Random voltage drop
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Joined: Jun 2012
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Random voltage drop
Hi All,
I noticed last night that my truck's voltage gauge will drop randomly (about every 20-30 seconds). This seems to happen at idle, under load, at speed, etc. It's not enough that it will stall, and the truck starts fine, but still not right.
Since the dash gauge isn't very accurate, I put a meter on the battery terminals, and sure enough, it drops from about 14.4v to around 12v (at idle) for a split second, and then goes back up.
Does this sound like a failing alternator or a bad ground? If so, where should I begin cleaning / testing?
Thank you!
The truck is a 94 f150 4x4 E4OD straight six with 135k. Only electrical add ons/upgrades are a trailer wiring harness, back up lights (on a dash switch with a proper fuse), and an aftermarket radio, but these have all been installed for years with no problems.
I noticed last night that my truck's voltage gauge will drop randomly (about every 20-30 seconds). This seems to happen at idle, under load, at speed, etc. It's not enough that it will stall, and the truck starts fine, but still not right.
Since the dash gauge isn't very accurate, I put a meter on the battery terminals, and sure enough, it drops from about 14.4v to around 12v (at idle) for a split second, and then goes back up.
Does this sound like a failing alternator or a bad ground? If so, where should I begin cleaning / testing?
Thank you!
The truck is a 94 f150 4x4 E4OD straight six with 135k. Only electrical add ons/upgrades are a trailer wiring harness, back up lights (on a dash switch with a proper fuse), and an aftermarket radio, but these have all been installed for years with no problems.
Posting Guru
Joined: May 2007
Posts: 1,208
Likes: 2
From: North Reading Mass
I would first look for bad grounds, then check the alternator wiring connections. The battery cables on these trucks have been known to fail as well as the end connectors over time.
Regards
rikard
Regards
rikard
Thread Starter
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Joined: Jun 2012
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Thank for the input. I did stop by the part store and have them test the alternator (in the vehicle though). Are the two tests different?
Is there a list of ground connections that I should check? I know there is one to the inner fender and one to the starter. Are there others that are problematic?
Is there a list of ground connections that I should check? I know there is one to the inner fender and one to the starter. Are there others that are problematic?
Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
If it were my truck I'd just disconnect the alternator (output cable AND regulator harness) and run the truck on battery power. Take a quick ride and see if the problem's still there. If not, it's likely the regulator or alternator.
Then I'd have to prove it out though... probably get the durn thing bench tested OUT of the truck.
Then I'd have to prove it out though... probably get the durn thing bench tested OUT of the truck.
Posting Guru
Joined: Nov 2012
Posts: 1,224
Likes: 1
From: New Sharon, IA
There is a ground wire that runs from the big plug in on the alternator to a wiring harness that went bad on my truck which wasn't allowing it to charge properly. Once I ran a new wire it has worked flawlessly ever since
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