If you run downhill as you did the vacuum created will only be from the butterfly to the valves not in the corrugated intake pipe so the oil would have to come via the valve guides/ rings -there is nothing else in that tract with oil.
Now that does not mean the valve guide seals/rings are faulty its just using 3rd caused an extreme vacuum for a long time .
If you clean it all out and take it for an Italian tune up it should be OK

 

Oh, I hope that is true.

 

There is a partial vacuum in the intake pipe. Otherwise there would be no air flow..But the air flow is toward the engine , not away from it . Oil mist from the engine side of any magnitude will not move against the flow and into the intake pipe.

Partial vacuum is also called a low pressure area.; not a full vacuum of course, but enough of a pressure differential to move the air. Which BTW is what moves weather systems across the planet



Z

 

the full load breather is the engine side of the small hose going to the intake pipe.


if you haven’t downloaded a shop manual from the sticky section do so. Having the manual lid invaluable.in troubleshooting.

Z

 

The coasting would create an extremely high vacuum which can draw oil down valve guides, but that mess inside the intake (Yes, that would have been under extreme vacuum) looks like it was inhaling oil from the vicinity of camshafts, via part load or full load breathers. The part load breather (left or B bank) is under vacuum but not the full load. Check to see if the full load breather and corrugated intake between MAF sensor and throttle body are oily, but that is highly unlikely. Normally, air runs through the full load breather into the engine with intake vacuum, but can allow inhaling engine fumes to the throttle body under low vacuum/heavy throttle. Remove the part load breather and see if that's where the oil came from. You can also make sure the small hole in the valve cover is open while you're at it.

Have you checked your dipstick lately?

Hopefully the rough running and low power were due to ECM cutting off injectors on the worst cylinders. Let's hope the oil did not permanently harm the catalytic converters nor O2 sensors.

I assume you cleared codes to the point of clearing pending and historic faults. Might not hurt to do a hard reset on the battery to wipe out that episode and have the ECM start relearning new values.

 

Well, I dug into the engine not really knowing what to look for, something I hated to do. What I found was copious amounts of engine oil in the intake manifold. Still not sure why. I cleaned it out, checked the fuel injectors and replaced the "O" rings. Installed new plugs and buttoned it back up. I still get the codes of multiple misfires on cylinder 1, 5 and 8. It has to be either spark or fuel related. How can I tell which it is? The code reader is no help.

 

Try changing the coil packs from the affected cylinders with those unaffected and see if the code moves.

 

Thanks Pistnroke, that sounds like a good idea. I should have thought of that.

 

Well I traded the coil pack on number 5 cylinder, one that the scanner had identified as missing with number 7, not showing a miss. I expected (hopefully) that the miss would follow. Instead the new scan shows all 8 cylinders now have misfire. (!) Before the switch it was "only" #1, 5 and 8.
I am totally mystified now. It runs just like it did before the plug pack switch, no better, no worse.
I am not a quitter, but for now I am walking away.

 

You say "It runs just like it did before the plug pack switch, no better, no worse." That doesn't really describe how it is running. Let me guess, is it doing more "shake, rattle and roll" than idling? The fact that all 8 cylinders are blamed for misfiring leads me to believe the shaking is giving the ECM the impression the cylinders are misfiring due to the erratic crank speed. It probably isn't really an injection nor ignition issue. Is it loading up with oil again? Check plugs to see if they're oily or wet. Clear codes again and retry. See if it starts out decent and then gets worse. If the ECM identifies cylinders it perceives are misfiring, it will cut off injection to those cylinders which will make it run worse.

 

Sounds like a compression test is in order ...dont forget to open the throttle butterfly when you are doing the cranking.

 

These cars are not made to use the engine as a brake for 7-8 miles down hills and mountains. That's my take away. I would guess that relatively high to huge vac could have pulled oil and oil mist from anywhere it could. Maybe creating a vac leak.

What do fuel trims say?

Is it possible that intake valves got completely gummed up in this, that brings readings past the misfire threshold,,, and that a good run (Italian tune up), ignoring the misfire alerts, could burn away the accumulated carbon deposits? After cleaning out the intake, plug wells, maybe even replacing cam cover seals, that is...

What's it look like down INTO the throttle body?

