Problem - Alternator or battery?
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
Likes: 2
From: Vancouver BC Canada
Problem - Alternator or battery?
I'm having a small issue with my 94 5.8. Truck starts fine and runs fine, but when I slow down at a stop, my electrical seems to drop. I notice it mostly as the windshield wipers slowing (it rains here all the time).
I have no idea how old the battery and alt are as they were both in the truck when purchased two years ago. I do plan on pulling both and having them tested at the parts store.
My questions are: what is the likely cause of low rpm voltage drop (I can see the truck gauge drop when off the throttle)? What amperage of alt does the truck have and can I get a higher one (alt part#GL-503-RM).
I've seen many references to 3G alts but have no idea if my truck has one. We will be towing the 5th wheel this summer and I want to make sure the electrical is up to it.
TIA
I have no idea how old the battery and alt are as they were both in the truck when purchased two years ago. I do plan on pulling both and having them tested at the parts store.
My questions are: what is the likely cause of low rpm voltage drop (I can see the truck gauge drop when off the throttle)? What amperage of alt does the truck have and can I get a higher one (alt part#GL-503-RM).
I've seen many references to 3G alts but have no idea if my truck has one. We will be towing the 5th wheel this summer and I want to make sure the electrical is up to it.
TIA
Posting Guru
Joined: Aug 2005
Posts: 1,069
Likes: 1
Problem could be(if u have one)low idle rpms or bad diode in alternator. You need to check voltage across the battery with engine idling and accessories on like wipers. Voltage should be in the 14-14.5 range for a normal reading. If your rpms are low at an idle, this could cause low output from alternator. Also check your alternator belt for tightness, but I don't suspect it is loose.
Thread Starter
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
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From: Vancouver BC Canada
Thanks for the response.
The belt is good. I will check the battery. Do I just put a multimeter probe on either terminal?
I should clarify about the alternator I have. That part# I gave is a number that the ford parts counter guy gave me. I haven't removed my alt yet to check the casting number.
The belt is good. I will check the battery. Do I just put a multimeter probe on either terminal?
I should clarify about the alternator I have. That part# I gave is a number that the ford parts counter guy gave me. I haven't removed my alt yet to check the casting number.
Hotshot
Joined: Sep 2001
Posts: 11,958
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I know that on my truck it does this quite a bit when the lights radio and wipers are on, even worse when the AC is on. It also drops more when the brake lights are on. My truck and my previous truck as well as most I have seen are somewhat like this. Does this sound like what your truck does?
I think our trucks already have 3G alts. I believe that 92 or so was when Ford switched to it. From what I understand is that if the alt has the fan on the pulley its not a 3G and if it doesn't have a fan then it is. Someone please correct this info if its incorrect.
I think our trucks already have 3G alts. I believe that 92 or so was when Ford switched to it. From what I understand is that if the alt has the fan on the pulley its not a 3G and if it doesn't have a fan then it is. Someone please correct this info if its incorrect.
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Fleet Mechanic
Joined: Apr 2008
Posts: 1,724
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From: Vancouver BC Canada
I called an Auto electric shop today and the guy was WAAAY more helpful than the parts guy at the Ford dealership. He said the same thing you are, that the truck already has a 3G alt at 95 amps and that it can be upgraded with a 130 amp, strictly plug and play. He says he sells reman'd Motorcraft and new Unipoint.
Like I said before, where I notice it is in the wipers mostly. Usually I have the wipers and the radio going, and being in Canada, the daytime running lights are always on as well.
I don't feel like I run alot, wipers, headlights, radio. I do have a set of KC lights on the front and some backup flood lights, but they don't get used very much. Mostly, I'm thinking about the summer when we're travelling with the 5th wheel, and the alt will be charging the trailer battery, running all the truck stuff plus a/c and sometimes the kids plugin toys. I'm thinking that the 130 amp is probably a good choice. Just not sure about following the guys info that the stock wire is sufficient.
Like I said before, where I notice it is in the wipers mostly. Usually I have the wipers and the radio going, and being in Canada, the daytime running lights are always on as well.
I don't feel like I run alot, wipers, headlights, radio. I do have a set of KC lights on the front and some backup flood lights, but they don't get used very much. Mostly, I'm thinking about the summer when we're travelling with the 5th wheel, and the alt will be charging the trailer battery, running all the truck stuff plus a/c and sometimes the kids plugin toys. I'm thinking that the 130 amp is probably a good choice. Just not sure about following the guys info that the stock wire is sufficient.
Posting Guru
Joined: Aug 2006
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From: Perry Georgia
Check around where you live for a starter/alternator shop. There is one local that will check both the alternator and the battery while they are both installed in the truck. That way if one is bad they can tell you right then. Could be both are bad. Make sure the battery connections are clean and making good contact. I have a 1987 F250 Diesel that cam,e with a 75 amp alternator. I was having trouble keeping everything going till I upgraded to the 130 amp 3G alternator off of a 1993 Taurus. Check your local "auto recycler" also known as the local junk yard for used 3G alternators. MUCH cheaper.
