Which came first, the blackened plugs or the rich mixture?

I know, lame spin-off of chicken/egg but blah! So my jeep has been parked for something like a year. I knew when I parked it that the mileage blew royal dead goat d!ck but now that it's back on all fours and "purring" again, there's quite alot of black smoke coming out. So I checked the plugs and they're horrible black. but dry/black. So I dunno if I'm getting black smoke out my pipe because the plugs can't burn the normal amount of fuel coming in or if the plugs are black because I have a severe rich problem. I did an oil change before I fired it up for the first time so I thought it might've been like old oil that had just leaked down past the valve seals but it's still doing it a week later. It's not insured yet so I couldn't tell you what kinda mileage it's actually getting. Also the idle seems a bit on the lumpy side and I'm contributing this to the plugs but I don't want to put a new set in just to foul them. Although it might be my only option at this point.

Rich mix - rich mix causes carbon fouling of the plugs. Plugs can't blacken on their own (especially if they're sitting.)

Carbon deposits are a product of incompleat combustion - either an ignition fault or a rich mix (which could have a number of causes.) If one or two plugs is blackened, check the HV wires. If they're all blackened - check the coil, cap, rotor, and the coil HV lead - then go after the rich mix.

Oil fouling is fairly distinctive. Sooty black deposits are incompleat combustion, and a different issue.

all of them are black. So I might not be getting full "oomph" to my plugs because of problem further up the ignition line... makes sense. At least it's a good place to start. What kind of tests (if any) can I perform before I just start slapping money onto parts that may or may not need replacing?

"Oomph" to the plugs will not cause blackened plugs for the most part. More likely is a bad O2 sensor, a bad temp sensor, a bad TPS, or a shot MAP, pretty much in that order.

You could have a clogged CAT as well.

to check the o2 sensor, which of the 3 wires do I want my voltmeter on?

bcsavage said:

all of them are black. So I might not be getting full "oomph" to my plugs because of problem further up the ignition line... makes sense. At least it's a good place to start. What kind of tests (if any) can I perform before I just start slapping money onto parts that may or may not need replacing?

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Do a resistance check on your coil lead. Check the underside of the cap towers - they're probably going to be a bit pitted and blackened, but they should all be roughly evenly pitted and blackened.

Since electronic ignition systems tend to have higher energy output (and also tend to fail parts "all at once," rather than gradually,) I'm leaning more toward a failed fuel metering sensor myself. Go with old-man's advice as well (and 1987-1990 & 1991-2001 HEGO sensors test differently, so give with your model year.)