I'm stumped. My '92 F150 5.8L had the alternator replaced last year. The battery (Die Hard Gold) is about 5 years old. The truck starts up fine but has intermittent charging while running. It gets 12.45 volts while stopped and between 12.75 and 14.55 while running. This just started a couple of days ago and I'm not sure what needs fixin'. What do you guys think?
Thanks for any input.

 

Thats a good battery but its on the downside of its life. You might want to see if you can have it load tested. Sears charges $$$ to test up here.

Also, clean up your grounds.

 

do all of the above and check your belt, it may be slippin, i had a simialr problem, it was where i shined up everything unger the hood and go too much on the belt and it made it slip

 

Is this is your alternator...Big pulley with fan blades on the outside and two big plastic electrical plugs going into it, and bought at Pep Boys, Oreillys, Autozone or other discount parts store, and came with a lifetime warranty Then just get a new one anyway cause it will strand you soon. I hope not cause then it would be one of the First gen alternators, they were no good. Go to a professional starter/alternator rebuilder and ask for a higher output, 2nd generation alt, with the internal fan and smaller pulley.
Your battery is a senior citizen abot to retire also. I would get the wallet out and go shopping!

PS your voltages are OK, but not great. What is the voltage at engine idle with all lights on, including flashers and heater or AC at full blast with the windshield wipers running????

 

Voltage varies under full load with all accessories going...fluctuates between 12.30-13.45.

hhmmmm?

 

Tiger, I have exactly the same problem. Truck runs excellent for 5 minutes then voltage will drop at stop sign or slowing down to stop. alternator is good and battery is ok. I have checked all grounds to engine and they are good. dhecked codes and only problem is the evp . Evp code appeared 12000 miles ago . I did not fix and will not. If i rev up engine volts will slowly climb to 14.4. If i turn on lights volts dropp to 12. This problem appeared last week after a long wet day in the black rock desert. I suspect we have a loose connection somewhere and it will take time to find.

 

how are you measuring your voltages? The guage is not reliable.

 

Yesss!! That's it exactly. Funny how mine started after a rain storm here too.

 

I'm using a voltmeter to measure...gauge readings correspond. I just double checked the receipt for the battery. It was purchased 5/8/1997! That makes this 7 year battery 8 years old....too old maybe?

 

Heres one for ya,
What if when you crank the engine up,battery guage moves to the red close to 8,idles rough,when put in gear or given gas,guage goes back up and runs fine?

 

Do as Popa Tim suggests.Have a load test on the battery.A defective battery has been known to take out an alternator .I personally don't like to be left sitting with a battery thats 5,6,7 or 8 years old.You should'nt be the least bit upset when the vehicle lets you down,at the most inoppertune time.
Autozone checks them free.Why chance it ?

 

i guess i must live on the edge, i normally run my batteries for 7 years plus. if yu can only get 5 yrs from a battery, maybe you buying the wrong brands. and i live in the land of ice and snow and have never been stranded.

 

The voltages quoted in the first post are fairly normal for a Ford 2nd gen alternator. This alternator cannot keep up with the demands of the EFI, the headlights, and the A/C blower, all at the same time, at an idle speed. This is by design. The voltage WILL drop as the engine slows to idle. The engine will still run just fine at 12.5 volts vs. 14.2. It is only as it starts to drop below about 11.5 that there is an issue.

You can make this better by cleaning up the grounds and dealing with the rather poor plug-in connectors Ford used for the main power feeds at the back of the alternator. One thing I did was to use a dual-post battey and ran a ground from the top post to the frame and block, and a second ground from the side post to the back of the alternator mount.

But if you want/expect a rock steady voltage output under all loads and at idle, you will have to try something like a 3rd gen alternator convesion or one of the big case 100 amp alternators.

 

fefarms, I'm calling my old alternator, i.e. the larger pulley with the aircooling fan just underneath , two plastic plugs, and 65A output a first gen, I have switched to a higher output 95A, smaller pulley internal cooling alt with a plug and two wires.

My truck was built late 91. Did I switch from 2nd gen to 3rd gen or 1st to 2nd? I have forgotten what gen I'm on.

 

If the main output wires connect to a large stud with a nut, it is what I am calling a "3rd gen" alternator. If the main output wires are connected via a plasitc plug, it is what I am calling a "2nd gen" alternator.

The plastic plug was one of the big weak points of the 2nd gen alternator. Do a web search an "Flaming Ford Alternators" to read of others that had their truck burn to the ground because of this issue.