Niels Jørgensen

I recently (6 months ago) had all cam-cover gaskets and o-rings replaced in both sides because oil was leaking into the holes that houses the spark plugs (very scientific description right? Sorry, but I have no idea what the correct english terms are for these things ).

About 4 weeks ago, the car was not running as it should so I decided to check the plugs and, once again, found them soaked in oil. I cleaned them up and everything went back to normal. I talked to the mechanic and he said that the only thing he could think of was that he might have neglected to clean it properly <img border="0" alt="[nono]" title="" src="graemlins/nono.gif" /> .

Would explain the oil, but not why it suddenly started running bad or why it improved after the oil was cleaned up.

The car has now been stranded 14 days on account of a broken speeder cable <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" /> . When I fired it up yesterday after replacing the cable, it was all cranky. Couldn't maintain idle properly and didn't accelerate as it should.

I've seen this before after not driving the car for a while but decided to check the plugs again anyway - I found a little oil on a couple of them, but nothing like last time or the time before that (when the gaskets and o-rings were replaced).

What I did notice was lots of soot on the plugs (see picture) - I'm don't know what a plug is supposed to look like after 6 months in a Porsche V8, does this look/sound right? Do I have a mixture problem, too lean/rich? Could this explain rough idle, or is there an idle stabilizer or something similar I need to look at?

A bit of additional info:

When cleaning up the oil, I also cleaned the plugs, so it could have been either that helped improve the situation.

The oil is clean and so is the exhaust so I don't think I'm burning oil.

Full power is usually restored after messing about with plugs/wires/dist. but then slowly deteriorates.

The car has had these symptoms since I got it almost 2 years ago - mostly it runs great, then suddenly won't accelerate like I know it can. After I (or my mechanic) mess around with a few things the problems go away for a while, but they always come back. It seems as if I've yet to discover the true problem.

Any ideas?

TIA

Niels
87 S4

<img src="http://www.porsche928.dk/images/plug.jpg" alt=" - " />

ErnestSw

I wonder whether it's really oil you're finding on the plugs or whether it's unburned fuel residue as you suggested. Possibly a MAF problem?

BrianG

If the oil is wetting the porcelain part of the plug and/or the spark-plug wire connector, you are losing spark to ground, through the oil, effectively killing the plug. That would make it run bad.

The seals at the base of the sparl-plug holes in the cam-cover can be the source of leakage into the spark-plug recess (search the archives for ideas on fixes) and I'd bet that's the case because the "clean" oil you are getting has no other source that I could imagine.

As for you pic of the plug, the porcelain around the electrode is supplsed to be light tan in color. Yours looks good. The soot around the bottom of the threads is not a concern.

jamesld

Niels,

Oil could be seeping into the plug tubes due to the incorrect installation of the o-ring seals in the valve covers, sometimes this happens when they are installed upside down.

I am not an expert, however, the photo you posted of the spark plug looks normal. You will have black sooty deposits on the outer rim of the plug, but as long as the ceramic core and electrode tip has a light grey appearance then the fuel/air ratio is normal.

You may need to replace your spark plug wires, if things seem to improve after you mess around with them, could be a fault in the wires.

Niels Jørgensen

Thanks for the suggestions guys - maybe I should clarify a couple of things:

ErnestSW: I'm 99% sure it's oil - it's on the washers and threads, not on the tip of the plug. Also it's thick golden-brown like the oil (mobil 1 5/50)

BrianG: The picture doesn't show, but the (upper) porcelain part of the plug is dry and clean. The seals around the plugs were replaced along with all the o-rings and the big cam-cover seal.

jamesld: My wires are original Porsche wires, 1.5 years old. No guarantee, I know, but it seems unlikely. The mechanic I use usually knows his way around the 928, but I guess we can all make mistakes - I'll check the plugs again in a few weeks, if there's oil there I'll suggest to him that he may have the seals in upside down and see what he says. Thanks for the tip.

Niels Jørgensen

BTW, ErnestSW: Is there a way to check the MAF sensor? Simple inspection perhaps? (If so what should I look for and how much do I need to take apart to get to it?)

I'm not a die-hard DIY type, but I hate to hand over an unspecifed problem to a $100/hour mechanic - It's kind of like writing your PIN code on the back of your credit card and then leaving it at the local bar

BrianG

The quick way to check the MAF is to unplug it while the car is running. If it does not change the idle character to do that, it's bad.
MAF sensor issues are not all that common, and I understand that it's not an "all-or-nothing" failure mode, so determining MAF issues is not going to be easy.... BUT, you car does have some computer diagnostis capability. Than would be a good place to start if you can access the Porsche tool.

ErnestSw

The MAF sensor has to be checked on an oscilloscope (sp?). From your description of the plugs it sounds unlikely that it's a fuel problem. It's more likely that it's the O ring seals.

BrianG

As much as I hate to concur with a physician........ <img border="0" alt="[icon501]" title="" src="graemlins/icon501.gif" />

Niels Jørgensen

Ok, thanks... I'll have'em readout the computer the next time I'm at the shop (which seems to be far too often these days :| )

Right now, my primary concern is the hesitation - not the oil (unless it's related 8)). Another possible clue is that it is definately worse when the engine is cold.

The response I get when flooring it is fast acceleration for a short period, then hesitation, then acceleration. When I let go of the gas, RPM drops violently to 5-600 then "sort of" stabilises at 900 RPM. Occasionaly, it doesn't stabilise in which case the engine dies (very annoying as I also loose power steering - my god that car is heavy).

Erik - Denmark

Hi Niels,
Not clear for me, are the oil coming from outside (The cam cover/head gaskets) or from inside (Piston rings, valve guides)
how big are your oil consumption?
I knew your engine has run more than 300,000 km, has it ever been total overhauled with new gaskets, valve guide/seals and eventual piston rings?
If not I think you shall check the condition with a compaction and blow-by test!
How did your V-bay look - Is is full of oily water? If yes, then most properly you have rotten head gaskets.
We can eventual meet one day and take a look together

ErnestSw

Hey Brian,
Even a blind hog can occasionally find an acorn. <img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />

Niels Jørgensen

Hi Erik, I'll be in touch - it's probably easier when actually looking at the car

My guess is that the oil originally came from under the cam covers because of old/worn seals. When the seals were replaced (6 months ago), the holes may not have been properly cleaned up.

I don't think the engine has had a major overhaul, but I haven't noticed water in the oil or v.v. either.

It does use oil, but within factory spec AFAIK (I think I've added 3L in 10KKm)

I'm more or less concentrating on electrical gremlins because of the problems intermittent nature. I would think faulty rings or head gasket would either be a constant problem or not a problem at all?

Erik - Denmark

Hi Niels,
Thanks for the 'more info' - Then I think you shall check your crankcase ventilation - It seams to be due to overpressure in the engine.

Niels Jørgensen

Um ok, now you got me

I think I'll need a little more information to figure that one out. Crankcase ventilation is what exactly? Where do I find it, how do I check it? (And, given my ignorance on the subject: Should I even consider doing this myself at all? )

Thanks