https://www.trailvoy.com/threads/4-2-motor-low-compression-issues.96729/
Apparently, no matter how well maintained and carefully driven, the 4.2l i6 will eventually lose compression in one or several cylinders. Compression leaks at the exhaust valve and seat....why this happens, I am not sure. Possibly valve seats are not hard enough, or valve sticks in valve guide initiating leak and erosion of the seat and valve face. I don't know what engine year of manufacture are subject to this problem, but definitely 2004.
Looks like it's the END of my Eco-Apocalypse truck (SUV). I kept pushing on this vehicle to "improve" it and instead I destroyed it!! I didn't realize how fragile the engine is. Oops.
it was an oil fouled spark plug.
Yes oil fouled probably due to the valve gasket leaking....
It ended up being the valve cover gasket around cylinders 5 and 6 (6 being the worse) had deteriorated and was leaking oil into the spark plug well. I guess eventually there was enough oil to mess with the coil. Got a new gasket and all the spark plug wells cleaned out and she's running great (better then she's run in a while).
Chevrolet Trailblazer Valve Cover Gasket Replacement Cost Estimate. The average cost for a Chevrolet Trailblazer valve cover gasket replacement is between $420 and $520. Labor costs are estimated between $384 and $484 while parts are priced at $36.
If that's the problem and NOT compression then I can get it fixed!
If the rings are worn or stuck, oil will be able to enter the combustion chamber, resulting in wet oil and/or ash deposits on the tip of the spark plug.
I think the too much oil got PAST the piston rings! I hope that's the cause. The problem got better after I got the oil changed again. So I think if I just get that spark plug changed it should fix the problem?
Oil leaking into the spark plug wells is an indication of a very serious issue. Most likely, this is a result of bad piston rings or a cracked valve cover.
When the Check Engine or Service Engine Soon light starts flashing, this means that a catalytic converter damaging condition is occurring. Usually you will be able to feel a noticeable difference in the performance of your vehicle.
Also of concern, the extra oil creates excessive pressure inside your engine that will look for an escape through various gaskets and seals. If one or more of those fail, that will lead to leaks and costly repairs.
PROBLEM IDENTIFIED
I can see the oil down around the spark plug now!! I used the boroscope.
Now I need to remove the spark plug - it's not a LOT of oil that I can see? Just sprayed around the spark plug.... Then I need to clean up the oil....
Water typically hits the #5 or #6 plug area after running down the hood when you open it in the rain.
How to Remove Oil From a Spark Plug Well : Car Repair Tips
If you can see some oil in the top of the spark plug holes then that could mean a blown gasket alright but if the oil is not in the spark plug holes and you can only see some oil when you remove the plugs, then that's not so bad at all as that's a safety issue to throw some oil into the cylinders / throttle bay etc as a means of getting rid of it.
Wow maybe my valve gasket is ok since I don't see much oil!!
using a small syringe fitted with a couple of feet of small-diameter clear tubing. Fit right over the nipple on the syringe push it down to the bottom of the well pull the plunger back oil gets sucked right out quick and simple.
This video is OK, but here is how I dealt with the same problem on my 1996 Honda Accord. Always start by doing the simplest "fix" and work your way up to the most complex "fix". 1) Go to Walmart and buy a can of spray carb cleaner ($2.50) and a bottle of Bar's Leaks ENGINE OIL Stop Leak concentrate ($7.00). 2) Go home. When your car engine is COOL, remove the spark plug wires and clean the ends with a clean rag. Spray some carb cleaner up into each spark plug wire and clean them out as much as possible. 3) Do Not remove spark plugs. Spray carb cleaner down into each spark plug well to break-up and thin the oil that has leaked into each well. Use a long thin phillips head screwdriver, or even a piece of wire, to stir-up the carb cleaner in the wells and break up the oil. Be careful NOT to damage the spark plugs. Now put a rag down into the wells to soak up the oil/carb cleaner mixture. 4) When you are sure you have soaked ALL of the oil out of the wells, remove the spark plugs one at a time, and clean them, and gap them correctly. With a rag and screwdriver, wipe the wells out again before you replace the spark plugs. (just like this video shows) 5) Pour the ENGINE OIL Stop Leak into your engine oil. This will make the seals in your engine swell up, including those seals around your spark plug tubes, and hopefully put a stop to the oil leaking into the tubes. 6) After two weeks of normal driving, check the spark plug tubes again, and clean them out if there is oil in them. Some oil probably will leak into them until the Stop Leak concentrate gets a chance to recondition the seals. 7) If oil still leaks into the tubes after a couple of months, the seals may have to be replaced. But you may as well try this method first. For less than $10 and about two hours, you might fix your problem.
Finally the mystery solved!!
With a particle size of only 0.5 µm, it is absolutely compatible with all filters.
Liquid Moly went past the piston ring in Cylinder six - and maybe all the cylinders? Anyway that's the only one that threw a code as a misfire.
So I cleaned out the spark plug well with a rag - and it was covered in Liquid Moly. I did that another time and then a third time and then I sprayed acetone into the spark plug well - not a lot at all.
Then I did the rag cleaning a few more times - the last time there was hardly any Liquid Moly.
Since Liquid Moly is METAL then it was shorting out the Spark Plug!!
Kind of funny actually - if it wasn't so serious!!
I'll have to spray more acetone tomorrow to make sure it's squeaky clean - I will have to get clean rags also. I can't wash that Liquid Moly oil in the laundry machine obviously. haha.
The spark plug definitely had Liquid Moly on it - not a LOT - just along the edges - the actual "gap" part didn't seem to have much liquid Moly on it.
I suppose there was some kind of electrical resistance to the metal in the liquid Moly - fascinating!!
https://gmtnation.com/forums/threads/opinions-wanted-4-2-cylinder-head.19937/
Could be worse? I don't think my valve gasket is leaking?
156 in-lbs = 13 foot-lbs torque spec as per Chilton book!
OK just took it for a test run - it started!! Yeah!! I cleared a general misfire code. Then I got the flashing service engine light again. It went off and then on - and would disappear and then reappear. I pulled over and scanned - and got a "general misfire" code again. So I turned around and I could smell oil burning off out of the exhaust. So I figured if I drive faster that should burn off more oil. Sure enough then the Service Engine light flashing went away and it didn't come back - for a bit. Then it came back again. And then it vanished again as I pulled back into the entry way for the compound.
So I think it is BETTER. Since it's now a "general misfire" then I have to change out and clean out the REST of the spark plug wells! Now I have the tools and the methodology. I'm NOT getting a Cylinder Six misfire - so that is great news.
I will keep at it and the others are NOT under the Firewall so they are much easier to reach. I have a second spark plug new - so I will now put that in once the engine cools down in a couple hours.
OK just installed the second new spark plug - after cleaning out MORE Liquid Moly!! hahaha.
So that one went five times faster since I now have the tools and technique down for cleaning out the spark plug well. I'm not gonna put on the Air Resonator Box again until I do the other four spark plugs. I have to go to the Auto Store again to get the rest of the spark plugs - should have just got them all this morning. Oops.
In the mean time I can take out the rest of the spark plugs and clean out the spark plug wells!
Then when I get the other car back I can go buy the new spark plugs and just need to put them in!!
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