Hello all. First and foremost, I wanted to thank this entire community of Ford truck experts, enthusiasts, and owners. I have found many fixes to many ford truck problems over the last 13 years. I have owned 2 thus far in my lifetime, and generally do all my own repairs.


Now, lets get to the important part. I have got an issue that I can't seem to resolve. I'm actually considering throwing in the towel and taking my rig in to the shop to have someone else chase this problem out. I'll start from what I think is the beginning....


My patient is a 1997 F150, standard cab, short bed, 4x4, manual transmission, 4.6 liter v8 (vin code 6). ~215,000 miles on her.


A few months ago, I pulled the whole engine out due to a blown head gasket on the passenger side engine bank. I brought the heads to a local guy to check them and get them cleaned up. Replaced a whole bunch of things while I took this project on. I had the flywheel resurfaced, new clutch, new timing chains, etc etc.....


Well, ever since I have got it put back together, I can't seem to get the alternator to function properly. It tests fine at local automotive shop. Puts out 14+ volts upon initial startup. However, once the truck warms up or is driven a few miles, things start to fail. I have intermittent flashing of the battery light on the dash. Headlights dim and bright intermittently. If I drive far enough, the truck will eventually deplete all stored power in the battery, and then it won't start back up. I have replaced the main leads (both positive and negative) from the battery to frame ground, starter, main fusible links. The 20 amp fuse below the fusible links tests out fine. I also get appropriate voltage at the alternator harness when I check it with the ignition switch on. If I run a jumper wire from the negative battery terminal to the ground test at the back of the voltage regulator, it will immediately kick in and start increasing charge voltage until I remove it.


Can anyone please give me something else to check? I hate admitting defeat, but I'm close to throwing up the white flag here.

 

I don't put a lot of faith in those places that test them. You can take your multi-meter and adapt it to a plug for the cig. lighter so as you drive you can watch the voltage. When that light flickers you should see a drop in voltage. Perhaps a sporadic diode in the alternator? If all the cables and connections are good it would (in my guess) have to trace back to the alternator.

 

Your right on top of the problem.
The regulator on the back of the Alternator is what controls the Alternator field winding to output current to the battery..
You have a marginal intermittent that causes the regulator to have an issue controlling the Alternator.
The intermittent charge light on the dash tells you the alternator has stopped outputting and the regulator applies a ground to the charge light to light it telling you the alternator has stopped outputting.
Of course the lights will dim as the voltage drops for any reason.
A ground, the regulator, the plugup connection or even the alternator brushes could be the problem.
Your just missing it.
I would replace the Alternator just on age and mileage alone for no other reason. It is showing it's heat sensitive.
Good luck.

 

I have a Tekonsha P3 brake controller mounted on the truck. It has a diagnostic view that allows me to monitor vehicle voltage in real time as I drive. I do like the cigarette lighter idea though for future diagnostics on other vehicles.

After racking my brain all weekend on this, I finally have had enough. I dropped the truck off with an automotive electrical specialist yesterday evening. I'll keep everyone posted with findings so maybe it can help someone else in the future.

 

Ok...Here is the low down:


After dropping my truck off at the mechanic (this was a SERIOUS blow to my pride), He couldn't find anything wrong with the truck. He was convinced that the alternator had a problem with it. The alternator was a lifetime warranty remanufactured product, from an auto parts chain store that will remain unnamed. He told me to swap it out for a different alternator. I was skeptical, due to the fact that the one that I had on the truck had bench tested with positive results. Well, I followed his advice and begged them to swap me for another one, even though it tested fine. Brought it home, installed it on the truck, fired her up, and BOOM! 14.5 volts! I took her on an hour long joyride and never experienced any problems. I am pretty confident in saying that the alternator was the problem the whole time....even though it was a "new" remanufactured part.


What a frustrating ride this has been.....I'm just glad that I seem to have found a solution.

 

Good to hear you have the issue cleared.
It has happened before that the test procedure misses a fault.
The store can only go by what they have to use.
It pays to know fully how the system works then one can analyze the symptoms and hit it right on.
Good luck.

 

Glad you got it. And thank you for getting back to us with what it was. I can't even count the threads I am in and the OP never replies or comes back with what they did. No one learns that way.

 

The other day my battery light came on. My voltmeter showed good on the dash, but the light came on for a reason. I checked the battery and it was 14 something, but the line side of the mega fuse shows only 12.2. At 250k miles I think that time has caught up with it, and to save time I will start with this.

 

EX Limited, always start your own thread, please.
At 250k you need to replace the alternator and have battery capacity tested.
You very lucky the alternator lasted this long.
Good luck.

 

This doesn't need a new thread. I'm agreeing with Hog Bandit that given these circumstances it is usually the alternator.

This isn't the original alternator either. I talked to the previous owner (Dad) and he says that he had it done years ago, but doesn't remember the exact year.

 

REALLY!
EXCUSE ME!

 

No need to shout. I'm sitting right here.