Alternator issue

[Durt D1ver]

How many volts should the alternator be putting out? My 04's gone dead 3x in the last 2 weeks. About every 4-5 days or so. Check the output with a multimeter, and under load (AC on, highest fan setting, Stereo on, headlights and high beams on, driving lights on, and door open) I'm only getting 13.5 volts at 2000+ rpm, off the post on the alternator, even with an almost dead battery. I cant check the amperage output with my multimeter, as it only recommend up to 10amps DC. Tried to have it checked at advance auto, but their machine said "unstable battery" and was unable to test it. I'm assuming that's because I'd just charged the battery before bringing it there.

Local alternator shop said "less than $140". They only have listings for bosch alternators in Discovery's, and my 04 came from the factory with a Valeo. He said Valeo's are cheaper to rebuild, but won't know until he sees it.

 

[p m]

Check the output with a multimeter, and under load (AC on, highest fan setting, Stereo on, headlights and high beams on, driving lights on, and door open) I'm only getting 13.5 volts at 2000+ rpm, off the post on the alternator, even with an almost dead battery.

I'd be happy if I had 13.5V under these conditions.
This measurement is pretty much most you can do with a DMM; current output will easily blow your DMM's 10A fuse if you attempted to measure.
A scope is a good thing to use to determine if one or more diodes (out of 6) are dead; the voltage regulator seems to be working to me.

My guess is either your battery is dead (won't accept/hold the charge), or you have some current drain in the vehicle that causes it to discharge.

 

[jhmover]

Put the volt meter on. Get a wire (like 10 guage). Hook it to the negative post on the battery. Fire up the D2. Then touch it to the housing on the alternator and see if the voltage rises. If it does you have ground issues. I had batteries dying all over the place for awhile, this turned out to be the problem. Cleaned all the grounds and now it's fine.

 

[braves6117]

Same symptoms when I had a grounding issue with my rack lights.

 

[Durt D1ver]

Hooked up an obd scanner, and while driving around, I get 12.5v with just the a/c and radio on. I'm gonna pull one of the batteries out of the boat, and put it in there for a few days to see if anything changes. Although, I should just pull the alternator and get it bench tested.

 

[p m]

Check the grounds indeed - living in SoCal, I forget about corrosion.
A very useful check is measuring the voltage between the battery (-) terminal, the body, and engine block. It should be very close to zero in nearly all conditions.

 

[Durt D1ver]

Thanks for the insights. I don't know why i didn't think grounds first, because living 2.5 miles from the ocean, and a block from a saltwater bay wouldnlt cause corrosion issues. My fault was in my testing. I tested the + terminal on the alternator, to the - post on the battery, getting 13.5 volts. I just tested the + terminal on the alternator to a couple spots on the engine and accessories, and was at over 14v at idle.

I think it's time for a new ground cable.