I have a 99 GA with ~152k miles, 2.4L engine that I have gone through 3 timing chain tensioners. Three weeks ago, I went to start my car and it kind of sounded like it seized up (or what I think sounded like that). When I tried to bump it afterwards, it didn't turn over at all. I had a friend try to help me jump it in case it was a battery problem. It then turned over, but there was a lot of rattling coming from the timing chain area. I figured at this point, I would be replacing my tensioner again.

I got the timing cover off and got all of the cam gears lined up in the timed position with an 8 mm bolt lined up in the holes. I lined up the crankshaft gear, installed the new tensioner, and then put the old timing chain on. It didn't line up with the gears as perfectly as I know it should have. I rotated the engine by hand, and the chain seemed to jump off the crankshaft sprocket and possibly jump a tooth. I eventually realized that the chain had stretched (and by more than a link), so I replaced it. When I put the new chain on, it fit perfectly, and I again hand cranked it. This time, the tension remained solid, and the gears stayed in the timed position through several rotations.

I cranked it and it turned over several times (~5 seconds), but didn't start. I noticed that I had not reconnected the connector to the cruise control module, and thought that may have something to do with it. I connected it and attempted to start. After a second, there was a loud boom, some flame from what appeared to be in the bottom end (crankcase), and a decent amount of smoke from holes out of the crankcase near the crankshaft timing gear.

Two things that I will be doing tonight are to check compression on the cylinders (100 psi minimum and 30% difference listed as acceptable in my Haynes manual), and check the computer to read codes.

Does anyone know what might have happened?

Your compression test will give you your answer.

I've never done one, but I assume I install the gauge at the spark plug, then rotate to TDC for piston 1, then read the gauge. If it is less than 100, that tells me I don't have enough compression, but having seen the large flame, i'm expecting almost no reading. Also, do you know of a leak down time? Ideally, it should hold pressure for a long time, correct? Should I put some oil in when I remove the spark plug to help seal around the piston rings (the engine has been sitting for a while)?

sting8282bird,

Welcome to AF.

Please read the advisory sticky at the top of this forum. The N Body forums are being removed so your post has been moved to the Grand Am forum.

sting8282bird, sounds like it back fired. You are sure that the timing mark were dead on ??

Other then that if it jumped time you could have bent a valve or two , which you'll know when doing your compression test.

Id do the first run on the test dry with all the p[lugs removed.
Record your reading, then put in 2-3 squirts of oil(the same for every cylinder unless it reads 0 on the first test) then see what it raises up to. Mainly looking for extremely low or no compression.

Here is a link that explains compr. testing with some pics.
http://www.automedia.com/Engine_Compression_Test/ccr20050801cc/1

Good Luck!