Compression test on a 2011 6.2
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5th Wheeling
Joined: Apr 2024
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Compression test on a 2011 6.2
Compression test results were all 170 except cyl 8 which was 140 psi. Truck has 270,000 but I was told the engine is not the original. Had a bunch of random misfire codes and cyl 8 misfire. Coil packs are crispy inside, only 1 has a resistor or something inside the boot, others are just a spring. Plugs are ngk, looks like a .050 gap or more, obviously way too much! I'm going to replace all plugs and coils, question is, should I pull the valve cover or is the lower compression passable? If it's been misfiring, maybe it's carbon buildup on the valves, or I've heard about broken springs too? I don't have a leak down tester. Many thanks.
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5th Wheeling
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Valve springs look decent
So I removed the valve cover to check the springs on the #8 cylinder with lower compression just to rule that out. I'm assuming that because it's been misfiring, possibly for years, that the valves are full of carbon deposits or that the rings are worse than the others. I've heard that putting oil in the cylinder and then checking compression will possibly tell me if the rings are the issue. If anyone has any reason that this is not a good idea, please let me know. I'll post findings later on regardless.
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So I removed the valve cover to check the springs on the #8 cylinder with lower compression just to rule that out. I'm assuming that because it's been misfiring, possibly for years, that the valves are full of carbon deposits or that the rings are worse than the others. I've heard that putting oil in the cylinder and then checking compression will possibly tell me if the rings are the issue. If anyone has any reason that this is not a good idea, please let me know. I'll post findings later on regardless.
With engines that have idled a lot, or have carbon build up for other reasons, it is actually really good to run them hard. Long pulls getting on the highway floored, kinda pulls.
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5th Wheeling
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Just make sure you don't put a ton of oil in, just a squirt. Turn it over with the spark plug out and the fuel injectors unplugged after you spray some oil in, to spread it around the cylinder, then take your compression reading.
With engines that have idled a lot, or have carbon build up for other reasons, it is actually really good to run them hard. Long pulls getting on the highway floored, kinda pulls.
With engines that have idled a lot, or have carbon build up for other reasons, it is actually really good to run them hard. Long pulls getting on the highway floored, kinda pulls.
Thank you for the reply. I will do that tomorrow and see if the pressure changes. If not, would you think that the valves might be full of carbon on that cylinder? I can't think of any other reason for lower compression if it's not the rings but I'm not very knowledgeable about engines. Once I replace the plugs and coil packs, maybe some cleaner would be a good idea. I only recently purchased the vehicle so I have no idea how long the misfire was going on, only that it desperately needed a tune up.
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You can perform a leak down test to determine if it's leaking past the valves or through the crank case. 140 isnt abysmal, so the engine is likely not trash, and it may simply be leaking past a valve.
Definitely fix the misfire, don't want to be driving with that unless you unplug the fuel injector on the missing cylinder. Once it runs good, rip it around like its a racecar for a while.
How many idle hours are on it?
Definitely fix the misfire, don't want to be driving with that unless you unplug the fuel injector on the missing cylinder. Once it runs good, rip it around like its a racecar for a while.
How many idle hours are on it?
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5th Wheeling
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You can perform a leak down test to determine if it's leaking past the valves or through the crank case. 140 isnt abysmal, so the engine is likely not trash, and it may simply be leaking past a valve.
Definitely fix the misfire, don't want to be driving with that unless you unplug the fuel injector on the missing cylinder. Once it runs good, rip it around like its a racecar for a while.
How many idle hours are on it?
Definitely fix the misfire, don't want to be driving with that unless you unplug the fuel injector on the missing cylinder. Once it runs good, rip it around like its a racecar for a while.
How many idle hours are on it?
Thank you for the reply
I don't know much about the history, but it was a work truck from up north, probably a few idle hours I imagine. I am going to get a camera to look into the cylinder and see if the piston is clean or full of carbon. I don't have a leak down tester but might need to invest in one, seems like a handy tool for someone that owns an older vehicle! At this point, I'm really hoping that the cylinder is not too damaged but just clogged up with carbon from the misfire. Wishful thinking perhaps.
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Thank you for the reply
I don't know much about the history, but it was a work truck from up north, probably a few idle hours I imagine. I am going to get a camera to look into the cylinder and see if the piston is clean or full of carbon. I don't have a leak down tester but might need to invest in one, seems like a handy tool for someone that owns an older vehicle! At this point, I'm really hoping that the cylinder is not too damaged but just clogged up with carbon from the misfire. Wishful thinking perhaps.
I don't know much about the history, but it was a work truck from up north, probably a few idle hours I imagine. I am going to get a camera to look into the cylinder and see if the piston is clean or full of carbon. I don't have a leak down tester but might need to invest in one, seems like a handy tool for someone that owns an older vehicle! At this point, I'm really hoping that the cylinder is not too damaged but just clogged up with carbon from the misfire. Wishful thinking perhaps.
