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Discussion Starter #1
My '01 RR 4.6 SE with 115k miles has started giving me a misfire and rough idle on cold start-ups, but it smooths out after 15-30 seconds or so and runs fine until the next cold start. It only does this on cylinder #7. Spark plugs and wires have all been done somewhat recently (Bosch +4 Platinum and Kingsborne 8mm wires). I pulled a few plugs and plug #7 was soaked with oil but the others looked fine for their age. I took it to the LR dealer for a diagnostic, and they confirmed a fouled #7 plug causing the misfire at cold starts (did not tell them my findings first).

The dealer said that only two things can cause oil fouling in the cylinder like that...either valve stem seals or a failed piston ring. The dealer added that with 115k miles it is certainly the rings, and recommended a full rebuild/engine replacement. Is this a correct assessment? What is making me skeptical is that I do not get any smoke in the exhaust at start up, and I am not loosing a significant amount of oil.

The dealer cleaned out the plug and said it should run a little better...but we will see tomorrow morning how it does at cold start. What are the chances that this really is a failed piston ring? And why would just one of them fail and not a bank, or at least a pair of cylinders? Also, is there another test I can do to confirm the bad news?

Thanks!
 

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Rings wear but rarely fail. If you were having ring issues I would suspect all would fail at an even rate. However at on 115K it is doubtful. Then again a single oil seal failing is rather odd as well. It is very possible that a bit of crud was introduced during an oil change and nicked the seal. My experience is that weak rings lead to oil burning while driving where a failed seal will result in oil pooling on the top of the cylinder while parked, which sounds like your issue.
 

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JACK'S GRANDAD
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Hmmm dealer....:roll:
And if they suspect bad rings, why did they not perform a simple compression test?
And, pray tell, does it foul a plug when the engine is not running? You running some magical oil that can travel UP onto the top of a piston to foul a plug when the motor is shut off?
Valve stem seal all the way in my experience.

Martin
 

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There's a possibility that the valve cover breather is blocked and pressurising the area above the heads thereby pushing oil through the seals when the engine is turned off... worth a check
 

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Ah crud, I never think about the breathers. Pull the seperator out of the valve cover and clean it up. As a temp test you could run without it and see if things get better. You aer still dealing with a weakest link. However a clogged breather could very well be the answer!
 

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JACK'S GRANDAD
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Bad breathers/PCV causing bad running and fouled plug(s) on a cold startup?
Doubtful indeed IMO, but free to check I guess.
If it did it when it had warmed up etc, then I would be more likely to suspect it, but not on a cold startup situation where there is only 1 plug getting fouled.
Just my .02

Martin
 

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Discussion Starter #7
Thanks for the input everyone! Sorry for my delay..I was out of town for a bit with work. I will check the breather this week..fingers crossed it's that simple.

There have been a few occasions where the engine had a brief misfire episode while driving at normal operating temp. Only a few times and I did not have any noticable smoke in the exhaust during the misfire. Just the flashing check engine light and a slightly noticable misfire...only lasted a few seconds though. Just about every cold start will trigger the misfire however.

I will post up with results of breather cleaning/testing.

Edit: Fun fact...When I picked up the Rover from the dealer (regretting going there for diagnostics the more and more I think about it), I asked him for a ball park price on fixing the problem. He said he'd just replace both rings and valve stem seals to fix it, but would recommend a new engine instead of the labor of rebuilding. Said ''I've never done one on a P38, but a new long block and 30-40 hours of labor, probably $15,000". I don't even remember if I laughed or not...just got in the car and drove off hah. I'm not sure what's more concerning...that the head of the service dept. has never done an engine replacement on a P38, or that he said $15,000 for a rebuild..:shock:
 
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