Spark plugs

[scotth48]

I hav a 1993 C4. I had some stumbling on my second fillup on vacation of about 2200 miles. After using some dry gas and now several fillups later it has improved. I thought at first ut was a fouled plug or bad wire. The engine has about 37000 miles on it as it was a replacement engine. The ebgine had about 32-3300 on it when I installed it. i transfered over my fairly new Dynaspark I had on the previous engine that had about 400 miles on it at time of swap. I put in new NGK 55GP plugs set at .047 usinf a feeler gauge as I didn't hav a wire gauge. I remove the plyg and looks ok other than it is a darker redish brown color to a normal lighter tan than normally have. Should I be concerned? Fuel pressure is at 42-43 psi. Currently have a k& n air filter and new O2 denso sensors put on prior to vacation. 2176 mies on vacation and averaged 27.89 mpg. Was disappointed in my mileage ate the fuel economy run at Eureka Springs Corvette Weekend as it was running ruff and stumbling, so had to shift down more than i thought had it been running better. The winner was at just over 29 and I am sure had it been runring better i could have. But what about the plugs that warrant a change or symptoms somewhere else?

 

[scotth48]

 

[DonB]

Normally, I ONLY use the factory recommended A/C Delco Plugs in my G.M. vehicles. Switching to other brands, I've found can cause "heat range" issues. This can lead to a bunch of other things including fuel mileage, efficiency and combustion temperature to name a few.

But,..Are you using an Octane Booster? Here's a partial post from another blog I found.


What I think you are describing is completely different than a light tan/brown color. Sounds like you are describing a copper/brown rust color(like an old penny or a brown crayon).

If this is the case, then you are looking at a plug that's been fowled by Methylcyclopentadienyl
Manganese Tricarbonyl (MMT).

MMT is a fuel additive that is seldom used here in the states. It's extremely controversial, just as TEL was in the 70's.

MMT is used frequently in Octane Boost, especially in the brand "104+ Octane Boost" and "Super104+ Octane Boost".

If you are using an octane boost, and have this kind of fowling, don't worry about it. MMT fowling is quite harmless, and should be viewed the same as a tan colored plug.