2004 F150 exhaust smell after plug change

I have a 2004 f150 LAriat supercab 5.4L triton with 120,000 mile on it. Without good reason, I let the dealer convince me to put new plugs in it. Ever since, I’ve had a serious smell in the cabin of gasoline and or exhaust, and a 2MPG drop in MPG. At first it smelled like gasoline. I took it back to the dealer and they said a connector had backed off, which is code for I don’t even want to know what. They “fixed it” but the smell remained. They then changed the rings on the fuel injectors. The smell got better, but there is more of an exhaust smell now. I checked many blogs about it and found several bloggers with almost the same exact situation. I suggested to the dealer that they need to check that the proper spark plugs were used and they were correctly seated. They of course confirmed this but God only knows if they actually checked. I also looked up to see if there is a cabin filter on this vehicle and there seams to be some dissagreement on the blogs about this fact as well. Now that the cold weather has arrived, I prefer not to take the cowl off or check the plugs myself until it gets a little warmer. The smell is noticable most of the time and esecially stopped at a light regardless of the heater or air conditioner. Should I be more worried about the smell or the fact that I actually took it to this dealer in the first place?

If that truck had the original plugs in it then the dealer did nothing wrong by recommending they be changed.
Spark plugs should never be allowed to remain in place for that long even if the engine appears to run fine to you.

There’s not enough info available to know what’s going on because we do not know if any codes are present, Check Engine Light on, if the engine was running rough or even had a slight vibration at idle before, etc, etc.

Maybe there’s some misinterpretation on this smell. You refer to it as an exhaust smell and the injector O-rings being changed. Neither of those smells is similar, at least to me. Raw gas does not smell like exhaust pipe emissions.

Sounds to me like a leaking fuel injector. Take it to a different shop and have them do what Tom and Ray do to identify the source of the leak. They use an emissions tester probe to “sniff” around each fuel injector. The emissions tester is extremely sensitive to unburned hydrocarbons (i.e. raw gas), and when the probe tip gets near the leaky injector, the “unburned hydrocarbons” reading on the emissions tester will spike.

The dealer apparently suspected a leaking injector also, because according to you he replaced the injector seals. But, obviously, the problem remains. The “Tom and Ray” method will remove guesswork and pinpoint the leak source.

I would agree with both entries from ok4450 and jesmed. It is also possible one of more of the exhaust manifold fasteners has broken off (Should be easily seen when looking thru both front wheel wells, look for missing bolts and /or black soot around the manifold to cylinder head interface)… I have also seen improperly torqued spark plugs do this… Typically you will get a fuel odor in the cab following a cold start which will typically lessen as the engine heats up… If the plug bores were damaged or one of more of the plugs is very loose, exhaust will vent from the plug bore. If severe enough, it will eventually melt the ignition coil (COP) boot. Obviously you can remove the oils and inspect for black soot in the plug bores, or damged boots, retorque the plugs. Another option which we use for these concerns is a combustible gas detector… The can detect faint quantities of flammible hydrocarbons and will emit an alarm proportional to the hydocarbon concentration… The tool cost about 140-170 bucks so probably nothing you would want to buy… It is extremy rare a dealer would even have one of these, but if push comes to shove, its an option and one I have used many times.