Hello,
I have a engine vibration at 1500-1700rpm. Started after changing spark plugs. It's pretty bad while driving down the road. I disengaged the overdrive and it's gone (once the rpm changed). In the driveway, I narrowed it down to this range.
Any suggestions would be very appreciated.

 

I work at a Ford dealership and have seen alot of these 4.6 and 5.4 liter engines coming in. Whats happening is water, or condensation moisture is building up around the ignition coil boots. It could also be bad coils, but with the change in weather, it's most often just the moisture issue. You'll want to pull each ignition coil and dry out the boot, inside and out. You can remove the boot from the coil. Take a good look at the boot and ask yourself if you really want to put it back in the engine. Look for cracking, ugly brown or white residue. The top of the boot is supposed to seal against the spark plug hole. If the seal area is cracking or hardened, you'll want to replace the boot. I've been selling a full set of the boots each time one comes in for a misfire as preventive maintenence(How bad would i lookif the truck came back with another misfire the next day?). Make sure the inside of the spark plug hole is completely dry. You can use compressed air to blow it out, a towel shoved down inside with a screwdriver and worked around(don't break the spark plug!) or whatever other way you can think of to get the moisture out. It needs to be completely dry.

When you re-install the boots, it won't hurt to put a little dielectric grease around the top sealing part of the boot as well as at the bottom where it rides over the spark plug.

Good luck, and if a moderater wants to put this up higher where ppl can see it right away, it would be good. There's going to be alot of this problem happening until winter goes away.

 

Thank you frdteck5. I'll check that out.