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Juan Crespo
Juan Crespo, Tech Trainer
Category: Mercury
Satisfied Customers: 1524
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a 01 Mercury Mountaineer with the 5.0 that I am on

Customer Question

I have a 01 Mercury Mountaineer with the 5.0 that I am on the second alt. Start 1 time and its not charging. Start the next time and its charging at 15.2 and the headlights are pulsing.
Submitted: 10 months ago.
Category: Mercury
Expert:  Juan Crespo replied 10 months ago.

Hi there.

That sounds like an internal regulator problem. Before installing the next one, check the wiring; Yellow/White and Black/Orange should have voltage at all times; Light Green/Red should have voltage only when the ignition is on. If those are OK, check engine ground for any possible voltage drops. If all checks out OK, then I would advise getting the next alternator from a different source.

Customer: replied 10 months ago.
only 2 wires on plug. yellow/white and green/brown
Expert:  Juan Crespo replied 10 months ago.

Should not be that way... (see attached diagram from Ford) What's the VIN?

Customer: replied 10 months ago.
vin is 4m2zu86p31uj05926
Expert:  Juan Crespo replied 10 months ago.

Let me do a little research on that VIN. Be back in a bit...

Expert:  Juan Crespo replied 10 months ago.

OK. Yours is a late production vehicle. These have the computer-controlled alternator, whereas the onboard computer serves as regulator.

Basically, the old alternator burnt the driver inside the computer, so now it needs a new computer (PCM) to correct the problem.

Customer: replied 10 months ago.
Is that a definite or are we guessing at that fact? Want to make sure before spending the money. And after installation, does it have to be flashed?
Expert:  Juan Crespo replied 10 months ago.

This issue can be easily confirmed with a NGS tester or equivalent scan tool capable of reading that PID.

The PCM would need to be configured to the VIN in order for the security/anti-theft system to work.

Best Regards.

Expert:  Juan Crespo replied 10 months ago.

I have to log out for the day. I’ll be back online ready to continue our conversation tomorrow from 2 to 8 PM EST. Please contact customer service at http://ww2.justanswer.com/help if you need immediate assistance.

Customer: replied 10 months ago.
Before I put in the ecm, why would this new alt pulse the lights when it is actually charging? When its not charging, the lights are steady and bright.
Expert:  Juan Crespo replied 10 months ago.

An alternator puts out current, not just voltage or amperes. Current is measured in Watts (Watt = Amp X Volt), which is how electrical loads are rated. For example, a starter motor that pulls 60 Amps is actually pulling 720 Watts from the battery (720 Watts = 60 Amps X 12 Volts) As the bad driver in the PCM is erratically exciting the alternator windings, it starts producing erratic amounts of current, which in turn make the electrical loads act erratically as well (lamps will get brighter and dimmer, motors will speed up and slow down, etc.)

In reading your posts, I get the impression that you are not completely convinced of my diagnosis. I understand that, but you also need to understand that Ford designed this computerized charging system to be diagnosed using specialized tools. So, the only way I could tell you what the problem was without any doubts, would be if you had access to a NGS/WDS or equivalent scan tool so I could guide you through all the correct diagnostic procedures. As is, all I can do is offer you my knowledge and experience.

Best Regards.

Customer: replied 10 months ago.
why then would the yellow/white wire show 12v and it charges and when it show 5 volts it doesn't?(koeo) That is why I am questioning the pcm replacement. And I am on this site because you are supposed to be the experts. I understand I don't have 20,000.00 for a ford scanner.
Expert:  Juan Crespo replied 10 months ago.

Please allow me to clarify that experts on this site are mostly OEM Master Technicians who have had OEM training and follow diagnosis and repair instructions set forth by the car manufacturers. In other words, being an expert does not mean we know how to diagnose and repair vehicles without using the correct tools.

Back to our Mountaineer, your mention of the Yellow/White wire makes me wonder if we're even talking about the same system. Could you look at the attached diagram and tell me if that fits the vehicle you're working on?

Expert:  Juan Crespo replied 10 months ago.

Here is that diagram.

Customer: replied 10 months ago.
No. The plug on the alt only has 2 wires. Yellow/white(large) green/brown(small)
Expert:  Juan Crespo replied 10 months ago.

OK. Then it's the one I'm attaching now. In which case, it is not computer controlled - PCM has nothing to do with it.

In this system, the Yellow/White wire is fed from the 30A Alt fuse in the Battery Junction Box and is supposed to have full voltage all the time. If you have fluctuating voltage there, check the fuse and the junction box to see if the connections are clean and tight. If all of that checks OK, then there is a problem with the internal regulator in the alternator.

In some cases, a bad battery will cause similar symptoms. Make sure the battery is load-tested and fully charged before connecting the new alternator.

Please let me know what you find.

Expert:  Juan Crespo replied 10 months ago.

Here is that last circuit diagram.

Customer: replied 10 months ago.
Fuse test good. Battery has been load tested multiple times. All test are above 10.85 volts. So what you are saying now is we have yet another bad alt? Meter isn't fast enough to catch fluctuations, but the lights do when it is actually charging. Does not always charge when truck is started.
Customer: replied 10 months ago.
The yellow wire has one time battery voltage and others around 5 volts
Expert:  Juan Crespo replied 10 months ago.

A battery that's fully charged will have 12.6 volts across the posts after a load test.

As shown on the diagram, the Yellow/White wire comes out of the battery junction box and should have 12 volts.

Do you have access to a Volt and Amp Tester (VAT) that could tell us what the charging rates are with different loads on?

Also, do you know the vehicle's service history that could tell us more on how this happened?

Customer: replied 10 months ago.
I could but after initial start, it doesn't charge. Will attempt tomorrow afternoon. Will get with you then.
Expert:  Juan Crespo replied 10 months ago.

Just thought about something; how about running a jumper straight from battery positive to where the Yellow/White wire connects to the alternator? Can you try that and see what happens?

Expert:  Juan Crespo replied 10 months ago.

I have to log out for the day. I’ll be back online ready to continue our conversation tomorrow from 2 to 8 PM EST. Please contact customer service at http://ww2.justanswer.com/help if you need immediate assistance.

Expert:  Juan Crespo replied 10 months ago.

Hey, man. Just wanted to check and see how you were doing with that Mountaineer.

Best Regards

Customer: replied 10 months ago.
Friend from dealership came over and the wire under fuse 30 in fuse panel was frayed causing voltage drop causing alt to not charge. Repaired wire and works fine.
Expert:  Juan Crespo replied 10 months ago.

Thank you for taking the time to give me feedback on this thing - it was certainly one of those I don't hear about everyday.

I hope the jumper I asked you to run helped you and your friend diagnose the issue.

I'm very glad you hung in there and got that puppy fixed!

Best Regards.

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