I've yet to hook up a tester, but this is something that worries me. Especially since I got $60 replacement (NAPA Reman) alternator about 4,000 miles ago. When driving, or if the pedal has been pushed at all, everything works fine. But when stopped, the headlights and dash lights dim, the blower slows down, and the radio display dims with the sound and volume. And sometimes, if it's been idling for a few minutes, the radio will randomly shut off, and turn back on again, I'm guessing due to low voltage. I have one of those alternator testers, and it says green, but at idle the LED noticeably flashes. I'm wondering what this is about, and if it's a serioous problem. I think it is, since I can't idle for extended periods.
Alternator doesn't work at idle?
- Thread starter Nick R
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Here's a pretty good troubleshooting guide to alternators: Alternator check.
I've found in the past when having alt problems replacing both the alt and the battery solved the problems.
IDK exactly why, I figured since they work together in the charging system that when one's on the way out it taxes the other.
I also am of the belief that reman alt's tend to be rather suspect. I know when it comes to my Ford's I'll only replace w/ OEM. Figured that one out after replacing 3 AAP remans in a '90 T-bird.
IDK exactly why, I figured since they work together in the charging system that when one's on the way out it taxes the other.
I also am of the belief that reman alt's tend to be rather suspect. I know when it comes to my Ford's I'll only replace w/ OEM. Figured that one out after replacing 3 AAP remans in a '90 T-bird.
It sounds like the battery is the problem.
If it is the alternator, how long ago did you purchase it, and do you still have the receipt. There probably is/was a waranty.
If it is the alternator, how long ago did you purchase it, and do you still have the receipt. There probably is/was a waranty.
Alternator is about 6 months old. But the battery seems to be fine. As soon as I hit the gas, or even tap it it works fine. It seems the alt just doesn't charge at idle which according to the AAP thing is about 550-600rpm. The battery is only 2 years old, a DieHard gold series.
Alternators rarely have full voltage at idle.
Some a little more, some a little less.
With the car off, turn your headlights on for 1/2 minute.
Wait 10 minutes and check the battery voltage. Aroung 12.5 is good.
Start the car, check you idle voltage, and also when revved up to 2000 RPM or so. It should be 14.5 or so at 2k. The idle should be higher than when off, but it depends on if the lights, fan, AC, etc are on.
Some a little more, some a little less.
With the car off, turn your headlights on for 1/2 minute.
Wait 10 minutes and check the battery voltage. Aroung 12.5 is good.
Start the car, check you idle voltage, and also when revved up to 2000 RPM or so. It should be 14.5 or so at 2k. The idle should be higher than when off, but it depends on if the lights, fan, AC, etc are on.
On my Cavi I ran a second line from the Alternator to the battery. An 8 gauge fused at 100A. The stock wire is a 10ga. Too small IMO. Then Since I had more 8ga I replaced the stock battery to underhood fuse box along with an additional ground from the alternator mount to the frame. I was going to relay the headlights which would remove that load from the headlight switch and by extension the rest of the cabin save for an insignificant relay load. I never got around to that though.
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Did you swap the pulleys? I've seen this happen when the new one has a slightly different size pulley.
sounds like a bad alternator. although it works sometimes, a good alternator works all the time
Tell me more about this radio. Fancy amp? (They draw lots of current.) Usually radios will work down to 10 volts when the battery is near dead.
It is normal to get some dimming at idle when running all sorts of stuff like the rear defroster. You have to have a noticeable dip before the battery switches from charging to discharging. Since your alt only makes 40 amps at idle compared to >100 at speed, you can overload it at times, which is why the battery is there.
Though I concur you might have a toasted battery.
It is normal to get some dimming at idle when running all sorts of stuff like the rear defroster. You have to have a noticeable dip before the battery switches from charging to discharging. Since your alt only makes 40 amps at idle compared to >100 at speed, you can overload it at times, which is why the battery is there.
Though I concur you might have a toasted battery.
Battery
Originally Posted By: eljefino
Tell me more about this radio. Fancy amp? (They draw lots of current.) Usually radios will work down to 10 volts when the battery is near dead.
It is normal to get some dimming at idle when running all sorts of stuff like the rear defroster. You have to have a noticeable dip before the battery switches from charging to discharging. Since your alt only makes 40 amps at idle compared to >100 at speed, you can overload it at times, which is why the battery is there.
Though I concur you might have a toasted battery.
Ther really is that big of a difference between 600RPM and like, 900 RPM? Wow wouldn't have thought. That's odd because the battery is like, new. The radio is a Kenwood KDC-MP142. 22wx4 RMS, 50w x 4 max power.
Tell me more about this radio. Fancy amp? (They draw lots of current.) Usually radios will work down to 10 volts when the battery is near dead.
It is normal to get some dimming at idle when running all sorts of stuff like the rear defroster. You have to have a noticeable dip before the battery switches from charging to discharging. Since your alt only makes 40 amps at idle compared to >100 at speed, you can overload it at times, which is why the battery is there.
Though I concur you might have a toasted battery.
Ther really is that big of a difference between 600RPM and like, 900 RPM? Wow wouldn't have thought. That's odd because the battery is like, new. The radio is a Kenwood KDC-MP142. 22wx4 RMS, 50w x 4 max power.
Yeah. And it tends to get worse if you increase the amperage without increasing the physical size of the alternator. You end up with more amperage at peak but same or less at idle. Im specifically talking about aftermarket high amperage units that use the same alternator albeit rewound with different wire.
Agreed with battery or connections, or perhaps a failed diode? You should not be getting a pulsing voltage at idle.
BTW, I add an extra ground wire (10 gauge or two 12 gauge) from the negative of the battery to the frame on my cars. Be sure to "SOLDER" lug to wire, and "SOLDER" wire to existing large ground wire from battery. Then tape the heck out of it with 3M electric tape. Also be sure to sand the paint away from below where you mount the lug to the frame.
Also, check that there is good bare metal (not old rust) below existing ground wire mounts, like the large wire from battery negative to engine.
Also, check that there is good bare metal (not old rust) below existing ground wire mounts, like the large wire from battery negative to engine.
Does the pully on the replacement Alternator have a larger diameter?
Extra ground wires never hurt.
Also, larger ones in the present location are good - many cars use marginally sized wire [German cars seem the worst to me, but it is widespread].
This applies to power leads.
An extra ground to the frame or firewall is good, but one to the engine/trans is the most important.
Also, larger ones in the present location are good - many cars use marginally sized wire [German cars seem the worst to me, but it is widespread].
This applies to power leads.
An extra ground to the frame or firewall is good, but one to the engine/trans is the most important.
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Did they give you the right replacement alternator? Did you re-use your old pulley on it or did it come with a pulley on it? If it came with a pulley, was it the same size as the one on your old alternator?
The pulley size being improper can cause this issue, as it will cause the alternator to spin slower and subsequently not charge.
The pulley size being improper can cause this issue, as it will cause the alternator to spin slower and subsequently not charge.
It is exactly the same as the OE alternator. Same model, Delphi Automotive Systems,same size pulley. Exact same, but with new bearings, diodes, brushes.
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Originally Posted By: rudolphna
It is exactly the same as the OE alternator. Same model, Delphi Automotive Systems,same size pulley. Exact same, but with new bearings, diodes, brushes.
Well, an easy fix would be a smaller pulley.
It is exactly the same as the OE alternator. Same model, Delphi Automotive Systems,same size pulley. Exact same, but with new bearings, diodes, brushes.
Well, an easy fix would be a smaller pulley.
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