1st Drive Alternator issues possibly??

[snap on pete]

So 1st drive in my newly imported Pick Up this afternoon...at last

All good Has a nice solid feel about it. Power steering is a dream and the heater system works well..

Got almost home and parked up for a moment and for a while sounded like engine was going to cut out.
I noticed the Voltmeter had dropped dramatically on the dash to no more than 9 volts where most of the drive was happy charging around 14 v

I know the battery was in a fully charged state before i left home, so i guess there must be an issue with the alternator..??

Any suggestions..... was thinking about getting RaC out to test it?

Its a fairly new chrome unit so dont want to replace this if i can help it.. ?

Thanks Pete

[OrrieG]

Quick redneck check to see if it is charging is to start the truck and hold a metal object (screw driver) at the back of the alternator, if it pull it like a magnet the alternator is charging and you have a wiring issue.

[snap on pete]

Had a check this morning.. Yes its the `one wire jobbie` and all connections are tight. I put a meter... and kicking out a perfect 14.4v at the terminal

Went out for a 25 mile drive keeping an eye on the voltmeter on the dash..
No lights on today so that wasnt an issue

But the voltmeter drops dramatically when i stop at a junction for instance.. Fine at high speeds...and the baby shifts wowee........!!!!!!
Especially with the 4spd box.!! The kickdown moves LOL..

The idle is ok and doesn't seem too slow imo.. I was reading something else and was thinking maybe an issue when the electric fan kicks in ?
Gauge seems ok but maybe a bit erratic ? VDO instrumentation fitted

[oldman3]

I'm no expert on alternators, but I think that might be an 85 amp, if it is, and your fans comes on at idle, the alternator isn't putting out enough to supply your needs, just a guess, take it for what it's worth....Jim

[mr48chev]

I"m not and never have been a fan of the one wire setups as they rely on engine speed to trigger them into working and may not trigger every time. Maybe you just aren't rapping the pipes enough as you drive around.

I think I would take the truck to a good auto electric shop that has the equipment and knowledge to test the alternator and the rest of the system. Find out exactly what the alternator is charging and find out what loads the rest of the system is putting out. 85 amps should keep up with the system you have but they also built alternators with the same case that had 37, 45 and 60 amp output along with possibly a few more. The good news is that you can swap the pieces from a similar but higher rated alternator of the same basic model into that case if the pieces aren't putting out enough amps keeping your chrome case.

[snap on pete]

Some sound advice there..thanks guys...

Had another good drive yesterday and it does seem the alternator isnt man enough for the truck. As soon as i put a load on (while driving along) ie., heater or the electric fan kicks in, the Voltmeter drops sub 10v

Will get it checked out to avoid any possible fails !

[G&R's57GMC]

Wire gauge could be a factor also.

If your running a 60 amp alternator 10 gauge would be about as small as you would want to go.

But if your going to run an 85 amp 8 gauge would be the ticket.

Now running electric fans, heater and lights you would want at least 105 amp alternator with 4 gauge wire.

Add fuel injection and A/C 145 amp alternator with at the very least 4 gauge wire.

If you have a large enough alternator and wire on your truck to handle your alternators output and the system is sized for your load then its possible a phase of the alternator is out.

Have the alternator tested off the vehicle.

Looking at your alternator its most likely only good for 60 Amps max.

[starterman99]

IF you want to check for diode problem hook up your volt meter to battery output on back of alternator set meter to AC voltage if you see any more than 0.5 volts you have a problem.With the 14.4 volt output I would expect everything is OK.If one phase had problem voltage should be down.with the shiny chrome pulley verify the belt not slipping under load.