Bad alternator - not carging at idle

[kapitein]

Howdy folks,

I think I know the answer, but never hurts to ask.

86 454. Std alternator (doesnt look old, but I dont know its history).

Car has quad LED headlight upgrade and electric fan conversion.

At idle with everything switched on (incl. AC) its only reading 12.4v at the battery.

Going down the road it charges nicely at 14.3-14.4v

With the summer season approaching, its going to be using a lot of AC and probably sitting a lot in traffic on the highway, so I want to get this solved.

Sound like a duff alternator? Reading the forums, it seems like throwing on a CS130 is the default answer - sound about right?

Thanks

 

[Snoots]

AD230 or AD244

 

[Edelbrock]

What is your idle speed? Wrong size alternator pulley? Bad voltage regulator?

 

[kapitein]

What is your idle speed? Wrong size alternator pulley? Bad voltage regulator?

Idle speed is a little lower than stock (mild cam).

 

[AuroraGirl]

Idle speed is a little lower than stock (mild cam).

drop pulley diameter at alternator, or get a better alternator
Pulley will swap to a cs130-ad23-cs144-ad244

 

[edgephoto]

Before you go tossing parts at it make sure it is not as simple as a voltage drop due to a bad ground or extra resistance in the wires.

While running at idle turn on all the consumers. Set your voltmeter to DC volts. Measure from the battery negative terminal and the case of the alternator. Voltage should read .1-.2 volts. Now measure from the battery positive to the output stud on the back of the alternator. Again you should read about .1-.2 volts. This way you know your wiring is good.

If the wiring is good and you have access to an inductive amp meter that can read DC amps. Turn everything on and measure how many amps are coming out of your alternator.

What size alternator does your truck have? That style alternator came with 66, 78 and 94 amp output. I am going by what I know for 1987, I would think your 1986 is the same.

For 1987 the RPO codes are K22=94 amp, K64=66 amp, K81=78 amp.

If you don't have a 94 amp and that will solve your problem you can replace it with the 94 amp without any issue. Replacing it with a different series you will need to adapt brackets and electrical connectors. I just rebuilt my original alternator and installed a 140 amp stator. I wanted better idle performance and this should help. There are also companies that make high output versions of your alternator. I believe you have a 12Si alternator. Post a picture of it and we can tell.

 

[kapitein]

These are my RPO codes.

Thanks

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