Engine compression test help

[Tim10]

Greetings everyone!

Can someone guide me with compression test on L83 engine (2016 Chevy Tahoe)
witch fuses I need to take out. I don't need to check all cylinders just one, Do I need to take all spark plugs or one should be enough. Most guides say to remove all spark plugs.
It's the first time I'm doing this so any advice will be appreciated

 

[OR VietVet]

I have always just disabled the ignition circuit(s) but you could remove your fuel pump relay I believe. I have an 02 so have no idea where that relay is on your rig and would take me more time to look for it than another member here chiming in with location.

Why just one cylinder compression test. If it is an end cylinder, all the way front or all the way back, I would check the cylinder next to it as well and compare. If is a middle cylinder, check the ones on each side as well and compare. Removal of all plugs allows the engine to crank evenly. If plugs all in the engine cranks under compression, unless of course valves/pistons are having problems. If all plugs out then they all have no compression and the engine cranks evenly again. Hell, do 'em all with all plugs out. If never done a compression test before, watch the videos of how to do it. Saves me time typing and telling you how. Look up what a wet test is as well.

By the way, why are you running a compression test?

 

[Tim10]

Some google search tells me that I need to remove ignition fuse, fuel pump fuse, injector fuse.
I was just thinking of quick check one or two spark plugs to have a general idea about the condition of my engine. Didn't want to go through the hassle with all spark plugs especially with #8.

 

[OR VietVet]

Check the plugs or check compression after remove the plugs? I assume the compression part. How old are the plugs? Having running problems or CEL or just checking for peace of mind? If I am running a compression check of the engine to see the shape, I would do all cylinders to see what if any major difference between the cylinders compression when compare all together.

 

[Tim10]

Check the plugs or check compression after remove the plugs? I assume the compression part. How old are the plugs? Having running problems or CEL or just checking for peace of mind? If I am running a compression check of the engine to see the shape, I would do all cylinders to see what if any major difference between the cylinders compression when compare all together.

Yes, removing plugs is the compression test part and was thinking just check 1 or 2 cylinders if they are good then no need to proceed, but I agree better to check them all. The reason for check it's just for peace of mind. Spark plugs and wires are fresh 1500miles on them. I'm having some low MPG issue (7 city 11 highway everything is stock) I'm trying to find and diagnose.
For now, I just found with a temperature gun that my Catalytic converter has the same temperature around 400F at upstream and the same downstream. I don't have any engine lights on or anything. A second finding is absolutely new car battery runs at 12 volts and lower, checked alternator voltage was fine and the second auxiliary battery has 12.86v witch if absolutely fine.
I heard at this voltage fuel pump runs slow witch can lower MPG. As of right now, I'm charging the battery and got 14.2v reading. Will check tomorrow morning for "parasitic drain test"

 

[wjburken]

Some google search tells me that I need to remove ignition fuse, fuel pump fuse, injector fuse.
I was just thinking of quick check one or two spark plugs to have a general idea about the condition of my engine. Didn't want to go through the hassle with all spark plugs especially with #8.

How many miles on your vehicle?

As Ron said, if you’re going to go through the effort to check a couple pistons, might as well get a current baseline on all of them. If you are within 15K-20K of 100K on the odometer, might as well put new plugs in instead of putting the old ones back in just to have to do it all over in 15K to 20K.

Don’t let the #8 plug scare you. I have not changed it on a 2016, but I have done it enough on the NNBS platform that I can get the #8 out just a quick as the rest of them. Others have their techniques that work for them, mine is to take a 3/8 drive plug socket and then a 3/8M-1/4F adapter, then a 1/4M-3/8F adapter and a 3/8 ratchet. That gets me out past the exhaust manifold and heat shield, but not so far as to be up against the a/c stuff. Just change my plugs a couple weeks ago and it took me right at 10 minutes per plug and that includes putting anti seize and dielectric grease on.

 

[Tim10]

How many miles on your vehicle?

As Ron said, if you’re going to go through the effort to check a couple pistons, might as well get a current baseline on all of them. If you are within 15K-20K of 100K on the odometer, might as well put new plugs in instead of putting the old ones back in just to have to do it all over in 15K to 20K.

