F150 low voltage
Thread Starter
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Member
Joined: Aug 2010
Posts: 10
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From: Mesa, Az
F150 low voltage
My dash gauge was taking a nose dive. Had it tested. They said it was bad. Replaced it. Still seems to have an issue. Here's where I'm at.
On 8/25/2010 with engine cold and outside temperature about 90 degrees F:
13.32 vdc at battery posts engine not running
14.56vdc with meter at battery posts with engine running @ 1500 rpm
14.8vdc with battery negative cable off, engine running, with meter at positive post to a ground
14.5vdc with battery negative cable back on but loose, engine running, with meter at positive post and to a ground
With engine up to operating temperature (idling @ about -1k)
14.12vdc with meter from ground to positive battery post
13.8vdc with engine running, and a/c on maximum
13.08vdc with engine running, a/c on maximum, and headlights on
12.9vdc with engine running, a/c on maximum, and headlights on high beam
12.9vdc with engine running, a/c on maximum, and headlights on high beam and radio full volume(cool tunes play’in)
With engine still running this time rpm @ 1k+
13.5vdc a/c on maximum, and headlights on high beam and radio full volume(cool tunes play’in)
13.79vdc a/c off and high beam and radio full volume(cool tunes play’in)
Is my alternator doing what it should or should the voltage be higher?
Is my battery ok?
Noticing when the a/c is turned on, the rpm drops below 1k, also the voltages lowers. With a/c turned off, rpm rises to 1k+ and voltage rises as well. Could I adjust the idle on the throttle body to keep rpm @1k?
On 8/25/2010 with engine cold and outside temperature about 90 degrees F:
13.32 vdc at battery posts engine not running
14.56vdc with meter at battery posts with engine running @ 1500 rpm
14.8vdc with battery negative cable off, engine running, with meter at positive post to a ground
14.5vdc with battery negative cable back on but loose, engine running, with meter at positive post and to a ground
With engine up to operating temperature (idling @ about -1k)
14.12vdc with meter from ground to positive battery post
13.8vdc with engine running, and a/c on maximum
13.08vdc with engine running, a/c on maximum, and headlights on
12.9vdc with engine running, a/c on maximum, and headlights on high beam
12.9vdc with engine running, a/c on maximum, and headlights on high beam and radio full volume(cool tunes play’in)
With engine still running this time rpm @ 1k+
13.5vdc a/c on maximum, and headlights on high beam and radio full volume(cool tunes play’in)
13.79vdc a/c off and high beam and radio full volume(cool tunes play’in)
Is my alternator doing what it should or should the voltage be higher?
Is my battery ok?
Noticing when the a/c is turned on, the rpm drops below 1k, also the voltages lowers. With a/c turned off, rpm rises to 1k+ and voltage rises as well. Could I adjust the idle on the throttle body to keep rpm @1k?
Senior Member
Joined: Nov 2006
Posts: 5,495
Likes: 7
From: Memphis, TN 38135, USA, Earth
You're damaging the alternator by running the engine with the battery disconnected, and those measurements are meaningless.
What "dash gauge" are you talking about? The entire cluster? The volt gauge? And who are "they"?
To test the alt, ground the screw on the back that says "GROUND HERE TO TEST". With the engine at ~1500RPM, voltage should go over 15VDC. Don't test it for more than a second or 2 - just long enough to measure.
To test the battery, take it to a shop that has a MidTronics battery tester.
Does the ALT light come on before cranking? If not, replace the bulb. It's part of the alternator's I circuit.
What "dash gauge" are you talking about? The entire cluster? The volt gauge? And who are "they"?
To test the alt, ground the screw on the back that says "GROUND HERE TO TEST". With the engine at ~1500RPM, voltage should go over 15VDC. Don't test it for more than a second or 2 - just long enough to measure.
To test the battery, take it to a shop that has a MidTronics battery tester.
Does the ALT light come on before cranking? If not, replace the bulb. It's part of the alternator's I circuit.
Thread Starter
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Member
Joined: Aug 2010
Posts: 10
Likes: 0
From: Mesa, Az
You're damaging the alternator by running the engine with the battery disconnected, and those measurements are meaningless.
