2008 f150 STX with a 4.6 liter engine. I’d turn the key and nothing happened except the sound of the starter relay clicking once. Battery good. Starter fuse good. Starter and PCM relay good. Had voltage to the bottom slot where the relay plugged in. Had voltage to the right slot where the relay plugged in when I turned the key to start. When I jumped the top & bottom slot with a piece of wire the starter would turn and the truck would start. As for the left slot the relay plugs into, I’m not sure how to establish wether or not the PCM is providing ground for it, but it seemed that was the issue. I replaced the neutral safety switch and the problem resolved with no further issues for a week. When I got in the truck to go to work a week later, same problem. Turned the key. No crank, no start. Could hear the starter relay click each time I turned the key. Battery still good. All relays and fuses still good. I jumped the starter relay to get to work. It wouldn’t start when I got there, but two hours later it started without issue. I ran a short errand and it started twice more with no issue. The next morning when I left work, same issue. No start, no crank. Battery still good. Everything else unchanged. I jumped the relay to get home. Stopped somewhere on the way home and had to jump it once more.It started without issue after I got home. Four hours later I got in the truck to go to town. Same issue. I jumped the relay. Once I got to town I turned it off &:started it back with no issue. Got home & started it twice more over two hours’ time with no issue. I have a sneaking suspicion it won’t start without jumping the relay tomorrow morning. I’ve read every forum thread and watched every YouTube video I could find on the subject. Still scratching my head.

 

If you have not already done this, I would make sure that battery terminals and connectors are absolutely clean. Even a light film on the connection between the terminal and the cable can cause intermittent problems. Clean them spotless.

 

It probably is the ignition switch mounted on top of the steering Colum behind the lower part of the instrument panel
They have a tendency to come apart thus causing an intermittent no connection in the start circuit

 

One thing to try when it won't start is to shift the transmission into neutral and then see if it turns over.

 

Take a look at the attached wiring diagram from a 2007. If you are able to jumper contacts 30 to 87 on the starter relay and get the truck to start then the problem likely lies up steam of the relay or it is the relay itself. Always measure voltage with the ground side of the meter attached to a known good ground. Keep in mind that this is an intermittent problem and therefore problem may or may not be present when you test. First check fuses F101 and F102, pull and inspect. Pull and reinsert multiple times to refresh the contact surfaces. Check for voltage across (both sides hot)
With key in Start do you have 12 volts at slot 86 of the starter relay?

If No, problem lies upstream of that point meaning it’s the ignition switch, digital transmission range sensor a broken conductor or a bad connection. My guess is a bad (corroded) connection at the DTR. In any case work your way back through the circuit until you find the problem.

If Yes, then problem is the relay, BCM, broken wire or bad ground in the BCM circuitry. If you live in the rust belt corrosion of ground points will lead to all sorts of weird electrical issues. I would check the grounds located behind the plastic kick panels at the driver's and passenger's feet area first as these are problematic in the rust belt.

I am sure others will chime in and we will get you a solution to your issue.

 

Opps, wrong posting

 

I’ve had this issue on a few vehicles, look into your starter it’s self. Sounds like an intermittent ground issue. I’ve had this happen just recently on my wife’s suv. Everything worked, would start and run. Then wouldn’t. Replaced the starter itself and it fixed the problem. Always check engine codes if they show. Starters will not appear on dtc though.

 

I forgot to update the thread when I figured it out. The wiring harness had gotten wedged between the right rear corner of the engine block & the firewall, and the coating on several wires had melted causing the intermittent ground issue. Eventually the intellistart wire (I believe it was yellow with a green stripe) had melted to the point that it was continuously grounded against the engine block. I had to remove the front right wheel & fender liner before I found the issue. I repaired each affected wire, wrapped that section with tape, and tied the harness up so it wouldn't fall back down there. Haven't had anymore issues since then. The intake manifold had been replaced the year before, and I believe that's when the harness wound up being displaced. Thanks for your reply.

 

SiskCFRN,

Many, many of the posts in this forum (and others) are open ended. Problem stated, solutions suggested but no closure. Thank you for posting feedback that allows future readers to understand and consider your experience with the issue.
Jimboy