I have a 2001 4.0L SOHC that has been having intermittent hard starts after sitting overnight, where it takes a couple seconds for the engine to catch, before it stumbles, then runs fine. Cycling the key on and off to prime the fuel system doesn't seem to do anything, so I assumed it wasn't the fuel pump, or the engine coolant temp sensor going bad. I took the truck to a shop who told me that the fuel pump check valve was bad. I didn't have time to work on it myself as it was my only vehicle at the time, so I had them change the fuel pump out. The very next morning I had the same issue, to which the shop shrugged their shoulders and told me it would cost too much to diagnose exactly what was wrong since a new fuel pump didn't fix the issue and they couldn't reproduce the problem (obviously not going back there). Fast forward a couple months to now, the truck runs fine except for the hard start but always starts. It leaks a lot of oil out the rear main seal and front timing cover, so I pulled the dipstick to check my oil after not checking it for quite a while expecting to see it low on the dipstick, but instead it was full, and smelled like gas. I'm assuming this means that an injector is leaking while the engine is off, and the computer is compensating while running. Is there a way for me to tell which injector is leaking? The truck comes up to operating temp for about 20 minutes of highway driving every time I take it to work, so should I drive it and hope that it burns off the gas in the oil until I get this fixed?

 

How many miles are on your '01? How much did a fuel pump replacement cost and did you specify a Motorcraft one?

The stuck injector guess sounds good. If one (or more) is bad, better to remove / inspect / clean them all, obviously.

Just for giggles, do a compression check beforehand just to rule out something really odd.

Also check for a clear PCV valve so the engine CAN suck in the fumes. Your leaking seals might be exacerbated by a non-functioning PCV system.

 

There's a test you can run for more info suggesting the problem is leaking injector(s). Cycle the key so you know the fuel manifold is presurized. Do a quick open/close on the Schrader valve of the test port and see how much of a squirt is fully presurized. Cycle the key again to get it fully presurized. Let it sit for several hours and then check the pressure by the squirt again. If you've got leaking injector(s) the difference between immediately after cycling the key and several hours later will be significant. Pressure should hold for several days. I assume a bad pressure regulator or the check valve that the shop assumed was the problem could also cause the same result in some situations. Maybe you could pressurize the system at the test port with a bicycle pump and listen for noises in the tank to rule those out.

Keep in mind that if one injector is gummed-up and not closing completely, there's five more that are in a similar condition. So if this isn't your only vehicle right now and you can shut it down for a couple days, I would also advise cleaning all of the injectors (see YouTube for ideas) rather than cleaning or replacing one. You can buy kits with screens, o-rings and pintel caps (if a 2001 still used that style) for very little (suggestion - The Injector Shop's EBay store) and it's almost the same amount of work to remove all of them as it is to remove one. Just remember, 9v to hold the injector open, not 12v. I also use throttle body cleaner rather than carb or brake cleaner.

It seems odd that you could have gas in your crankcase if the problem is some leaking when injector(s) should be closed. And cycling the key usually bypasses the hard start from loosing fuel manifold pressure. But it also seems odd that it would run fine if you have really bad injector leaking. A compression test would probably be good info to have before going after the injectors.

 

I don't have a way to test the compression currently but since it runs fine I feel like it's probably (?) not a bad ring. The truck has 212k miles and the fuel pump change cost me around $1200 a year ago with the "diagnostics" fees they stacked on. Cycling the key doesn't seem to do anything, I've tried cycling it 3 or 4 times before and it didn't seem to make a difference. I'd check the Schrader valve but I don't have one lol. I'll check out the PCV and make sure it isn't clogged. I'm kind of in a bind because I'm supposed to be making a 600 mile round trip drive with it this weekend to pick up a mower and this is my only vehicle that can haul 😅 so I figured I'd change the oil right before and hope for the best since I don't have the time to tear it down this week. If it makes a difference, I've been moving and pulled a car trailer fully loaded down with no problems, engine codes or complaints which I would have expected to exacerbate any existing problems.