Slight miss/rpms up down on idle?

[Wyatt]

Originally Posted by wxman13

Well, #7 spark plug seems to be the issue, notice the carbon trace from the top to the base, there is one on both sides of the plug, new plug installed no misses so far, still need to fix the charcoal canister hose, if I can find out the correct routing of the hose.

So, the ceramic insulator was cracked, which meant the voltage went right to the threaded ground, and not through to the tip inside, which is why it’s also black on the gap end.

Happy it was something that easy.

[Elkman]

Also a good idea to add a bottle of fuel injector cleaner to the gas tank the next time you fill it up. Even with good gasoline (or diesel) there buildup on the injector nozzles and so there is not the fine spray pattern needed for good combustion to take place.

[wxman13]

I have added Berryman's B12 last fill up, and stp last year sometime.
Discovered with my scan tool again I still had a slight miss even after changing out the #7 plug with the carbon trace, the scanner showed #4 with the most this time, which was also showing misfires when #7 was showing quite a lot, sure enough removed #4 spark plug and it also had carbon tracing, running smooth now, but need to go ahead and change them all.

While changing the #4 plug I noticed a unusual hole where the intake manifold is, circled in white in the picture, what is this hole for? I know its there on other 6.8L V10s as well , but just doesn't look normal.

[Elkman]

The plug wires and the coild wire can start to fail as they age and are subjected to high temperatures inside the engine compartment. Not difficult to check the Ohms resistance with a multimeter for each wire to detect a bad one. If I find one bad wire I replace the entire set of wires to be done with it.

Actually removing the lead from gasoline, which was done to eliminate the largest source of lead pollution and brain damage to children, greatly increased engine durability. GM who had the patent on tetraethylead that it cut engine life by more than half but Al Sloan told the engineers that there was too much money to be made from the royalties on the patent to worry about the engines.

Taking lead out of gasoline in the 1970's concided with auto engines lasting for 200,000 miles or more whereas previously a car that went 100,000 miles without an engine repair was remarkable. When the children not exposed to lead from auto and truck exhaust became adults they were less prone to violence and the crime rate dropped across the country. Of course the politicians and the police pretended that it was the "tough on crime" practices that were the reason but scientists know the truth.

[DryCreek]

Originally Posted by Elkman

Taking lead out of gasoline in the 1970's concided with auto engines lasting for 200,000 miles or more whereas previously a car that went 100,000 miles without an engine repair was remarkable.

Well, that sounds noble and all, but the truth is that the adoption of fuel injection is what actually extended engine life. No more extra rich mixtures to wash down the cylinder walls and dilute the oil. Maintaining a stoichiometric ratio over all RPM ranges and loads will preserve an engine. The higher operating temperatures also help burn off the volatile mixtures and moisture that used to contaminate oil.