My 2004 F-150 4.2 6cyl started running rough (sputtering at take off and hesitation between 40 and 60 mph) recently (it idles just fine). I replaced the fuel filter and added fuel treatement which helped for a day or two. Now it is back to running rough again. I have had friends and mechanics tell me to replace the fuel pressure regulator, some say change the fuel pump module, some say change the fuel pump itself, some say change the plugs. I don't want to take it to a shop unless I absolutely have to. Anyone have suggestions on what I should do next?

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I would pull the plugs and have a look at them. You can check the fuel pressure fairly easily to determine the health of the fuel pump/regulator.

How many miles on the truck? The TPS might be acting up as well.

 

How many miles on the plugs? Are they the originals or have they been replaced, and if so, with what brand? Any OBD2 codes?

 

Have you recently run the tank very low? That can suck sediment from the bottom of the tank into the lines, and maybe there was enough gunk to clog the second filter as well.

The symptoms sure do sound like a clogged fuel filter, even though you just replaced it.

These trucks are certainly finicky about the brand of plugs. FWIW, I replaced my stock plugs with Bosch. After about 20,000 miles one of the Bosch plugs went bad. At first, the truck ran bad when hot and on the freeway, and it gradually got worse and worse. Eventually it generated a code indicating a misfire on #6, but the truck ran bad for a month or more before the code came up. I had ruled out plugs becuase I knew they had low miles, but replacing the Bosch plugs cured it 100%.

 

The truck has 68000 mi on it, still has new plugs. The tank hasn't been run low that I can think of. I haven't checked any codes. I replaced a vacuum hose which made my service engine light come on, I fixed that right away but I never have had the service light turned off. How hard is it to change a TPS sensor if it turns out to be the problem?

 

Inspect the top of your coil for a crack or cracks. Also, inspect your harness in relation to the AC accumulator. Make sure it's not touching or very close to.

 

TPS is very easy to change. Just a couple bolts and an electrical connection.

 

Check the codes. If the CEL is still on, there's still a problem.

Huh? Please clarify.

 

Doggone, the post should have read that the truck still has the old original plugs. I heard the plugs were a SOB to change and they break as well, which makes that the last thing I want to do. I am gonna try and check the codes tomorrow.

 

Plugs only break on the 5.4 V8. You shouldn't have any issues changing plugs on a 4.2 V6.

 

Well, checked the codes at Advanced Auto for starters and came up with PO171 - Bank 1 system too lean and PO172 Bank 2 system too lean. The codes online tell me that the first thing to check in the Mass Air Flow sensor and clean it. So I took out of it's home and cleaned the ever lovin sh*t out of it. Turns out that it didn't help. I think the next thing I am going to try is to change the upper intake gasket and isolator bolts. There have been quite a few places where I have read that changing those will help cure the problem.

 

Whoa! Don't jump in that deep so quick.

You may be right about the bolts and gaskets but go for the easy stuff first. It could be as simple as a bad PCV hose (very common) or an exhaust leak.

Check every vacuum hose for integrity, even the brake booster. Check for silly stuff like a missing oil filler cap, or any place the motor could suck in extra air.

P0171/174 are lean codes and can be caused by air entering the motor after the MAF. Even a loose air cleaner tube at the throttle body can cause it. So before you dive into it do a little detective work and maybe save some time and money.

Good luck----been there done that.
Jim

 

Okey dokey. I see. I will check all that I can. Where is the PCV valve? Is it tough to replace?

 

The PCV should be on the passenger side of the throttle body. It could be bad but more likely it's the plumbing that connects it to the pass side rocker cover. Usually if that is the issue it's the hose right where it goes into the PCV.

Also the PCV is heated and has 2 small hoses connected to it, make sure your cooling system isn't under pressure if you remove them- you could get burned.

 

Awesome. Thanks for your help. I am finally gonna try and get to checking the hoses and PCV today. I just drove the truck and im gonna have to wait for it to cool off. I hope I find the problem.