My 2005 GT is giving me some trouble. When I try to start it, it has to crank over for 3-4 seconds before it fires. And sometimes it just barely starts, then sorta bogs and stumbles for a couple of seconds before it evens out. It used to fire really quickly. The strange thing is that once I start it, if I shut it off and try to re-start, it fires instantly. But if I let it sit for a while, it gives me the hard start issue again.
I thought it was a fuel pump issue, but that doesn't seem to be the problem. (Side note: My stock fuel pump crapped out last year, and I replaced it with aftermarket junk. It works ok, but doesn't draw all the fuel from the passenger side tank, and I stall out with 70 miles until empty showing... but that is a separate issue). I pulled the rear seat, and even pulled the pump out, and it checks out. I've tried turning the key to run for a few seconds before trying to start, to prime the system, but that doesn't help. I've also replaced the fuel filter. Once it is running, there are no issues. I can redline it through the gears and it doesn't run out of fuel or spark.

It is strange that it is hard starting after sitting, but will immediately fire if I shut it off and restart it. Any thoughts? Fuel pressure sensor? Crank position sensor? That FPDM thing in the trunk?

Other possible related facts: 1) I just replaced the Mishimoto radiator. I had one in there and it started leaking, so they replaced it. Could I have damaged something taking it out? 2) I have an Edelbrock supercharger on it.

Thanks!

 

There are two possible issues I can think of for you to check out:

1. A faulty fuel pump check valve that's allowing fuel pressure to bleed off at the injector rails.

2. Loose or corroded ground or 12v positive electrical connections in the engine bay.

 

Op, does this happen more often with less fuel in the tank? Like if it's full, does it do it all or not as often/as long? If the fulness of the tank has any impact, it's a pickup tube issue *cracked or not seated all the way) If not, then i'd go with option one above.

 

Looks like it is the check valve with the crap pump. When I turn the key on and off a few times before starting it, it starts just fine. I have my old original pump, so I may just try to swap out the check valve. If that doesn't look like it will work, I'll just bite the bullet and buy a new pump, and this time I'll spend the cash and get the Ford replacement pump instead of the crap they have at the local store...

 

Most electronic parts from auto parts stores, unless they are Bosch, Nippon, or other OEM supplier, are junk..aka store brand like dura-junk. They are one step up from Dorman.