Alternator issue (cold start)?
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Alternator issue (cold start)? Not sure where to start but I'll try my best.
I replaced my alternator about 2-3 years ago with Advance Auto's "ToughOne" alternator (seems to be the same part number as a Remy -- 91411). Around that time I noticed strange cold starts where the RPM would drop briefly (seems to be when the AIR pump kicks in, because the RPM drop does not happen on warm starts, or any other time the alternator is "stressed"). I can't remember if that issue really started after the alternator swap or if it started before.
Regarding the alternator itself, volt gauge readout is always between 13 and the next line (on cold starts it's almost on that line after 13). When warm and at idle, it's right between 13 and that line. When in gear and at night (all the lights on), it goes closer to 13 and if I play the stereo loud it drops slightly below 13 but will go back above 13 when I start moving again. RPM's never drop in any of these conditions I just described (Except on immediate cold start when the AIR pump turns on).
Based on what I just described, is my alternator OK? Can bad alternators cause an RPM drop when first starting? Sorry if this sounds like a dumb question but I think I somewhat narrowed my "cold start" issue to the AIR pump (which already had the recall done, and never blew a fuse or set off a SES light). But another board kinda suggests the alternator may be causing my issue (though it seems to be working fine as the battery is never dead after stopping the car and the volts seem to be at the "11:30 o'clock" position, and has no trouble starting back up).
I replaced my alternator about 2-3 years ago with Advance Auto's "ToughOne" alternator (seems to be the same part number as a Remy -- 91411). Around that time I noticed strange cold starts where the RPM would drop briefly (seems to be when the AIR pump kicks in, because the RPM drop does not happen on warm starts, or any other time the alternator is "stressed"). I can't remember if that issue really started after the alternator swap or if it started before.
Regarding the alternator itself, volt gauge readout is always between 13 and the next line (on cold starts it's almost on that line after 13). When warm and at idle, it's right between 13 and that line. When in gear and at night (all the lights on), it goes closer to 13 and if I play the stereo loud it drops slightly below 13 but will go back above 13 when I start moving again. RPM's never drop in any of these conditions I just described (Except on immediate cold start when the AIR pump turns on).
Based on what I just described, is my alternator OK? Can bad alternators cause an RPM drop when first starting? Sorry if this sounds like a dumb question but I think I somewhat narrowed my "cold start" issue to the AIR pump (which already had the recall done, and never blew a fuse or set off a SES light). But another board kinda suggests the alternator may be causing my issue (though it seems to be working fine as the battery is never dead after stopping the car and the volts seem to be at the "11:30 o'clock" position, and has no trouble starting back up).
Last edited by Jeff 97 Formula; Nov 20, 2014 at 06:38 AM.
what year and how many miles on car?
from everything you said it sounds like your alternator is fine.
it is somewhat normal when a huge load is placed on the alternator at once for the engine rpm to drop a little, but it should recover. the more electrical load on the alternator, the harder it is to turn which requires power from the engine. normally the PCM handles all this and you see minimal affects, but with age and mileage other things on the engine like idle air control valve and sticking throttle bodies can have an affect on engine idle performance. and with the air pump and other emission devices they are all notorious for going bad or having some kind of problems with age, so if extra air is pushed into the exhaust then the pcm has to compensate for it and does not surprise me if you see minor rpm dips as those things turn on/off.
from everything you said it sounds like your alternator is fine.
it is somewhat normal when a huge load is placed on the alternator at once for the engine rpm to drop a little, but it should recover. the more electrical load on the alternator, the harder it is to turn which requires power from the engine. normally the PCM handles all this and you see minimal affects, but with age and mileage other things on the engine like idle air control valve and sticking throttle bodies can have an affect on engine idle performance. and with the air pump and other emission devices they are all notorious for going bad or having some kind of problems with age, so if extra air is pushed into the exhaust then the pcm has to compensate for it and does not surprise me if you see minor rpm dips as those things turn on/off.
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1997 formula LT1. 34600 miles. Strange how the rpm surge only happens when the AIR pump first kicks in during cold start. All other times seem normal (also the volt is rising just before the RPM drop....and during the drop in RPM the volt kinda stays in the spot, then continues to rise to 13-14 volts). RPMS never drop Otherwise.
Just wondering if there is an easy way to test the alternator without removal (if I really need to). I guess a voltmeter would be an option.
Just wondering if there is an easy way to test the alternator without removal (if I really need to). I guess a voltmeter would be an option.
