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Potential engine rebuild necessary, need resources
For what its worth, my dad has a 2004 GT3 with ~28k miles, he is the second owner the vehicle.
It has always driven well but unfortunately it sees very little driving except for a single 50 mile open road race annually and a few track days here and there. It receives annual oil changes regardless of miles and the fuel is treated before it sits over the winter months. It is never beat on, bounced off the limiter etc., we only have 91 octane gas here in NE but I would think that the DME would has been well adjusted to that by now.
We just drove it about 200miles to an event here in Nebraska were they have a open road race, this annual race had really been about the only "hard use" the vehicle had seen for the last 12 years.
Upon crossing the finish line it was clear the engine had a misfire and soon thereafter the dash light came on, a basic cheap scantool was used to determine it was cyl.# 5 misfire.
We had the vehicle trailered home, I hoped it was a bad coil or plug but what happened was much worse.
The spark plug of cylinder #5 had lost the majority of it's porcelain and the one of the electrodes was smashed against the ground post. The electrode doesn't look Iike it melted itself to the post but was hit against it, although I can't see any marks to confirm that. It looks like the porcelain may have come out and gotten trapped between the electrode/piston possibly.
A borescope in the cylinder revealed damage to the piston, I have yet to do a leakdown and/or compression test but I wouldn't be surprised it there is also damage to the valves,head and cylinder walls.
I found some oil in cylinders 5 and 6 and the times in was started after the damage occured white smoke puffed out the tailpipe for a brief amount of time, it has never done that.
Sorry for the long post, I am going to drop the engine, but am looking for any resources on where to send it.
I am currently doing my research but just could use some help. It's such a bummer, we want to keep this vehicle we both love but who knows what damage there is or parts availability at this point. I just hope there are still competent places to send this engine to for repair.
Well, that plug is the reason for the misfire. Can't really tell with the pictures, but it may not be bad news. A leakdown test will give you more information. Do all 6 cylinders if you can to get a baseline.
Just take your time and work through this logically and methodically.
I am sorry to hear about this. This is the first time I’ve heard about such a failure mode. I wonder if it was just a bad or compromised spark plug. The good news is that it is very much rebuildAble. Parts are still plentiful and unlike the non-996 motors, The investment to rebuild is more than worth it. And for not much more money, you can go to a 3.8 or 3.9. As Marc Said all may not be lost, but I agree you should send it to a competent place.
I am sorry to hear about this. This is the first time I’ve heard about such a failure mode. I wonder if it was just a bad or compromised spark plug. The good news is that it is very much rebuildAble. Parts are still plentiful and unlike the non-996 motors, The investment to rebuild is more than worth it. And for not much more money, you can go to a 3.8 or 3.9. As Marc Said all may not be lost, but I agree you should send it to a competent place.
So the fact it's a Mezger won't necessarily affect parts availability? I own a 2004 M3 and I some engine parts are not readily available and BMW produced a lot more S54 engines than these 996 GT3 engines.
I'm glad to hear you say that parts availability wont be such a big deal. I just hope this engine shares as much as possible with the base 911's as far as engine internals/architecture.
I am not very educated on this topic unfortunately, my dad is the Porsche guys and BMWs are my thing. I love the Porsches, don't get me wrong!
I will be testing/pulling this engine if and when it comes to it. I'll need to start educating myself as much as possible on these engines. Thanks for the help, I'll likely be around the forums with updates/questions.
So the fact it's a Mezger won't necessarily affect parts availability? I own a 2004 M3 and I some engine parts are not readily available and BMW produced a lot more S54 engines than these 996 GT3 engines.
I'm glad to hear you say that parts availability wont be such a big deal. I just hope this engine shares as much as possible with the base 911's as far as engine internals/architecture.
I am not very educated on this topic unfortunately, my dad is the Porsche guys and BMWs are my thing. I love the Porsches, don't get me wrong!
I will be testing/pulling this engine if and when it comes to it. I'll need to start educating myself as much as possible on these engines. Thanks for the help, I'll likely be around the forums with updates/questions.
The Carrera and the GT3 are two completely different engines. The only thing they share is their color.
However, the Mezger engine (996 and 997 GT3) is shared with the 996 and 997 Turbo.
I'm a bit of an optimist here and the damage you see may be superficial. Any parts of the plug are probably long gone out of the exhaust port. Nevertheless, a leakdown can be done while the motor is still in the car. I would get those numbers and then call a shop that specializes in these engines and tell your story.
Additionally, an oil sample test would not hurt, but may not tell you much. Worst case is a top end rebuild, which opens up the possibility of larger displacement, but that's another rabbit hole.
If you get a pass from this I would replace every single spark plug just incase it's a batch issue.
Have your coolant pipes been pinned or welded? That's something you should address if the engine comes out.
I can't help diagnose your issue but I can second Autometrics for Mezger builds. I've worked in the high-performance car parts and racing business for 20 years and *everyone* thinks highly of Autometrics for Porsche engine work and race prep. Service too. Everything, really.
