Re: 1999 Grand Am 2.4l Twin Cam engine issues.. Updated
I would have focused on this as an original problem. what was the mark? did any of the plugs have a scoring mark down the side of the porcelain? thats a hallmark for a bad coil or plug wire causing arc-ing down the side of the plug. which will cause that cylinder to miss something fierce.
anywho, you did a compression test but you didnt do a leakdown test? as said, these engines have super long timing chains (cant remember if they are interferance or not though). you get enough slack and you can slightly bend a valve. you might even have a burnt valve.
I always do a compression and leak down test on an unknown engine before I proceed with anything else. If the long block is in decent shape then you know its something else lol. even with #4 @ 190, thats only about 12% loss which isnt bad compared to the others, but the leakdown would help narrow that to whether you might have a valve or ring problem in that cylinder.
you said later on there was a map sensor code and earlier that there was one in the glove box....obviously you checking the map sensor is a good thing but I've never really checked one with the engine running? this is how I do it.
http://www.youtube.com/watch?v=B8EVhFc5Yqw
also, you should definitely have more than 6"hg @ idle...and dont these engines idle @ 900rpm, not 600? here's a nifty engine vacuum diagnosis tool regardless:
http://sbftech.com/index.php/topic,3020.0.html
I would have focused on this as an original problem. what was the mark? did any of the plugs have a scoring mark down the side of the porcelain? thats a hallmark for a bad coil or plug wire causing arc-ing down the side of the plug. which will cause that cylinder to miss something fierce.
anywho, you did a compression test but you didnt do a leakdown test? as said, these engines have super long timing chains (cant remember if they are interferance or not though). you get enough slack and you can slightly bend a valve. you might even have a burnt valve.
I always do a compression and leak down test on an unknown engine before I proceed with anything else. If the long block is in decent shape then you know its something else lol. even with #4 @ 190, thats only about 12% loss which isnt bad compared to the others, but the leakdown would help narrow that to whether you might have a valve or ring problem in that cylinder.
you said later on there was a map sensor code and earlier that there was one in the glove box....obviously you checking the map sensor is a good thing but I've never really checked one with the engine running? this is how I do it.
http://www.youtube.com/watch?v=B8EVhFc5Yqw
also, you should definitely have more than 6"hg @ idle...and dont these engines idle @ 900rpm, not 600? here's a nifty engine vacuum diagnosis tool regardless:
http://sbftech.com/index.php/topic,3020.0.html
