Low compression on cylinder #6
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Teching In
Joined: Sep 2015
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Low compression on cylinder #6 I have a 2001 Z28, 6 speed with 110,000 miles that I bought from the original owner. The car is bone stock with no mods. I have been through most of the common issues on these cars such as the ABS lights on dash (sent ABS module off for repair) and the body control module (radio and power windows shutting off intermittently).
I thought I had all the kinks worked out of this car and then I get a check engine soon light. Took it to get the code scanned at Autozone and it comes back as cylinder head ground wire/ #2 cylinder misfire. Decided to take it to the dealer and they called to inform me that #6 cylinder had low compression of 90 psi.
Car has been running great previously, no smoke or nothing. I spoke with the mechanic at the dealer and he states it could be any number of things and would require more testing to diagnose the exact issue. I didn't ask and he didn't mention if the other cylinders tested okay. I was sickened and just wanted to leave.
One possibility mentioned was a failed cam shaft which he said was common for these engines (chrome off a lobe/ worn).
I am baffled as this is not high miles for an LS1 and I find it hard to believe the rings are bad. Are the stock cams known to fail in these cars? What is my best option, pull the engine for rebuild or just pull the cam for inspection? I know there are a lot of unknowns here, I greatly appreciate any advice.
I thought I had all the kinks worked out of this car and then I get a check engine soon light. Took it to get the code scanned at Autozone and it comes back as cylinder head ground wire/ #2 cylinder misfire. Decided to take it to the dealer and they called to inform me that #6 cylinder had low compression of 90 psi.
Car has been running great previously, no smoke or nothing. I spoke with the mechanic at the dealer and he states it could be any number of things and would require more testing to diagnose the exact issue. I didn't ask and he didn't mention if the other cylinders tested okay. I was sickened and just wanted to leave.
One possibility mentioned was a failed cam shaft which he said was common for these engines (chrome off a lobe/ worn).
I am baffled as this is not high miles for an LS1 and I find it hard to believe the rings are bad. Are the stock cams known to fail in these cars? What is my best option, pull the engine for rebuild or just pull the cam for inspection? I know there are a lot of unknowns here, I greatly appreciate any advice.
Teching In
Joined: Apr 2009
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Try a leak down test on all cylinders. It might give you more insight into the problem.
https://mobiloil.com/en/article/car-...-leakdown-test
https://mobiloil.com/en/article/car-...-leakdown-test
TECH Addict
Joined: Mar 2013
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Taking your car to the dealer for repairs is about equal to believing in Santa Claus. It would be nice to think the dealer could repair it properly, BUT THEY CAN"T!
I don't know where you are, if you post up maybe we can find you a decent shop to help.
psssst there isn't any "chrome" on the lobes or on anything in your engine. If he actually told you that he's full-o-****.
I actually had a dealers TOP TECH ask me if my WS6 came with a v6 in it! I'm not shitting you! He was dead serious....................they couldn't find the simple fact that piece of number 7 piston decided it wanted to break off and go into the exhaust. My TRUCK DRIVER neighbor found the problem in 10 mins.
Go to the dealer and ask for a KISS cause you're GONNA GET UCKED!
If you look closely in the dealers break room you will find the dart board GM issues every dealer with diagnoses.
I don't know where you are, if you post up maybe we can find you a decent shop to help.
psssst there isn't any "chrome" on the lobes or on anything in your engine. If he actually told you that he's full-o-****.
I actually had a dealers TOP TECH ask me if my WS6 came with a v6 in it! I'm not shitting you! He was dead serious....................they couldn't find the simple fact that piece of number 7 piston decided it wanted to break off and go into the exhaust. My TRUCK DRIVER neighbor found the problem in 10 mins.
Go to the dealer and ask for a KISS cause you're GONNA GET UCKED!
If you look closely in the dealers break room you will find the dart board GM issues every dealer with diagnoses.
Last edited by RockinWs6; Sep 6, 2015 at 01:21 AM.
