I have a 2006 Cobalt SS/SC which is turbo swapped and made 425whp. After a year of driving it, I wanted to make more power. So, I upgraded all of the internal but the sleeves. I am running 10:1 compression, stage 2 turbo cams, and balance shaft delete. As I was breaking in the motor one day, a G37 started messing around with me and trying to get me to race him. At this point I was just above 500 miles on the motor. So i raced him and did work on him. He wanted me to race him again and I did. When racing him second time my car would fall out of power and then the power kick in again and then it fall out of power again so I just let off. My low coolant light came on and then I started smelling the coolant. I checked my coolant temp and it was around 180 degrees which isn't bad. I drove 20 some miles to home and looked at everything. Pretty sure I pushed coolant, so I torqued the head studs down to 90 ft lbs and filled up the coolant. The next day I took it to DTM to get tuned. While at DTM I replaced my injectors to 160lbs. Brian was messing around to get it started with the new injectors and got it to fire up. He told me that it didn't sound right and seemed like it was running on 2 or 3 cylinders. So, I took it back home and did a compression test on all cylinders: #1 135, #2 155, #3 140, #4 110. So I took the car apart and replaced the head gasket, the piston rings and then put it back together. Did a compression test again: #1 170, #2 175, #3 170, #4 50. The compression is 50 in cylinder 4. So I took the car back apart and looked at the valves to see if they where bent which they are not but did look like there was some burn marks on one of the exhaust seats in cylinder 4. I bought a new valve and relapped all of the valves. Put the car back together and cylinder 4 is still at 50! Does it sound like my head is warped or is it more?

 

sounds like a cracked sleeve or a burnt valve on that cylinder i would pull it down and get the head inspeced and a valve job done and re assemble and see if that fixed the problem you may need to get another head as the seat could be destroyed and why its back apart inspect the sleeve really closely

sometimes a lapping the valves dosent work

 

Okay so my head was warped in a couple of spots and cylinder 4 had a bad seats. Had to get a valve job and a resurface. Got it all bad together and now it starts up but shortly after it dies. I scanned it with hptuners and it is not showing any codes. The timing was setup correctly and cam sensor was put in the correct position. Any ideas to why it could be dying after startup?

 

Also leak down shows a 10% air loss in each cylinder.

 

Found out the issue, bad camshaft.

 

What was wrong with the cam?

 

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