I have a 4.2 V6 and I have recently been having problems with my electrical system. In first through fourth gear if I accelerate if I push the throttle at all my low battery light comes on and my battery gauge goes crazy. If I have my lights on then my brights switch on. Once I let off of the gas and the RPM's settle back down to a cruising level then everything goes back to normal. At first I thought all of this was just because of a bad battery but my battery died and I replaced it and I am still having the same problems. I had my alternator checked and it is running fine. What else could this be? Has anyone ever heard of a problem like this, it is driving me nuts. It doesn't seem to affect performance, but I would like to be able to accelerate like normal again and not have to worry about breaking something. I would appreciate any help, thank you.

 

Remove, check, clean, and reinstall the ground battery cable where it attaches to the engine block. Don't just tug on it and call it good. They sometimes get loose there and cause very strange intermittent problems like the one you are describing. It's a dirty job but it NEEDS to be ruled out. Old, badly corroded battery cables might also cause your problem.


Not as common but worth a look - check the belt that drives the generator. It should be just tight enough that you can not turn the generator pulley by hand with the engine off. I once had a very loose belt that would charge ok when the car was at idle but when the engine sped up the belt would slip and the voltage (on the dead battery) would fall to 8-9 volts.


Next I suspect your voltage regulator. They should have checked it with the generator if the check was done on the car. But you can do a quick and dirty check yourself. Do you have a volt meter? Even one of those 15 dollar specials will work fine. With the car off, check the battery voltage at the terminals. Then check the voltage at a low idle. Watch the voltage as a friend slowly brings the engine speed up. A charged battery will have about 12.5 Volts (engine off). At idle the regulator will cause the generator to charge slightly higher around 13 - 13.9 Volts. As the engine speeds up the voltage should climb a bit (14 - 14.7 Volts) but not much. A bad regulator will sometimes allow the voltage to climb up to 16, 17 volts or higher. If it fails, it will usually fail completely and you will see either no charging or overcharging. A voltage much higher than 15 will begin to overcharge your battery and will begin to boil the water out of the battery - leading to a very short battery life and risk your engine electronics.

If it is not one of the above I would start cleaning all my wiring connections at the generator, battery, etc and then start looking for electrical wiring shorts that happen under acceleration.

Good Luck

 

Well I appreciate all of your ideas. But, unfortunately the problem was bigger, my alternator burned up. It would register completely fine one second then it wouldn't even run the next. But everything is taken care of now and back to normal (except for a burned out pair of brights). Thank you for your help!

 

Yes i have 2000 F-150 with the 4.2 5 speed and i have been having a lot of problems with my Ele. system toothe gagues and light on the dash go off and go crazy when i hit a hard bump it is in the fuse panel under your left leg the fuse panel is a joke and the small fuse are bad they get loose and do not work right htis is a bad problem with this truck from Ford

 

Thanks for the help, i checked the fuse box and it turns out i had blown that particular fuse. My brights are up and running again. Thank you everybody for your help!