CONative17

All,

I bought a 2006 F150 5.4L Flex (V) 3V engine truck with 175,000 miles. The truck runs great minus some exhaust leaks from the manifold gaskets (will get to this eventually) and inconsistent starts. On occasion, i have to crank the engine over for 5-10 seconds to get it to start, other times, it jumps right up and running.

I have replaced the battery, this seemed to help make it better.... I then replaced the fuel filter, cleaned the MAF, and I removed the throttle body, cleaned it, and put a new gasket in and reinstalled. I performed the reidle learn procedure after the MAF / throttle body clean... but now the inconsistent starts (longer starts) are more common than before (lets say 50% of the time now). The truck always starts after 1-2 5-10 second crank sessions but this has to be hard on the new battery I just put in. Idle seems pretty good, the truck may need new plugs soonish (but haven't tackled that job yet or looked for misfires via torque yet...). I've taken the truck on several longer camping trips and the truck runs great here in Colorado in the mountains, but I would like to get to the bottom of this starting inconsistency.

Any ideas on this? Is there a way with torque app and OBD II to ensure fuel pressure is good to the engine? Next thing I would likely replace would be the starter motor, but is it a common failure mode of them to be inconsistent? What else would be causing this? Is there anything else I can look at via OBD II to help troubleshoot?

Thanks!

needsmoarturbo

If the starter is cranking but the motor doesn't start I don't think your problem is the starter. I guess there could be a rare problem if it's cranking really slowly but I haven't heard of that with these trucks.
Yes you can check fuel pressure with torque app.

Does it always have this problem, or only after sitting a while? Or is it random?
some ideas would be if you have a stuck injector that could leak the fuel pressure out and then it has to build the pressure up next time before it starts. I think you'd see other symptoms with that though like gas smell or diluted oil, etc.
These trucks don't have a fuel pressure regulator they modulate the fuel pump with the fpdm based on ECU demand. It may be possible there is a check valve in the fuel pump that keeps fuel from running back into the tank from the fuel lines when the truck is turned off and it's gone bad. I'm not sure on that though.
Hopefully someone else will chime in with ideas.

CONative17

Appreciate the comments. That's what I was thinking about the starter, and why I have not replaced it but im a DYI mechanic (mechanical engineer but not in the auto industry). I've wondered if it is a fuel pressure issue due to the pump or the FPDM. I just ran out to the driveway and it doesnt look like the FPDM has ever been replaced (didn't look horrible from the side but the spare tire was still up). I went ahead and ordered a dorman replacement (usually im 100% OEM guy, but $60 vs $195). Ill know by Friday if that helps relieve the issue and i will follow up.

I hope others chime in as well, i want to solve this issue. At the moment, it seems random, I havent been able to isolate warm vs cold engine, low vs. high fuel tank level, or anything else but I can try and start a sticky note with some variables and record when it occurs and what conditions the car was at.

Kyle G.

My FPDM didn't look too bad from the outside when it failed but when I pulled it off the entire bottom (the side against the frame) was completely corroded and circuits exposed. This is a good repair to make even if it doesn't solve your problem (but hopefully it does).

FoMoCoGuy

I had the same issue on my old 2002 Ram 1500. If the truck sat for longer than 30 minutes, I'd have to crank and crank and crank to get it to start. If I'd turn it off and leave it sit for a couple of minutes, it would fire right up. I was told the check valve in the fuel pump was the issue, but I never changed it out to find out. One thing I noticed that helped was turning the key into the on position a couple of times before actually cranking it over. By doing that, it started faster. Also, if I only cranked it over a couple of times on the first attempt, then turned the key back to off position and then tried cranking it over again, it usually started much faster (2-3 cranks). If I just tried to start it cold without priming it, it would crank 8-10 times or more before it fired.