# 2000 Navigator altternator output low in drive, normal in park?



## Drachenfire (Jun 6, 2017)

It is possible the accuracy of that in-dash gauge is off. 

I recommend you get a decent volt/ohm meter and test the alternator output at its terminals.

A good meter can be found at big box stores or online for as little as $20-$25.

For a little more, you can get a better quality meter.

Home Depot has a Klein tester kit which includes the multi-meter, non-contact voltage tester and receptacle tester for $40.

Hint hint - Christmas gift.


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## Oso954 (Jun 23, 2012)

If I got the numbers correct, you are dropping from about 800 rpm in park to about 620 in gear. Without knowing what engine it is, that 180 rpm drop seems a little on the high side. The rpm was also jumping around more than I like to see. Don’t know how many miles are on that engine or how warm/cold it was.

But the bottom line is low alt output at extreme low rpm is pretty normal. How much time do you spend sitting in traffic in gear foot on brake ? If not a lot, it won’t hurt you. And you can always shift to park or neutral, some folks do it at stop lights.

Without trying to locate a multitude of answers as to why the rpm drop is what it is, one answer would be to put an over drive pulley (smaller diameter) on the alternator. That would boost alternator rpm enough to produce the higher voltage even with engine rpm around 600.


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## Bigplanz (Apr 10, 2009)

Oso954 said:


> If I got the numbers correct, you are dropping from about 800 rpm in park to about 620 in gear. Without knowing what engine it is, that 180 rpm drop seems a little on the high side. The rpm was also jumping around more than I like to see. Don’t know how many miles are on that engine or how warm/cold it was.
> 
> But the bottom line is low alt output at extreme low rpm is pretty normal. How much time do you spend sitting in traffic in gear foot on brake ? If not a lot, it won’t hurt you. And you can always shift to park or neutral, some folks do it at stop lights.
> 
> Without trying to locate a multitude of answers as to why the rpm drop is what it is, one answer would be to put an over drive pulley (smaller diameter) on the alternator. That would boost alternator rpm enough to produce the higher voltage even with engine rpm around 600.


5.4L, 32-valve engine. 89,900 miles. Englne runs fine at idle, in drive or park. Battery starts the engine, but leave the door open for 5 minutes and it won't start the truck.


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## Bigplanz (Apr 10, 2009)

Drachenfire said:


> It is possible the accuracy of that in-dash gauge is off.
> 
> I recommend you get a decent volt/ohm meter and test the alternator output at its terminals.
> 
> ...


The voltage output numbers come straight from the computer via the OBD service port.


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## Oso954 (Jun 23, 2012)

You either have a big drain with that open door, or a battery problem. 
How old is the battery ?

When was that battery last fully charged by battery charger ?

Has the battery been tested recently ?

You could have have a bad cell in it ?


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## Bigplanz (Apr 10, 2009)

Oso954 said:


> You either have a big drain with that open door, or a battery problem.
> How old is the battery ?
> 
> When was that battery last fully charged by battery charger ?
> ...


 Battery is a year old. Charged and tested it six weeks ago. Tsted good fully charged.


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## ukrkoz (Dec 31, 2010)

Tighten belt. You should be getting around 14V off alternator. Either belt is loose, or stretched or alternator is going south. It's undercharging battery.


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## iamrfixit (Jan 30, 2011)

How did you test the battery? A load test is needed to show if the battery is weak, even then I've had more than a few batteries test as OK and still turn out to be the problem. You get some good ones and you get bad ones, I've had batteries that last 8-9 years and others of the same brand fail in less than a year. 

Only two or three battery manufacturers left in the US and between them they build batteries for all the brands sold here. I always buy super start extreme from Oreilly auto parts. Buy those because I've had good luck with them but mostly because I can buy them through my account and they keep track of the warranty. With about a dozen batteries in my fleet of vehicles, that's one less thing to keep track of. Three year replacement warranty, prorated after that. You can save a few bucks with a one year full replacement but in my experience it's not worth it.


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## u3b3rg33k (Jul 17, 2018)

I had issues with an alternator putting out 11.8V (fresh reman). lower voltage isn't uncommon at low idle, but mine wouldn't clear 12.2V even at 3000 RPM. just a bad voltage regulator.


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## de-nagorg (Feb 23, 2014)

ukrkoz said:


> Tighten belt. You should be getting around 14V off alternator. Either belt is loose, or stretched or alternator is going south. It's undercharging battery.


FWIW, I agree here, loose belt, or wore out pulleys, look into the drive pulleys, if the bottom is shiny, the pulley is wore out, or the belt is wore out, or the wrong belt in the first place. 

And slipping to cause a low output.


ED


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## Bigplanz (Apr 10, 2009)

I am pretty sure the idler pully and tensioner are worn out. Belt too. Gosh, I wish I still had a heated garage. Noise is pretty bad!


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## Bigplanz (Apr 10, 2009)

Here is the alternator charging test I did today.


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## ukrkoz (Dec 31, 2010)

That screeching noise in the background is alternator bearing. Oh do I know it too well! I say your alternator is "getting there". 



_A fully charged battery should read *over* 12.6 volts. The actual *output voltage* produced by the *alternator* will typically be about 1-1/2 to 2 volts higher than battery *voltage*. *At idle*, most charging systems will produce *13.8 to 14.3* volts with no lights or accessories on_

So your alternator should be producing 14.1-14.6V.


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## carmusic (Oct 11, 2011)

it should never drop under 12.6v with all loads on (lights, fan,...) even on idle, on my gm truck at idle i am always over 14v


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## Brainbucket (Mar 30, 2015)

Put a socket on your alternator pulley and see if you can turn it. If you can, either bad belt, tensioner, or alt pulley. If you can't, your good on the drive belt grip. Need to find out what's making that noise. Probably your problem. Stethoscope time.:vs_cool:


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## ron45 (Feb 25, 2014)

I purchased this tool last year from Harbor Freight and I'm pleased with it.


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## ron45 (Feb 25, 2014)

This video seems to be better.


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## Bigplanz (Apr 10, 2009)

Stethescope on the belt tensioner was growling. Got sidetracked on fixiing the drier (bad thermal cut off switch) so the alternator is pushed back to the weekend. Drier works again, though.


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