99 XJR; recently had a misfire, P0300 & P1316. Found that the valve covers were cracked underneath and spark plug seal at left bank #3 was blown. Seal at right bank #3 was close to going, too. I replaced the valve covers and the codes are gone. Still running rough at idle, with a horrible noise that appears to be coming from the s/c. I understand that may not be the s/c at all, but a small misfire on the left bank #3. If so, it does not seem to be bad enough to register a fault code yet. I am also curious about the right hand secondary timing chain. Newer generation tensioners were installed before I bought the car, but when i had the cover off, I noticed that the chain on the right side looks pretty loose. The bottom side seems to have good tension, and since the loose side would be the trailing end of the chain, I am not sure if this is a normal condition. Timing is aligned, as checked with the cam lock tool. I have no frame of reference on these cars, so I would appreciate any opinions, to the extent you can tell from the photo below.



You can also view the other photos of the cracked cover, etc. at the following link:

http://s900.photobucket.com/albums/ac203/SouthTexSC/

 

I think this will answer your question about the chain slack:

https://www.jaguarforums.com/forum/s...light=camshaft

 

JTO, I think I'm picking up what you're laying down. But, I have 11 week old twins and my brain is firing as poorly as the car at this hour. I understand the exhaust cam's "natural" tendency to rotate under valve spring force because the primary chains are not under tension because no oil pressure activates primary chain tensioners. Once oil pressure engages the primary chain tensioners, the exhaust cam is brought back to alignment. So, once started, the slack should disappear as exhaust cam is brought back around. Not sure my brain is completely wrapped around the concept, but maybe I will see it more clearly in the morning when the synapses are firing a little better. I'll get there, eventually.

I really appreciate you taking the time to point me in the right direction. Let me know when and if I can ever return the favor.

 

Kind of you to say, you're quite welcomed. If you look at the engine again, and re-read, it will be more clear. You already understand the concept. And with two 11 week old twins, you sure have the bravery!

 

Thanks for the compliment, but I think bravery is probably a bit off the mark; more likely desperation than anything.

Going back to my chain, I have now had some time to think about this with somewhat less fuzz in the brain. At the risk of showing my ignorance, it occurs to me that maybe I should back up a bit and talk . . . err, write my way through this. Bear with me, and I thank you in advance if you do, but I want to think logically through the problem so I can understand what’s going on. Let me know where I get off track. If you can't bear with me, there is a short answer below.

THE LONG ANSWER:

What I know from the beginning:

On a hot as hell day, I was happily driving my 99 XJR with 110,000 miles home from an out of town trip. Spark plugs changed 2-3 months prior. Misfire occurred under hard acceleration while passing an 18 wheeler; codes P0300 (Random/Multiple Misfire Detected) & P1316 (Misfire Rate Exceeds Emissions). Seeing P0300, my first guess was upper chain tensioners. However, I found the plug well on B3 was full of oil, leading me to the cracked valve covers. The cams appeared to line up correctly, so I assumed the flooded plug well caused the misfire. I replaced the covers & seals, cleaned the plug, plug well, and coil, and put it all back together. Nope, still runs rough enough to leave it parked and I hear noise coming from the s/c. No codes yet, although I have not let it run for long.

My initial thoughts on possible causes:

Cause # 1: Injector at B3. Did I get too much oil into the cylinder when removing the plug, fouling the injector with excess oil? Yes, a possibility, but is it a likely possibility, given the circumstances? I decide probably not, for several reasons; one, because the misfire still seems too harsh; two, the absence of a P0306 code; three, my luck is not that good. I decide to research the issue anyway, but I find nothing convincing. I now have several new suggestions for cleaning the injector, though.

Cause #2: S/C bearing failure: Bad bearings have revealed themselves when belt tension removed? Certainly bad bearings could cause the s/c noise, and poor air flow could cause a rich condition, though such codes yet. But rich enough to mimic a less severe misfire than the previous? Again, I decide this is not the likely cause, but the noise still bothers me.

