Valve cover for GMC 4.3L

Asked by Apr 12, 2017 at 02:38 AM about the 1999 GMC Sierra 1500 SL Standard Cab SB

Question type: Maintenance & Repair

My fifth cylinder is misfiring. I changed all the
spark plugs and I noticed that spark plug in the
fifth cylinder was covered in oil when I took it out. I
looked in my repair manual and it said it could be a
bad valve seal or worn piston ring. I want to check
if the valve seal is still good. Everyone that I spoke
with say that I pretty much have to take the engine
apart to get to the valve covers but the valves do
seem accessible with taking too much off .Please
could some one tell me (preferably someone who
has changed the valve seals on a truck like mine)
what I really have to do ?

7 Answers


Well, TrannyMan is right in how to replace a valve seal, it would be a umbrella type of seal going back in. But is the oil on the outside of the spark plug, or on the inside electrode? It may be just a valve cover gasket that needs replacing if the oil is on the outside of the spark plug.

1 of 1 people found this helpful.

Rowefast the oil is in the inside where the spark plug screws in


You know, I wouldn't even mess with this for 1 cylinder. If you put Autolights spark plugs in there made of course for that engine, they are designed to burn oil so the cylinder would keep firing. You should probably check the cylinder compression, if it is too low, a valve seal wouldn't even help it.

Ill try anything to stop it from misfiring. That's the reason why my check engine light is on.


Yea, you have a po305 miss fire code. P0305 GMC - Cylinder 5 Misfire Detected...Possible causes; Faulty spark plug 5, Clogged or faulty fuel injector 5, Faulty ignition coil 5, Fuel injector 5 harness is open or shorted,Fuel injector 5 circuit poor electrical connection, Ignition coil 5 harness is open or shorted, Ignition coil 5 circuit poor electrical connection, Insufficient cylinder 5 compression, Incorrect fuel pressure, Intake air leak, Spark Plugs Wires (if equipped)...The P0305 code means that the cylinder 5 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 5. If the problem persists more tests needs to be done to diagnose problem.

Thanks Rowefast you've been very helpful


Your welcome.

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