New User
Joined: Jun 2009
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Simplest alternator test is to start the truck, then disconnect the positive connection at the battery.
If the truck dies your alternator is not providing a proper charging.
If it continues to run, increase the electrical load on the alternator by turning on head lights, AC, etc... If you load the alternator and the truck continues to run, your battery is not holding a charge.
The battery is only required to start a vehicle, then the alternator provides 100% of the required electrical load AND charges the battery for the next start.
If the truck dies your alternator is not providing a proper charging.
If it continues to run, increase the electrical load on the alternator by turning on head lights, AC, etc... If you load the alternator and the truck continues to run, your battery is not holding a charge.
The battery is only required to start a vehicle, then the alternator provides 100% of the required electrical load AND charges the battery for the next start.
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Former Vendor
Joined: Mar 2009
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From: Westford, MA
Make sure the battery terminals are clean too,and that the cables aren't corroded or anything.
If the battery looks pretty old.I'd probably start there and buy a new one.
If the battery looks pretty old.I'd probably start there and buy a new one.
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Thread Starter
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Fleet Mechanic
Joined: Apr 2008
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From: Vancouver BC Canada
Thanks for the replies. Yes, I think I'll replace the battery regardless. I'd rather be certain of its condition and lifespan.
When you do test a battery though, do you literally put a multimeter probe on each terminal, or will that give a nasty shock. Electrical is definately my weak spot.
When you do test a battery though, do you literally put a multimeter probe on each terminal, or will that give a nasty shock. Electrical is definately my weak spot.
New User
Joined: Jun 2009
Posts: 8
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You can check the battery voltage by using a multimeter across the neg and pos terminals. Make sure the meter is in DC mode and it does not matter if + or - are reversed. The value will be the same regardless, but it will result in + or - readings. Won't hurt the meter.
If the truck is not running, this will tell you the voltage available in the battery. If the truck is running it will tell you the amount of voltage the alternator is producing.
Removing the positive cable as I described above will tell you where the problem is occurring, battery or alternator.
Cable condition is critical and these notes assume they are not the problem.
If the truck is not running, this will tell you the voltage available in the battery. If the truck is running it will tell you the amount of voltage the alternator is producing.
Removing the positive cable as I described above will tell you where the problem is occurring, battery or alternator.
Cable condition is critical and these notes assume they are not the problem.
New User
Joined: Mar 2010
Posts: 2
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I too live in Canada with a 92' flareside... same exact symptoms.
Due to age, and recent testing I have already replaced...
- Alternator (2 times, one due to bad rebuilt)
- Battery
- Solenoid
- Confirmed all grounds and battery connections (good, clean and tight).
Curious about this possibility of low rpms, how do I confirm while in drive?? I have been driving my "mech" nuts with this problem, seems electrical... other symptoms I seem to get and noticeable is if you have your turn signal on, off course with heater (which seems to have the most draw in stages as you set it to high) the signal click seems slow then tap the gas and all of sudden it clicks normal.
This rpm thing might be my issue.... hehe I hope!!
Due to age, and recent testing I have already replaced...
- Alternator (2 times, one due to bad rebuilt)
- Battery
- Solenoid
- Confirmed all grounds and battery connections (good, clean and tight).
Curious about this possibility of low rpms, how do I confirm while in drive?? I have been driving my "mech" nuts with this problem, seems electrical... other symptoms I seem to get and noticeable is if you have your turn signal on, off course with heater (which seems to have the most draw in stages as you set it to high) the signal click seems slow then tap the gas and all of sudden it clicks normal.
This rpm thing might be my issue.... hehe I hope!!
Posting Guru
Joined: Aug 2006
Posts: 1,049
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From: Perry Georgia
Just testing your batteries with a multi meter will tell you what the voltage is but you need to have it tested with a load meter. That will tell you if the battery will hold up under a load.
Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
Sears will load test a battery for you.
Posting Guru
Joined: Aug 2005
Posts: 1,069
Likes: 1
You can check the battery voltage by using a multimeter across the neg and pos terminals. Make sure the meter is in DC mode and it does not matter if + or - are reversed. The value will be the same regardless, but it will result in + or - readings. Won't hurt the meter.
If the truck is not running, this will tell you the voltage available in the battery. If the truck is running it will tell you the amount of voltage the alternator is producing.
Removing the positive cable as I described above will tell you where the problem is occurring, battery or alternator.
Cable condition is critical and these notes assume they are not the problem.
If the truck is not running, this will tell you the voltage available in the battery. If the truck is running it will tell you the amount of voltage the alternator is producing.
Removing the positive cable as I described above will tell you where the problem is occurring, battery or alternator.
Cable condition is critical and these notes assume they are not the problem.
New User
Joined: Jun 2009
Posts: 8
Likes: 0
Yes, I should have said this, but I thought it a safe assumption he was not. Otherwise, he would probably not be asking these questions.