Hope my sig is still here. The truck still runs tip friggin top(and always has since the swap). But my fuel mileage went down when towing,and towing power maybe off a bit. Was getting 13-13.5 towing small SUVs over the pass, now its at 10-11.5mpg.Empty it feels like normal and runs the same ETs in my marked spot.I pulled 1 plug(OE) and it looks fine although it looks like i have been running additive(octain boost) which i have not (DK reddish)fuel filter is fine.Still using Chevron Premo. I would like to hear from guys that have tried different sparkplugs and want to hear what you have to say and why about the different plugs on the market. Thanks Gonz.


Had an SS muffler on,felt like power was down when towing and re-installed my HD muffler seemed to pull a better.

 

Is it just me or does everyone have a question about spark plugs these days?
(Including me).

 

On my dad's '99 6.0L we changed the plugs and wires thinking they may be the cause for his mileage dropping off a bit. New plugs and wires made NO difference over the old 100K+ mile ones. They ohmed out the same also. Personally, I think new plugs and wires are overrated especially with the ignition systems on these trucks. Unless you need a certain type for a boosted or nitrous app.

The only thing aftermarket wires(Taylors) have gotten me is radio interference.

 

It's like this ****** is in a bad mood when towing.

 

If you were to change the plugs, I've heard good things about the NGK TR55 plug. I always run the TR6 because its a colder plug and better for spray or boost.

Have you put the HD muffler back on?

 

I did put it back on, i did gain most of the towing power ,just the fuel consumption,makes me think i didnt get all my power back.