Can anyone tell me what the at idle Voltage should be for a 05 F350 6.0? It seems low on my trueck, but no knows for sure in my area(without taking it into a shop). My batteries don't seem to be getting enough charge to restore their health and the parts shop said it may be my alternator.

It checking, at idle I am getting between 13 and 13.5 volts with the AC off. However with it on(I live in Phoenix so that is 99% on) it is about 12.5 avg. The last few days I have had issues starting and I think its cause my batteries have a low charge, but I don't want to simply change em out if the problem is really a bad alternator.

My readings are from my Edge Insight, as well as the Checker Auto tester on my truck while running.

Any help would be appreciated,

-John.

 

I can not remember what my exact numbers where but that seems low. I'm sure someone will jump in here that actually wrote there numbers down.
But I would also make sure you load test both batteries as well.

 

Normal voltages are in the link below.

You are in Phoenix, the land of battery eaters.

1 year life is not bad there..

 

Your voltages are low. Normal is 13.5 to 14.2. You might want to check the voltage at the batteries, just to be sure. Check all of the battery wiring, battery cables and the charge wire from the battery to the alternator. Then get the alternator tested.

You can also have the batteries load tested to be sure, but only after you've taken them out and charged them completely. Charge and test them independently.

 

Batteries in PHX tend to fail well ahead of other regions, from the heat.

So if the batteries are longer than 1 summer old, it can be already dead.

12.5V with AC on, at the early part of a trip while the batteries are being charged from starting is not unusual.

FYI, my brand new (high tech) alternator is pulled down to 12.5V right after starting.

However, if after running for 15 minutes --- or longer, and you are still only seeing 12.5V at over 30mph (1,000 rpm), you got a problem.

Have you tested alternator output.

 

CAN and ARE are two different things. Hence this notion of diagnostics and actually gathering real data instead of guessing.

 

The hard data from my truck with a brand new alternator, load tested batteries (by my Ford dealer), is

12.5V with AC running at the early stages of a trip.

That is hard data.

There is nothing wrong with my charging system --- and I can have voltages go up to 13.5 normal, or as high as 14.2 with a very light electrical load.

That is hard data.


Therefore, from the data as presented, without knowing actual voltages from "static", KOEO / Glow plug on / off, Cranking, running (initial) and after XYZ time, and the actual electrical load in the vehicle;

We cannot conclude this:


By this analysis, my truck has a electrical / battery / alternator problem.

I assure you, I don't.

 

The chart below is directly from the Ford service manual. The OP has below spec voltages while his engine is running with the A/C on. He is also experiencing difficulty starting. He needs to have his alternator checked, and he needs to individually charge and then load test his battery.

 

The service manual test assumes that NO A/C running, no headlamps (unless DRL is on), and no unusual electrical loads.


Under those circumstances, the data you present for engine running shows 13 to 15 volt is normal.


Where in this chart above does it says, "voltage while AC is running"?

It does not.

Unless you made it up.

Show us the text in the manual that specifically tell us what voltage should be with AC running.

Have you considered checking the facts and manufacturer's specifications before concluding that "voltages are low"?


OP is reporting 13 to 13.5 volt against factory spec of 13 to 15V

Therefore, according to your own data, OP does not have a problem. At least -- the problem is not likely in the alternator, yet.


Having said that, the prime suspect is the batteries.

That is best checked using an individual battery load test after they are fully charged.

Because the batteries are in parallel, a weakness in one often is masked by the other.

Running around with bad batteries will often kill the alternator quickly.

 

Wow. I didn't expect to cause such a war. anyway, to clarify my information. At Start with glow plugs likely still on I have seen as lost as 10s(low) and then a few minutes later the voltage jumps to 11.5 or so. After running the vehicle for a bit the idle numbers level out to about 12.5 as I originally stated.

Originally the checker auto did a battery test individually (disconnected each from the truck to test) and the battaries tested ok needed charge, however the health was listed as bad. This is why I inquired about the alternator as it appears to not be providing the voltage to properly charge my batteries.

Given my regular driving is a 10mile 1 way trip, I don't think my batteries ever get a solid amount of time to recharge, except for my occasional weekend drives.

 

Wow I guess you started something as well.

I went out and tested mine for you to compare it to and here are the numbers.

Truck not running and nothing on- 12.7
Key on with glow plugs running, but truck not- 11.7
Right after truck started so glow plugs are still on-- 12.2
After a few seconds of truck running and glow plugs shut off- 14.1
Truck running with AC on- 14.0
Truck runnning with ac on and all light and radio- 13.8

Hope this helps you compare it to.

 

Based on your data -

I believe your batteries are marginal.

The tester only supplies a nominal (far lower than actual) load on the batteries.

Your starter draw alone is somewhere around 3.6kw

That is before glow plugs, FICM, etc.

In PHX, you have 2 choices.

A) get the cheapest batteries out there that will start the car, and then replace them ANNUALLY after the summer (when the heat fries it).

B) get top of the line batteries with the longest warranties and then replace them as needed under warranty.

Quite frankly, one of the most heat resistant batteries out there is Optima AGM batteries.

If you want to do (B), I would do Optima.



Now... it is not a war.

I have watched many people on this site recommend what I feel are unnecessary and costly "repairs".

These are the exact same kind of problems I have fixed with simple things like cleaning contacts, resetting computers, or just by kludging some electronics or the infamous Italian tuneup.

People are doing things like changing out HPOPs, electronics modules, etc. that on my quick look see --- I believe they are not defective.

Often, a code is not a certain / necessary indication of a defect.

It can be caused by a computer glitch.

So --- I like to do very through diagnostics before I conclude something is "broke".


In your case, the special operating conditions of Phoenix summers, high underhood temperatures, is not something that everyone understands.

You can charge your batteries with a charger --- but I don't think that is the biggest problem --- it is the heat killing batteries.

BTW, if there is a small chance your batteries are "northern" batteries rather than "southern" batteries, that is another issue.

Northern batteries are optimized for maximum cranking amps, but die very quickly in high heat.

Southern batteries are optimized for maximum heat resistance, but are lower in cranking amps.

Is there a chance your truck was a northern truck (with northern batteries installed) and shipped to Phoenix?



So get a new PAIR of batteries! Do it now at the onset of winter --- it is the summers that kill batteries where you are.



FYI, I have a perfectly good pair of batteries.

On my worse case condition (glow plugs on, Starting in -40F), yes, read it --- MINUS 40C or MINUS 40F, I have recorded voltages of 9.7 volts cranking with the batteries fully charged overnight.

And I am perfectly fine with that.

 

Your numbers are perfect for a mild weather truck.

I note the 12.2 volt reading after truck started but glow plugs running would have (by some poster) qualified you for battery / alternator testing because it is "below" 13-15V spec!

Needless to say, your truck is showing great numbers.

Assuming you do not use the 4 aux lights, headlights, etc. all the time!

 

I do not live in a mild weather, I live in SW Florida.

 

To me, "not mild" is Phoenix (100F plus temperature)

Or -30F (where I am in winter)