What do y'all make of these plugs?

 

I reckon you need to change them more often!
Does she burn much oil? There seems to be quite a lot of ash on the four light coloured ones.

 

burns quite a bit of oil

 

You have some nasty detonation going on! Sumthin' ain't raht! You need to verify your timing, and probably do a compression and leak-down test.

 

Judging from the plugs, these are in a 2000-2001, correct? I say that because 5 & 2 fire together with a coil rail and it looks like you're getting a weaker spark on those two. The weaker spark allows carbon to build up when idling and causes detonation when accelerating hard under load, like going up hills at highway speed. Also, with a coil rail, you should be using NGK ZFR5N plugs, which are recommended for the "waste spark" system. If you plan on keeping the jeep for a while, maybe even replacing or rebuilding the engine at a later date, you should try switching to the so called "Viper" coil system. Check it out at ksuspension.com

 

X2 on the viper coil

 

It's a 1991. Does that matter?

 

Are those spark plugs from 1991? Good grief. Even if there wasn't the possibility of detonation and weak spark on 2 & 5, these things should have been found and replaced A LONG TIME AGO....
I'm guessing there is a decent reason for this.
Would you care to elaborate on the condition of the motor, how many miles it gets driven routinely, how much oil it eats in a month, what your MPG's are, and any other info that would be pertinent to the troubleshooting of this problem?

 

Get that compression test done. Easy to do on the 4.0 engine and if you don't have a compression tester, they can often be rented inexpensively from your local parts store, call around. Those plugs don't look good (how many miles on them?) but the actual compression test results will tell you a lot more.

A compression test is a very good "snapshot in time" of the internal condition of the engine. The compression spec for the 4.0 is 120-150 psi with not more than a 30 psi variation between cylinders. Let us know what you find out.

 

I estimate the plugs had about 40k miles on them. Motor has about 220k miles and was running decently until the exhaust manifold cracked. It failed smog for high HCs and I figured it was the exhaust leak. Failed smog with high HC's at idle and 2500rpm AFTER installing new manifold and plugs/wires/cap/rotor. It's driven about 150-200 miles a week. Hard to say how much oil is actually getting eaten as opposed to draining out the airbox, but I add about 1-2 quarts per month. No idea what kind of MPGs I get. It's running a bit rough currently.

 

Okay, so a lot of that oil on the plugs is entering thru the CCV system. If this is the case, the intake valve heads and stems inside the passages must be really carboned up as well. What did they look like when you had the intake manifold off?

This sounds just like my WJ just before I put a rebuilt motor in it. 252K miles on that one and I was putting over 20K miles a year on it doing newspapers. I couldn't let it idle longer than about 20 minutes without fouling a plug or two. It didn't start using oil until the 0331 head cracked and I replaced it at 165K miles. Then the rings couldn't take the compression caused by new valves. I put an oil catch-can on it which helped. It was catching about 6 oz a week.

 

Sounds like time for new rings. Maybe faster to put another motor in hahaha....

 

I bought new everything from the head to the rear bumper, including cat and O2 sensor because everything appears original or damn close and I want it here before the weekend. BUT, I intend to do a compression test prior, so I can return stuff if it won't matter. Someone mentioned leakdown. Is that the fuel pressure? I do not have long starts in the morning, so it seems like I wouldn't be losing pressure overnight.

What else is worth checking before I put the new exhaust system in this weekend? How hard/easy is it to check the injectors? I read something about cleaning the MAF sensor. Check all Vacuum lines; what's the preferred method for this? Gonna MMA today and Seafoam the fuel as well.

 

you are using a lot of oil 1 quart per month...is it leaking?...how many miles per month do you do...mine uses none at all between changes, 210k miles

a compression test will tell you a lot...a leakdown test will refine where the leak is coming from...with that much oil "use" assuming it isnt leaking out, low compression would be indicative of a heavily worn engine

 

A cylinder leakdown test is where you put air pressure in the spark plug hole and see where it comes out. This has to be done with whichever cylinder at TDC compression and you'll hear air coming out the oil fill cap if it's rings, throttle body if it's the intake valve, or exhaust pipe if it's the exhaust valve. A complete test is where you put a regulated quantity of air into the cylinder and see how long it takes to bleed down. Then you can do the leak location investigation afterwards. We barnyard mechanics used to use the full pressure test, but now shop mechanics squirt a measured pressure shot into the cylinder and time how long it takes for the gauge to drop, then try to find out where it went. If you use the full pressure test, the cylinder MUST be at EXACTLY TDC or the crank will flip around.

The full pressure test is good for finding head gasket leaks as well.