We have a 1999 4.6L F150 I bought over 10 years ago up in Ohio. We live in Maryland and it was the only reasonably priced 4x4 extended cab I could find at the time. Other than being rusted out from Ohio's bad winters and heavily salty roads, it ran decent for the first year we owned it.
After the first year, the transmission never had issues but the engine started running poorly and had excessive "popping" noise under the hood with extreme loss of power under heavy loads- hauling anything from our camper trailer to lawnmowers and lumber or firewood with our landscaping single axle trailer.
I replaced as much as I could on my own to give it a good tune-up with the best quality parts I could find: K&N Cold Air intake, NGK spark plugs and MSD coil packs as well as a new OEM ford fuel filter and ran Gumout FI cleaner in the tank as instructed. It still continued popping under heavy loads so I took it in to a reputable, honest auto shop I often use called Martin's Garage in Maugansville, MD which is run by Mennonites. They diagnosed it as a cracked exhaust manifold which is common for these F150's.
Took the truck back home and ordered a BBK exhaust header set from autoanything dot com. They arrived and I broke two of the existing header bolts trying to remove the stock header which was cracked, so I took it back to Martin's garage and they welded a couple nuts onto the broken studs to have them removed. With the new BBK headers, the truck ran better than any standard brand new F150 right off the lot. So we then proceeded to order a stainless Flowmaster full dual exhaust kit and the truck really opened up.
I've replaced the spark plugs at least four times now since then with an additional 100k miles added, but have noticed the one plug directly under the power steering reservoir gets fouled first before any others, and when that happens the engine runs poorly again. I should get 20-30k miles out of each set of plugs, but perhaps the way we haul heavy loads quite often- I'm having to change the plugs around every 10k miles. The best ones I've found are not the NGK Iridiums I started out with, but the cheaper Autolite $2 a plug Part No. 764 (check the user reviews on advanceauto dot com) for our truck. Hope this helps someone as you many not think it's the spark plugs since you've recently changed them in the last 10k miles, but if you take them out and see one fouled out. It may be time to change them and see if your power's restored. Now we keep at least one set of 8 Autolite 764 plugs in our truck glove box ready for anytime it starts acting up. The truck runs strong with these upgrades and it sure beats any truck payment. Good luck!
Friday, August 26th, 2016 AT 5:20 AM