Two frontmost cylinders misfiring. Fuel pressure issue? Or plugs? Or ???
 

My 2003 4.6L has had a #1 cylinder misfire for some time already. Now the #5 cylinder is also misfiring. Given the fact that both misfires are on the two cylinders furthest from the fuel pump, should my first diagnostic effort be to check the fuel pressure?

Or should I check something else first?

I installed new Bosch Platinum (or maybe Iridium?) plugs about two years ago and haven't had any problems with the engine until these front two cylinder started misfiring. But I have also seen reports that Ford modular engines don't like Bosch plugs for some reason. Is there any truth to this rumor?

I recommend using Motorcraft parts.

The cheapest option is to put in Motorcraft plugs and make sure to gap them properly. See if the results change.

Bosch plugs do not work worth a crap in a Ford Triton. Get them out of there and replace them with Motorcraft plugs. Clear the codes and see if any come back. If it's still missing, swap coils around to confirm, if any coils are bad replace with only Motorcraft, Denso, or Delphi coils. If it's STILL missing in the same cylinders, swap injectors around to confirm, replace injectors as necessary.

If the fuel pressure were low, it wouldn't run at all. The rail system and pressure regulator ensures that the pressure is the same to all injectors.

Got it, thanks glc.

I may have made a mistake on the brand name of the current plugs. I think I bought and installed NGKs rather than Bosch. But it won't matter after I get my new Motorcraft plugs. Yesterday I ordered a set of eight Motorcraft SP-493 AGSF32PM plugs online via amazon. They should be here in a couple days.

I remember swapping the #1 and #2 coils a couple years ago when I had a #1 misfire BEFORE I installed the current plugs. The misfire remained on #1 so that's one reason why I bought and installed new plugs ... and the misfire did go away after installing the new plugs.

Since I'm already waiting for my new Motorcraft plugs to arrive, I think I'll clear the codes, swap the #1 and #5 coils with the #2 and #6 coils, and see which codes it gives me after the swap. There's no reason not to do this now, correct?

I did a thorough cleaning of the injectors a year or two ago with a special tool that fed a can of "Berryman 1126 B-12 Chemtool Thru-Rail Fuel Injection Cleaner" through the injectors via the Schrader valve on the fuel rail. Since then I've mixed a can of "Berryman 0116 B-12 Chemtool Carburetor/Fuel Treatment and Injector Cleaner" into the gas at fillup every 3-4 months to maintain injector cleanliness. So while the injectors might be the problem, I tend to think (or hope) that my cleaning efforts are working, and instead this misfire problem might be caused by something else.

I recommend Techron for fuel treatment.

The B-12 is good for using it as you did through the rail, but Techron is the best to use in the gas tank.

I wouldn't swap coils around until you have the new plugs installed.

NOTE: Torque the plugs to 28 ft/lb to prevent loosening and blowout. Antiseize is not necessary with Motorcraft plugs because the threads are nickel plated.

In that case I'll get some Techron to put in the gas.

Okay.

Got it, thanks.

I'm sure that the motorcraft plugs I installed in my 02 were nickel coated only on the body of the plug, not the threads.

http://www.blownoutsparkplug.com/faqs.htm

Q: Do you use Anti-Seize when you install new spark plugs?
A: No, we always use Motorcraft nickel plated spark plugs to stop any issues with electrolysis.

Next time you are in a parts store take a look at one and see for yourself.

I'm wondering if the amount of Techron that's added to Chevron gas is enough to allow me to avoid buying it in bottles and adding it to my gas manually?

Chevron gas is typically a bit more expensive where I live, so I usually buy gas somewhere else. But given your recommendations for Techron, it might make sense for me to spend a little more at the pump for Chevron gas -- because it already has Techron in it.

I don't know what the concentration is in the gas. Using Chevron gas would help, but I'd still put a bottle or two in the gas once a year.