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Cylinder misfire, gasket blown inside bore


Go to solution Solved by Domiac,

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Breaking news, I performed a leak down test but please note that this was done on a _cold_ engine without oil inside it (engine temperature 30C / 85F).

Cyl #1 = 83 / 90 PSI

Cyl #6 = 77 / 90 PSI

Cyl #2 = 84 / 90 PSI

Cyl #4 = 38 / 90 PSI (intake and exhaust passes air)

Cyl #3 = 28 / 90 PSI (exhaust passes air)

Cyl #5 = 84 / 90 PSI

Great :huh: Bad values in both banks. After my last cleaning session, cyl #4 improved around 10% but that is insignificant. I have not rigorously cleaned cyl #3 yet, but based on my borescope session, it should be reasonably clean, hard to see the places where valves actually tighten themselves against the head, I might get it better but too tired to engage into that adventure today.

What do you think I should do?

1) put the engine back to the car and try it out?

- if it runs OK and sounds good, let it warm 30 minutes on idle, do durametric checkup and finally perform another leak down test properly using a warm engine

- after all, I think there is a chance that the combustion and heat can remove the gunk?

- this option is fine for me, I don't mind the job but I'd be hesitant to crank this baby up if you guys think there is a fair chance it could go worse

2) start spending serious $$$, haul engine to a shop and be prepared for valve / lifter job

- I recently moved to Europe and the sad story is that I think there's no shops on Finland that do these kind of things reliably with reasonable amount of money

- for me it would probably mean shipping this engine 1000 km to Germany but I have to research my options..

What can I say, BIG thanks to you guys .. again ...

Edited by Domiac
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As the head gaskets on these engines are multilayer steel, and never fail, I doubt that is head gasket material. More likely, that is a build up of dried coolant from a crack area. Time to run a lea

If you have suffered a cylinder head crack, which is not that uncommon, you can often (but not always) catch this with a leak down test which pressurizes each cylinder while the piston is at TDC and o

Boy, you have come up with a real gem of an issue. Rather than trying to rotate the assembly or blow the bits out, which may worsen the problems, probably your best bet short of pulling the cylinder

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Breaking news, I performed a leak down test but please note that this was done on a _cold_ engine without oil inside it (engine temperature 30C / 85F).

Cyl #1 = 83 / 90 PSI

Cyl #6 = 77 / 90 PSI

Cyl #2 = 84 / 90 PSI

Cyl #4 = 38 / 90 PSI (intake and exhaust passes air)

Cyl #3 = 28 / 90 PSI (exhaust passes air)

Cyl #5 = 84 / 90 PSI

Great :huh: Bad values in both banks. After my last cleaning session, cyl #4 improved around 10% but that is insignificant. I have not rigorously cleaned cyl #3 yet, but based on my borescope session, it should be reasonably clean, hard to see the places where valves actually tighten themselves against the head, I might get it better but too tired to engage into that adventure today.

What do you think I should do?

1) put the engine back to the car and try it out?

- if it runs OK and sounds good, let it warm 30 minutes on idle, do durametric checkup and finally perform another leak down test properly using a warm engine

- after all, I think there is a chance that the combustion and heat can remove the gunk?

- this option is fine for me, I don't mind the job but I'd be hesitant to crank this baby up if you guys think there is a fair chance it could go worse

2) start spending serious $$$, haul engine to a shop and be prepared for valve / lifter job

- I recently moved to Europe and the sad story is that I think there's no shops on Finland that do these kind of things reliably with reasonable amount of money

- for me it would probably mean shipping this engine 1000 km to Germany but I have to research my options..

What can I say, BIG thanks to you guys .. again ...

Assuming there was nothing wrong with the engine or its leak down values before your experiment in towel inhalation, it would be a fair assumption that the values on cylinders 3 and 4 are as the result of the clean out campaign (either residual towel, loosened carbon, or a mechanical scratch on the valve seat somewhere). As cold leak downs are notoriously inaccurate, and because you are going to be facing a major cash outlay to pull the heads off and send them out for a retread, I would be of the mind to put the car back together and light it up, assuming there is nothing visible left in any cylinder or head runners. Once warmed up, I would specifically look at the leak down of two currently weakest cylinders; if they "heal", you are back in business. If they don't, you are no worse off, or any poorer, than you are currently.

