alternator
05-19-2001, 12:10 PM
#1
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alternator
it was making a weird hissing noise like a supercharger, so we replaced it with a remanufactered 105amp alt. I started the car up and it started fine, but it wont hold the charge and dies. So I put the old one back on and it and it still wont stay running. HELP! 
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1988 Pontiac GTA 5.0 TPI
Mods: K&N Filter, Hypertech Air Foil, Hypertech Perf. Chip, 2.5in Flowmaster Muffler, Catco Hi-flow Cat
Maryland Int. Speedway Bracket Racing Trophy Winner
15.32@88mph 2.077 60-ft.
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94 Probe GT, 95 Mustang GT, 96 Impala SS, 85 Thunderbird 5.0, 95 Accord V6, 98 Integra VTEC, 70 Chevelle Malibu, CRX w/ Turbo and Intercooler (have it on tape to prove it)
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1988 Pontiac GTA 5.0 TPI
Mods: K&N Filter, Hypertech Air Foil, Hypertech Perf. Chip, 2.5in Flowmaster Muffler, Catco Hi-flow Cat
Maryland Int. Speedway Bracket Racing Trophy Winner
15.32@88mph 2.077 60-ft.
Kills
94 Probe GT, 95 Mustang GT, 96 Impala SS, 85 Thunderbird 5.0, 95 Accord V6, 98 Integra VTEC, 70 Chevelle Malibu, CRX w/ Turbo and Intercooler (have it on tape to prove it)
05-19-2001, 01:27 PM
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The "hissing noise" I would guess to be bad bearings, which are replacable.
How many volts does the battery have fully charged? With the engine running at 2000RMP? With the engine running at 2000RMP under load (lights/fan on high, etc.)? Use a digital voltmeter (DMM) for the best accuracy. Use the car voltmeter if you do not have a DMM - its better than nothing.
At night with all the electrical accessories on (including the headlights) to provide a load to the alternator, do the lights become dimmer at idle? If so, this is normal. If not, it may or may not be normal. Do they become brighter when the engine speeds up from idle? This should be easy to see. If they appear to be the same brightness, either the alternator is able to provide all the current for your vehicle (which is good) or the alternator is unable to provide enough current regardless of engine/alternator speed. Alternator output is higher the faster it turns, so this simple test will at least let you know if it's providing some output - but that's just about all. Most alternators cannot supply much power (current) at idle, which is why you'll see battery voltage drop to <13 volts (or lower, depending upon load) at idle. Below 12.6 volts the battery is providing the power that the alternator cannot supply. A good charging system will provide ~13.6-14.8 volts at speed (dependent upon ambient temperature). Generally, a voltage reading >12.8 volts indicates that the alternator is supplying all the current and the battery is acting as a filter for the pulsating DC (albeit at a very high frequency) the alternator is providing.
It could be a bad battery in addition to a bad alternator. See my post in Alternator OK, Car doesn't charge HELP!! next to this post also.
[This message has been edited by Stuart Moss (edited May 19, 2001).]
How many volts does the battery have fully charged? With the engine running at 2000RMP? With the engine running at 2000RMP under load (lights/fan on high, etc.)? Use a digital voltmeter (DMM) for the best accuracy. Use the car voltmeter if you do not have a DMM - its better than nothing.
At night with all the electrical accessories on (including the headlights) to provide a load to the alternator, do the lights become dimmer at idle? If so, this is normal. If not, it may or may not be normal. Do they become brighter when the engine speeds up from idle? This should be easy to see. If they appear to be the same brightness, either the alternator is able to provide all the current for your vehicle (which is good) or the alternator is unable to provide enough current regardless of engine/alternator speed. Alternator output is higher the faster it turns, so this simple test will at least let you know if it's providing some output - but that's just about all. Most alternators cannot supply much power (current) at idle, which is why you'll see battery voltage drop to <13 volts (or lower, depending upon load) at idle. Below 12.6 volts the battery is providing the power that the alternator cannot supply. A good charging system will provide ~13.6-14.8 volts at speed (dependent upon ambient temperature). Generally, a voltage reading >12.8 volts indicates that the alternator is supplying all the current and the battery is acting as a filter for the pulsating DC (albeit at a very high frequency) the alternator is providing.
It could be a bad battery in addition to a bad alternator. See my post in Alternator OK, Car doesn't charge HELP!! next to this post also.
[This message has been edited by Stuart Moss (edited May 19, 2001).]
05-19-2001, 05:02 PM
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Hey, My ALt makes that noise! 
I sorta dig it, actually. Prolly gonna die on me at a really bad time, too.
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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride
Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype
I sorta dig it, actually. Prolly gonna die on me at a really bad time, too.
------------------
60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride
Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype
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