E450 V10 Engine Miss

The spark plugs and coil over plugs installed back at 98,000 miles were Ford OEM parts. Since I have a Scan Gauge installed I just thought to check for engine codes and found none set. Puzzling problem!

First, are you certain it is a engine miss ? A good scanner will report the error code or even a "pending" code.

A cheap and easy fix, once you know which cylinder has the miss, is to remove and inspect the spark plug and coil. Look carefully for any sign of carbon tracks on the plug or the boot. If you see signs of carbon tracks, replace the plug and the boot and thoroughly clean the contact on the end of the coil. When re-assembling, grease the outside of the plug and the inside of the boot and the tip of the coil with silicon dielectric grease.

Plugs and coils replaced 10,000 miles ago makes them unlikely suspects- assuming you don't have a cylinder-specific misfire code. Electronic parts generally fail fairly new because they are made wrong (infant mortality) or when they are old because they are worn out. Plug or coil failure is a possibility of course but I would rule out other causes first, like a dirty MAF sensor. You don't run a K&N air filter by chance, do you? When I've had coils fail the motor idled fine but would miss under load, the opposite of what you're seeing.

Our previous MH had misfire that none of suggestions above corrected. Close inspection of plugs found cracked insulators (white ceramic part). New plugs fixed it right up. Mine was more misfire under load than at idle, though.

See if any codes show up and fix what code says... If no codes show up because not big enough problem yet...unplug a coil over plug (COP) and see if miss gets worse or better or maybe the same. If worse then that cop is NOT your problem, and that cop is working right, plug back in COP and go to next one. Process of elimination. Be carefull of the small rubber gasket in connection, pain to replace and easy to loose. If your cop's turns out ok, my next would be injectors. Injectors same as above. The parts you used when you changed them prior...I only use ford replacement parts, because I've had to many failures with brand X. If still not fixed right, break out the book and go step by step. I carry a spare cop and injector.

Doing the above is assuming you've already looked for the obvious...vacuum leak from cracked rubber hose, fuel filter etc. Did you put anything in tank to "clean" injectors? Maybe it did to good of job... After giving mine a present around 90,000 miles and replacing a bunch of stuff I treated it to some Seafoam. The seafoam freed up small filings from when OEM drilled hole for generator fuel line. Filings broke free that were stuck in bottom of fuel tank all this time. And they plugged up fuel filter and filter in "bypass mode" small filings were caught in "injector bucket". And you might be in the year models that Ford spark plugs were not one of Fords better ideas. 2 piece plug then not enough threads and spitting them out of hole etc.

I too heard bad things from those parts made in China.

One other thing I suggest is to remove the dog house and inspect the wires for rodent damage. They love to crawl up high and chew on wire insulation which can happen during outdoor winter storage.

just changed all 10 of mine recently, and my miss went away completely

one question... did you use motorcraft coils, or the chinese eBay ones that cost 1/10 the price? ... I have heard all kinds of bad stories about the cheap ones

Were boots changed when the plugs were changed? If not, probably should change them. If they are good, you should scan for codes, and chances are it will show which cylinder is missing, and then swap out the coil.

I had an '02 Ford V6 with spark plug coils, and when they went bad it started popping engine miss codes. Maybe the plug coils are failing? If it has that type of plug. Just a wild guess.