Sporadic delayed starting

JKERLEY14

MEMBER
2003 FORD F-150
5.4L
V8
2WD
AUTOMATIC
332,000 MILES

Every once in awhile, maybe once a week (typically during times of frequent engine starting, but not always) the engine takes an extra five or so seconds to start up. It is turning over, but never fully catching. If I stop the process when this happens, it almost always starts like normal. Only once has it not started at all (and then about an hour later it did start). So far I've used a 1/2 can of seafoam fuel treatment, a full can of seafoam motor treatment, replaced the fuel filter, and replaced the air filter. It seems to be slightly less frequent, but its still happening.

Other notes:
It has been over 5 years since the spark plugs and fuel injectors were changed. I would suspect a fuel pump or fuel pump relay, but it is hard to diagnose since it is not a consistent problem. Again I would think that if the fuel pump or relay were bad it would be a more consistent no-start condition. Could it also be something with the timing?

I also have an engine stutter under hard acceleration. The transmission shop said it was the rear differential, and the differential shop said there wasn't anything wrong with the diff. Not sure if it is related, but maybe?

What could be causing this?

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Hi,

If it has been this long since you replaced the plugs then I would definitely do this because it is going to cause a hard start at times and hesitation.

Also, if you have not changed them they are probably due to be changed anyway and this is not going to hurt anything if it doesn't fix the issue because they need to be done.

Also, this could be a fuel pump issue. It is unlikely that this is the relay itself because then the fuel pump would not come on at all when this is happening. Also, when you said if you stop and restart while this is happening it starts, this sounds like a fuel pump. I had a truck that did the same thing and the pump was failing.

The way to confirm the pump is to just hook up a fuel pressure gauge to the rail and then just tape it to the windshield so that it is always hooked up and the next time it does it, you can compare the pressure to the times it did not do it. If it is lower, then that is your issue. Clearly this does not have the best look when it is taped to the window, but it is only temporary and you don't have to try to "catch" it acting up. You will already have it set up and all you have to do is watch it.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find and we can go from there. Thanks

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Friday, September 13th, 2019 AT 4:59 PM

JKERLEY14

MEMBER
10 POSTS

I was able to test the fuel pressure a few weeks ago. I found that there was no fuel pressure at the rail after cycling the key to the on position 10+ times. After cranking, the fuel pressure increased to about 30 psi. Once I turned the engine off, the pressure went to zero almost immediately.

This past Friday I replaced the fuel pump and tested the fuel pressure on Saturday. I was able to establish 30psi with the key in the on-position, and after cranking the pressure went up to high 30's, low 40's (I can't remember exactly now). Since then there has been no hesitation on starting up. Hopefully that was it!

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Monday, October 7th, 2019 AT 8:18 AM

KASEKENNY