Over the past few months, my 4.2 V6 has gone from always starting instantly, to being inconsistent. Starts right up when hot; i.e. after filling up with gas. Takes a second to start when cold. When warm, it can take 2 seconds or so. Once started, it runs fine. I've visited forums for starting issues, and nothing seems to fit my symptoms. Have done the normal things; changed the fuel filter, checked the plugs.

I have noticed that if I turn the key to 'run' I'll hear the fuel pump run until it pressurizes the fuel line. After that, I'll hear a brief hiss coming from under the hood. Does anyone know if this hiss is normal, and if it could be related to the starting issue? I've also noticed that if the truck is warm, if I turn the key to run and back off a couple of times, then start, it usually fires up pretty quickly.

I did take the truck in for service awhile back and mentioned the problem. When I picked it up, the service advisor told me that the tech did notice the problem once, and told me that it "could be the fuel pump." I hate the idea of spending the money on a fuel pump replacement on "could be."

 

I would check the fuel pressure and see if you're at spec on the rail. I had a '95 with the 4.9l I6 that had starting issues like what you mentioned. When the truck was cold, or was hot and had been shut down for less than 5 minutes, it would usually start fine. If the truck was warm and had been shut down between say 5 minutes and 2 hours or so, I would have to bump the ignition (fuel pump) 5 times to get it to fire.

I​​​​​​I checked the fuel pressure and it was just over half of what it should have been (30s instead of 60 psi). I think with the lower pressure, the heat in the engine compartment was enough to vaporize some of the fuel in the rail. Either way, I replaced the fuel pumps (it was one of those two tank abominations, one of the pumps was dead when I got the truck, and the other was obviously going) and the problem vanished.

 

Thanks for the suggestion. I've seen a lot of posts where they've said the fuel pressure was fine, but it looks like it's pretty easy to do a basic check. I'll have to research how to tell the difference between fuel pump and pressure regulator problems. I wonder why the shop didn't suggest that they test for that. Again, thanks.