Thread Starter
Teching In
Joined: Sep 2015
Posts: 8
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Thanks for the comments. I agree that dealers are retards, I always do my own wrenching but I had a weak moment and was hoping for a quick fix. I just recently replaced my motor mounts/transmission mount and I have to say that working on that LS1 stuffed in that camaro bay is exhausting.
I live in central Mississippi and I am limited on quality shops that specialize in LS1s. Wish I was close to a shop like Texas Speed...
I live in central Mississippi and I am limited on quality shops that specialize in LS1s. Wish I was close to a shop like Texas Speed...
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Do a compression test to verify that cylinder is low. If it is pull that valve cover, roll the engine over and watch the rocker arms, see if one looks different than the other, check for broken valve springs. Roll the engine over till that piston is at the top. Take the rocker arms off, check the push rods for straightness. Do a leak down test. When you do the leak down test; take the oil filler cap off the valve cover, take the inlet tube off the throttle body. If you hear rushing out the t/b its a bent/damaged intake valve, if you here it coming out of the valve cover its the rings and if its coming out of the tail pipe its an exhaust valve.
Don't just pull the head and inspect it. Because at that point you can't do any testing and have no idea why you have low compression. If it's not visually obvious you've f'd yourself.
I love internet mechanics.
If you don't have a compression gauge and/or a leakdown gauge most auto parts stores will let you rent them.
The low compression can be anything from a bent pushrod to a cracked piston. Test don't guess.
Don't just pull the head and inspect it. Because at that point you can't do any testing and have no idea why you have low compression. If it's not visually obvious you've f'd yourself.
I love internet mechanics.
If you don't have a compression gauge and/or a leakdown gauge most auto parts stores will let you rent them.
The low compression can be anything from a bent pushrod to a cracked piston. Test don't guess.
Thread Starter
Teching In
Joined: Sep 2015
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Thanks again for all the input, I was hoping for a miracle cure but thats not going to happen. At this point I am with Rixtrix, just going to pull the motor and deal with whatever I find. So disappointed to be doing this to a ls 1 with 110,000 miles.
Quick trick for you. Squirt a shot of oil into the low cylinder. If it comes up that indicates rings. If not it indicates valves leaking past the seats.
My bottom end is still fine at 155k. I wouldn't expect any issues at 110 unless it was severely neglected
My bottom end is still fine at 155k. I wouldn't expect any issues at 110 unless it was severely neglected
sounds good. let us know how it turns out.
On The Tree
Joined: Jun 2015
Posts: 182
Likes: 3
From: Portland OR
Don't do any teardown until you do a leak down.
And if the leakage is a valve smack the valve with a deadblow hammer while air is applied and see if it fixes itself.
Crumbly bits of carbon (or other debris) may have lodged on the seat and popping the valve will dislodge them.
Does the plug for that cylinder look like any bad things have happened? (Assuming whoever worked on it put them back in the same hole)
Just arbitrarily rebuilding will just create a black hole where your wallet was. Plus you need to ID the How and Why's of your problem so a rebuild is not spoiled.
I once ruined 6 cranks before I found a solution to my problem. You might have a bad injector or an ignition problem that led to the mechanical problem.
And if the leakage is a valve smack the valve with a deadblow hammer while air is applied and see if it fixes itself.
Crumbly bits of carbon (or other debris) may have lodged on the seat and popping the valve will dislodge them.
Does the plug for that cylinder look like any bad things have happened? (Assuming whoever worked on it put them back in the same hole)
Just arbitrarily rebuilding will just create a black hole where your wallet was. Plus you need to ID the How and Why's of your problem so a rebuild is not spoiled.
I once ruined 6 cranks before I found a solution to my problem. You might have a bad injector or an ignition problem that led to the mechanical problem.