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I'm with JFP. Given your circumstances it's clearly the best option.

Once it's warm, rev it up a few times past 4k. If you've got valve issues, you'll most likely hear a miss or a backfire especially on decelleration.

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I'm with JFP. Given your circumstances it's clearly the best option.

Once it's warm, rev it up a few times past 4k. If you've got valve issues, you'll most likely hear a miss or a backfire especially on decelleration.

Roger that. I'll plug my Durametric too and see how this turns out.

Once again, my sincere thanks to JFP especially and Steve too!

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  • 3 weeks later...

One last thing before I reinstall my engine. Is there a safe way to activate variocam manually when turning the crank manually with a ratchet? The rationality here is to get the intake valves open all the way up to 10mm, not just 2mm, so that I can perform a final cleanup for my intake valves. I know there is some crud on the valves and on the head and I could carefully remove some of it if I can get more clearance.

Previously I noticed that if I tilt the engine 8 degrees, I can spray some clean oil inside the bore through spark plug hole and vacuum everything out from exhaust valves, it seemed to work really good and I could vacuum gunk out with the help of viscous oil. Notice, if the engine is tilted a bit, then the oil will flow towards the exhaust valves (instead of piston rings). Gravity is your friend here.

When I'm done with more important things, I'll post a few (ridiculous) videos to youtube and more tips here about which tools I used for my cleanup, most likely they will offer a few laughs for the pros here :king:

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One last thing before I reinstall my engine. Is there a safe way to activate variocam manually when turning the crank manually with a ratchet? The rationality here is to get the intake valves open all the way up to 10mm, not just 2mm, so that I can perform a final cleanup for my intake valves. I know there is some crud on the valves and on the head and I could carefully remove some of it if I can get more clearance.

Previously I noticed that if I tilt the engine 8 degrees, I can spray some clean oil inside the bore through spark plug hole and vacuum everything out from exhaust valves, it seemed to work really good and I could vacuum gunk out with the help of viscous oil. Notice, if the engine is tilted a bit, then the oil will flow towards the exhaust valves (instead of piston rings). Gravity is your friend here.

When I'm done with more important things, I'll post a few (ridiculous) videos to youtube and more tips here about which tools I used for my cleanup, most likely they will offer a few laughs for the pros here :king:

Um...I don't think you can activate the extra lift because there's no oil pressure for the hydraulic involved. Sure you can activate the lift solenoid to hear a click but wihout oil pressure, the cam follower will not lockup for the high lift. At least that's the way I understand how it works.

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One last thing before I reinstall my engine. Is there a safe way to activate variocam manually when turning the crank manually with a ratchet? The rationality here is to get the intake valves open all the way up to 10mm, not just 2mm, so that I can perform a final cleanup for my intake valves. I know there is some crud on the valves and on the head and I could carefully remove some of it if I can get more clearance.

Previously I noticed that if I tilt the engine 8 degrees, I can spray some clean oil inside the bore through spark plug hole and vacuum everything out from exhaust valves, it seemed to work really good and I could vacuum gunk out with the help of viscous oil. Notice, if the engine is tilted a bit, then the oil will flow towards the exhaust valves (instead of piston rings). Gravity is your friend here.

When I'm done with more important things, I'll post a few (ridiculous) videos to youtube and more tips here about which tools I used for my cleanup, most likely they will offer a few laughs for the pros here :king:

You will not be able to rotate the engine fast enough to get the VarioCam system to kick in (no oil pressure).

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  • 4 weeks later...
Engine and transmission is now back and it started like a champ! No error codes and almost all works as expected.




Really happy that I got it back together without issues, oil pressure came right to the top and once warm it held between 3-5. But here comes the catch. Once engine warmed a bit and I gave it some RPMs, knocking became more evident. Bank 2 as expected and I suspect it was Cylinder #4. Also #4 fuel injector was full of paper gunk which seemed to be easy to clean, microscoping all injectors gave me the impression that my cleanup was successfull but I really do not know for sure.