Don’t let the #8 plug scare you. I have not changed it on a 2016, but I have done it enough on the NNBS platform that I can get the #8 out just a quick as the rest of them. Others have their techniques that work for them, mine is to take a 3/8 drive plug socket and then a 3/8M-1/4F adapter, then a 1/4M-3/8F adapter and a 3/8 ratchet. That gets me out past the exhaust manifold and heat shield, but not so far as to be up against the a/c stuff. Just change my plugs a couple weeks ago and it took me right at 10 minutes per plug and that includes putting anti seize and dielectric grease on.

I did spark plugs myself a month ago, had a hard time to remove the wire from #8, had to rip it with pliers. But I put some dielectric grease and anti-seize so should come off easily.
I didn't use anything except 3/8 spark plug socket, I removed it from the top was SO tight but I managed it

 

[OR VietVet]

Now we are getting some place. You want to be sure the engine is in good shape and I see the plugs are just 1500 miles ago. Do them all and run the compression test and now you have them out to inspect them as well. MPG was not mentioned till just now. Best to do all concerns in your OP. We need all pertinent info in any attempt to help. Complete story behind the story, so to speak. When you did the plugs did you do the fuel filter? Did you clean the MAF and throttle body? Did you do complete plug wires? Did you use good quality parts? What type of gas do you run? Need to stick to good quality fuel for sure and I always recommend at least the mid grade and not just plain regular. Better additives to help keep fuel system clean as long as you start with good quality fuel. This all started with you asking about doing the compression test and what to disable before you do. This new info opens up a whole new can of worms. We are here for you. Ask anything. Don't assume anything. No such thing as a dumb question either, as some members have apologized for when they shouldn't have. A dumb question is one not asked.

 

[Tim10]

Now we are getting some place. You want to be sure the engine is in good shape and I see the plugs are just 1500 miles ago. Do them all and run the compression test and now you have them out to inspect them as well. MPG was not mentioned till just now. Best to do all concerns in your OP. We need all pertinent info in any attempt to help. Complete story behind the story, so to speak. When you did the plugs did you do the fuel filter? Did you clean the AF and throttle body? Did you do complete plug wires? Did you use good quality parts? What type of gas do you run? Need to stick to good quality fuel for sure and I always recommend at least the mid grade and not just plain regular. Better additives to help keep fuel system clean as long as you start with good quality fuel. This all started with you asking about doing the compression test and what to disable before you do. This new info opens up a whole new can of worms. We are here for you. Ask anything. Don't assume anything. No such thing as a dumb question either, as some members have apologized for when they shouldn't have. A dumb question is one not asked.

Thanks, appreciate that.
So what I did was cleaned the MAF sensor, new air filter, throttle body cleaned, new spark plugs and wires (Acdelco), transmission fluid flush(Valvoline), oil change(Pennzoil). I drove about 3k miles and didn't see any drop in the oil level witch I think is a good sign. I use regular gas, but as you said I will try midgrade. I was thinking to change the fuel filter but didn't find in a part catalogue any for 2016 Tahoe and dropped this idea and focused on catalytic converters. My question is getting same temperature at up/downstream is a sign of bad cats or clogged cats? I don't feel while driving that they are clogged but had p0420 code and its gone after I used lacquer thinner for a half tank I put one gallon and drove on freeway and code gone and never came back.

 

[OR VietVet]

Now the complete story. By the way, where did you come up with lacquer thinner in the fuel? I have never heard of doing that. Is that an old wives tale? Not saying there may not be a good reason for it but never heard that before. The fuel filter suggestion by me was me rambling on. No fuel filter on the outside, like my 2002. Yours is in the tank with the pump. Change to mid range fuel at least and even the premium to see if you get a big enough jump in MPG to notice. You can always go down to mid grade. You did not say what fuel you use though. Tell me it isn't Shell. I did not know it till on this forum but there are some horror stories on here about that fuel. I see the temp you posted for the cat(s) and that looks good. If was way different that would indicate a clog. Miles on your engine? Miles on the oxygen sensors? Need to monitor the alternator output while driving. You can charge the battery to 14.6 but while driving and under load conditions you need to see what it charges. Load by lights on, fans on, radio on.....basically anything you can turn on. Do you have a Tech 2?