Mike Frye

I've got a miss in one of my cylinders (thought the change of LH the other day got rid of it, but not so). Also it still surges when cold.

I've done a lot of things to this car including:
tb/wp (and replaced cam gears, which may not be perfect and is next on my list to check)
top end refresh (there are NO vacuum leaks) all sensors have been replaced and tested good. Included new Ford Racing 24lb 4 hole injectors.

The plugs were replaced when I got the car in 10/06 along with wires, caps and rotors (I didn't replace the coils). The rest look OK, this one (#3) is really bad:


Here's a pic of the set and my compression numbers (warm, but not hot):
Top of pic is front of engine, so it's
5- 170----1- 165
6- 174----2- 164
7- 160----3- 165
8- 171----4- 156


As you can see the threads on plug #3 also seem much cleaner than the rest. I don't think I wiped it off after I pulled it, but I may have.

So, could the cam timing cause this or is it something like a blown head gasket or worse?

Thanks in advance for any opinions and questions.

hacker-pschorr

Looks like oil deposits.

My #1 spark plug looked like that after a few hundred miles. New guides / seals fixed the problem.

Mike Frye

Thanks Erik,

If that were the case, wouldn't it take a while for the new plug to start getting fouled and start missing again? My car still has a miss with new plugs in it. Could it be that bad?

hacker-pschorr

It didn't take long for my #1 spark plug to look like it was dipped in margarita salt. I posted pics somewhere around here. Not sure where.

Mrmerlin

if its the guides or valve seal then it begins to leak when its shut down.
You could try a test install a clean set and run then check the condition of the plugs.
You could also have a leaking injector, but its probably oil your seeing
.BTW what kind of oil are you using, you might consider a switch to another brand.
Also add some techron to the fuel

hacker-pschorr

+1 - my car would smoke like a chimney if it sat for a few weeks, burning off all the oil in the combustion chamber.

Schocki

Mike,

how much oil do you burn? This spark plug looks exactly like the one out of my 944 S2 when the oil control ring on piston #1 was worn.

Does your car smoke blue at high RPM's (4000+)?

Mike Frye

Ah, that makes sense. I just put new plugs in last night, I'll take a look this evening and see if it's bad again already. The injectors are new so I hope they're not leaking.
Mine doesn't usually sit for that long, since I drive it 5 days a week, but it doesn't much chance to burn anything off either, it's only about a 10 minute drive to the train station. I try to blow it out on the weekends, but the daily run is barely enough to warm it up. I have been able to see the exhaust when I started it up over the winter, but I thought that was just because it was cold out. It doesn't smell like I'm burning a lot.
Ah! Rings! I hope not.

I barely burn any oil. I use Amsoil, I think it's 'European formula' 5w40?

Since I don't put that many miles on it (11k in 2 years) I'd have to really be burning a lot to notice it in that few miles. No smoke that I'm aware of at high RPMs, but I haven't really been above 4500 rpms in a while because I was showing up lean at the top end at the dyno last fall, so I'm taking it easy until I can confirm that it's OK with a split second AFM I plan to install in the next few weeks.

Schocki

As long as yo stay in moderate RPM's there is nearlly no oil burning. Rev the engine in Neutral (about 10 seconds) and observe the exhaust.

Mike Frye

Even if it's an oil control ring? I would think that would burn oil all the time, no?

So the consensus is that it's excessive oil in cylinder #3 though, right? Now I have to figure out if it's the oil control ring or the valve guides or seals.

If it's the seals then it should be smoking at startup and if it's the rings then it shouldn't be any worse at startup than any other time, but it should be smoking a bit at higher RPMs (but not all that much if it's only one cylinder).

If I understand this correctly then I can test it out by first warming it up and revving it to 4k+ rpms in neutral and watching for smoke. If no smoke, I might try letting it sit for a few days and see if it smokes when I first start it up. Does that sound about right?

Valve stem seals=top end, can be done in situ?
rings=bottom end, and possible engine rebuild

I wonder where this one is going to lead me...

hacker-pschorr

My car only smoked if it sat, I'm talking a couple of weeks.

Seals yes - guides, no.
215,000 miles with original heads, I am suprised all eight of your spark plugs do not look like that. All three of my Porsche's needed new guides with under 100,000 on hte odo.

MY 944S did not show any signs of bad guides. I had the head off due to a broken cam chain so out came the valves. All of the exhaust guides were worn beyond spec.

Mike Frye

Thanks again.

Any way to tell if it's one or the other without pulling the heads? I'm not willing to let it sit for a few weeks just to see if it's on the top end or the rings, but I guess if it doesn't smoke at high RPMs it must be something up top leaking down, right?
Did I mention I use Amsoil? This car repairs itself! No seriously though, I have no way of knowing, but when I did the pan gasket it looked brand new in there. No play on the conn rods, hardly any sludge in the pan, no filings anywhere. It may have had some work done at some point, especially considering the beating the 5-speeds generally have to deal with.

I knew I should have just pulled the engine when I had it down for the top-end refresh. I've heard it's relatively easy and then I could clean everything up in the engine bay the way I've wanted to. I'm just afraid I'll get hung up and not be able to drive it to SITM or anywhere else this summer.



Next step is to check for smoke at high RPMs I guess...

blown 87

That aint good, especially if it tastes like piston.

Schocki

How to test for a bad valve guide seal: Accelerate the car quickly and as soon as you hit about 4000 RPM let go of the throttle. If you have a worn seal, the very high vacuum will draw oil in the combustion chamber. The car will smoke blue. It is sometimes easier to diagnose the problem if somebody follw yoou and observes the exhaust (since there is not a lot of oil burning as you mentioned).

Mike Frye

Thanks, will do.