Cause #3: Bad coil: Old, overworked, bathed in oil. Could be going bad and causing weak fire? Interestingly, I found some misfires that were first thought to be s/c problems due to the noise. This one looks more promising, but I still have not tested the coil, removed the s/c belt to see if the noise ceases, nor had a cylinder specific code.

Cause #4: Secondary Tensioner Failure/Skipped Chain: Finally, my gut tells me that loose chain is too loose. This is probably a more likely cause of a misfire with P0300. Not sure if related to the s/c noise, though.

What Do I Do Now?

So, now the question is whether I can apply JTO’s shared knowledge to arrive at a diagnosis. My newfound understanding tells me that under normal conditions, engine off=no oil pressure=slack primary chains. In other words, the system “relaxes” when oil pressure drops. But, unlike the primary tensioners, the upper tensioners don’t operate on oil pressure, so the upper chain should remain tight. At TDC, valve spring pressure causes the exhaust cam to rotate out of alignment until oil pressure is resumed on start-up. The upper chain on the A bank in my photo shows both slack chain and aligned cams. If start-up brings exhaust cam back into alignment when timing properly set, then start-up in my case would take the cams out of alignment. If I am correct so far, then I am back where I started and I suspect new upper tensioners are in order.

THE SHORT ANSWER:

If oil pressure on start up would tend to bring the exhaust cam back into alignment, I would expect that slack in the chain while the cams are aligned would tend to take the cams out of alignment. If that is correct, I suspect the chain has skipped and tensioner should be replaced.

I already have the tensioners, cam locking tool, crankshaft plug, sprocket wrench, etc. If I have to do one, I might as well do both, right? One question, though. With the crankshaft plug installed, is it necessary to lock both cams? Seems that removing sprocket on one should not affect the other bank.

If I have gone down the wrong path completely, feel free to send me down another. As always, the assistance is greatly appreciated

 

Ugh. The secondary chains can't jump unless the slipper is missing from the secondary tensioner. Put the crank index tool in the flex plate, put the cam setting tool on the camshafts, rotate the camshafts carefully with grips if you have to line them up but the cam locking tool shoiuld bolt down flush to the head and both camshaft flats will be in the right place. That means you're looking in the wrong place for the problem, and you're in exactly in the right place to prevent a future one. Replace the secondary tensioners. Yes, you only need one cam locking bar because you are only replacing one tensioner at a time. Watch the A bank exhaust camshaft rotate as you remove the tool, for the reason I described. Now you will see that you have slack in the A bank secondary chain, which will not be there when the engine is running.

 

"Ugh" is right. I suppose that is what I get for trying. Told you I would show my ignorance. I thought I had it right the first time, but I second-guessed myself and over-analyzed. I'll keep at it. Thanks for indulging me, though.

 

You're OK, I just got dizzy reading and that's the sound I make before I hurl. With two 11 week old children, you'll learn to recognize the sound.

The way the whole timing set-up is designed, it's a little abstract. You're actually ahead of the game, most people get through replacing the secondary tensioners without really understanding what all is going on. If it all doesn't go by wrote and they have a problem, they don't know what to do. Sometimes the results are expensive.

 

I also have a 3 1/2 yr old daughter, so my world is chock full of unexpected and unwelcome noises from a variety of sources. I just get pissed when my car happens to be one of the sources. I shouldn't really complain. I have a pretty good job, I get free advice from my dad the diesel mechanic and free towing from my father-in-law who owns a repo company, and I even stumbled into a loaner set of timing tools from a local Ford dealership (still in the sealed shipping box, never used). My wife really can't complain, either, because she gets to pretty much spend all the money I have saved while I am either at work or working on the car. But, I still have little room for extra expenses, so I truly appreciate your expertise and your time. Hopefully I will get it all figured out before the kids start college. Any chance my other theories are worth exploring?

 

As for what's wrong with your car? Didn't read it, I was following up with an answer to my original answer to your original question. Screw the car together, drive it, read codes and post the results. If you didn't put new plugs and make sure the wells were clear of oil yet, do it now.

 

Cool. Thanks again. New plugs about 2-3 months ago, but Denso, not NGK.