Alternator issue

Reply Subscribe

Thread Tools

Search this Thread

Oct 25, 2009 | 11:21 AM

rustynuts

Thread Starter

Senior User

Joined: Nov 2002

Posts: 163

Likes: 0

From: chicago

Alternator issue

I think my alternator may be going south. First noticed this a while back, when towing my enclosed trailer at night with the heater fan on high, lights, trailer lights, etc. At a stoplight, blower fan would slow down, headlights got a little dim, as soon as i touched the throttle fan sped up and lights got brighter.

Put a voltmeter on the battery, only 12.5 idling, and when I increased rpm to like 1500, went up to 13.6 or so.

Does this sound like a alternator, or ecu issue?

Oct 25, 2009 | 12:20 PM

toolman05kr

Senior User

Joined: Oct 2005

Posts: 465

Likes: 1

From: Nesconset NY

Have your batteries checked, a bad battery can cause this, also have the charging system checked as well, could also be a bad diode.

Oct 25, 2009 | 12:51 PM

rustynuts

Thread Starter

Senior User

Joined: Nov 2002

Posts: 163

Likes: 0

From: chicago

Both batteries are only a yr old, had them checked at auto parts store and they said they were ok..I drive like 2 miles to work everyday, and lately, if i dont drive the truck far, like a highway trip during the week, come thurs/fri the truck needs a jump. I know the short trips to work dont allow much recharging time, but this was never a issue until recently.

Oct 25, 2009 | 02:00 PM

69cj

Hotshot

Joined: Jul 2005

Posts: 13,834

Likes: 25

From: Middle Tn.

a 2 mile drive will not compensate for the starting and glow plug drain. I did have a battery take a dump at 1 year old. When they tested the batteries did you isolate them from each other. If not then the test is bogus.

Oct 25, 2009 | 07:38 PM

rustynuts

Thread Starter

Senior User

Joined: Nov 2002

Posts: 163

Likes: 0

From: chicago

Hooked a meter up to it, had the truck running at idle for about 5-10 minutes, best at idle was 12.3. Had to rev it to 2k rpm to get up to 12.6-12.7. Replaced alt just now and at idle im getting around 13.0-13.1 at 1200 and higher about 13.6-13.7. Should be better now. Thanks

Oct 25, 2009 | 07:58 PM

cmcowboy

Senior User

Joined: Aug 2006

Posts: 288

Likes: 0

From: Bradenton Florida

Quote:

Originally Posted by rustynuts

I just had to replace both of mine and they where only 1 1/2 years old.
Like 69cj said make sure when you have the test done you isolate the batteries from one another. And if they tested your batteries they should of tested your alternator at the same time. Also just 13 volts at idle is a little weak I believe. When I tested mine, as soon as the glow plugs turned off I beleive remember seeing mine right around 14 at idle.

Oct 25, 2009 | 09:12 PM

rustynuts

Thread Starter

Senior User

Joined: Nov 2002

Posts: 163

Likes: 0

From: chicago

I brought the batteries in and had them tested on the bench. They tested good. When I put the meter on it tonight, the batteries were run down quite a bit, not sure if that would have a effect on the low reading at idle??