I have a 1999 F150 4.6 and I don't remember this ever happening before. When I start the truck both the tach and speedo go to max setting, then drop to 0, then tach shows correct idle speed of about 650. It's like the system keeps having to reset itself. Anyone ever have this issue?

 

I have heard this can be caused by a bad battery. Might want to check it.

 

battery is on its way out..

 

First signs of a battery going bad. Replace it soon or you may get stranded.

 

thats what my battery did when it was shot and it was time to get a new one.

 

Thanks guys, I had a suspicion it might be the battery but truck starts up good. Guess only true way to tell is do a load test, been meaning to get one of those from harbor freight.

 

go to a parts store, they do 'em for free