Battery or Alternator issue??
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Junior User
Joined: Nov 2011
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Battery or Alternator issue??
Hi Guys
Having a issue on my 79 F150 Super, battery is like 2 months old and have confirmed the charge is good, but the engine is very slow in turning over and sometimes it starts others it does not have enough battery juice to turn.
Checked battery and showing 12.5v and running 13.6 (a little low) seems we are losing about .5v in the wiring somewhere, I thought running we should get mid 14V from showing? Trying to work out what is causing this issue? I had a few issues on a short the Auto electrician shorted for my indicators but now it is like either my battery is dying (checked and showing perfect) or the alternator is not working correct (will check belt tomorrow) so looking for ideas on what else can cause this issue?
Thoughts?
Having a issue on my 79 F150 Super, battery is like 2 months old and have confirmed the charge is good, but the engine is very slow in turning over and sometimes it starts others it does not have enough battery juice to turn.
Checked battery and showing 12.5v and running 13.6 (a little low) seems we are losing about .5v in the wiring somewhere, I thought running we should get mid 14V from showing? Trying to work out what is causing this issue? I had a few issues on a short the Auto electrician shorted for my indicators but now it is like either my battery is dying (checked and showing perfect) or the alternator is not working correct (will check belt tomorrow) so looking for ideas on what else can cause this issue?
Thoughts?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Those numbers are good. You charging system is fine. I agree with GFW; it sounds like an issue with the starter itself or the wiring to the starter. If you want to be absolutely sure, check the voltage across the battery posts while a friend cranks the engine. It will be lower than 12 of course, but shouldn't fall on its face.
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Junior User
Joined: Nov 2011
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Those numbers are good. You charging system is fine. I agree with GFW; it sounds like an issue with the starter itself or the wiring to the starter. If you want to be absolutely sure, check the voltage across the battery posts while a friend cranks the engine. It will be lower than 12 of course, but shouldn't fall on its face.
Also read something about checking the grey motorcraft box (Ignition module I think) on the drivers fender wall....any ideas?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
That has nothing to do with your problem. There is a feature of the ignition module that retards ignition timing to help make the starter not have to work as hard, but the absence of that feature won't make it slow to turn over. Ignore whatever it is you read.
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Cheers
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I don't agree with your mechanic. It's all in the numbers. Your measurements indicate a healthy battery that has been properly charged. If the alternator was leaving the battery with too little power to start, it would have shown up in the measurement. A fresh engine rebuild, regardless of displacement, has no bearing on the alternator amperage. A stock 60-amp alternator will handle any stock engine with standard loads just fine. Air conditioning does not increase the load on the alternator any more than the heater because both use the blower motor. The only additional current needed for air conditioning is that which engages the clutch. The engine does the rest of the work.
If there's an underlying issue with the charging system, an upgraded alternator may mask or hide the issue, but it's a waste of money, because a replacement 60-amp would have been fine. However, I do not agree that your charging system is related at all. Numbers are numbers. I think you should do the test I outlined.
Let me guess, your mechanic that's suggesting all these electrical upgrades will be the one getting paid to do the work?
If there's an underlying issue with the charging system, an upgraded alternator may mask or hide the issue, but it's a waste of money, because a replacement 60-amp would have been fine. However, I do not agree that your charging system is related at all. Numbers are numbers. I think you should do the test I outlined.
Let me guess, your mechanic that's suggesting all these electrical upgrades will be the one getting paid to do the work?
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Cross-Country
Joined: Dec 2013
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I'm far from an expert but I also disagree with your mechanic. Just makes no sense. I have a plain jane alternator on my 79. Not sure of amperage but it's nothing high. I had this alternator with an 1,800 watt amplifier. That amp really dimmed all the lights. The stereo would shut off at idle. The alternator was just not enough to feed that amp. Needed far more juice than any air conditioning needs. BUUUUT the truck still started just fine. No issues whatsoever! So I just don't see the issue being your alternator
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Goodness grief, what a sham.
That research means the test I described in my first post.
That research means the test I described in my first post.
Cross-Country
Joined: Dec 2013
Posts: 86
Likes: 1
You're mechanic is making his pocket fat. Listen to fmc400. Save yourself the money
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Junior User
Joined: Nov 2011
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lol, I am heading to the get my truck from the Auto electrician and go back to my mechanic to test this all again as per FMC400.
Now come to think of it when i put the the rebuilt engine back in (same engine just rebuilt) we put a new starter motor in and she worked perfectly. It just had the 600 mile first service and a short issue on the indicators fixed (new steering column) and now we have the issue so you 100% right......the truck worked perfectly before so why not now?
Starter is 100% new so must be a wiring or connection issue. Will complete tests today and see what we find....thanks all for your help to date!!!
Now come to think of it when i put the the rebuilt engine back in (same engine just rebuilt) we put a new starter motor in and she worked perfectly. It just had the 600 mile first service and a short issue on the indicators fixed (new steering column) and now we have the issue so you 100% right......the truck worked perfectly before so why not now?
Starter is 100% new so must be a wiring or connection issue. Will complete tests today and see what we find....thanks all for your help to date!!!
Posting Guru
Joined: Feb 2007
Posts: 1,735
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From: Wingo, Ky
I've had new starters go bad shortly after getting them and then finally get a good one. They don't make em like they use to, lol.
The government wants our old beasts to die and go to hell. lol.
The government wants our old beasts to die and go to hell. lol.