having problem with my 08 f150 lariat. while driving check charging system warning light comes on and all gauges shut off head lights went really bright and have grinding sound that sounds like hubs trying to lock in. slow down and everything goes back to normal. i pulled alternator and had it checked at 3 different places, they all said it was fine. iv seen a similar problem on forums before but never really got an answer to what the real problem was, anyone got any ideas

 

The alternator sounds like the voltage regulator is failing or it's shorting out. That sounds like high voltage to me if your lights are going really bright. If so I would fix that ASAP before you burn out electronics. You can't see the battery gauge I'm guessing either? The hubs might be locking because there is slight power going to the IWE solenoid as a self test (I believe) and with high voltage it may be partially locking the hubs on you. I can't remember which way the power to the IWE solenoid is however the voltage difference is likely contributing to this. I can tell you vacuum goes through to release the hubs and is blocked to engage.

To me that sounds like the regulator is allowing high voltage if the rpms are high enough or the alternator is shorting at certain rpms (which means it's probably on its way out). A test at shops may not show this properly especially if it's only at certain rpms.

I'd find a way to get a volt meter on there (through cigarette lighter or somewhere) and watch it when it does it. Do you have a multimeter to watch the voltage as you drive and it does it?

 

i will try that thanks, i have noticed when this happens i saw that the volt meter i truck was jumping alot higher than normal

 

No worries, let us know how it goes. If the voltmeter is jumping up as well, that's likely a sign. The two things I could think of is the alternator is shorting, or regulator is acting up... or, your battery is loose (as the resistance drops the voltage). I highly doubt it's the battery because you can slow down (drop your RPMs), and you'd likely have starting issues in that case. Honestly, I think in the end you'll likely be stuck changing the alternator. Just my thoughts from what you've described

 

thanks for the help, i was also told that i may have to take to dealer and have the pcm flashed after changing alternator.

 

not that I'm aware off...

 

I agree with 07_F150_XLT_SCab, I doubt you'd need a reflash. From what you're describing, it sounds still more like a short or the regulator allowing too high voltage.

Our trucks do have the PCM controlled charging (Smart Charging Alternator) but if you needed a reflash I doubt your alternator would be working at all. We changed one on a Focus without a reflash and it worked just fine (brushes were done).