In addition, the cranking rpm has a fairly significant impact on expected compression value during testing. Most curves show that relationship and why it’s important you’re doing the test under more or less normal operating conditions to get an accurate reading.
I replaced the entire pcv system (grommet, valve and hose), and the valve cover gasket for the side of the engine that was fouling the cyl 4 plug. I drove it a few days then pulled the spark plug again to check and i only saw a tiny bit of oil on the threads only, but the electrodes were clean!
This baffles me because the old pcv valve rattled so it was presumably working and the plastic hose and grommet weren’t broken in any obvious places but I replaced all 3 anyway. Also the valve cover gasket was a very unlikely culprit due to the design of the engine so the fact that my problems a lot better is puzzling considering I only replaced unlikely things that could have caused the issue
Just to be clear here because of Ford’s odd cylinder order, you are talking about the cylinder closest to the front of the engine on the drivers side?
If you haven’t already done so, you’d probably be better off starting a new thread with your specific make/model, miles, maintenance history etc.
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Yes correct
Is it feasible that the valve cover gasket was causing the issue?
A leaking valve cover may get oil on the outside of the plug. If the electrodes are getting sooted or caked with burned oil, that is not due to the valve cover but something internal.
The reason I asked is that I have seen engines burn oil because the drain back holes plugged up, but that is always the cylinder at the back of the engine.
If you suspect that the valve cover gaskets are leaking, you should replace them. While you are at it you can observe if there is a build up of sludge under the valve covers. If there is, then the drain back holes could also be getting closed up and should be cleaned out. But I don’t think that is your current issue as it is a front cylinder that is the issue, not the back.
Since your Mustang has an OHV engine instead of OHC, the spark plugs do not go through the valve cover so you don’t have those little gaskets around each plug like the 4v DOHC engines have.
I was getting oil mostly on the spark plug threads but only a tiny bit on the electrode. After replacing the valve cover gasket and pcv line, now there isn’t any on the electrode and a very small amount on the threads. Maybe i’ll just have to drive it longer and see what happens
If before you replaced the valve cover gasket, the oil on the tip of the plug was wet, it is possible that the oil got on the tip as you were removing the plug and not when the engine was running. So you could have fixed your problem, time will tell.
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