305 engine woes (1989 firebird), Engine knock?

I let my car sit over the winter outside with a cover on it and half a tank of gas.This spring I got it out and it Ran BAD,even after i filled it up with mid grade gasoline, and carb cleaner.
in fact Shortly after filling it I parked it for the night then started having troubles getting it to fire up and start running the next morning. It would turn over like crazy but not catch and fire up. It did a day or 2 later and I got it to my friends house to do some work on it

First I gave it a tune up since I already had the stuff for it (cap,rotor,plugs, wires,filters) fire it up and it runs nicely for a very short time and then back to running bad, same issue with starting.

Next I ran an error code and found that the coolent temp sensor was bad Replaced that and it started running better but still not great, I only let it Idle and a friend of mine mentioned it might be water in the tank.

So finaly I put ISO DRY into the fuel let her sit and fire her up and she runs like a dream!

After a short drive (less then a mile), I start hearing some kind of a rattle or knock coming from the engine and by the time I get home it's LOUD, Sounds like a piece of mettal banging either under the air cleaner or closer to the front of the engine block behind the water pump.

Now it's seeming to have no issues starting at all and it's running pretty strong but that knock is there full time. If i leave it idle it will stall out but if I drive it, it seems to run well.

Since the car was still running bad after the tune up and started knocking on the test run. I never got around to changing the oil. Oil on the stick still looks pretty good still.

Any Ideas what to do next?

I've heard suggestions of changing the oil, but like i said the oil looks pretty good.. When it gets hot sometimes the pressure gage will go down. It did that for the prior owner too, he figured something was wrong with the sensor as it always ran strong.

Also it was suggested I drain the gas and put new in. I already put drygas, injection cleaner and 1/2 a tank of new mid lvl gas..

Would either of those two suggestions help a loud knock?

 

Might be a lifter going down. Are you getting any smoke or burnt oil smell from the exhaust?

 

before the tuneup it did blow some thick black smoke for a bit. I have a few locals here convinced that it's a broken rod that hasn't smashed through the block (but will If i drive it!!)
A friend of mine says he's got a rebuilt 350 sitting in his garage the last 2(3?) years that I can have if I get it out of there. I'm going to go check that thing out and see if it still cranks and probably drop that in. If it's realy rebuilt and runs stong i'm happy as a pig in **** that my rod broke.

 

could be a spun rod bearing

i spun my rod bearing , and it didnt always knock, somedays it would run like a dream, others it would knock, die, and be impossible to start!

http://www.youtube.com/watch?v=NRtSUoTevJA

does it sound like that?

 

how's the oil pressure look at idle? also you say it doesn't knock under load, i think that would rule out a main bearing, does the knock speed up or slow down with the engine? i think too it could be the timing chain, being as thats where you say the noise is coming from

 

mine didnt knock under load listen to the video
bearing can come and go with noise and screw everything up
mine would knock, causign the k.s to take out timing so it felt like i had a 3000 rpm rev limiter sometimes too!

another common place is if you have an auto, could be flexplate

 

main bearings usually are the ones to knock under load, rod bearing knock all the time

 

it almost sounds like the Youtube video, however it's louder more like clang clang ,clang, Roughly the same tempo though. Oil pressure seems alright while it idles, however it was dropping realy low after I'd run it around for a bit (this was before the knock, it's just sitting there now waiting for me to make my next move)

 

does it speed up in relation with the engine when you rev it up?

 

I don't think so. I think it stays the same. However i'm afraid to realy rev it up right now, I don't want the rod to come flying out.

 

ok another thing i did with my ford when it was knocking, is unplug each plug wire one at a time and see if the knocking stops, thats one way you'll be able to tell which cylinder

 

If i have to do a rebuild on it. i'm going for the crate motor or the motor in my step dads garage if it will work. I'm wondering how a TBI on a 305 will handle a swap to a 350 or
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if i'd have to carb it. I think the computer will go nuts and flash all sorts of lights and I don't know a thing about setting them up.

 

ah not to bad, my 89 tbi swap has really been easy, even though i cuss it so much, i don't even think my check engine light is on when it runs, if i could go back and do it all over again i would have bought the 260 horse goodwrench 350"