Alright fellas, hopefully this isn't anything too serious.

Right now, my '91 XJ sits due to a bad rear main leak/drip, a rich running condition, AND a leaking P/S pump. And something (hopefully just excess rear main leakage) dripping near the tranny pan, but it's dark brown and my tranny fluid is light red/tan.

SO, I went to pull a couple plugs to see what's going on. Pull plug #1, and I get this:

(sorry for Cell pics)



Crud all over it, and the two prongs appear to have melted slightly or something like that. These ARE Bosch Platinum +2's because I installed these back when I was a newbie "IDKWTF I'M DOING" idiot and I believed anything to sales dude told me. I've come to learn Bosch is crap and I plan on replacing these with Champions. Anyways, is this a 'normal' Bosch is crap type failure? The fouling is likely from where I am running quite rich (plan on replacing o2 sensor as well as stuck open thermostat). What concerns me most though is I also pulled cylinder #3's plug, and got this:



Looks damn near excellent to me. Why would there be such a variation in the colors? Could it be possible because the #1 plug had its 'melt down' and wasn't firing correctly, allowing unburnt fuel and junk to accumulate? I hope this is the case and not something serious.

Also, way back when I first bought my rig when I installed the Bosch +2's, I had a blow out in the sense that the #1 plug blew out of its hole. Inspection of that old plug revealed the threads on the plug looked messed up and thin. I figured it was a factory problem, as replacement of said plug with a now prevented any blowouts. But I noticed once I got the old plug out that when trying to put it back in it didn't seem to want to tighten as the #3 one did. Meaning, the #3 plug went it fine and eventully hit that "tight at the hand" point, in which time I connect the socket wrench and give it a 1/2-3/4 turn more. The #1 plug seemed like it just didn't wanna tighten all the way, and it seemed like I had to jimmy it a little to get the plug to find its sweet spot and start threading. It's probably just paranoia on my end, and I was so cautious in returning the plug that I just didn't turn it enough times. Idk, guess we'll find out when I get the replacements.

So what do ya'll think? What's going on with that #1 plug, in terms of both it's meltdown and it's turning troubles?

Also, if it matters, here is some more random info about my rig:

• APN Header (but I think the bolts are due for a torque check)
• Air box silencer removed
• #703 Neon injectors
• No CEL light
• Thermostat is either failed or AutoSuck sold me a 160* one because it barely gets above the second tick mark before the 210 mark.
• High Flow Exhaust (2.5" tailpipe, High flow cat, Flowmaster Super44) but stock downpipe.
• I do burn a little oil, but nothing too drastic

If I can offer any more info, please ask! Thanks for any help!

 

sounds like you have water in your tranny fluid.

 

The jeep motors run best on the OEM recommended copper plugs, in my opinion. That first plug looks almost like the pistion came up and smacked it a few times. Have you ever had any knocking?

 

Change the plugs to Champion Copper or NGK. When's the last time it had cap, rotor and wires?

As far as the oil leak being the rear main seal, here's my standard response:

I'd be looking up above first. A leak at the back of the valve cover could produce the same symptoms. Don't jump on the RMS/oil pan gasket bandwagon just yet.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for 2 simple reasons. First off, the engine sits nose-up and oil will run back to that area. Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber's adage apply here. "$hit flows downhill".

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket have to be eliminated as possibilities first.
Revised 3-23-2012

 

Negative. Tranny fluid is good (just a little old) and AW4 works fine with no hiccups. I want to change the fluid, but considering my drivetrain has 207k miles on it, Idk if it's the best idea.

Aside from the usual 4.0 noises, nothing bad. At cold start, I have slight piston slap and valve noise per the comment above stating my mileage. But when the engine is warm, the 5w40 Rotella really calmed a lot of the noise down. Very nice sounding.

Way ahead of you. O-rings and valve cover gasket have been replaced in the past 2 years. Dizzy cap and rotor are at most only 3 years old with 20k miles. At the absolute most. Plug wires are about 2 years old, quality units and the insides look fine with no burning insulation or anything. Ignition coil was replaced 2 years ago as well. Oil pressure sending unit is also replaced and not leaking. And finally, the XJ will be getting Champions per what came in the ol' girl when she was on the lot brand new. I've learned these Bosch magic plugs and BS are nothing more than that... BS.

Thanks for the replies so far guys! Any idea what may have happened with that first plug?

 

Stuck open thermostat can cause rich running. Because the truck never really gets to operating temp that quickly. At least is stuck open and not closed

 

Never hurts to run a compression test on all cylinders. It's a good snapshot in time of the internal condition of the engine. The spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

And yes, specialty plugs are not necessary in the 4.0 Champion coppers work fine for your vintage. Verify gap is at .035 before installing; never trust the gap out of the box.

 

To be honest, I really don't think it's stuck open. When I start the ol' girl cold, coolant will take the same amount of time as before with a good thermostat to warm up, then once it gets near that 160* mark, BAM. It refuses to heat up anymore. I think the people at my local AutoSuck are as clueless as a stump with anything automotive. A good Stant from Advance is my next t-stat.

Compression test scares me to be honest... last thing I want is to see something bad that says "HEY! ENGINE WORK BUDDY!" and cost $$$. But you're right, it's a necessary thing which I'll rent the compression gauge to do. Simple as unhooking the ignition coil wire and unplugging the injectors, right? Then pull one plug at a time and go.

Also, thanks for the spark plug advice. Def going with Champs, and I'm glad you mentioned the gap because for some reason I thought the XJ was a .40 gap. And I always check the gaps, no matter what. Good practice to do!

 

Unplug the CPS for the compression test.

Your engine temp is too low. I have had 3 Stant super stats not get my engine warm enough even though they were 195*. I only use factory stats with the "jiggle valve" from the dealer. Part number is 83501426.

 

So instead of unhooking everything else, just unplug the CPS? Simple enough. And also thanks for the part number on that 'stat!

 

Friends don't let friends use Bosch platinums

 

True story. Champion Coppers or my favorite---NGKs.

 

Tell me about it. But sadly... 17 year old newb goes into AutoSuck. "Hey, I need spark plugs for my Jeep." "Oh, you want these. The 2 prongs make the gas combust better and last much longer. They're the best plugs for you." "DERRR... Ok! Give me 6!"


Do Bosch Platinums have a habit of ever possible melting or whatever like mine did? Like I mentioned earlier... never had any issue with piston-hitting-plug noises, or anything random. Nothing my jeep had been possible doing would have made me think this is what I'd see on the #1 spark plug.

Edit: Just read this doing a google search. Makes me wonder:

What is the normal heat range for the XJ? Is it possible it's range was higher than these +2's and hence the melted donkey donk?

 

Throw some NGKs in it. Never been a fan of Bosch, especially their gimmicky plugs.........

 

Champions going in my XJ.

NGK's going into my mother's 09 Patriot.

My lesson has been learned... with spark plugs, OEM FTW.