Stumped with engine problems
#1
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Car: 91 Firebird Formula
Engine: 305 TBI
Axle/Gears: 2.73
Stumped with engine problems
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
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
#2
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Car: 1987 Trans AM
Engine: Twin Turbo 6.0 LS2
Transmission: T56
Re: Stumped with engine problems
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?
#3
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Car: 91 Firebird Formula
Engine: 305 TBI
Axle/Gears: 2.73
Re: Stumped with engine problems
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.
#5
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Car: 91 Firebird Formula
Engine: 305 TBI
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Re: Stumped with engine problems
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.
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Car: 1987 Trans AM
Engine: Twin Turbo 6.0 LS2
Transmission: T56
Re: Stumped with engine problems
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.
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Car: 91 Firebird Formula
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#8
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Car: 91 Firebird Formula
Engine: 305 TBI
Axle/Gears: 2.73
Re: Stumped with engine problems
(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)
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)
#10
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Car: 91 Firebird Formula
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#11
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Car: 1987 Trans AM
Engine: Twin Turbo 6.0 LS2
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Re: Stumped with engine problems
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.
![Frown](https://www.thirdgen.org/forums/images/smilies/frown.gif)
#12
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Re: Stumped with engine problems
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Last edited by rrims; 08-30-2010 at 11:00 PM.
#13
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Car: 91 Firebird Formula
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Re: Stumped with engine problems
(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?
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?
#15
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Car: 91 Firebird Formula
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Re: Stumped with engine problems
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)
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Car: 1987 Trans AM
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Transmission: T56
Re: Stumped with engine problems
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.
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