Misfire Cylinder 5 - Advice?

[ihawkr]

Hello Everyone!

New to the LRW Forum

Just picked up an LR4 5.0 w/ 145k miles and a cylinder #5 misfire at a fair price(Purchased w/ the misfire intending to repair).

Getting it home I put the scanner on it and obtained CEL P0305 & P0316
P0305: Cylinder #5 misfire
P0316: Misfire on the first 1000 RPMs

Looking at a misfire count while driving, you can make it a couple of miles and see about 200-500 misfire counts on #5.

I tried spraying some valve cleaner into the throttle body which seemed to make things run smoother for a few miles, took it for a test drive for about 10 miles, only about 70 misfire counts on #5, tried wide open throttle, and then a harsh shudder and loss of power, limp mode activates, cylinder 7 misfired around 700 times out of nowhere! Then the CEL for cylinder #7 misfire went away on its own, haven't seen it since.

On cold start it seems like there is no misfire, then it appears after idling for a short time.

WORK DONE SO FAR:
1. Swapped the ignition coils around to see if the misfire followed - No Change

2. Replaced all spark plugs - Seemingly fixed? (But only for a few miles)

3. Replaced the fuel injector on cylinder #5 - No change

4. Took spark plug on #5 back out to check the condition and it is covered in oil on the threads
(Fairly sure it is oil as there doesn't seem to be any fuel smell)
Also worth noting there is no evidence of oil in the spark plug channel indicating a valve cover leak.

I am going to purchase a leak-down tester this week and see if I can't get more insight into the issue...

The only two things I can gather are either the piston rings are worn and creating blowby in the cylinder causing the spark plug to be fouled with oil, or the valve seal is leaking oil down on the spark plug.

Coolant doesn't seem to have oil in it, oil doesn't seem to have coolant in it.

It seems that the misfire goes away for a bit if I replace the spark plug, which makes me think the oil on the plug is the cause of the misfire.

Any advice or opinions would be greatly appreciated!
Thanks!

 

[ihawkr]

Photos of cylinder #5 spark plug channel, as well as cylinder #5 spark plug after roughly 20-30 miles of test driving.

 

[ktm525]

You shouldn't have oil on the threads if it is worn piston rings since the threads are not in the combustion chamber. They would become oily as you backed the plug out if the leak is from the top... Those threads look so evenly coated. Are the threads stripped in the spark plug hole?

Are you getting any blue smoke? If so on startup (leaking valveguide) or when you put the boot (accelerate) to it (rings). If negative on both then IDK

 

[ihawkr]

I don't believe the threads are stripped as the plug has no problem threading in or out, and it torques up just fine when tightening. Hard to visually inspect the threads without an endoscope though. No visible smoke on startup or while driving that I've been able to notice either! This one has me pretty stumped for now!

 

[ktm525]

I am going to go out on a limb and say some of that dark stuff is fuel and you are running rich in the cylinder. Intake/Exhaust valves not behaving properly? Dirty?

 

[ihawkr]

I just pulled a few more plugs on that bank, looks like 3/4 had this dark fluid on them. Some smelled more like oil, others more like fuel so perhaps it's just fuel. I'm now thinking the same thing and wondering if a head rebuild is in my future. I'll try and get a leak-down test going tonight and post any updates I find. I appreciate your input @ktm525

Also to eliminate the possibility of me just being a ***** and replacing the wrong injector...
Cylinder numbers are as follows correct?
(7)--(8)
(5)--(6)
(3)--(4)
(1)--(2)
FRONT OF ENGINE

 

[ktm525]

yuppers.

 

[ihawkr]

Leaking injectors.

The injector on cylinder #5 was just replaced, but that could definitely be the case for the other cylinders. I just ordered the other 7 injectors and plan on replacing the rest of them tomorrow, just wanted to replace 1 to try and isolate the problem since they aren't too terribly hard to get to. Is it possible that leaking or clogged injectors in the other cylinders could be causing the whole bank to run improperly and the misfire on cylinder 5 is the result of the other cylinders?

 

[ktm525]

did you have trouble pulling the injectors?

 

[ihawkr]

did you have trouble pulling the injectors?

Not much trouble, the fuel rail was on there pretty good, but once it was removed the #5 injector came right out with the fuel rail. Replaced O-rings on the other 3 that were still in the head, threw in the new injector on cyl #5 and it all went back together easily without leaks.