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Thread: Bad alternator?

  1. #1
    Join Date
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    Bad alternator?

    Hey gang!

    Just wanted to bounce a question off the group collective. I am seeing my volt meter flicker around erratically. With the subsequent dimming of lights, hvac blower, etc.

    Would I be correct to assume the alternator is shot? Should I replace with the stock OEM unit or is there a "better"/more durable unit?

    Thanks,

  2. #2
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    Before you replace it put a volt meter at the battery with the engine running and check for atleast 13.5V

  3. #3
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    Same Problem??

    I had an issue ever since owning my car with the volts dropping and spiking like crazy. It wasn't all the time but every now and then and especially when it got wet. When sitting at idle sometimes the volts would drop below 12 with no A/C or lights on to where the battery light would come on. I spent over $2000 having it diagnosed by multiple shops and dealerships with everyone saying the same bull*****. Everyone will tell you it is the alternator and voltage regulator or a bad ground. I left my car at the local ford dealership for a week and told the mechanic to take it home so he could see. He went through the entire car and inspected every ground to be sure none were loose. In the end they could not figure it out. The car still ran great but as you said at night it looked like I was flashing my lights. At its worst the volts jumped from 12-17 up and down like crazy, I thought the computer was gonna fry.

    Long story short I finally skipped the dealers and mechanic shops I took it to an electrical shop, that is all they do. At first they told me my alternator and sold me that, but I knew it was the same old song and dance. I left and sure enough 10 min down the road it started again. I took it back and they sent all day testing all the wire.

    It boiled down to either a wire that runs directly from the alternator to somewhere on the driverside of the firewall and the main computer. The computer was gonna cost at least $1000, but luckily they said the wire from the alternator was not creating a constant current. Somewhere within the wire was a break that was shorting out while driving. It made sense because the problem usually got worse over bumps and stuff.

    I dont exactly remember what the wire was called or went to, but my advice is first replace the alternator to be on the safe side. If it still persist let me know and I will go back to the shop and ask them exactly what the replaced. If I get a chance I will take some pictures. Hope this helps.

  4. #4
    Most likely if the battery light doesn't come on then it's not the alternator. Check all your voltages first.
    FRPP dealer owner of SpartaPerformance.com
    We are an authorized independent AMSOIL dealer.

  5. #5
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    Old-school trick: put something like a screwdriver behind the alternator while the car is running. A good alternator creates a magnetic field that will attract the screwdriver shank to the case.
    '04 Silver Marauder w/ sunroof - HID lighting, JL Audio / Eclipse DVD/NAV/iPod/camera, 4.10's, 2" drop, Progard Bumper Baffle, Delete tips, Billet Pedals, BC4E dead pedal, Lidio Tune, Mach1 chin spoiler, K&N CAI, TCE lines, Super40's, tinted tails, SS Inserts, Heinous Control Arms, Real oil gauge, lighted door handles. Currently installing Eaton M112.

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  6. #6
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    If anyone else has this problem, swap the voltage regulator out for one on the Mustang. It bolts right up and plugs in, but does not use the wire from the computer to control it. This also means it does not cut out at WOT, but will you really miss the .3 HP? I think not.

    The cause is the chaffing of the wiring harness across the back of the motor that can also cause all sorts of weird failures. Mine eventually killed the starter circuit and the computer would reboot causing the tranny to go into neutral (ala MV VII).

    Too bad there are no more looms available direct from Ford.

  7. #7
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  8. #8
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    the regulator you want was used in 2000-2002 civilian crownvics. you need a 4G alternator regulator to swap into your 2003-2004 marauder. a mustang 6G regulator won't physically fit in a 4G alternator.

    below are a few alternator pictures to help you identify the alternator generation.

    Quote Originally Posted by TooManyFords View Post
    If anyone else has this problem, swap the voltage regulator out for one on the Mustang. It bolts right up and plugs in, but does not use the wire from the computer to control it. This also means it does not cut out at WOT, but will you really miss the .3 HP? I think not.

    The cause is the chaffing of the wiring harness across the back of the motor that can also cause all sorts of weird failures. Mine eventually killed the starter circuit and the computer would reboot causing the tranny to go into neutral (ala MV VII).

    Too bad there are no more looms available direct from Ford.
    a 4G marauder alternator with the factory clutch.





    a 4G crown victoria alternator without the pulley clutch



    a 6G crown victoria alternator




  9. #9
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    running a non-pcm controlled voltage regulator in a later ford vehicle that requires a pcm regulator usually results in powertrain code:

    P0622 (Generator Field "F" Control Circuit Malfunction)

    i'm not sure whether the state emissions smog inspection stations can pick this code up or not. or whether you even have smog inspections in your area of the country.

  10. #10
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    i was playing with a recent pcm controlled crownvic alternator and was suprised to find that the alternator charged without the regulator plug connected at all. the battery voltage was 13.4V which is kind of low, but it did charge and the alternator did self excite without any external input on the regulator.

    had you tried unplugging the regulator connector and starting up your car to see what the voltage would be. 13.4V would be a better than the 17V reading which is high enough to damage numerous electronic modules in your car.

  11. #11
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    here's an interesting document about how the pcm controls the alternator regulator:

    http://www.p71interceptor.com/altern...techpoint1.pdf

    and here's some info about a bench tester for these regulators:

    http://www.p71interceptor.com/altern...lternator5.pdf

  12. #12
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    Well I changed out the alternator and a few miles down the road the voltage started floppying around again

    Took it to the local flaps and they tested it and said bad battery. Replaced with a genuine Motorcraft Battery.......and a few miles down the road and the voltage is floppying around again

    I guess I need to start looking around in the wiring.

    John; Can you expand on what happened with your car?

  13. #13
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    if you suspect problems with the wiring harness, i'd just run a couple new wires directly from the pcm to the alternator. cut the old wires a couple inches after the pcm and splice the new wires on. then cut the two genmon/gencom wires a few inches from the regulator plug and splice the new wires on that end.

    the gencom/genmon wires are just signal wires that don't carry any real amperage per say. so lightweight stranded wire like 16AWG or 18AWG should be good.
    Last edited by 2vmodular; 05-12-2010 at 07:59 PM.

  14. #14
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    Had a few minutes to look at the wiring today. With the Trilogy kit I had to extend both wires to the alternator. I checked the wires to the plug and I used crimp-connectors on those. One of the connections came apart with a gently tug I re-crimped it, so we will see if that solves the problem. I plan on soldering the wires this weekend. Stay tuned.

  15. #15
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    a little offtopic, but have any of you marauder owners tried upgrading to the 200amp police interceptor alternator?





    this unit has an overrunning clutch like the original equipment alternator in your car does. and it's a lot higher output which would be good for people with an aftermarket high power stereo system.

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