A misfire, but no mechanical noise/issues?
Occurred crossing the line? Close to redline one would assume. So you drove back to the paddock without some ungodly noise? And you've replaced the plug and restarted it and no noises?
The piston damage looks pretty minor. If a piston struck the spark plug, one would expect there would be some sever crank bearing/connecting rod/wrist pin/whatever damage and resultant noise.
My opinion. Don't stress the rebuild possibility, just focus on diagnostics.
Chris Cervelli is the one I would highly recommend. He's built numerous race and street Mezgers for me over the years including 3.8 and 4.0 race builds. Arguably one of the best engine builders in the US. Located in Denver. He's also a Motec dealer and tuner with an engine dyno on site.
Last edited by powdrhound; 08-14-2024 at 04:24 PM.
A misfire, but no mechanical noise/issues?
Occurred crossing the line? Close to redline one would assume. So you drove back to the paddock without some ungodly noise? And you've replaced the plug and restarted it and no noises?
The piston damage looks pretty minor. If a piston struck the spark plug, one would expect there would be some sever crank bearing/connecting rod/wrist pin/whatever damage and resultant noise.
My opinion. Don't stress the rebuild possibility, just focus on diagnostics.
Yeah, just a misfire, I don't doubt I could throw a new plug into cylinder 5 and the engine will run well. I have yet to do a leakdown on the engine.
My orginal post was a but confusing, when we crossed the finish line of this open road race we noticed the bad idling, not nasty marbles in a tin can noise or rod knock etc. The car was never really even past 7k during this road race.
My scan tool showed a cylinder 5 misfire, we made a decision to drive it back to where we were staying about 25miles away, this may have been a bad decision but is what it is. I was hoping it was just a bad plug/coil/injector etc.
The Carrera and the GT3 are two completely different engines. The only thing they share is their color.
However, the Mezger engine (996 and 997 GT3) is shared with the 996 and 997 Turbo.
I'm a bit of an optimist here and the damage you see may be superficial. Any parts of the plug are probably long gone out of the exhaust port. Nevertheless, a leakdown can be done while the motor is still in the car. I would get those numbers and then call a shop that specializes in these engines and tell your story.
Additionally, an oil sample test would not hurt, but may not tell you much. Worst case is a top end rebuild, which opens up the possibility of larger displacement, but that's another rabbit hole.
If you get a pass from this I would replace every single spark plug just incase it's a batch issue.
Have your coolant pipes been pinned or welded? That's something you should address if the engine comes out.
The coolant pipes have been pinned previously. I just worry about hot spots on the piston surface down the road with the damage I *think* I see on the borescope.
I will try to remain optimistic as well!
I think you had a very unlucky spark plug failure. I am suspicious of the fuel additive/stabilizer. I would recommend not using old or stabilized fuel in any kind of hard use. This is pure speculation at this point though.
I also think a new set of plugs would have the engine running on 6 cylinders again. There is a potential problem with doing that though: these engines very effectively trade debris between cylinders. The debris bounces up the intake runners and randomly goes into any of the other cylinders, so it's likely that the other cylinders have similar damage as the one you borescoped. The inside of the intake manifold is going to have pieces of that insulator everywhere. The intake will need to be disassembled and ultrasonically cleaned, which is normally done as part of a rebuild anyway.
Getting parts for this engine won't be a big problem.
I think you had a very unlucky spark plug failure. I am suspicious of the fuel additive/stabilizer. I would recommend not using old or stabilized fuel in any kind of hard use. This is pure speculation at this point though.
I also think a new set of plugs would have the engine running on 6 cylinders again. There is a potential problem with doing that though: these engines very effectively trade debris between cylinders. The debris bounces up the intake runners and randomly goes into any of the other cylinders, so it's likely that the other cylinders have similar damage as the one you borescoped. The inside of the intake manifold is going to have pieces of that insulator everywhere. The intake will need to be disassembled and ultrasonically cleaned, which is normally done as part of a rebuild anyway.
Getting parts for this engine won't be a big problem.
What brand is the spark plug?
Chris
I did see what I thought was debris in cylinder 6 as well but no physical damage to the top of the cylinder was notes. That is unfortunate to hear this stuff may be effectively spread throughout the motor, but I very much appreciate that information. This makes me less apt to simply throw plugs in it and go.
With all respect, it seems that you're over-thinking this and doing random things.
You already drove 25 miles?
Why don't you check the compression in that cylinder AND
Why would you not put a plug in and start it?
Occam's razor and "KISS", man.
I would agree, but a leakdown test may be a better choice simply because there is no need to actually crank the engine. Leakdown can also help pinpoint the issue: i.e., whistling or hissing in the exhaust is likely an exhaust valve and the same in the intake manifold would be an intake valve, etc. Not so easy with compression testing.
If it passes, and you probably did dodge a bullet, you could always drain and flush the crank case oil if you feel the need for belts and suspenders. Won't hurt.
08-13-2024, 09:46 PM
Potential engine rebuild necessary, need resources
