical issues before dropping major coin on a dealer alternator, which might not solve the problem and also may be non-returnable.

I will have to check out the relays, thanks for the tip. The stereo fuse will be pulled to see if the issue goes away first. Hadn't thought to do that yet

Originally Posted by Trevor

“The Idle drops momentarily,” I gather the engine normal RPM at idle drops, but the engine only hesitates rather than stalls. Simultaneously the voltage drops from 13.8 volts to battery voltage, when the engine is runs below idle speed.

This is what one would expect of a normal charging system. In fact a 13.8 volts at idle would indicate a well functioning alternator. At less than idle speed, the alternator can not be expected to produce charging current.

This is what I was sort of referring to in my original post - I wasn't sure if the alternator fuzzing out was causing the momentary low idle, or if something else was causing the idle issue, which in turn caused the alt to momentarily stop charging while it was occurring.

”I think whatever this is, it fried my stereo amp too It now refuses to come out of "protection mode".

This appears to be the crucial clue.

The Amp. output i.e. speakers or wiring could be shorting, or some other internal fault result in the amp. drawing excess current. As a result the protective circuitry would be shutting down the amp, but immediately restoring the circuit as soon as the current becomes reduced. This sort of cycling is not that unusual and would as you have observed, have a fixed time ratio.

The excessive load pulsing on/off would dim the dash lights and could upset the ECU. An intermittent load would also be applied to the alternator. Either could be causing the engine to surge in sequence with the applied electrical load.

First off, disconnect the supply to amp. and see what happens. You may not need an alternator. Happy Christmas.

I did check the amp wiring, power connections, speaker leads, etc. Everything (that I could see) looked perfect. However after reading everyone's replies, now I am beginning to suspect an internal amplifier fault, since everything seems to point to that. I noticed the amp stopped working this morning (it worked fine yesterday), and noticed the surging for the first time today as well. I figured the surging had something to do with knocking out the amp, but maybe it was the other way 'round.

Will investigate further tomorrow, and will let everyone know what I find out. Perhaps instead of an alternator, I'll have to buy a new 4 channel amp. Thanks to everyone who has replied so far, the suggestions have been very helpful!

[Trevor]

I noticed the amp stopped working this morning (it worked fine yesterday), and noticed the surging for the first time today as well. I figured the surging had something to do with knocking out the amp, but maybe it was the other way 'round.

Will investigate further tomorrow, and will let everyone know what I find out. Perhaps instead of an alternator, I'll have to buy a new 4 channel amp. Thanks to everyone who has replied so far, the suggestions have been very helpful!

Please read carefully, what I described as significant, regarding the cycling of the of the Amp protection circuitry. Everything indicates that the Amp is your problem. Even If the outputs are shot, it should still be repairable.

[dcarrb]

Originally Posted by Black88GTA

Both Advance and Autozone near me are showing it as a special order part. This is no good, since I need it tomorrow. Wednesday at the VERY latest.

If it turns out you need it, Advance Auto Parts had a reman alternator for me in under 24 hours, for under $200.

dcb

[Sean486]

Originally Posted by Trevor

Please read carefully, what I described as significant, regarding the cycling of the of the Amp protection circuitry. Everything indicates that the Amp is your problem. Even If the outputs are shot, it should still be repairable.

Good point. I only had the dimming lights symptoms and uneven idle. I never had a aftemarket stereo on mine.

[Black88GTA]

Well, I got it sorted. I am shopping for an amplifier.

I started the car, then (carefully) undid all speaker outputs from the amp. No change, so it's not my speaker wiring. Then, I pulled the amp's power cord from the battery terminal. Voila, pulsing stopped.

This sucks hard because now I have to drive 10 hours with no music. At least I don't have to worry about finding an alternator, I guess. I suppose I could temporarily rig up the old 2 channel amp I have laying around from sometime in the early '90s. I think it still works...

[Trevor]

Originally Posted by Black88GTA

Well, I got it sorted. I am shopping for an amplifier.

I started the car, then (carefully) undid all speaker outputs from the amp. No change, so it's not my speaker wiring. Then, I pulled the amp's power cord from the battery terminal. Voila, pulsing stopped.

This sucks hard because now I have to drive 10 hours with no music. At least I don't have to worry about finding an alternator, I guess. I suppose I could temporarily rig up the old 2 channel amp I have laying around from sometime in the early '90s. I think it still works...

Told you so. A little logic usually brings results.

Merry Chistmas, Trevor.

[SoCal LS-L]

Originally Posted by SoCal LS-L

I would just eliminate your stereo setup and any weird electrical issues before dropping major coin on a dealer alternator, which might not solve the problem and also may be non-returnable.

Beat you to it T

At any rate, postcount +whatever!