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I had a nice little surprise show up in my intake last week which has caused a great deal of damage, so before I go putting it back together I thought I'd hit up the experts as to the cause of the problem. Background: My 93TTZ developed a valve cover leak which wasn't bad, but since it was leaking onto the exhaust manifold I felt it was something that was better fixed than left as a fire hazard. My 5sp transmission had also developed a leak out of either the reverse switch or neutral switch (I can't remember which as I replaced both) and that was repaired at the same time. So, we pulled the plenum, put a fresh bead of silicone sealant on the valve covers, installed new plenum gaskets, pcv's while we were there, and a bunch of hoses/etc. While taking it apart we realized that there were some nice boost leaks along with a few other minor things (hey, it is 10 years old) and when we put it back together it was better than before. Boy does it make a difference on spool-up when boost leaks are gone. My car would hold 14psi of boost before (stg III), but it would take longer to get there. Problem: A few days and 50 miles after putting everything back together, I was turning into a parking lot when the engine really started to stumble and hesitate. The fuel light had been on for a little while, so I assumed I was running out of gas. Fortunately there was a gas station 100 yards away, so I lumbered into the station and shut the engine off just as it was dying. After filling it up I went to start it, and it continued to stumble, and at this point I could hear an occassional ping, almost like a golf ball being dropped on concrete. So, I shut it off and looked everything over, checking connectors, hoses, etc. and finding nothing out of the ordinary. Thinking the engine was just vapor-locked or something, I started it back up. This time it really stumbled, like it was running on 4 or 5 cylinders, and then bang bang bang - definite metal to metal contact in one of the cylinders. I immediately shut it off and called a tow truck. What we found: Got it home and pulled the spark plugs. Nothing. Turned the crank by hand and found definite resistance, so things are not looking good at this point at all. Get the magnet on a stick out and go fishing in cylinder #4 (did I mention the spark plug in cyl #4 was damaged pretty good - aperture crushed against anode so there was my answer to why it was running on 5 cylinders). Nothing. No metal. No nothing. So, we pulled the plenum and looked behind the intake valves - nothing. Tried to get a better look into the cylinder, but still nothing. So, time to pull the engine and take it to a machine shop. Machine shop: We get it pulled a few days later, get everything stripped off of it, and get it to a machine shop. The machinist pulls the heads off and.........finds a small piece of aluminum - yep aluminum - in cylinder #4. All other cylinders look clean, and the damage isn't too bad to the cylinder wall or head. But, the cylinders are at their wear limit, so time for cylinder boring, new pistons, valve job, pocket porting the heads, etc. Question: My engine is now being essentially rebuilt from the ground up. I'm doing a few things to make the block solid and better than it was before, and overall the process is costing a hell of a lot of money. So, here's my question. I still don't have any idea how the piece of aluminum got into cylinder #4. According to the machinist, it is the size of a bb and looks like it was round at some point, although it was somewhat flattened from being squished between the piston and the head. I have spent countless hours trying to think of where the piece of aluminum could have come from, but have yet to come up with a good answer - at least one I'm comfortable with. It is possible that it was inside the intake before fixing the valve cover leak, and when it was put back together the tighter intake (ie, fewer boost leaks) forced it from wherever it had been hiding and in through the intake valve. At first we thought it was a nut or something that we dropped into the intake when we had the plenum off, but what could we have dropped that was round and aluminum? I'd love to hear what you guys think. I'm stumped and scared that when we put it all back together this might happen again. Thanks for making it through the post - I know it was long, but I wanted to provide as much info as possible. Brian (Z-less for now)
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