Engine/Transmission (1994 - 1998) volt meter discharging

[jkh]

I noticed that when I am at idle with any load on(ie: air cond, heater,lights, etc. ) my volt meter shows discharge. It goes down real far like to 10 volts. As soon as I start to drive it goes back up to 14.

Is my alternator shot? Can I replace the brushes?Any ideas?

Thanks

Jerry

 

[Skydiver]

Idle too low or one of the 3 phases in the alternator is not working. Normally if a phase is bad it will not reach 14 volts.

Start with the easy stuff first. Raise idle,,,Remove, clean and reconnect grounds.

 

[KYOUNG]

Sounds like Alternator time!!

Just replaced mine on my 98 with 220k on it... ..... 140 out the door at oreillys

 

[jkh]

Idle is good(aboutt 750 rpm in D with brakes on), grounds are clean.

Aren't these alternators rebuildable?

 

[mfburns]

Check the belt. Is it tight? Condition? Easy and cheap place to start.

 

[fest3er]

Use a voltmeter to check for voltage drop across various connections: grounds and positives. Drops in the millivolt range are OK. 1/2 volt or higher? Clean the connection!

If you're going to Spring Fling this weekend and haven't fixed it yet, I can bring my sillyscope to see what the output looks like. Hmmm. I should bring it anyway.

 

[CCiatteo]

Just had mine go out on my 97, local rebuild with all new parts $165. Seemed like a better option than an offshore reman unit. Mine was acting the same way, except no so dramatic. It would slowly come up to 14v, but then after a few minutes of driving drift down and never recover. After checking all the ground, cables etc. , it turned out to be the alt.

 

[Grumpy John 4x4]

voltmeter

Mine has been doing that for 15 years, thats normal!

 

[WilsonF]

Idle is good(aboutt 750 rpm in D with brakes on), grounds are clean.

Aren't these alternators rebuildable?

Yes they are. I had mine done at a local shop, slip ring had to be replaced,cost me $80. As was mentioned in another post, with a reman. you don't know what you are getting.



Floyd

 

[DieselDoghouse]

IMHO skydivers on the right track - you have a 2/3's alternator. If you are gonna test voltages and all that remember this - an alternator should output a constant voltage (within reason) - its effective current will change with engine speed BECAUSE - its frequency rises with speed: it makes a faster AC output that is rectified to DC - unless a diode(s) goes bad. THEN? it all goes to H*LL since for part of a cycle the bad winding dumps its power into the other windings due to the lack of the 'blocking' effect of a diode thats gone south. increasing engine speed helps to "hide" the problem behind the good winding (shorter period where the bad winding bleeds out) BUT…on a test bench the alternator could NEVER meet its maximum rated output (we call it Full Field Excitation). Bad news - most shops won't find this without an ancient tool called an oscilloscope - you can actually see the AC output as peak-peak-poop… These days they just rebuild or replace.

 

[Champane Flight]

Hold on!

Is the intake heater grid cycling? Sounds like it to me... .

 

[Stark_Ent9802]

Hey JKH,

Did you find a solution to your problem? The reason im asking is because I just started seeing this problem on my 98 12v with 215k. Batteries and Volt meter read 12 volts at idle , but at around 1200+ they rise to 14 volts. I am going to check all connections tomorrow. I also just replaced the serp belt a week ago, i guess i'll check tension on that also. Is a new alternator in my near future ???