You can get the idle hours from the vehicle info, prompted by buttons on the steering wheel.
I wouldn't lose sleep over the compression reading. If it was running with a misfire then the rings are probably caked with resisual gas crud, and some seafoam or atf soak with some hard running will clean it up enough to control oil consumption. We can go over that after you bore scope and correct the misfire. Make sure you bore a few cylinders so you have something to compare against
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Tuned
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If you don't want to unplug all the fuel injectors you can always crank while doing flood clear, which is where you turn on the key, hold the accelerator to the floor and also crank while holding the accelerator down.
I always do this when I change oil in my wife's expedition so it can build some oil pressure before fire up.
also don't forget that the 6.2 has 16 spark plugs, the lower plugs on the passenger side are a pain to change out.
I always do this when I change oil in my wife's expedition so it can build some oil pressure before fire up.
also don't forget that the 6.2 has 16 spark plugs, the lower plugs on the passenger side are a pain to change out.
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5th Wheeling
Joined: Apr 2024
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You can get the idle hours from the vehicle info, prompted by buttons on the steering wheel.
I wouldn't lose sleep over the compression reading. If it was running with a misfire then the rings are probably caked with resisual gas crud, and some seafoam or atf soak with some hard running will clean it up enough to control oil consumption. We can go over that after you bore scope and correct the misfire. Make sure you bore a few cylinders so you have something to compare against
I wouldn't lose sleep over the compression reading. If it was running with a misfire then the rings are probably caked with resisual gas crud, and some seafoam or atf soak with some hard running will clean it up enough to control oil consumption. We can go over that after you bore scope and correct the misfire. Make sure you bore a few cylinders so you have something to compare against
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5th Wheeling
Joined: Apr 2024
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If you don't want to unplug all the fuel injectors you can always crank while doing flood clear, which is where you turn on the key, hold the accelerator to the floor and also crank while holding the accelerator down.
I always do this when I change oil in my wife's expedition so it can build some oil pressure before fire up.
also don't forget that the 6.2 has 16 spark plugs, the lower plugs on the passenger side are a pain to change out.
I always do this when I change oil in my wife's expedition so it can build some oil pressure before fire up.
also don't forget that the 6.2 has 16 spark plugs, the lower plugs on the passenger side are a pain to change out.
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I used the scope to look into a few cylinders. All are blackish but number 8 looks like a dirty stove pipe. I should mention that my camera scope and compression tester are dollar store quality, so I didn't get a very clear view, but they're certainly not clean pistons. I did see the edge of the valve and it's also very black and cruddy looking. Added oil to 8, checked compression again and it's 155 psi with oil, 140 without. That's about all I can think of doing with my limited tools and ability. I'll replace the plugs, coil packs and add some cleaner, take it for a run and post results next week. I thank you so much for the info.
Report back what you try, and what the results are. Don't forget, fresh oil and hard driving. Once you get the carbon loosened up in the cylinder, the way to get it out is to blow it out with explosions.
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5th Wheeling
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So the cylinder is probably fine, or good enough, and the carbon cake is all in the rings. You could soak the cylinder with something, just make sure you always crank it over with a plug removed before starting.
Report back what you try, and what the results are. Don't forget, fresh oil and hard driving. Once you get the carbon loosened up in the cylinder, the way to get it out is to blow it out with explosions.
Report back what you try, and what the results are. Don't forget, fresh oil and hard driving. Once you get the carbon loosened up in the cylinder, the way to get it out is to blow it out with explosions.
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5th Wheeling
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New plugs and coil packs
I just replaced 16 plugs and 8 coil packs. Engine was running much better, very noticeable difference compared to before, sounded smooth. I took it out on the highway for 15 minutes, a bit sluggish but much better, shut it off, started it back up and within a minute P0420 and 0430 came back on, nothing else yet. I'm not sure if those codes affect the engine but it does have a slight chug at idle compared to a smooth steady sound. Is it possible that running with misfires has blocked the cats? Anything I can look for on the OBD scanner? MAF or any other readings that might determine something?
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I just replaced 16 plugs and 8 coil packs. Engine was running much better, very noticeable difference compared to before, sounded smooth. I took it out on the highway for 15 minutes, a bit sluggish but much better, shut it off, started it back up and within a minute P0420 and 0430 came back on, nothing else yet. I'm not sure if those codes affect the engine but it does have a slight chug at idle compared to a smooth steady sound. Is it possible that running with misfires has blocked the cats? Anything I can look for on the OBD scanner? MAF or any other readings that might determine something?
Those are both cat codes. I'm not bulishltlting ya when i say to go out and drive it hard....that code may clear with some really hot pulls. At the very least, I bet it idled better even if the code doesn't clear......after a multitude of high rpm rips of course.
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5th Wheeling
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I did take it on the highway, pressed down a good amount on the accelerator but didn't want to do anything too serious until it ran for a bit, probably only to 4000 rpm, then the engine light came back on and I got worried about doing damage.