Just the other day, my 5.4 (1999 F250SD 4x4, 5-speed) started to take longer than normal to start. It used to be instant, and now cranks for a short period before starting.

I suspect some sort of problem with a cold engine temp sensor, so extra fuel is not being delivered during cranking to ensure a quick start. (When the engine is hot, it seems to start right up.)

But that's a generic thought as I don't know much about the Ford system. I just suspect the fuel injection is not doing what it should when it simulates a carb choke...i.e. fuel mixture isn't rich enough during cold starting.

Any thoughts on where to start troubleshooting?

 

Don't take this as the gospel but it does seem the fuel supply is slightly problematic. It might be best to do a fuel pressure test at the test port for this check. Your fuel pump, filter or regulator could each be the problem.

I'm speculating when restarting the already-warm engine there is enough residual fuel pressure available, that its not leaked down over a longer cooling down period such as overnight.

Please let us know what you find---could help others too!

 

Thank-you for your reply. I do believe you've hit the nail on the head. The fuel pressure is likely dropping off when the truck sits overnight.

I think I have eliminated the sensors as a problem. The cylinder head temperature sensor also feeds the temp gauge (as well as the computer), and the gauge is is working fine. SO I believe it's OK. (My book says one has to remove the intake manifold to change it,... that seems hard to believe!)

I tried disconnecting the Air Intake Sensor (to fool the computer into thinking it was really cold outside and maybe richen the mixture) and the truck started immediately. I then took a resistance reading of the sensor, and got about 24 Kohms, which form the specs I can find on the net, is just where it should be for outside temps in the high 60's.

I then plugged the sensor back in, and the truck started up immediately again. So that didn't tell me too much, other than the sensor appears to be fine at this point.

So it now looks like it's taking time for the fuel to build up pressure (as you said). I'll be checking out the fuel pressure next. With all the tools and test equipment I have, the one thing i don't have is a high pressure fuel pressure gauge. So I'll either make one from a well pump gauge, or maybe bite the bullet and buy one.

If all else fails, I'll take it to the Dealer. So I expect a report back will eventually happen.

The only reason that might delay things, is if the problem is intermittent. I might have to wait until it happens all the time, or gets worse.

Thanks again for the reponse.

 

Just a follow-up. Pressure was dropping over night due to a tiny, tiny hole/crack in the fuel filter. Hard to tell as it was rusty...and wet.

Problem seems fixed now. Cheaper than a new fuel pump (which is what I thought it was... one-valve leaking, or that sort of thing)