Let me provide some back story first.

I bought this car from a local craigslist ad (turns out he's registered here), its a 1991 firebird with the 305 tbi. Now the other week my water pump went while i was driving home (30 minute drive) so about half the way home i had to really take it as easy as i could with smoke going everywhere. So i pulled it in, next day got the pump, installed and i was happy. But i start it up and i hear this...rocking sound. I don't know if i should call it a rock, or a rattle. But either way its making a sound it shouldn't. So now about 1-2 weeks later, its getting bad. When im at low RPM its thumping along.

So i brought it in to my auto class and my teacher says its not a mis-fire and to do a compression test. So i do a compression test on all 6 cylinders (passenger fronts and driver fronts) but can't seem to get to the two back ones. The compression was 135. So i check the oil and it looks a tad low, so i bought some more (synthetic by the way) and its still rocking/rattling. I bought new spark plugs, still the same. I tried seafoam thinking its carbon from being to hot when the water pump went, nope nothing.

I'm stumped, please help

 

Sounds like she overheated, hows the coolant look? How's the oil look? Is it milky? Is it hard to start? And how hot did it get?

 

Yea it really overheated. She was smoking up the whole garage and left a water trail down the street. The oil looks good as far as i can see. Its not hard to start but when it starts it rocks/rattle/thumps like i described.

 

time to tear her down im afraid.

 

Thats what i was afraid of. Luckly i got all winter and a backup car (a 98 jimmy that seems to be leaking oil onto the headers, so gotta fix that to) and ill be able to tear her down and if i need all new rings and/or pistons, then i may just look into a craigslist 350 to replace this 305.

 

Go 350, you can snag a good running one for less than $300. :P Where in northern il are you btw? I'm in the quad cities.

 

I'm in Rockford. I think i may just go to a 350, but now i gotta look into getting one and a cherry picker.

 

(double post i know)

I just thought of something, when i installed the water pump could i have, by accident, hit the timing mark on the front of the block and now retarded the timing? Would that cause such problems?

(If my questions sound noobish, i apologize, i am learning everything i know through the internet and this website about cars)

 

Hitting the timing comb wouldn't have affected anything.

 

Well....that sucks. Any suggestions then?

 

Time to tear down. If you ever need help finding parts, or need help working on it, let me know. Not that far of a drive to help out a fellow thirdgen owner.

 

Thanks man, ill try and work on it myself but don't be surprised if i PM you.

 

(another double post!)

So i just finished doing the compression test (the back two were a bitch to get to) and they're all reading 135. So i'm guessing that all my valves and rings are good? Now my other question is; If my rings and valves are good, would the Y pipe gasket that goes from the stock headers to the stock Y pipe be blown and causing a no-back-pressure backfire/running like crap?

 

Nah, I've ran a bunch of SBC's open headers/manifolds. You can't tell the difference :P

 

Yea i narrowed the problem to this plastic vacuum piece that comes off the stock intake manifold that broke. I have no idea what it does, but its inbetween the dizzy and secondary vacuum (i think thats what it called)

 

From what you've described that would be the MAP port on the intake. Kinda a huge vacuum leak, and without a correct MAP reading, it isn't going to run too hot.