I recently changed cracked valve covers, upper tensioners on my 99 XJR (see previous posts, links below):

https://www.jaguarforums.com/forum/s...ad.php?t=21135

https://www.jaguarforums.com/forum/s...ad.php?t=21959

I have it back together and I am still having a misfire. Got a chance to drive it for 10 or 15 minutes today and it popped same codes as before, P0300 and P1316. Also getting some noise from the s/c. No smoke and exhaust is clear but smells rich. I used to have white smoke on cold start up, but not since recent repairs. Also, spark plugs were changed about 2 months before the misfire began, but Denso rather than stock NGK. Any word on Denso plugs and or oil-flooded plug wells causing the coils to fail? Any suggestions or recommendations for what to check next?

As always, thanks in advance for your help!

 

Update:

I located a small leak in one of the silencer tubes on on the intake pipe and repaired it. I also discovered that after my drive yesterday, I had an abnormal amount of blow-by from the full load breather. However, I was able to go through two drive cycles today and was unable to replicate the P0300 and P1316 codes and there seems to be some improvement in the misfire condition, although it is still quite noticeable.

Two things that are unknowns to me, since this is the only Jag I have worked on I have no experience with a known working example. One, I removed the full load breather tube to check blow-by while the engine was idling and the engine had a very noticeable stumble. Never done that in the past. Two, while engine is idling, I can hear the very distinct sound of air movement near the EGR valve. Not a whistle, but much like a constant suction. This happened while engine was cold as well as warm. If from the EGR valve, then I would suspect that it should not occur at idle or when cold.

When time allows over the next few days, I intend to check compression, ignition, fuel delivery and pressure, vacuum and EGR valve. Because I have only seen P0300 and P1316 codes and the misfire seems to be much worse at idle, I am leaning towards a vacuum or EGR issue. I understand that vacuum problems from the part load breather can cause increased blow-by on the full load side, but the increased blow-by also makes me worry about compression issues. Any advice or suggestions on what order I should follow when performing the above checks? Anything I am missing here?

I appreciate any help you can give. Thanks.

 

That makes three misfire causes down and at least one more to go. This weekend I pulled the spark plugs to do a compression test. Left side looked good, but the right side did not look so good. A1 plug ground electrode was beginning to melt, A2 plug ground electrode was completely melted and the insulator tip was broken, and A3 & A4 plugs had some oil fouling. The plugs were Denso Platinum and were only about 2 months old. I replaced with NGK iridium of the same heat range as the stock NGK's. P0300 random misfire code was then replaced by p0302. Tonight I tracked a vacuum leak to the bypass valve hose and repaired that leak. Now, the misfire is noticeable and the idle is rough, but no codes after several drive cycles. My biggest concern is that with each progressive repair, the blow-by from the A bank has gotten progressively worse. I never got to do the compression test because my gauge has crapped out on me, but it seems that if this was a nikasil issue, it would not have been such a sudden increase in blow-by. Any chance the broken insulator tip entered the chamber and damaged the valve seals or something else. I will try to pick up a new compression test gauge tomorrow and check, but I would appreciate any advice on finding and fixing the problem. Thanks in advance.

 

That does not sound real good, Tex.

The melted ground electrode suggests extreme combustion chamber temperatures due to lean running. A2 could quite possibly have damaged the cylinder bore, so your next step of testing compression at a minimum is indicated. If this is the road you find yourself on, the piston crowns may not look too happy either. Hope for the best.

PS there is mail in your other box. Thanks again!

 

I checked compression this afternoon and here are the results:

A1, A4, B1, B3 - 120 psi
B2 - 110 psi
B4 - 130 psi
A3 - 150 psi
A2 - 0!!!!!!! (dry and wet)

How screwed am I?!?!

 

That does not sound any gooder, Tex.

Next test is a leakdown, pumping compressed air into A2 when it is at Top Dead Center on compression stroke (valves closed).

The melted ground electrode and broken ceramic insulator could have done their share of damage, but you wouldn't be getting ZERO on a wet compression test. If in fact the ground electrode is melted off, you could very likely have a hole melted through the piston crown. That will give you a zero.

If the ground electrode was instead broken off, then it is more likely that you dropped a valve. That will give you zero. It will also smash the piston crown, and damage to that cylinder bore caused by the valve head or by the damaged piston is very likely.

