Silverado Alternator not putting out proper volts - Already changed the alternator...

[someday31]

I took my reading at idle, 500rpm. I hooked the negative wire of the meter to an alternator bolt for ground and the positive I touched to the middle prong I believe, I am under the assumption that that wire comes from the pcm?
I believe my battery was an acid battery - Duralast Gold 800CCA 1000CA 78 Size.
If the pcm is putting out too much voltage 9.77 versus the 5 that I think it should could that cause the volt regulator to not put out enough volts?
Thanks.

[consultIII]

I'll check a similar truck tommorow.

This system should be charging the battery reguardless of 14.5 volts or 14.1 volts ...both are over 12.6 so it should be taking a charge. Stranger things have happened though.

Just to make sure we are not chasing zebra's...
You should be testing at 2500 rpm because ecm controlled alternators don't put out much at idle...and aren't designed to charge dead batteries but rather maintain the system...asking todays compact alternators to charge dead batteries can overheat the stator windings. I've seem it before when people don't drive enough or their driving habits don't allow the car to charge the batteries.

New batteries are not fully charged so charge it for 8 hours with a battery charger and see how long it goes.

[someday31]

consultIII Could you also check your wire harness going into the alternator...how many volts do you get coming into the harness with the truck at idle? I want to see if me getting 9.77 volts is too high. Thanks!

[someday31]

I took the harness off the alternator and then applied 12 volts to the voltage reg terminal that gets energized from the pcm. I still got 14.10 out of the alternator, so I think the pcm is not my problem. I get 55amps out of the alternator with the lights and blower on at idle and about 13.90volts. That seems low???

[old_master]

Checking alternator output at idle tells you nothing. The engine needs to be at 2500RPM for the alternator to produce maximum output.

[someday31]

What output should I expect at 2500rpm on a 150amp alternator?

[old_master]

With all accessories turned off, battery fully charged, engine at 2,500 RPM, max alternator output should be approximately 130 to 140 amps, and voltage, ideally, should be at 14.2 volts.

[someday31]

Ok...is there a way I can test this by myself, its electronic throttle

[old_master]

If your ammeter is inductive, you don't need anyone else. Put the inductive probe on the alternator output, (red wire), apply B+ to the field, gas her up and watch the ammeter.

[j cAT]

Originally Posted by someday31

I took the harness off the alternator and then applied 12 volts to the voltage reg terminal that gets energized from the pcm. I still got 14.10 out of the alternator, so I think the pcm is not my problem. I get 55amps out of the alternator with the lights and blower on at idle and about 13.90volts. That seems low???

once again you display data that shows your charging system is running correctly...this is what I have observed on my vehicle with a fully charged battery ....volts and current are correct...


with your other questions on alternator output , the alternator will not output max current unless you place a load on the electrical system to force this to occur..

the pcm does not control alternator current.. this only monitors the alternator..the internal regulator controls the alternator current ..the voltage generated is also controlled by the internal regulator of the alternator..


your problem of the battery losing charge is , because at rest no engine on , the battery is being discharged..

[someday31]

What do you guys think of this......

http://www.zzperformance.com/grand_prix/products1.php?id=517&catid=107

[old_master]

I'd be skeptical... If charging voltage is higher than 14.2 volts, it will shorten the life of the light bulbs, the battery, any motor, including the fuel pump, and other electrical devices along with possibly setting a DTC. I trust the factory engineers more than I trust.... what was the name of the company?? But, it's your vehicle, and they sell it! Just my opinion... and some facts

[j cAT]

Originally Posted by someday31

What do you guys think of this......

http://www.zzperformance.com/grand_p...=517&catid=107

Only a fool would buy that crap ! like I said your charging system is working correctly...

you have a battery leakage issue , not a charging issue...find the componet that is sucking the power out of the battery when the engine is OFF .

[someday31]

Originally Posted by j cAT

Only a fool would buy that crap ! like I said your charging system is working correctly...

you have a battery leakage issue , not a charging issue...find the componet that is sucking the power out of the battery when the engine is OFF .

I have done a parisitic draw test and I get 2 milliamps with the key off. Its not a draw issue based on this test.

[consultIII]

here are the numbers someday31

tested a 2003 6.0l 2500hd. Has the same charging system wiring and controls.

checked voltages at alternator connector (backprobed terminals with connectors connected) with truck off, koeo and koer at idle; results as follows:

terminal c at alternator which is gry wire...goes to pcm... and is the off/run/crank volts field duty cycle signal

key off eng off 0v, koeo 2.074v, keor 3.98v


terminal b at alternator which is brown wire...goes to pcm... and is the serial data charge indicator control

key off eng off 0v, koeo 1.311v, koer 11.22v

of course forgot to check alt output amp and volts...but I know the charging system is good on this truck.