​​​​​​

 

The throttle body did show traces of oil when I had the intake disassembled. It makes me think that was the source of the oil ingestion was probably having to do with the PCV system. I have replaced all the "O" ring seals while reinstalling the intake manifold. I bench tested each fuel injector to confirm that it is at least opening when probed. I replaced the "O" rings on the injectors. I replaced the spark plugs with new. As I mentioned, I swapped the number 5 plug pack ( showing a misfire) with the number 7 hoping the misfire would follow. I checked the fuel pressure ,approx 45 lbs. Then I cleared the codes and restarted the engine. Although it will start and run, it is rough. When I rev it up at first it will wind up ( around 4K) then the "reduced performance" message comes on, then the check engine message, at first blinking on and off, then steady. Then the P0300, multiple misfires, then eventually P0301 through P0308. No real smoking out of the tailpipe. I have run it until the coolant temp comes up to normal, hoping the "Italian tuneup" would clear something. I did not run it long enough, I guess, to get fuel trim readings.
Maybe I am just wishing and hoping, but I really think it is one big thing that is keeping it from running right. Not a lot of small things like vacuum leaks and bad coil packs or dirty mass air sensor, etc. I confess, this engine is a mystery to me, I am much more comfortable with my old American hot rod engines. The PCV system on this thing seems overly complicated. I do remember that before all this happened my fuel trims were on the high side, maybe that is a clue. But it ran well. Thanks to all that are trying to help. As said, I am not a quitter, but for now I am sort of stumped. I am going to try to "read" the electrical signals going to the injectors and the coil packs using my oscilloscope using inductive coupling. I will post what I find, if I can find anything.

 

are you revving the engine in park or neutral ?


Not sure if this has been mentioned already, but it may be helpful in the troubleshooting process to know that these cars are electronically rev limited and will not rev much over 3,000 rpm when in park or neutral. I don’t know if that applies to all X-100 models, but it certain might.

​​​​​​…..sorry if this has been mentioned already.

Z

 

Don't dismiss a vacuum leak.

I had a similar hair-pulling XK8 rough idle problem about 2 weeks ago and finally discovered the brake booster line had become disconnected from the throttle body. ECM never gave gave a lean mixture warning.

About the same time, my wife's supercharged MG TD started running very rough. A shot of MAF sensor cleaner revealed the intake manifold gasket had a vacuum leak.

They say everything happens in threes, so now I'm worried another car is about to give me trouble.

 

Well, I have finally found something that probably explains my problem (s) . Yesterday I did a compression test on my engine. The first thing I noticed as I removed the plugs was that in cylinder #5 the plug was shiny as new, just like I had installed it. The other 7 plugs looked like they had been running extremely rich. When I ran the compression test I found all cylinders at around 175 lbs except for number 5. It was ZERO! The gauge didn't even wiggle while pumping. I at first thought the gauge was not working, but no, it was working fine. The only thing that I can think of is that there is a valve broken or stuck open. Probably the intake valve since I detected a faint noise in that area when I was running the engine. And it might explain the oil in the intake manifold. I probably should have started with the compression test and saved myself a lot of trouble. But, there it is.
At this point I am not sure what I am going to do with the car. I am fortunate that it is a hobby car, one of several that I own. I don't need it for transportation, and I have a nice shop to work in and plenty of time on my hands. But I am not sure it makes since to keep plugging time and money into a car that really has limited resale value. The rest of the car is in what I would call good driver quality shape. Newish tires, and a new radiator, no rust, decent top as so forth. My hot rod friends say "yank that thing out and put a chevy in it". I could, but I won't. I have enough hot rods. I have rebuilt several more conventual engines, so I know my way around the process. But I am not sure if I want to tackle this one. Maybe a replacement engine, or just sell it as a parts car. Not sure yet what I will do. But thanks to all of you who offered your help. I would never had gotten this far with the car without the help that I have received over the years from this forum.

 

If you put compressed air to the plug hole and listen at the exhaust or inlet you will know which has gone.
Sounds like you need one head or one valve seat replaced.

 

I agree.

There are 10 easy to get to bolts in the NA XK8 that hold down the plastic intake. Then a few hoses and plugs that go to the throttle body. The tough bolts to get to (it's not that bad) are the two at the base of the throttle body (you'll see em). All and all it takes 30min tops to get the top end off of the engine. Wish the 928 was like that, lol

Removal of the top end will give you a good look down each of the intake ports. This may be a dumb 'probably' BUT (and this will make clear my lack of understanding of the anatomy of the xk cylinder head) is it possible that the intake or exhaust valve was put under such and extreme while engine braking that it went to it's extreme travel and just got STUCK in it's extended position? Of course, in an interference engine that could mean all sorts of BAD, but it might be worth a look see. The noise you heard may have been the cylinder coming into contact with the I or E valve...?

I'd say spend the 30min removing the top end and have a look down there. I would LOVE to see a photo or two of what you are looking at.

 

That is a great idea Pistnbroke. It won't fix the problem, but it will verify what I am thinking or not.

 

I am embarrassed to admit that I have already done most of that. I went in not really knowing what to look for. I checked and tested the injectors and replaced all the "O" ring seals. It was how I found that the intake manifold had a lot of oil in inside. So, I know what is involved with taking the top off. I think what has me worried is the complicated variable timed dual overhead cam system. That looks like a nightmare to me. Thank you for the advice. I am going to "stew" over this for awhile, maybe put the car on the back burner while until I quit kicking myself for not checking this earlier.