I am having a problem with my (2000 F-150 Ext cab 5.4L V8 4x4 AT) not starting. I will give you some back ground as a way to try and explain what is going on.

4-5 weeks ago, Truck seemed a little sluggish starting every once in a while. Slow turning over. Eventually had to be jumped but started fine with a jump. Replaced battery.
A few days after replacing battery Alternator went bad. Probably what was wrong in the first place, but battery was 5 years old so replacing it is no big deal. I replaced the Alternator and battery and the Truck was running fine.
2 weeks ago, began to notice Truck turning over but it didn't seem to crank real strong. I assumed the battery may be defective, but it was still starting so I waited for the weekend to take back to advanced.
2 days ago, I noticed a delay when key is turned to "START" position before starter cranks engine. Thought is was still "defective" Battery no big deal.

Yesterday, Come out in the morning and nothing, ALL lights come on turn the key and here CLICK, A single click not a low battery CLICKKKKKKKK. Almost like a hammer "TAP" down by the starter. So I push it out of the parking spot and attach Jumper cables, what do you know it starts. I go to work, I brought cables and would stop and exchange battery on the way home.

Come out of work and nothing, "Single CLICK" (tap sound). Attach jumper cables and nothing battery is reading 14.2V with cables attached and nothing. I begin the trouble shooting. I have Voltage at starter and relay. Little wire on relay goes from 4.5 volts to 12 volts when key is turned and back. I tried jumping the relay and still the same "SINGLE CLICK", sounds like the starter it hitting the flywheel when it tries to engage. Try moving the shifter to neutral same thing.
The starter is only 2 years old, It was replaced at the dealer when the Overdrive solenoid and torque converter were replaced for check engine light. so I got down to business and started removing it. I noticed that the insulation on the big red power wire is broke and could have been touching the starter body. so I clean it up and fixed it and reconnected. Same thing, SINGLE CLICK or KNOCK whatever it is, it is getting under my skin, So I order a new starter and put it in. New nuts and washers cleaned up the terminals and still. SAME DAMN THING. TAP, KNOCK, TAP every time I turn the key. I have no idea what to try.
I have an ammeter I can put around the wire at the starter. but not sure I will get an accurate reading if it is not working properly.

Any suggestions would be greatly appreciated.

Thanks in advance,

Jason

 

Take a breaker on the crank bolt and turn the engine over by hand to make sure nothing
isn't seized up.

 

i have seen this on two diffrent fords at my shop and i have done everything you have done changed the battery, new starter, new plugs, cables, 4 coils and two new cats and nothing i changed most of them items cause i had to but i really thought that the starter would do it if i figure it out i will be sure to post for you

 

Update!
IT ended up being the Starter Power Cable. The big Red cable coming straight from battery that is always hot. I did not remove it, I simply ran a new 4 AWG power wire from the bottom (HOT 12V) side of the firewall Relay switch to the starter. The Resistance was unusually high on original so I just ran the new wire in parallel mostly because the harness would be too difficult to take apart and try to fish new wire. I did not want to cause any more problems.
There simply wasn't enough current to spin the starter. The starter would engage but not spin, that was the single knock I was hearing.

Wire was $5.99 at Advance Auto already made with 2 eyelets.
New starter was staying in, no way was I going to risk doing that again anytime soon.