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  #1  
Old 08-01-2011, 12:42 PM
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Default random voltage drop

this is on darlingreject's 98 v6. alt is new, battery is new, charge wire is new, ground is good, battery connections tight. when the car is idling, im getting 14 volts at the battery, 13.1 at the gauge in the dash. the problem is it will randomly drop. i was thinking a/c or fans, but thats not the issue. it will drop to 13.3 at the battery, and there is other random drops to 11.5 volts. i checked the controller wire, the pin is clean and tight. the wire is good back around the intake. the alternator is computer controlled on these models, correct? we will be swapping out the ecm in a few weeks for a tuned one. if that doesnt correct the issue, what could it be? the alt is a new delco remy. it did this with the original alt and one reman
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Old 08-01-2011, 01:17 PM
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Do you know how to do a local voltage drop test with your voltmeter? I would install a simple short lead on the back of the altenator and do a voltage test there first then do a voltage drop test. This should tell you if it is the charging system or the wiring.
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  #3  
Old 08-01-2011, 08:21 PM
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Are you getting a DTC P0560 code or any other codes?

Maybe this sheds some light, also alternator performance at operating temp can be as much as 20% below cold operating temp.


Document ID# 1540541
1998 Chevrolet/Geo Camaro


--------------------------------------------------------------------------------

Info - Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output #02-06-03-008A - (Jul 28, 2004)
Low Voltage Display on IP Gauge, Lights Dim at Stop Lights, Battery Discharged, No Start, Slow Cranking, Dim Lights at Idle, Low Generator Output
1990-2005 Passenger Cars and Light Duty Trucks

2003-2005 HUMMER H2

This bulletin is being revised to add the 2004 and 2005 model years. Please discard Corporate Bulletin Number 02-06-03-008 (Section 06 -- Engine).

Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed.

During normal driving conditions, when engine speed is above 1000 RPM, the generator is designed to do two things:

Supply the current necessary to operate the vehicle's originally equipped electrical devices (loads).
Recharge/ maintain the battery's state of charge.
The following factors may affect generator and battery performance:

Non-usage of the vehicle for extended periods of time. The vehicle's computers, clocks and the like will cause the battery state of charge to drop (For example; 30 days in a parking lot and the vehicle may not start because of a dead battery or a vehicle which is driven only a short distance once a week may end up with a discharged battery to the point where the vehicle may not start). This would be considered abnormal usage of the vehicle and the normally expected result for the vehicle battery, generator and electrical systems.
At idle, vehicle electrical loads may exceed the low speed current (amperage) output of the generator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand. This is equivalent to the brown outs experienced by homes and businesses when the electrical demand is more than the supply. See Figure 1.
Extended periods of engine idling, with high electrical loads, may result in a discharged battery. Attempting to recharge a battery by letting the engine run at idle may not be beneficial unless all electrical loads are turned "OFF".
Increased internal generator temperatures from extended idling can also contribute to lower electrical system voltage. As the generator's internal temperature rises, the generator's output capability is reduced due to increased electrical resistance.
The following are some typical examples of electrical loads:

System
Amperage Load

Rear Window defogger
25

Electric AIR Pump
25

Heated Seats
5 Amps per seat

Headlamps (high)
20

Blower Motor (High)
20

Headlamps (low)
15

Brake Lights
6

Windshield Wipers
6

Ignition
6





Depending on the vehicle application, generator current (amperage) output at engine idle speeds of 600-700 RPM can be as low as 35 percent of the full rated output. With enough electrical loads "ON", it is easy to exceed the generator current (amperage) output when the engine is at an idle of 600-700 RPM. This is a normal condition. The battery supplements for short periods of time. Items that affect the vehicle's electrical system current and voltage at idle are the number of electrical loads being used, including add-on accessories, and extended idle times. When the vehicle speed is above approximately 24 km/h (15 mph), the engine/generator RPM is high enough and the generator current (amperage ) output is sufficient to supply the current (amperage) requirements of the vehicle as originally equipped and recharge the battery.

Dimming lights at idle may be considered normal for two reasons:

As the engine/generator speed changes, so will the current (amperage) output of the generator. As a vehicle slows, engine/generator RPM slows, and the current (amperage) output of the generator may not be sufficient to supply the loads, the vehicle system voltage will drop and the lights will dim. Dimming of the lights is an indication that current is being pulled from the battery. If the battery is in a low state-of-charge (discharged condition), the driver will notice a more pronounced dimming than a vehicle with a fully charged battery.
When high current loads (blower, rear defogger, headlamps, cooling fan, heated seats, power seats, electric "AIR" pump, or power windows) are operating or cycled "ON", the generator's voltage regulator can delay the rise in output. This effect, usually at lower engine speeds, can take up to ten seconds to ramp up the generator output. This is done to avoid loading the engine severely. To increase current (amperage) output, additional torque is consumed by the generator. The engine computer (PCM) will ramp up engine/generator speed in small steps so engine speed variations are not noticeable to the driver.
For diagnosis of the battery and or the generator, refer to the appropriate Service Information or Corporate Bulletin Number 02-06-03-006A.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION
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Old 08-01-2011, 09:42 PM
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alt output is the same as at the battery. it just randomly drops down real low for no reason and the engine stumbles, then revs up and the volts come back. theres nothing else turned. forgot to mention the belt and tensioner are also new and in good working order

p.s. not concerned at all of the innaccuracy of the gauge. its gm, i expect it
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Quote:
Originally Posted by DarlingReject View Post
If I have 300hp...I wanna be able to hear, smell, and feel it...
Mmm cam.
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Old 08-02-2011, 12:22 AM
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^ Maybe you have a lemon alternator -- it's happened to me before! :-(
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Old 08-02-2011, 12:30 AM
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I agree I bought a reman alternator for a 01 cavalier and it didn't even work had to send it back for a different one. Do you have after market amplifiers installed? I've heard stories of the amps shorting out and killing the alternator with it.
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Old 08-02-2011, 09:22 AM
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+1 on the lemon alternator, I've installed one on my Camaro.
Does she have an amp that might be frying it?
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Old 08-02-2011, 12:03 PM
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there is an amp, but it was turned off. she doesnt typcily have it up loud. lights dont dim at idle until the voltage drops, otherwise it holds 14 volts consistantly. could try disconnecting it and trying that. i dont think i would have 3 defective alternators in a row
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1986 Camaro Z28. TPI 383-430HP 466TQ. Still 10 bolt... 40k miles, getting faster all the time

Quote:
Originally Posted by DarlingReject View Post
If I have 300hp...I wanna be able to hear, smell, and feel it...
Mmm cam.
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  #9  
Old 08-02-2011, 01:42 PM
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i think the voltage regulator is in the alternator and the pcm can tell it what to do. at least mine seems to have a mind of its own. picked up a new one set at 14v and it went to 14 for the first run and went to the 13.1 its always been at after that.
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Old 08-02-2011, 01:53 PM
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If you ever had a bad or failing weak battery connected to your alternator -- even a brand new alternator, that could be a cause of gradual failure, even if you later put a good battery in. It has happened to me.
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Old 08-02-2011, 01:53 PM
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