Last edited by Jeff 97 Formula; Nov 20, 2014 at 01:12 PM.
kinda hard to tell over the internet vs seeing it first hand.
sounds like you might be worrying about nothing, i'd run it till you get a check engine light or observe or more obvious problem.
on newer cars the engine computer programming gets pretty involved where they regulate the alternator under certain conditions by making it output less voltage to help fuel economy. i wouldn't expect the alternator output reduction to be used on your car i only read about it being used on 2010+ cars in an article,
but there's all kinds of algorithms in the computer happening while the engine is running to make things work as desired, and i'm familiar with the LS1 charging system but i honestly know nothing about how it was done on the LT1. it may be normal. from what you described there is no real problem you always have system voltage over 13.0 volts.
the easiest way to verify is buy a volt meter and you can get them that plug into the cig lighter for convenience. a digital volt meter or multimeter is good and will give you a decently accurate reading to 1/10 of a volt but their display doesn't update fast enough sometimes so it might be worth finding an analog meter that has a needle where you can observe it bounce.
sounds like you might be worrying about nothing, i'd run it till you get a check engine light or observe or more obvious problem.
on newer cars the engine computer programming gets pretty involved where they regulate the alternator under certain conditions by making it output less voltage to help fuel economy. i wouldn't expect the alternator output reduction to be used on your car i only read about it being used on 2010+ cars in an article,
but there's all kinds of algorithms in the computer happening while the engine is running to make things work as desired, and i'm familiar with the LS1 charging system but i honestly know nothing about how it was done on the LT1. it may be normal. from what you described there is no real problem you always have system voltage over 13.0 volts.
the easiest way to verify is buy a volt meter and you can get them that plug into the cig lighter for convenience. a digital volt meter or multimeter is good and will give you a decently accurate reading to 1/10 of a volt but their display doesn't update fast enough sometimes so it might be worth finding an analog meter that has a needle where you can observe it bounce.
take it to advanced or some place like that they can hook to your battery and test the charging system while your a/c is on and lights. But i was on the stock alt and had to goto a larger alt 400A up from the 100 or 120...but I did a zero gauge upgrade of the ground and positive side that helped steady the charge a bit although i do get a bit of fluctuation from time to time is stays at 13.5 and that is cause i have a cap not that its needed its just a good measure with the amps doesnt draw as much at once...but if your wanting it even more steady i would say hook another battery up with 0 gauge OFC or welding cable and than itll sit at 14.5 all the time period
Also take some CRC electonic cleaner and get the dirt out of it ...sometimes they tend to run hot because of road dust and debris build up
Also take some CRC electonic cleaner and get the dirt out of it ...sometimes they tend to run hot because of road dust and debris build up
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Does an alternator "turn on" or "kick in" about 1/4 to 1/2 seconds after a "cold start"? is it based on how "good" the battery is (fully charged vs getting weak/not fully charged)? Trying to see if the alternator really has something to do with my RPM surge that only happens once, and only on a cold engine (never happens when warm). I have thought about the AIR pump a few times since that's the only thing I can think of that turns on during a cold start (wondering if the reason I do not experience this RPM drop issue on a "warm engine" startup is because the pump has overcome mechanical resistance that was present on a "cold engine".
Also, seems that the volt gauge immediately rises to 14 volts on cold start (the line after 13), and is between 13 and the mark after 13 when warm. I believe the volts are normal, but am wondering if its ok that it rises so quick after starting.
Volts are very steady while driving (only time the volts drop are at night, warm engine in gear, all the lights on, etc. but the RPMS do not drop at all when the volts drop).
Also wanted to add that during the RPM surge on cold start the volts don't "drop", the gauge just "slows down" a little during the RPM drop but continues to rise, then rises quicker after the RPM's recover.
Also, seems that the volt gauge immediately rises to 14 volts on cold start (the line after 13), and is between 13 and the mark after 13 when warm. I believe the volts are normal, but am wondering if its ok that it rises so quick after starting.
Volts are very steady while driving (only time the volts drop are at night, warm engine in gear, all the lights on, etc. but the RPMS do not drop at all when the volts drop).
Also wanted to add that during the RPM surge on cold start the volts don't "drop", the gauge just "slows down" a little during the RPM drop but continues to rise, then rises quicker after the RPM's recover.
Last edited by Jeff 97 Formula; Nov 26, 2014 at 05:51 AM.
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regarding alternator kicking in after 1/2 second on cold start, yes that may be normal also. I know for the LS1 because i have the service manual, that the pcm sends the turn on signal to the alternator, i can only assume it works similarly for the LT1. so it's however GM programmed the PCM to control when the alternator turns on, and it stands to reason that just after the engine fires and reaches idle rpm would the pcm then command the alternator on, in order to reduce load on the engine during cranking and initial startup. also, the volt gauge on your dash is most likely controlled by the pcm, it is in the 1998+ cars. so your volt gauge in the dash cluster is not measuring system voltage directly, the needle only points to whatever the pcm tells it to point to. so that 1/4 to 1/2 second after cold start can simply be the delay in network data from the pcm to the dash cluster.
yes it is normal on a cold start for the volt gauge to read higher around 14 volts for a little while, then as the battery is charged and engine compartment warms up voltage drops down around 13.0 to 13.5.
you are worrying about nothing, from everything you said your alternator seems to be working perfectly fine.
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