What "dash gauge" are you talking about? The entire cluster? The volt gauge? And who are "they"?
To test the alt, ground the screw on the back that says "GROUND HERE TO TEST". With the engine at ~1500RPM, voltage should go over 15VDC. Don't test it for more than a second or 2 - just long enough to measure.
To test the battery, take it to a shop that has a MidTronics battery tester.
Does the ALT light come on before cranking? If not, replace the bulb. It's part of the alternator's I circuit.
What "dash gauge" are you talking about? The entire cluster? The volt gauge? And who are "they"?
To test the alt, ground the screw on the back that says "GROUND HERE TO TEST". With the engine at ~1500RPM, voltage should go over 15VDC. Don't test it for more than a second or 2 - just long enough to measure.
To test the battery, take it to a shop that has a MidTronics battery tester.
Does the ALT light come on before cranking? If not, replace the bulb. It's part of the alternator's I circuit.
I followed a procedure from an "ask a pro" forum. I thought they, ASE Certified" guys and the automotive box store guys, knew what they were talking about. May be not.
The electrical gauge on the dash by the temp, oil pressure, and gas gauge in the dash. It's been staying on the very low side of the gauge.
Where exactly is the "GROUND HERE TO TEST" point?
When you say to "ground the screw on the back", exactly what do you mean?
Where do I put the meter probes?
What if it doesn't go over 15vdc?
Do you know what places might have this battery tester? It could save me some time searching.
I do not see any light come on before cranking. The bulb might be burnt out. Where exactly do I find this bulb?
As you might be able to tell, I'm not an expert in these matters. I'm thinking I do know just enough to get myself in trouble. What I do know is my truck is old and things are going south. This is why I joined this forum. Good help is hard to find. Seems I might be headed in the right direction.
All help is very much appreciated.
Senior Member
Joined: Nov 2006
Posts: 5,495
Likes: 7
From: Memphis, TN 38135, USA, Earth
I'm also ASE, and Ford-trained, and both ASE & Ford agree that you should never operate an alternator with no battery.
So it was the stock volt gauge within the cluster that was replaced? Read this caption:
Virtually every dealership (of every make) is required by the factory to have a MidTronics battery tester for warranty battery returns. Many independent shops also have them. Here's mine, but there are many models:
The bulb is in the back of the cluster, so the cluster has to come out of the dash to replace any bulbs. It's the bulb labelled "AMP" or "ALT" on the film circuit. This caption also contains a link showing how to remove the cluster.
Look thru the other pics in that album (Low Fuel Light) for more info.
The factory voltage regulator has "GROUND HERE TO TEST" & an arrow molded into it, and it's mounted to the back of the alternator. "Ground" means to use a jumper wire to connect something to the vehicle chassis ground, which includes the frame, body sheet metal, engine block, and almost every other exposed piece of metal. The meter probes go across the battery posts. If the voltage doesn't jump, then the alternator is weak or dead, or not wired correctly. Your truck is wired almost identically to this:
So it was the stock volt gauge within the cluster that was replaced? Read this caption:
Virtually every dealership (of every make) is required by the factory to have a MidTronics battery tester for warranty battery returns. Many independent shops also have them. Here's mine, but there are many models:
The bulb is in the back of the cluster, so the cluster has to come out of the dash to replace any bulbs. It's the bulb labelled "AMP" or "ALT" on the film circuit. This caption also contains a link showing how to remove the cluster.
Look thru the other pics in that album (Low Fuel Light) for more info.
The factory voltage regulator has "GROUND HERE TO TEST" & an arrow molded into it, and it's mounted to the back of the alternator. "Ground" means to use a jumper wire to connect something to the vehicle chassis ground, which includes the frame, body sheet metal, engine block, and almost every other exposed piece of metal. The meter probes go across the battery posts. If the voltage doesn't jump, then the alternator is weak or dead, or not wired correctly. Your truck is wired almost identically to this:
Last edited by Steve83; Aug 26, 2010 at 12:47 PM.