I just blew $52.00 on some Bosch Platinum +4’s and $40 on some new Injector o-rings since the 5.4’s plugs are so damn hard to get to with the fuel rails on. Since I have done this, I get a feeling of misfire or a stagger in the engine when running at very low speeds (Under 10 MPH). First thing I did was I inspected everything in the engine compartment to make sure I hooked everything back up. I also tore it down again to check voltage and for blockage on the Injectors. The system isn’t holding any trouble codes and the fuel pressure is perfect. Everything checks out, all sensors and connections. I’m about to spend even more time tearing it back down to put Motorcraft platinum OEM back in. Any advice before the extreme?

 

The misfire/stagger (in conjuction w/ a plug change) tells me it is one of two things:

1. A coil was either not seated well on the plug/connector to the coil not seated well.

or

2. one of the connectors for one of the injectors not seated well.

Personally, I would look at the back 2 on each side: both the plugs AND the injectors. Real tight back there and easy to overlook those...
I replaced my OEM plugs (which looked perfect after 70k) w/ Platinum +4's and i feel i wasted the $50 on them. After I use these for a few yrs, i plan on going to Autolite platinums.
Good luck.

 

Thanks, That's what I was thinking, but I tore it completely down again just to make sure before posting. I tripple checked all connections, fuel pressure, sesnors ect... I'm thinking the plugs just arent cutting the mustard. I would think some trouble codes would pop if it was something that drastic.

 

one other suggestion:
Don't know how you feel about all of these "new fangled computer sensors" but, after my plug change, i disconnected the battery for 3 hrs to allow the computer to reset. Don't know if anyone else agrees but i figured that since EVERY-FU*KING-THANG is computer controlled, it couldn't hurt...

 

I didn't remove the fuel rails, but when I put in my +4's, I felt the same thing in mine. Thought I had developed the "rough idle" syndrome. But now, after the plugs have been in for @ 10K miles, It runs very smooth now. Actually has been for some time.

I'd agree with the computer reset, but I'm also thinking that you should have disconnected the battery to begin with. I did, since I was messing around with the connectors and such when I changed my plugs.

It'll take a couple hunderd miles to really get the computer back in shape again too. Be patient and it should come back around.

The only reason I went to the +4's was the "No gapping required" property. They cost the same as the replacement Motorcraft ones from the dealer, so just wanted to try them out. Only 10k on them, so they won't see a socket for another 10k at least.

 

Did you reapply the dielectric grease to the spark plug boots? Do a search. Not appling the grease has caused some problems for people that have new plugs.

 

Fixed the problem. After reading evything on the sight even remotely close to the problem, I unhooked the battery cables last night to erase any computer memory. I drove it to work today and also to lunch. It's running great now. No more stumble, stagger or feeling of misfire.