5.0 Motorcraft Alternator

[C420sailor]

Guys, need some quick help.

Got a 99 5.0 EB. Alternator has a bad diode. Looking to replace it with a Motorcraft.

Rockauto lists two reman alternators from Motorcraft for the 5.0. Doesn’t say the difference, of course. One PN starts with GL, another is GLV. About a $50 diff.

Tried looking up via VIN on Tasca Ford. Yet another part number.

Anyone got a known good PN for a 99 5.0? Thanks.

 

[tinman_72]

I don't know the answer to your question, but personally, if I were buying a reman anyway I would just go to a local parts store. If it ends up being defective it is easy to swap out and no need to deal with the hassle of shipping back and forth.

 

[C420sailor]

I don’t have the funds to buy an alternator from the dealer. Big money.

I could get an alternator from a chain store, but I’d be paying more for Chinese junk than a Motorcraft.

 

[Fix4Dirt]

GL was used on more models, but both GL and GLV fit the 99 v8. GL was used on the v6 sports too it seems and maybe ranger. on FPG i can verify the glv on the v8 on the gl it says unable to verify. if you click more info thats how i see this info. both are 130 amp, so id say maybe the glv?

 

[C420sailor]

Well, I’m an asshole.

The alternator was OEM and was pushing out 31.5VAC, so I figured the diodes were bad.

Ended up getting a ****ing Carquest for way too much money because the Motorcraft was going to take at least a week to come in.

Installed it, still putting out 31.5VAC.

But if I swapped polarity on the multimeter, 0VAC. That shouldn’t be, it’s alternating current.

Turns out, cheap-ish digital multi meters use a ****ty trick to estimate AC voltage, but it only works with a perfect, clean sine wave, like with single phase coming out of a wall outlet. DC voltage muddies the waters and gives erroneous AC readings on them.

In short, nothing was wrong with my first alternator. Fortunately, I kept it—so I’ll rebuild it myself and keep it as a spare. OEM rebuilds are very stout.

I really need to invest in an oscilloscope. It’s time.

 

[CDW6212R]

I didn't know there was a different variation of the 5.0/SOHC alternator, but maybe for the amperage.

I need to find a way to mount a lower amperage alternator into the 5.0 bracket. If anyone has a best idea of how to do that, I'd be grateful. I have a special PhFe4 battery in my Ranchero that cannot take more than 80 amps charging. I figure I might have to modify a 4G 5.0 alternator case to fit an old alternator guts into that, that's my first idea I came up with.

 

[Fix4Dirt]

I didn't know there was a different variation of the 5.0/SOHC alternator, but maybe for the amperage.

base equipment was 95 amps iirc upgraded was 130 i think

 

[410Fortune]

try fitting a gen I 95 amp alternator to the 5.0 bracket?
The 5.0 spacing between the two bolts is much greater, you should be able to make a simple bracket/bridge that will clamp the alt down in place?

heck I have an older 4.0 alternator here and a "few" 5.0 brackets let me see if I can get some pics

what kind of crazy battery are you dealing with here LOL
any way to just drop the voltage down with a resistor?

 

[CDW6212R]

try fitting a gen I 95 amp alternator to the 5.0 bracket?
The 5.0 spacing between the two bolts is much greater, you should be able to make a simple bracket/bridge that will clamp the alt down in place?

heck I have an older 4.0 alternator here and a "few" 5.0 brackets let me see if I can get some pics

what kind of crazy battery are you dealing with here LOL
any way to just drop the voltage down with a resistor?

It's a Dakota Digital battery, 11 year warrantee, but the new technology can't handle high amperage. This one can handle 80 amps, which is more than other similar car batteries. I like it for being able to take long periods without starting the engine, like a deep cycle battery that also can be drained a long way without dying. It was the first made in a normal car battery size, this one a 24F, that bolts into my 73 Ford.

 

[J_C]

Have you actually measured the charge current and found that it exceeded or even got anywhere near 80A? That would seem a highly unusual situation, like you had to jump start it with a dead (very drained) battery and give it throttle right away to make that happen.

 

[J_C]

In short, nothing was wrong with my first alternator.

I'm confused. If there was nothing wrong with the alternator, why were you testing it... bad battery or cable?

 

[C420sailor]

My battery was leaking acid up onto the terminals. I thought the alternator was potentially overcharging the battery, causing it to boil and leak.

Now it’s seeming like the battery is just a piece of junk with leaky caps.

 

[1998Exp]

Well, I’m an asshole.

The alternator was OEM and was pushing out 31.5VAC, so I figured the diodes were bad.

Ended up getting a ****ing Carquest for way too much money because the Motorcraft was going to take at least a week to come in.

Installed it, still putting out 31.5VAC.

But if I swapped polarity on the multimeter, 0VAC. That shouldn’t be, it’s alternating current.

Turns out, cheap-ish digital multi meters use a ****ty trick to estimate AC voltage, but it only works with a perfect, clean sine wave, like with single phase coming out of a wall outlet. DC voltage muddies the waters and gives erroneous AC readings on them.

In short, nothing was wrong with my first alternator. Fortunately, I kept it—so I’ll rebuild it myself and keep it as a spare. OEM rebuilds are very stout.

I really need to invest in an oscilloscope. It’s time.

Out of curiosity, I took my ancient (but trustworthy) Fluke 77 multimeter and repeated your measurement on my '98 V8. It read 0.009VAC (9mVAC). This instrument is not true rms, and measures peak-to-peak, dividing by 2.83 to convert to rms (for a presumed sine wave), most likely same way yours works. Next, I took one of the super-cheap Chinese meters that Harbor Freight used to give away. The lowest AC scale on that thing is 200V, on which it read a perfect zero. So I am wondering whether, by some chance, you read millivolts as volts. To make sure that your instrument is not totally broken, measure your house voltage; it should be about 115VAC. Otherwise, perhaps something is terribly wrong with your battery or battery cables allowing these large spikes from the alternator to register. I was too lazy to drag an oscilloscope to the truck, but may do it next...

 

[1.8TTony]

Guys, need some quick help.

Got a 99 5.0 EB. Alternator has a bad diode. Looking to replace it with a Motorcraft.

Rockauto lists two reman alternators from Motorcraft for the 5.0. Doesn’t say the difference, of course. One PN starts with GL, another is GLV. About a $50 diff.

Tried looking up via VIN on Tasca Ford. Yet another part number.

Anyone got a known good PN for a 99 5.0? Thanks.

The difference will be the shape of the electrical connector for the voltage regulator. Some alternators have D shaped connector, some have a connector shaped more like an oval. The difference in shape differentiates voltage regulator specifications.

The voltage regulator is the plastic component attached onto the back of the alternator. This voltage regulator is secured with four T-20 torx screws.

That being said, why not just replace the faulty diode. Seems like a waste of $$$ buying a complete alternator when all it needs is a $7 diode replaced. If you aren't confident in replacing the diode, you can simply replace the rectifier plate with a new one. The rectifier plate will come with all new diodes installed on it. This rectifier plate only cost $40.