1999 F150 5.4L XLT 2wd

Ive been noticing that it takes a few extra seconds to start after the truck has been driven, engine is hot and it sits for about 2-3hours. I havent noticed any problems on quick start and stops when hot. Normally after its sat for a couple hours... Not easy to reproduce, but seeing a pattern.

Sometimes i turn over for a few seconds, wait a few seconds, then on a second try it starts fine.

-By slow start, i mean longer start...startup is strong, but taking extra few seconds...
-First noticed this about two years ago, but only happens now and then.
-Always starts after sitting all night or all day.
-Only notice if engine is hot, and has been sitting for a couple hours.
-Truck ALWAYS starts...has not left me. Just notice a slower/longer start.
-Truck runs fine once started.

I was thinking fuel pump since its original, but thinking its temperature related have not replaced.
(But may put it on the list...just because its easier to do this over a weekend, then on the side of the road)

Considered voltage issue, but battery seems strong...good voltage on startups.
(I have not checked voltage at relay or pump...so intermitant that not sure it would show up)

My first guess, because ive had a similar issue on Honda's, is a sticking fuel pump relay? It is located under the hood, near the firewall...and i guess the higher temps and sitting could cause it to stick. Like i mentioned, i had a Honda Civic and Odyssey both have fuel pump relays stick and cause similar situations.

At this point i've not changed any parts...
Didnt want to start throwing money at it until i had a better idea of whats going on. But with my son driving it now, i would like to fix it.
Ive explained this situation to him and he has reported that its taken a little longer to start a few times, in the same situation. Last night he went to a friends house for about 2-3hours, and noted that it turned over a few extra seconds before starting....then fine. But even after sitting in a hot parking lot all day at school, it seems to start fine. So not outside temps, but hot engine temps...??

Thanks for any advice...

 

Symptoms are reminiscent of vapor lock that were seen on carb'd engines of yore.

 

That's what i've been told...
Truck was bought new in 99 has never left me in 18years.
(all ive changed is alternator, EGR valve and had the passenger side head gasket leak fixed under warranty)
I've just noticed this over the past couple of years.
But like ive mentioned, with my son driving, I'm just trying to prevent a future break down if something is going out.
But with it only acting up for seconds...weeks apart in this situation, its hard to start changing parts out..haha

If i can put together a short list of possibilities i dont mind throwing a little time and money at it over the weekends...
To see if i can clear it up.

Thinking fuel pump relay first...
if it does it again, maybe the fuel pump another weekend...
etc... Things are easier to change at home than on the side of the road.haha

Again, thanks for any and all advice...

 

Can you hear the fuel pump prime when you turn the key on?

One possibility is leaky fuel injectors, flooding the engine when you shut it off.

Hook up a fuel pressure gauge, how well does it hold pressure when you shut the engine off?