Richard Cranium Posted March 30, 2017 Report Share Posted March 30, 2017 Just curious what people think. Car came into school yesterday, think it's a 2012 Impala. Has a miss on cylinder number 1. Ran a compression test and only had 60 psi on number 1. Ran a leak down test. Think it's something like 80% leak, but the compression is coming out the number 3 spark plug hole. On a V6 this wouldn't be odd, but I guess the car is a 4 cylinder. Does this sound like anything anyone has heard of before? Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted March 30, 2017 Report Share Posted March 30, 2017 On a V6 this wouldn't be odd, but I guess the car is a 4 cylinder. I don't think there was a 4 cylinder available on the 2012 impala. 3.5-3.9 v6s and a 5.3 v8 were the only engines (but I could be wrong). sounds valve train related...maybe slightly bent valve, worn out seat, or wiped cam lobe? don't the v6 engines have a problem pulling the rocker arm bolts out of the head? I had a friend whose impala did that but it was an older one. Quote Link to comment Share on other sites More sharing options...
aussiek2000 Posted March 30, 2017 Report Share Posted March 30, 2017 3.6 V6 was the only engine in 2012, Unless you mean malibu and not impala. Doesn't sound familiar, but I've seen the 2.5/2.0 malibu crack pistons and 3.6 impalas have cam/valve train issues. EDIT: 2012 malibu would be 2.4 or 3.6, not the engines I mentioned above. Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted March 31, 2017 Author Report Share Posted March 31, 2017 Could be a Malibu, I just got a quick description of the problem. I know it's a 4 cylinder. Confusing that when we put air to it with number 1 TDC that the pressure comes out number 3 combustion chamber. Nothing on number 2, nothing noticable coming out the throttle body, the crank case or the exhaust. Could the exhaust manifold create enough back pressure that if number 1 has a leaking exhaust valve that there would be noticeable air flow on 3 if that exhaust valve happens to be open? If it was one the intake side then I assume there would be more noticeable flow coming out the throttle body than the number 3 combustion chamber. Quote Link to comment Share on other sites More sharing options...
aussiek2000 Posted March 31, 2017 Report Share Posted March 31, 2017 Could be a Malibu, I just got a quick description of the problem. I know it's a 4 cylinder. Confusing that when we put air to it with number 1 TDC that the pressure comes out number 3 combustion chamber. Nothing on number 2, nothing noticable coming out the throttle body, the crank case or the exhaust. Could the exhaust manifold create enough back pressure that if number 1 has a leaking exhaust valve that there would be noticeable air flow on 3 if that exhaust valve happens to be open? If it was one the intake side then I assume there would be more noticeable flow coming out the throttle body than the number 3 combustion chamber. I suppose it could be possible. But if cylinder 1 is already down on compression, I wouldn't even waste my time trying to figure out the #3 deal. Just find a used/reman engine and swap in. I guess if its a school, pull valve cover and see if its still in time. Quote Link to comment Share on other sites More sharing options...
Farkas Posted March 31, 2017 Report Share Posted March 31, 2017 Sounds like valves aren't sealing on cylinder 1 and the air is coming back through the manifold and since cylinder 3 would be the next to fire, the valve events have already begun and you're just hearing the air leaking past those valves? Quote Link to comment Share on other sites More sharing options...
aussiek2000 Posted March 31, 2017 Report Share Posted March 31, 2017 Whats compression on #3 like? Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted April 1, 2017 Author Report Share Posted April 1, 2017 Sounds like valves aren't sealing on cylinder 1 and the air is coming back through the manifold and since cylinder 3 would be the next to fire, the valve events have already begun and you're just hearing the air leaking past those valves? That's what we're thinking. It's taken a few days to accept that's probably what it is, and he's reluctant to pull the head without being more confident in the diagnosis. Whats compression on #3 like? Compression on 2 - 4 are great. I don't remember the numbers but they were good. Quote Link to comment Share on other sites More sharing options...
aussiek2000 Posted April 1, 2017 Report Share Posted April 1, 2017 That's what we're thinking. It's taken a few days to accept that's probably what it is, and he's reluctant to pull the head without being more confident in the diagnosis. Compression on 2 - 4 are great. I don't remember the numbers but they were good. No compression means head needs to come off regardless. Quote Link to comment Share on other sites More sharing options...
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