Thread Starter
Teching In
Joined: Sep 2015
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Low compression cylinder #6/ random misfire Dealers mechanics are idiots !!!!!!!!! I changed plugs and wires and code/ miss is gone. Car runs fantastic! I can't thanks you guys enough for responding to posts, when you are troubleshooting problems it is very frustrating and you guys advice and encouragement really helps. I hope this post will help others, I had read several forum posts on this misfire and most were solved with plugs/ wires. I did not realize that Denso are the factory installed plugs and mine had 110K miles on them. I used the NGK G-power plugs and Omni power wires from Oreillys. Since I purchased the car 2 years ago there was always a bit of vibration in the shifter from the engine, now the shifter sits perfectly still. So relieved.... 
Thanks for posting back what you found.
Random thought here, but I wonder how well they were able to check compression on #6, since it's the hardest one to get to - and I've seen people use the kind you hold on with hand pressure and don't thread in. That type of checker would certainly give a low number in such a tight spot. If they actually even checked it...
Random thought here, but I wonder how well they were able to check compression on #6, since it's the hardest one to get to - and I've seen people use the kind you hold on with hand pressure and don't thread in. That type of checker would certainly give a low number in such a tight spot. If they actually even checked it...
Thread Starter
Teching In
Joined: Sep 2015
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Saga continues Put about 40 miles on the car and service engine light is back on. 
The light is not flashing, it is constant so I head back to auto zone for a scan and now it is code P0327, knock sensor.
This code has not been an issue before, I have owned the car two years so here is what I have changed or have done to cause this: Obviously I just changed plugs/ wires and I also washed the engine bay before I started this work. Is it possible that the NGK G-power plugs are not a good fit? Or is it likely I caused this with the wash job?
I am thinking about changing plugs to the NGK V power as that seems to be a popular plug, is the T5 nickel okay to use? Starting to lose interest in my Z28, anybody looking?
The light is not flashing, it is constant so I head back to auto zone for a scan and now it is code P0327, knock sensor. This code has not been an issue before, I have owned the car two years so here is what I have changed or have done to cause this: Obviously I just changed plugs/ wires and I also washed the engine bay before I started this work. Is it possible that the NGK G-power plugs are not a good fit? Or is it likely I caused this with the wash job?
I am thinking about changing plugs to the NGK V power as that seems to be a popular plug, is the T5 nickel okay to use? Starting to lose interest in my Z28, anybody looking?
On The Tree
Joined: Jun 2015
Posts: 182
Likes: 3
From: Portland OR
Don't use exotic plugs, there is little or no gain and often there is a downside.
Use the plug the car came with unless you have a definite and very good reason.
Exotic wires are not any better than stock, if they were worth a crap GM would use them.
Modern ignition systems are so good there is very little you can do to improve them, and lots you can do to screw them up.
Use the plug the car came with unless you have a definite and very good reason.
Exotic wires are not any better than stock, if they were worth a crap GM would use them.
Modern ignition systems are so good there is very little you can do to improve them, and lots you can do to screw them up.
TECH Addict
Joined: Mar 2013
Posts: 2,628
Likes: 30
Put about 40 miles on the car and service engine light is back on. The light is not flashing, it is constant so I head back to auto zone for a scan and now it is code P0327, knock sensor.
This code has not been an issue before, I have owned the car two years so here is what I have changed or have done to cause this: Obviously I just changed plugs/ wires and I also washed the engine bay before I started this work. Is it possible that the NGK G-power plugs are not a good fit? Or is it likely I caused this with the wash job?
I am thinking about changing plugs to the NGK V power as that seems to be a popular plug, is the T5 nickel okay to use? Starting to lose interest in my Z28, anybody looking?
The light is not flashing, it is constant so I head back to auto zone for a scan and now it is code P0327, knock sensor. This code has not been an issue before, I have owned the car two years so here is what I have changed or have done to cause this: Obviously I just changed plugs/ wires and I also washed the engine bay before I started this work. Is it possible that the NGK G-power plugs are not a good fit? Or is it likely I caused this with the wash job?
I am thinking about changing plugs to the NGK V power as that seems to be a popular plug, is the T5 nickel okay to use? Starting to lose interest in my Z28, anybody looking?