Voltage Drop on 2005 F150
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Joined: Oct 2010
Posts: 68
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From: Athens, GA
Voltage Drop on 2005 F150
Hey guys,
I've got a 2005 4WD with the 5.4L. The past few weeks i've noticed a voltage while the engine is cranked.
The past few weeks the truck has been really bad about high idling on startup. Usually jumps to around 1800 for about 5 seconds, then drops to 1000 for about 30 seconds before it mozys down to the normal 600-750. Additionally i've been getting a raspy noise from under the hood. I presumed it was just the oil (1st time in ages the truck didn't get motorcraft oil and a filter, as I got it changed when the starter went **** up about a month ago), and it doesn't sound like its coming from the alternator, but could be a belt driven accessory.
So back do the voltage drop. When the truck is cranked, its done it both while idling and when driving, i'll see a voltage drop from the normal 14.4+ it runs, to around 12.9-13.2 for about 10 seconds. The only reason i know this is my gryphon. The battery is about a year old, optima yellow top. I just added a winch earlier this winter.
I personally think this is the first signs of my alternator going out. I've run a 800w RMS stereo from the day i've gotten it. But i'm wondering if the couple of times ive needed to use the winch, including one where I was probably drawing the max amps (502), might have the alternator starting on its last leg.
I've tried cleaning the connectors, and later today i'm going to try what I found on another post from Labnerd stating : "Here's a simple test for you to tell if the alternator has any issues. First check the output voltage by starting the truck, let it run a few minutes, then put a volt meter on it. It should read about 13.8 at the lowest to 14.8 at the highest although I've seen some high capacity alternators have higher voltage outputs. If that checks out, look at the alternator. You will have a shielded cable/wire that bolts to the back or the top of the alternator. Remove the bolt. Now, when you remove the wire, if you see any minor arching of electricity, the final diode is bad allowing the juice to flow back out of the battery into ground via the alternator. No arching- no problems with the alternator. "
What do you guys think? Might be the excuse i need for that 250 amp alternator i've been wanting......
I've got a 2005 4WD with the 5.4L. The past few weeks i've noticed a voltage while the engine is cranked.
The past few weeks the truck has been really bad about high idling on startup. Usually jumps to around 1800 for about 5 seconds, then drops to 1000 for about 30 seconds before it mozys down to the normal 600-750. Additionally i've been getting a raspy noise from under the hood. I presumed it was just the oil (1st time in ages the truck didn't get motorcraft oil and a filter, as I got it changed when the starter went **** up about a month ago), and it doesn't sound like its coming from the alternator, but could be a belt driven accessory.
So back do the voltage drop. When the truck is cranked, its done it both while idling and when driving, i'll see a voltage drop from the normal 14.4+ it runs, to around 12.9-13.2 for about 10 seconds. The only reason i know this is my gryphon. The battery is about a year old, optima yellow top. I just added a winch earlier this winter.
I personally think this is the first signs of my alternator going out. I've run a 800w RMS stereo from the day i've gotten it. But i'm wondering if the couple of times ive needed to use the winch, including one where I was probably drawing the max amps (502), might have the alternator starting on its last leg.
I've tried cleaning the connectors, and later today i'm going to try what I found on another post from Labnerd stating : "Here's a simple test for you to tell if the alternator has any issues. First check the output voltage by starting the truck, let it run a few minutes, then put a volt meter on it. It should read about 13.8 at the lowest to 14.8 at the highest although I've seen some high capacity alternators have higher voltage outputs. If that checks out, look at the alternator. You will have a shielded cable/wire that bolts to the back or the top of the alternator. Remove the bolt. Now, when you remove the wire, if you see any minor arching of electricity, the final diode is bad allowing the juice to flow back out of the battery into ground via the alternator. No arching- no problems with the alternator. "
What do you guys think? Might be the excuse i need for that 250 amp alternator i've been wanting......
Technical Article Contributor
Joined: Apr 2009
Posts: 10,697
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From: In the fast lane from LA to Tokyo...
Get a motorcraft oil filter back on it....that the most important thing....
yes your alt could be going but so could your battery.....it would be best to get them proffesionally load tested at a reputable mechanic or dealer....not at an auto parts store....
yes your alt could be going but so could your battery.....it would be best to get them proffesionally load tested at a reputable mechanic or dealer....not at an auto parts store....
Senior Member
Joined: Jul 2000
Posts: 488
Likes: 1
From: MI
Couple notes
- Optima batteries are not what they used to be
- If voltage is good, then the alternator is good when running
- If there is a current draw then the battery voltage will be below 12.7v after it has sat for awhile (like more than 8 hours). This could be the alternator or any other item connected to the battery.
- It is normal for voltage to drop when cranking, it is pulling around 200A to crank the engine, voltage will drop.
- I'm betting along with 88 your idle/noise problem is more related to a switch in oil & filter.
- Does your headlights dim when the stereo is cranked at all? If not, alternator size is fine. Before getting a bigger alternator, do the Big 4 upgrade.
- Optima batteries are not what they used to be
- If voltage is good, then the alternator is good when running
- If there is a current draw then the battery voltage will be below 12.7v after it has sat for awhile (like more than 8 hours). This could be the alternator or any other item connected to the battery.
- It is normal for voltage to drop when cranking, it is pulling around 200A to crank the engine, voltage will drop.
- I'm betting along with 88 your idle/noise problem is more related to a switch in oil & filter.
- Does your headlights dim when the stereo is cranked at all? If not, alternator size is fine. Before getting a bigger alternator, do the Big 4 upgrade.
Thread Starter
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Member
Joined: Oct 2010
Posts: 68
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From: Athens, GA
I figured the noise was the oil filter. Damn not motorcraft oil.
Went and got the alternator and battery tested today. Couldn't find a problem with either. the more I think about it, I bet it has to be a ground. It would explain everything, and as much as I beat my truck up in the mud I bet somethings gotten loose/needs replacing. Looks like I get to order some wire. Thanks!
Headlights can't dim, their HID's which run off a relay.
Went and got the alternator and battery tested today. Couldn't find a problem with either. the more I think about it, I bet it has to be a ground. It would explain everything, and as much as I beat my truck up in the mud I bet somethings gotten loose/needs replacing. Looks like I get to order some wire. Thanks!
Headlights can't dim, their HID's which run off a relay.