Pulled the #7 spark plug. I don't know a lot about plugs and I've never done much "mechanic-ing" but this plug sure looks bad. Will attempt to attach picture.

 

Well, the good news is it looks like this could be the problem... the bad news is it looks like you have oil blow by in that cylinder....

 

As I've indicated, I'm not much of a car guy - so what usually causes oil blow - and just how "bad" is it to fix? Or is it one of those . . . "well it might be . . ."

 

It might be be worn piston rings :-)....

However, one thing I forgot to mention is that it could be the PVC valve...

I know I had issues with oil blowing down my throttle body due to a rebreather (or whatever they call it ) valve being clogged on the front, drivers side of the engine. Somewhere in the forums a very nice Jag tech described the process of cleaning it.

Hoping a new plug will resolve the problem and get you going again.

 

Replaced the VERY fouled #7 plug. Seems to have solved the problem. Going to drive it see if it throws any codes or get CEL light. And anyway have to go to Home Depot to get a new ratchet so I can do the rest of the plugs - some coils are too tight for hand drive. Will report back.

Of course the question remains how that #7 plug got so gunked up in the first place. If as someone suggested that I might have oil blow by (eeeeek), anyone care to guess as to how long before I'd be faced with this issue again?

 

Woo Hoo! Nice to have those easy fixes on a Jag....

I would clean out the rebreather/pcv valve and call it a day... If it is the piston rings you'll probably just roll it down a hill somewhere when you see what an engine rebuild will cost :-)

 

Just went on test drive - running sweet again. Now plan to let it cool and replace the rest of the plugs. Who knows, might get smoother yet.

As far as engine rebuild - not even gonna think about that.

Rebreather/Pcv - is that the little "tube" that's on the driver's side toward the front of the engine, kinda on top? The one I read about people cleaning out with a drill bit. (Can you tell it's time for me to buy a manual - or get a different car?!)

 

I have an all new problem . . . I think

As mentioned above, after I put the first two plugs in, I started it, drove and everything was great.

Finished the driver's side bank then I went off and did other stuff without starting it up.

Tonight I went to drive somewhere - started it and it barely started - never really got going anywhere near normal, there was some kind of loud tapping/clanking sound - I shut it right down.

Figure I'll double check my work in the AM, make sure everything is together properly. Hoping I made some kind of stupid mistake

But I fear I have a whole new very big problem

Anyone? Anyone?

Sick in San Diego

 

1. the picture you posted is definitely oil fouling

2. what "other stuff"? did you have any part of the internals open?

3. aside from #2, if it sounded like a loose bicycle chain dragging against the guard, it is a cam chain/tensioner problem. just search on "tensioner" on this site.

do not start it up again until you figure it out, or at least rule out #3

#3 is your most likely culprit unless you put something back wrong in the earlier work.

In addition, from your opening post: "Suddenly running very rough at pretty much all rpms." is symptomatic of #3 in addition to the clanking.

What happens is the exhaust cam sprocket chain skips a tooth -> bad cam timing -> rough running. That advances to parts clanging around.

Ruling out #3 requires removal of the valve covers for visual inspection. Of course you must have searched out the pictures to know what it should all look like for this to do you any good. Should take 1.5-2.0 hours working slowly.

 

By "other stuff" I meant non-car stuff - sorry.

It wasn't like a chain dragging - more like a clang clang clang - steady, maybe at intervals of 2 times per second

To be clear, when the new plug went into number 7 it was running smooth as can be. All problems disappeared - no codes.

 

Are you saying you only changed one bank of plugs, and the other bank has the 100k milers still in it? Talk about confusing your ECM if you did. Sounds like major misfiring...any chance CEL came on?

Schedule some time, and re-pull all the plugs and coils, recheck the gap (maybe it was dropped into the plug well, closing the gap?) clean your coil and make sure snapped onto the plug, and coil bolts nice and tight against the manifold. Do both sides at once, make sure oil dipstick is in and cap is tight, vacuum hoses didn't come off the engine, etc...the manifold must be totally sealed to have good pressure.

 

All of the above is fine.

But, keep in mind it drove fine after the plugs, then it rested, then it didn't drive fine.

Not saying it's not worth checking out, but be careful about starting the motor again unless it is known what caused it. For example, finding a loose widget that came off during the test drive.

 

It reads to me more like he replaced two plugs and it drove fine, then he replaced the other two plugs and went away for a while without starting it.... then later, when attempting to start for the first time with 4 new plugs (2 installed earlier in the day that had been driven on, 2 brand new that hadn't been run yet), it was not running right, with the described noises.

I'd pull those two newest plugs, see if there's anything unusual, and try it again... If the noise he's hearing is interference between valve and piston, the damage is already done - so it won't hurt to try, for a short period, again - after checking for any anomalies in the two newest plugs and their installation, and perhaps the first two also, just to see if one of the plugs has suffered from some kind of infant failure.

 

good catch.

just didn't want him to start the engine again until the cause of "some kind of loud tapping/clanking sound" is determined.

guess the best place to start is to check everything that was done after the first successful drive.

who knows? it could be a leftover rag whipping around the fan.

 

Quadmaniac - your understanding of what I did in what order is correct. I put two plugs in, test drove, put two more plugs in, then didn't start up until later when the problem was immediately apparent.

I'm going to follow the suggestions - backtracking on what I've already done, checking plugs, coils etc. Which raises the question - what is considered the preferred gap on the plugs for this 2000 XJ8

Thanks for hanging with me guys!

 

That is a nasty looking plug -- and most likely would cause a misfire. The question is why ?

Looks to be oil? Whenever I have encountered a fouled plug that I can definitely trace to a failing/ failed coil they look wet but not oiled like yours. More of a carbon wet ....... obviously not a technical term

Is this engine one with Nikasil linings?

A failing coil can be a pain to diagnose -- because they appear to work most of the time -- but the plugs normally don't look all that much different and replacing the coil normally solves the problem. Although replacing the plugs may be advised.

You have something else going on -- oil coming from the top down through the common valve cover seals leaking into the plug channel is not going to get to the inside of the cylinder.


How rough was then engine running? Does it have its original tensioners?

I would hate to think that the rough running stressed dying tensioners causing your start up noise. I can't see how what you did would cause your noise.

If you had put the plugs in wrong -- it would not have started and run correctly. Say -- for some reason one of the plugs did not seat correctly and you had combustion gasses coming out.

I would look very closely prior to starting it up again -- Good Luck

 

1999-2003 4.0 take iridium aj84575, gap at .035-.039. But per our pm's carefully check the gap on ir's. You can knock the tip off if to err brutal. I can say i have never had to regap ir's only ck

 

Re the plugs - local parts joint sold me Bosch Platinum - saying they were the correct plug. Were they wrong? Guess I need to know that before I go any further.

 

I don't have the manual in front of me - I think it may list OE plug

 

Closely comparing the old plugs and the new ones that the autoparts store said were the right ones, the old are overall about 1/8 inch longer. Anything to be concerned about?