What would you do? Failed compression.

What should I do?

  • Buy new head

    Votes: 0 0.0%
  • buy new block

    Votes: 0 0.0%
  • sell car, cut losses

    Votes: 0 0.0%
  • other, please explain

    Votes: 4 100.0%

  • Total voters


Torque Junkie
Layton, Utah USA
'85 Mustang Gt 5.0
Anyone who doesn't know, I blew up my cobalt a while ago...I took the car to a mechanic that I thought I could trust and he screwed me. Not going to tell the long version of the story.


rebuilt block and head, reinstalled and tuned, then the problems started.

lots of problems...another long story that I won't tell, short version: I have been chasing problems ever since I got the car back from the shady mechanic.

car runs, but always seems like on 3 cylinders


I finally went ahead and did a compression test.

#1 0 psi... That's right. Zero.

#2 90 psi holding

#3 130 psi holding

#4 60 psi and dropping

What do you think the problem is?

Already spent a lot of money, keep that in mind when answering the following:

What would you do in this situation?

The cobalt fits me better than pretty much any car I can think of.

but while I make payments on the car, it's almost impossible to save up money to fix it.

I found a block online for about $1500

I can get a used head on the cobalt forum here for about $200-300

Oh, yeah. They decked the block and head, then used stock head gasket thickness. I think I hit a valve(s) during WOT because piston to valve clearance is too low. That's my theory. but I am no expert.
No sir. The mustang is a v8. My 2006 Cobalt SS, however, is a 2.0 supercharged. It's actually faster than my mustang (when it's healthy)

Mustang 200whp 280wtq

Cobalt ss 280whp 230wtq

both cars were measured on the same dyno on warm days

Legacy 166bhp 165tq
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You have another car to use? What I would do is pull it apart and see what the damage is and go from there. Not sure why you think you need a new block and head when this is very very rarely the case and might just get away with a couple of valves (for example).
Good input MA. I'm a little nervous about pulling the head off, but if I ever brave up, that would be an awesome idea. I wish I lived close to you guys. There would be a case of beer in your future if you helped me pull it off....

That just gave me an idea....
Only way to find out is to pull engine apart if you haven't got a scope.

It can be either block or head related. Zero compression just menas that there is somewhere a hole. where is a matter of visual inspection.

Not want you want to hear.

Alternatively it might work out cheaper to start all over with another engine.
There is no compression at all on one cylinder and another two are low (if not a third, don't know what it's meant to be on these engines), I think we're beyond checking oil and water levels lol.
he means the oil and water could escape and that's a start.
did he bore out the block?
you could be losing pressure from damaged valves and/or seats, bad rings, head gasket
i would check all of these, my rebuild has cost me 200 aud so it's cheaper to fix than replace
Needs to be stripped, head off and check valves, springs etc and any other damage or cracks. Then measure valve to piston clearances. Could be piston/bore related if the head is okay then it would point to pistons, rings and bore diameter. Sounds like the engine may have been damaged, ring thrown and not properly repaired or not rebored if scored and maybe mismatched pistons to bores?

When I have lost an engine due to ring failure etc I always get the bores measured and checked for ovality and if damaged get them overbored and with matched pistons and rings. Any decent machine shop always machine them as a matched set after measuring them.

Sounds like your 'mechanic' was out of his depth. With supercharged engines you must always use the correct specification parts, if he did replace anything were they the right ones? Pistons would be different and most likely forged.
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