My father in law has a 96 F250, 4x4 with the 460 V8. In recent weeks, after being driven, the truck refuses to start. It acts as though the battery is dead. He's replaced the starter, and today the battery, but it's still doing the same thing. Any help would be greatly appreciated.

 

Have you verified the voltage output of the alternator? Output should be about +13.5vdc with No-Load (nothing on, just engine running) and go up to about +14.5vdc with a load on it (turn all lights on, Hi-beams, fan on HIGH, A/C (if equipped), radio and if possible, have somebody apply the brake lights).

 

Alternator has been tested and output verified, all is good. When the truck sits and cools off, it starts right up. The only things he hasn't replaced are the solenoid on the firewall, the coil and ignition module.

 

Hope this helps some...

Normally a failing coil will break down under heat and cause your engine to sputter and or die while driving and not re-start until it cools down some. A failing TFI module will also tend to cause the engine to sputter and die when hot and not start until it cools down to a certain temp.

When you mention " It acts as though the battery is dead". What is actually happening? Does the engine turn over real slow, or not at all? If not at all, to verify the solenoid, you could try crossing the solenoid terminals when you get the symptom. This would let you know if the solenoid is at fault.

 

Engine turns over slow. But after it sits and gets cold it fires right up. Wondering if it's the computer.

 

Until Use Common Sense gets a chance to get back to you, slow cranking can be caused by high resistance in the starter supply circuit. Make sure the battery connections are clean and if there is any corrosion in the battery cables or where the cables, BOTH, attach to the engine and solenoid. If the starter is original there could be an internal problem within the starter motor. Hopefully that will provide some things to check in the meantime.
Computer does not usually affect starter motor speed.

 

Well, common sense would say read all the previous posts as I stated the starter and battery are both NEW. Both replaced within a week of each other in the past 2 weeks. All connections have been cleaned and checked for tightness. He attempted to bypass the solenoid on the firewall with the same result. Starter turns slow as if battery is low when the truck is warm, starts up after sitting for a few hours of sitting and cools off.

 

If you can get hold of a digital voltmeter, you may be able to rent one if you don't have access to one, do a voltage drop check of the battery cables. If there is corrosion under the insulation and causing a hi resistance circuit the voltage drop check will show that. Or,,, just because a part is new is no guarantee it is good.

 

He was originally told the starter was bad so he replaced it. Then because of the way it was acting, he decided to replace the battery. He had the alternator checked with both the old and new battery, checked good and amps were good. We both have volt meters, so I'll have him check voltage from the battery to the solenoid, then solenoid to starter.
Thanks for the help. Merry Christmas.

 

Thank You and Merry Christmas to you also.
Please remember when doing a voltage drop check , the circuit has to be under load and in this case has to be done when attempting to start the vehicle. The fuel pump fuse or the inertia switch can be used to prevent the vehicle from starting. If you are unsure how to do a correct voltage drop test there are many videos on u tube demonstrating the correct procedure. You can do it !