It ain't gonna rub out.

 

Funny how I have never used the word "gooder", or even heard it used, when things really are gooder. I pretty much knew I was screwed when I saw the melted electrode on a spark plug with less than 2,000 miles. That was confirmed yesterday when I pulled the new A2 plug with only 20 miles or so and found it to be almost pristine except for blackened negative electrode tip. The other 7 look like they have been in an enclosed chamber with exploding gas and fire, although a little on the oily side. I wonder if using the Denso plugs was a bad idea made worse by the lean condition.

I will probably get to the leakdown test this weekend and will post results. I peeked in at the piston crown and found nothing shocking; all 8 look about the same. I will need a borescope to get a better look, of course, unless I want to start taking the head off now. Any tricks for getting a better look in the cylinder or finding/making a "poor man's" borescope?

What I should do is destroy it and start from scratch, but, just my luck, Cash for Clunkers ends on Monday.

 

Heyo Tex,

I don't think it was a denso move selecting those spark plugs, I use NGK's but your engine didn't get hurt from your plug choice.

I don't have an answer to the boroscope question, I have never used one. It is a time saving tool but not a necessary one. When you do the requisite tests, you know pretty much what you're going to see before you see it.

No engine noise and no damage to the new spark plug means it's not a broken valve problem anyway, and the engine would likely be running alot worse than hitting on 7 like it is now.

You'll know when you do the leakdown, you just listen for where all the air is escaping from A2 when you try to pressurize it. Likely you'll hear it huffing out the full load breather stub pipe, as it blows straight into the crancase.

The piston might be melted out at the circumference, but there has to be an ugly amount of damage to the piston and/ or bore to result in a zero compression reading when tested wet.

As for the "Cash for Clunkers", I think there is a guy down your way named Smilin' Jimmy who has extended that program indefinitely. If not, there is a guy I know in Ohio who buys broken Jaguars and starts from scratch. Sometimes a plan like that is gooder than dumping alot of money into a car that won't pay you back. I'm not trying to make light of your situation, just pat you on the back and give you the only bad answer that fits..."It is what it is".

 

Hey Tex,
Harbor Freight tools has some reasonable prices. Especially if it is something you do not use that often. Hope this helps!

http://www.harborfreight.com/cpi/cta...and=Cen%2DTech

 

Thanks Bob, $140 for the boroscope is pretty cool. Not all their pricing is the best from the looks of it, I got an IR pyrometer for alot less at Advance Auto Parts on sale.

 

Bob - thanks for the tip. I replaced my compression tester there on Thursday for a whopping ten bucks. Maybe that was $1.50 per cylinder and I ran out of quarters before I got to A2. I'll check out their borescopes. Even if this one goes where I think it is going, at least I can use the scope to inspect every nook and cranny of the next one.

JTO - I talked to Smilin' Jimmy today and unfotunately his program is a little backward - I give him the cash; he gives me the clunker. I got that same deal back in January and its not what its cracked up to be. On a brighter note, I hear 7 cylinder supercharged V8's go for almost 3 times more in Ohio than they do in Texas. You hear the same thing? And, the best part of my day, I re-tested compression today with BBQ sauce from the place next to Smilin' Jimmy's. Still got zero compression, but it also spit a chopped beef sandwich out the full load breather. Seems previous owner's need for aftermarket performance enhancement lead him to intall a George Foreman grill in there somewhere, which I hear also raises the sales price in Ohio.

What puzzles me the most about this whole damn thing is that this car sophisticated and sensitive enough to alert me to the fact that I have crappy taillight bulbs that cause occasional "rear bulb fail" messages when I brake, but which is completely ignorant of a cylinder with zero compression. After I changed the bypass hose, I drove around for more than enough time and never got a single diagnostic code.

 

I have no idea what your car is worth, but your sense of humor is flat out priceless. You deserve a "well done", but you might coincidentally perceive that as a remote mechanical diagnosis.

If I ever again hear someone utter the famous phrase "Where's the beef?", I will forever have a ready answer....

A2.

 

Yes Harbor Frieght is good on some items but as all places you should shop around and exercise a little jurors prudence! Thanks for the tip on the additional source Andy....!