Note that before start I tried to prime oil pressure without C4 fuse, spark plugs and coils by cranking 8 seconds, waiting for a while and cranking another 8 seconds. Seemed not to do anything in my case, oil pressure kept around 0.5 or so.


Now the big question, if this would be your car, what would you do next?


1. Try to get rid of the gunk on bank 2 head by carefully driving it on a freeway?

2. Start it again and use car thethoscope to pinpoint where the knock comes?

3. Not start it again, take bank 2 head out and have the valves and seats machined?

4. Not start it again, take both banks out and have valves and seats machined?

5. Something else?


Some background info follows..


Everything in the engine looked really clean, I even used a small USB microscope to inspect various places when IMS and chain tensioners were out. Also filter and oilpan was really clean.


I have also done the following

- engine + transmission washed (all elect. off) and protector sprayed

- inspected / buffed flywheel, pressure plate, bearing, clutch disc

- all fuel injectors "kind of cleaned" from outside with isopropyl alcohol

- all tubes cleaned

- all electrical connectors cleaned + protector sprayed

- all intake parts cleaned

- all exhaust + cat parts cleaned

- all coolant hoses cleaned (vacuumed and rinsed with battery water)

- all plastic parts serviced with silicone

- pre o2 sensor tips gently brushed with toothbrush & isopropyl alcohol

- oilpan + oil pickup cleaned

- fixed small leak in cooling system (large tube)

- new AOS + gaskets around the AOS system

- new gaskets for exhaust + cats

- new waterpump + gasket

- new thermostat + housing

- new RMS

- new IMS + flange + bolts (upgraded to LN Engineering)

- new chain tensioners (all three)

- new engine mounts

- new clutch line, kinked a bit during jacking (stupid me)

- new oil cooler gaskets

- new intake housing gaskets

- new intake gaskets

- new Throttle body gaskets

- new magnetic oil plug + oil filter

- new coils + sparkplugs

- new brake fluid

- new coolant

- new coolant cap

- new transmission oil

- new engine oil and filter

- new air filter

- new power steering fluid

- some misc small parts replaced

- 20 liters of new gas, I guess tank contained max. 5 liters five month old gas


PS. Completely drained my system out from coolant with my shop vacuum and I found a really nice trick to refill it without "burping" or air issues. When refilling your 23 liters back, use shop vacuum to suck the coolant in 1 second pulses (depending how strong vacuum you got), always filling coolant tank in between, worked like a charm and I got over 20 liters in the system! I'll post a separate thread with pics, again later once more pressing matters are taken care.


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Spark plugs are properly torqued to 22 ft-lbs, always using torque wrench. During my 15 min test run (no load on the engine), Durametric showed 0 misfires.

Even though I checked that plug seatings are clean on my heads, there is a possibility that some dirt is between a plug and my head. I'll put your idea to my work list (get bank 2 plugs out, clean plug area, put plugs back). It does not hurt to

Some people think that I should simply ride it hard, it should fix the issue. My gut tells me that it is best to get for some ideas first from renntech.org.

I am on a work trip in Germany but will get back after a week. Feel free to throw more ideas to my work list :-)

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Any ideas are appreciated on how to diagnose this a bit further and get tip what could be causing this, e.g.

1. some part might be loose or leaking (I did tear everything apart except engine itself and the heads)

2. intake valves

3. exhaust valves

4. cylinder ring / liner (I hope it is not this)

I have a very good microscope with mirrors, it fits perfectly through my spark plug holes. I also have a cheap digital stethoscope and good leak down tester. I am considering warming up the engine again for 15 mins and performing a proper leak down test for bank 2.

PS. My camshaft deviations changed from 1.53 and 2.58 to 0.42 and 1.97, however all values are without load between 700-4000 RPMs.

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Any ideas are appreciated on how to diagnose this a bit further and get tip what could be causing this, e.g.

1. some part might be loose or leaking (I did tear everything apart except engine itself and the heads)

2. intake valves

3. exhaust valves

4. cylinder ring / liner (I hope it is not this)

I have a very good microscope with mirrors, it fits perfectly through my spark plug holes. I also have a cheap digital stethoscope and good leak down tester. I am considering warming up the engine again for 15 mins and performing a proper leak down test for bank 2.

