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Not sure what exactly is the problem but I think I have narrowed it down to a weak injector. I broke in my engine with the colder NA plugs with intentions of changing them once I found out if the TT plugs would fit and not interfere with the pistons. After 1000 miles, I raised the boost to 14psi and had a lot of mistire because the plug gap was too large (stock 0.044") so I regapped them to 0.037" and the misfire went away. Well, I ran the car like that for a few weeks and then I got more misfire. I pulled the plugs to inspect and found that cylinder #2 had burned the electrode off. There was just a nub left. Shortly before this I had found that the TT plugs would work in my converted NA engine and I had ordered them and was driving around with them for a little while.. While I had the plugs out I ran a compression and leakdown test. Every cylinder was 155psi and I had 3-4% leakdown. So I figured all was well and I put the TT plugs in (gapped to 0.035"). The car ran great from that point on. This past weekend a buddy of mine was setting up a deal on a C6 for a friend and we were taking it over to his house so I drove my Z so that we could have a little fun on the way there. We rolled out of Fred's shop onto Waldo Rd. and I though he was going to get on it but he didn't so I turned my attention to my boost control and saw that I had it only dialed in for ~10psi. So I started to turn up the boost when I saw the C6 squat and a puff of black smoke come from the exhaust. So I nailed it too. As I was coming to the top of 2nd, I heard audible detonation so I let off for a sec and went to 3rd. More audible detonation. Sheeat. But I had held on to the C6, not losing any ground util mid 3rd gear when I decided there was no reason to pound my pistons to death.. So I check my boost level and see that I had accidentally bumped it to 21psi.. :-( I was running pump fuel and it was about 94 degrees out. Waaaay too much for stock turbos. So I turned the boost back down to 17 and was continually getting a misfire. I figured I had burned up another electrode. So we get back to Fred's shop and I start pulling plugs. When I get to #2 I see that it looks different from the rest of them and has some hard ashy-white deposits on almost all of the surfaces that are exposed to the combustion chamber. I couldn't scratch it off though - it was very hard.. So I decided to do a leakdown and compression test.. All of the cylinders came back with a 3-4% leakdown and 155psi compression, except for cylinder #2! It had a 45% leakdown and was only making 93psi of compression! So I figured that it took a shit. Wasn't sure if it was the exhaust valves or the rings, but I knew it wasn't the intake valves because I listened through the hole on the plenum where the balance tube connects for any hissing. I didn't check the exhaust pipe for any leaking sounds though - I had enough at that point and was feeling prettty shitty. This was saturday afternoon.. So I went to the springs sunday with the family and let the Z sit. Searched through classifieds for any forged pistons to just build the motor up, along with some sport 600's. Found some good deals on both and figured I'd get the fundage together and buy them.. So at lunch I went home and got the Z and drove over to Fred's shop again.. I pulled out the leakdown tester and decided to give it another shot. Well, interestingly enough, the cylinder is fine. It has a 4% leakdown and was making 155psi. Now I'm not sure what's going on with this, perhaps a little piece of carbon or aluminum from the piston had gotten itself between a valve and valve seat and it just got burned off and is no longer a problem, but it doesn't take much of anything stuck in that position to cause a cylinder to get 95% leakdown. I'm convinced that it isn't the cylinder wall being scratched by something like the little piece of platinum that was in the electrode that I burned off several thousand miles ago, because if it were, a cylinder is not going to fix itself. It must have been something there that is not there anymore, i.e. something stuck in a valve. Has anyone ever seen something like this or heard of something along these lines? I was thrilled to find that the problem was gone, but I dont want to see it again! I'm thinking of pulling the injectors and having RC engineering flowtest and calibrate them at this point, it will be $150 well spent..
[ ashleypowers.com ]
[ agpowers@bellsouth.net ] When pigs dance, you better get it on video...
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