Did a tune-up today on my 03 Quadcab 4.7L with 103,000 miles. First thing I did was seafoam by using the vacuum line, some in oil and the rest in the gas tank. Followed directions, smoke, drove it about 10 miles then changed the plugs. Was original plugs and went with ngk iridium 6441's and put in a k&n air filter. Changed the oil from penzoil 10w30 to mobil 5w30 (not synthetic) and am using a fram hp-1 filter. Also changed the pcv valve.The engine runs smooth except we broke the end of the electrode of one of the spark plugs (the ngk tapers down pretty small) but we believe it is firing as no pull down in engine when plug is unhooked from the coil so ill call that good. That was the only issue or problem during the tune up.Took the truck for a test drive and after a few miles it sounded like a gust of air under the hood and a slight stagger in performance then normal( a little noise like the fan was loose or something just after the air noise). Drove it another short distance and the same thing. Also on my overhead mileage guage it has dropped from normally about 14-15 mpg to 8-10. Another thing I noticed...before when driving 70 mph the rpm's would be around 1800 and now they are running around 2-2100 rpm's...dont know why it would be different.What has happened? Anyone else ever experience something like this?

 

If you broke an electrode, you're very likely running on seven cylinders. You might pull the broken plug and one other and compare them. I'd guess the broken one will look a bit different. Seven cylinders doing the work of eight might raise the rpm at a given speed.

 

Wouldnt it pull the engine down....it is running smoother and with more pep than before the tune-up with the exception of the few seconds that the spurt of air sound was heard. We pulled several coil wires off to see if that plug was firing and we had to pull 3 off before there was noticable engine pull down during idling and when the coil with the broke plug was hooked back up the engine idled smoother like it was firing so we assumed it was good. Just seems that if it wasnt firing that it would run rough period but that doesnt explain the air sound from the engine compartment. Kind of sounds like when you turn your air conditioner on full blast except with the noise outside instead of coming through the vents.

 

Double check all of your vacuum lines that you disconnected, replace that plug and fram filters are garbage. Oh and check the clutch fan....might just be a coincidence and it took a crap on you while test driving the tune up. Might have seized up in full lock...

 

I just thought about this, I had the a/c running on low the whole time and I had came across a couple of older posts about a loud hissing or something with the air conditioner. Wonder if this is related to what I heard? Anyone else?

 

Could be...see what the hi and lo pressure is.