08 expy intermittent Crank No Start

[Justn]

Hey guys new to the forum and could really use some help.

I have a 2008 expedition limited that has a intermittent crank but no start issue. There doesnt seem to be a pattern with the issue it will do it hot or cold. It's my wife's car so naturally it never does it when I am around except yesterday when we are running late for a funeral. I did a couple test before we had to leave and this is what I got. It has fuel pressure at the rail, has crank input, has power to the cop's(didnt verify spark). Using a test light I checked for power at the fuel injectors and got nothing KOEO.

From what I understand with KOEO there should power at the injectors and the PCM switches ground to fire when running. Is that correct on this model? Because what is happening is when the key is turned to run for about 2 seconds I get power to the injector connector then it goes off. Once you try to crank the vehicle you get constant power. That's what's happened when the expy starts. I did the same test and didnt have power at all when it would not start but I was kinda rushed and I'm kinda second guessing myself.

 

[stamp11127]

Welcome to the site.

Start a conversation (go to your inbox) with me, include your email address and I'll send you the wiring diagrams for the engine performance - which include the pcm/injector wiring.

Looks like the injectors get power from the fuel pump circuit. Pcm doesn't detect the engine is running it will kill the fuel/injector circuit.

 

[Justn]

Hey just want to share the fix and give a through description of the problem in case anyone else runs into this issue.

So I will start with the problem. The 08 expedition limited had an intermittent crank but no start issue. When it had this issue it would crank for 10 seconds after the key was released witch is a feature of the vehicle but it feels like the thing is not going to stop and kinda freaks you out. It was completely random. Sometimes you would have to let it sit 10 mins, sometimes 40 before the vehicle would actually start. When it did crank it ran perfectly.

The Fix! It turned out to be the fuel pump motor diode which is located in the battery junction box. Pretty uncommon part to fail and I had to go to ford to get it. Once i suspected the diode I wanted to confirm it so there is one other diode in that fuse box. It is located right above the fuel pump motor diode and it's for the run/crank relay. I swapped those two which would change the problem from crank no start to turn the key and nothing. Took about a day before it did it but I had a confirmed diagnosis to a pain in the ass problem. Part is 10 bucks! Hope this is helpful to someone!

 

[pitdexion]

Thanks for the info. Going to have to remember that as odd as it is. Good find on your part.