My 2003 F-250 (gas V8) will always start right up when it is cold. However, once it has warmed up, it often will not start. Cranks fine, but not even wanting to start (like someone pulled all the plug wires) and has left me stranded until I wait for 3+ hours for it to cool back down. Doesn't trip the check engine light, but seems to be due to the engine being hot. Any idea what this could be? Thanks!

 

Sounds like a sensor issue of some kind. A bad sensor can cause the PCM to think a hot engine is cold, and cause the incorrect mixture to be delivered to the cylinders. Crank or cam position sensors could fail and cause a no start as well.

Have you scanned for trouble codes? That would be my first step.

 

Thanks Tom. Initially, no codes came up, which was really frustrating. A mechanic told me that he did find a code that indicated that it was something to do with the fuel pump which doesn't make too much sense since it is located in the fuel tank. Any thoughts? Really appreciate your input!

 

Fuel pump could definitely cause this, but of course it doesn't care if the engine is warm or not. Try hooking up a fuel pressure gauge next time it acts up. When it won't start, can you hear the fuel pump run when you turn the ignition on?

I'd find a way to read live data to see what the sensors are showing. An inexpensive Bluetooth reader combined with an Android phone or tablet can show live data with the Torque app. Look for an ELM327 OBD adapter online, they can be had for as little as $20. Won't work with iOS devices, though.

https://www.amazon.com/ELM327-Wirele...=elm327+obd-ii

 

I've seen the fuel pump relay int the cjb go bad. It's solid state so can only. Replace with a new. (Central junction box) that may have been an older model though. You may have the sub (smart junction box) the cab mounted fuse box. When it happens check the power and ground to the fuel pump. If so check fuel pressure. That will let you know quick if the pump is working or not

 

Nope u don't have a sjb I didn't see the year

 

Get you a good OBDII scan tool and look at engine data. I think you can figure it out without randomly changing parts. The codes are not that helpful. What is helpful is looking at the actual data.

for example, if the crank sensor is not working, but has in-range voltage, the ECM might not set a code, because it doesn't have anything to compare to. You would know that rpms are not zero during cranking, but the ECM might believe it's zero. Engine temperature is the same way. If the temperature is wrong, the ECM has no idea how to figure that out. But a person can figure it out easily.

I am also a big fan of measuring fuel pressure. You might need to consider whether you have boiling fuel/ vapor lock.

 

Thanks for all the comments. Turns out, it was the fuel pump. Replaced that, and now it starts every time! Apparently, this is a fairly common issue...