PS. My camshaft deviations changed from 1.53 and 2.58 to 0.42 and 1.97, however all values are without load between 700-4000 RPMs.

I'd would run a leak down test on the cylinders in question; anything beyond 10% is problematic.

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I'll change the spark plugs and coils between cyls #1 and #4. Also check for debris before putting plugs back. Both the plugs and coils are brand new but you never know. After that warm up the engine at least to 130F (Durametric oil temp) and then perform a leak down test for all cyls starting from #4.

Getting back home to the land of genuine sauna and Santa Claus tonight, I should have some free time in a couple of days..

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While the engine is running, how could I diagnose if the cylinder ring is leaking? Could I feel the back pressure e.g. by removing air filter parts while running the engine on clean garage? I know I need to keep MAF working should I do that..

Of course the leak down test will give best results, but I'd like to understand if there is anything else I could do while the engine is running.

Thanks!

Edited by Domiac
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While the engine is running, how could I diagnose if the cylinder ring is leaking? Could I feel the back pressure e.g. by removing air filter parts while running the engine on clean garage? I know I need to keep MAF working should I do that..

Of course the leak down test will give best results, but I'd like to understand if there is anything else I could do while the engine is running.

Thanks!

A warm leak down is the best test for this.

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  • 2 weeks later...

Breaking news... I decided to take one more borescope run with a better mirror alignment and noticed that the area between my exhaust valves contained a sharp trail of gunk. I suspect that this causes incandescence and therefore pre-ignition. The sound of my bank 2 just kept getting worse as my engine warmed up.

I fabricated a brush tool which I could tilt >90 degrees after one pushes it through the spark plug hole, when I pull the wire the brush part tilts >90 degrees. Worked like a charm and I got rid all of the visible gunk. However, I got careless and while extracting the tool, the brush head dropped inside my cylinder. Game over. (I now know how to do it right though).

Next I soldered some white leds togethers which I could insert through the exhaust valves and see the battle area. Using wires I could align the brush to the only position in two axis that I could extract it. With the help of pushing down the cylinder, I got it jammed inside the spark plug cylinder and finally using hot iron and copper, pull it out. The piece was 0.49" x 0.57"x 1.3" but the brush part compresses somewhat.

Should you be interested of this insane journey, see the ludicrous pictures on my attachment :P

Hopefully I have the time to put my engine back soon and fire it up. If this does not help then I'll give up, extract bank 2 head and ship it to a shop for proper maintenance.

post-93239-0-51208100-1401482651_thumb.j

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The last time I saw paper towels sucked into an engine and cause no start and missfires...

the method i saw to solve that issue at the time was to fill the chambers with something like break cleaner and set fire to it. Once everything turned to ash it easily blew out the tailpipe..

this is a story about a method that worked but i might not recommend it...

all the best...

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Breaking news... I decided to take one more borescope run with a better mirror alignment and noticed that the area between my exhaust valves contained a sharp trail of gunk. I suspect that this causes incandescence and therefore pre-ignition. The sound of my bank 2 just kept getting worse as my engine warmed up.

I fabricated a brush tool which I could tilt >90 degrees after one pushes it through the spark plug hole, when I pull the wire the brush part tilts >90 degrees. Worked like a charm and I got rid all of the visible gunk. However, I got careless and while extracting the tool, the brush head dropped inside my cylinder. Game over. (I now know how to do it right though).

Next I soldered some white leds togethers which I could insert through the exhaust valves and see the battle area. Using wires I could align the brush to the only position in two axis that I could extract it. With the help of pushing down the cylinder, I got it jammed inside the spark plug cylinder and finally using hot iron and copper, pull it out. The piece was 0.49" x 0.57"x 1.3" but the brush part compresses somewhat.

Should you be interested of this insane journey, see the ludicrous pictures on my attachment :P

Hopefully I have the time to put my engine back soon and fire it up. If this does not help then I'll give up, extract bank 2 head and ship it to a shop for proper maintenance.

Necessity has always been the motherhood of invention, so congratulations on inventing yet another new Porsche tool! :thumbup:

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  • 2 weeks later...

While the engine is running, how could I diagnose if the cylinder ring is leaking? Could I feel the back pressure e.g. by removing air filter parts while running the engine on clean garage? I know I need to keep MAF working should I do that..

Of course the leak down test will give best results, but I'd like to understand if there is anything else I could do while the engine is running.

Thanks!

A warm leak down is the best test for this.

Huge cleaning work behind for cylinder #4. Today I managed to get my engine and transmission back, started my engine, warmed it up to op temperature, took a short 5 minute drive. No error codes. After shutdown, I performed a leak down test for cylinder #4. Result was 100 / 96 PSI, which is excellent news (most likely worst case scenario no longer applies) :clapping:

While running, after idle dropped to 700 RPM, bank 2 is still giving out a nasty knocking / pinging sound, not as bad as previously but noticeable still.

Any suggestions what to do next? :) What fields should I log using Durametric?

My schedule is hectic but I have free time this Tuesday evening. I plan to warm it up again and perform leak down test for all cylinders. I suspect all my other cyls are good as the paper was stuck on cyl #4. It can be that some parts on my camshaft (valve lifters or such) did not like paper getting stuck.

Please see a quick 30 sec video here: https://www.youtube.com/watch?v=uLSUKtKnlkk

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Edited by Domiac
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Forgot that I did log some Durametric values, here's a simplified version of it, small snapshots from three different time periods. First soon after the start (yellow), three minutes after (yellow) and finally over 10 minutes from the start (red). Rough running on cyl #4 gets quite high values, are those OK?

Camshaft position deviations are good: worst values are 0.66 and 2.05

I'd be happy to know which values I should log to diagnose this further, suggestions are welcome.

post-93239-0-20666600-1402251541_thumb.p

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Also, since last run I changed my injector o-rings (12 pcs), re-attached intake and exhaust parts again and moved across the following parts between bank 1 and 2:

- fuel injectors

- spark plugs

- coils

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Those Durametric numbers look fine. However, if the DME has been reset recently, 10 min may not be enough to get a steady state values. The best is to drive the car for a while say half a day then re-measure everything. Also the MAF reading of 20 kg/hr sounds high at 700 rpm. I think it should be around 15-18kg/hr.

Btw, are you sure the sound is from cyl 4 and it was not there before the shop towel ingestion?

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Those Durametric numbers look fine. However, if the DME has been reset recently, 10 min may not be enough to get a steady state values. The best is to drive the car for a while say half a day then re-measure everything. Also the MAF reading of 20 kg/hr sounds high at 700 rpm. I think it should be around 15-18kg/hr.

Btw, are you sure the sound is from cyl 4 and it was not there before the shop towel ingestion?

Thanks for checking my data out.

Right now I know that bank 2 is louder than bank 1 but I do not know if it comes from Cyl #4. I am reasonably confident that my bank 2 did not have such a loud sound previously, the video shows that bank 2 is louder than bank 1.

Perhaps I should just drive the car for multiple hours and see how it goes. The engineer in me says I should trust DME and just drive it as there are no error codes. However the geek in me says insane things like I should attach a digital stethoscope to my bank 2 and let my computer show spectrogram and RPM while I am driving, it would be trivial to do.

Next time when I run my engine, I'll use my digital stethoscope to diagnose where the noise is most audible.

Any ideas what to log with Durametric?

Edited by Domiac
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BTW, here's a sample spectrogram of my 996 start with old tensioners. The rattle can be "seen" in between 5,0 and 6,9 second interval. You can see that after around 9 seconds (cranking included), the engine is running smooth. First few second spikes are due to cranking, the following ones due to "rattling" which occurs with any 996 engine to some extent.

Requires some tweaking with software to filter out normal engine sound but quite easy to do. After I changed my tensioners and oil, the rattle is easier. Then again, the rattle was quite OK even before. Anyway, to do this properly, one needs to repeat recording and analysis in exact same manner before and after changing parts. This is just for the fun of it, not that scientific :king:

I could let someone else drive the car so that I can do some Durametric testing and ensure that knocking is not getting much louder, also with the help of spectrogram.

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Edited by Domiac
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