Nikasil Bore Scoring

Hey all, I have a 2003 4s with 135k miles, full engine rebuild at 119k due to bore scoring. I did the assembly myself, LN Engineering did the crankcase work, Len Hoffman did the cylinder head work. I had been chasing an intermittent misfire in cyl 1 for a couple months. It would throw P0300 and P0301 maybe once a month. Fuel trims were typically showing RKAT a little lean on bank 1 and FRA at tiny bit rich but all within spec. I had a road trip planned for this weekend, decided to bring the car to a pretty well respected local Porsche indy to diagnose and fix the problem before I left on the trip. They smoke tested the car and spotted a couple vacuum leaks but couldn't pin point them with out removing throttle body and plenum. They said they were super busy and asked if I wanted to chase them down and correct the leaks. I asked if they would have time to squeeze me in, but totally understand that they are busy and this is short notice so no big deal if they can't. Service writer said he'd talk to his tech and get back to me in couple hours, that was yesterday morning. Mid day today he called to tell me that when they started the car up today it belched a big cloud of smoke that smelled like coolant and "recommend checking further". I've never experienced a big cloud of smoke on cold start before. I gave the go ahead for scoping cylinder 1. They suspect that I have a coolant leak in cyl 1 which is washing cylinder walls down and has now caused scoring on the cylinder wall. Left the car with them for the weekend so they can leave the cooling system pressurized and see how much coolant is in the cylinder on Monday. Now, here's what I'm hoping to get opinions on, I know that nikasil "streaks" and that is totally normal but scoring obviously is cause for concern. I just don't know enough to spot the difference between streaking and scoring. Really hoping Charles from LN or Skip can chime in. EDIT: should also note that I've UOA at each oil change and every sample comes back looking great. I followed the recommended break in and break in oil schedule from LN and have been using Driven DT40 since full synthetic was allowed per their schedule. Attached are the images they took in the cylinder. Thanks in advance.

The missfire symptom could be a sticking intake lifter on cyl #1 ;( very common on 996.2 engines) The smoking on start-up could be just a failing AOS ( or overwhelmed AOS) ::: ( the frail OEM AOS system is the reason Invented/developed the UAOS System) With no prior coolant loose or no slow-flashing warning,..coolant leaking into the cylinder is a stretch at this point... If the pressure testing over the weekend turns out to be conclusive that coolant is entering the cylinder ...Then that will condemn the engine .. I would not be ready to condemn the engine at this point since condemning the engine is a $30k decision... I would want to see pictures of the other 5 cylinders to compare .. I would also want to do a Compression Test , a Leak Down Test, and a Blow-by Test to fully evaluate the engine health... Just my opinion if this was my engine that I had just bought..........I would want more "facts" before dropping $30k or 100 hours labor...

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Thank you for the quick reply, Skip. I greatly appreciate it. An additional bit of info for you, I have your UAOS installed and as far as I could tell it was functioning properly when I dropped the car off. Your suggestions of getting scope images of the other cylinders is a great place to start. I will also bring up doing compression, leak down and blow by tests when I talk to them on Monday. Aside from those items, what other "facts" should I be searching/asking for from the shop? Just want to set myself up to make the best decisions possible for this scenario. Thanks again.

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Ok, with the UAOS System you can dissmiss any thoughts of the crankcase ventilation system causing any symptoms... That brings us back to the shops observation of the huge cloud of smoke with a "coolant smell" on start-up.. If the pressure test over the weekend is conclusive that coolant is entering the #1 cylinder , that will condemn the engine ... no need for doing any Compression, Leak down, or Blow-by Tests.... Did the Missfire Symptom only occur right after start-up ? When there is a very small coolant leak into a cylinder it usually will accumulate after sitting overnite as the cooling system is under pressure untill it fully cools down...This will cause a Missfire for a few seconds when re-started the next day, then will clear up in just a few seconds as the spark plug drys off... Have you not had to top-off the coolant at all lately ??

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The misfire symptom was NOT present at start up. It typically would occur only when hot/at operating temp. Some days it would be almost non existent and other days it was pretty noticeable at idle. And on the day I drove it to this shop it was running GREAT. Another misfire observation was with durametric hooked up, the misfire would disappear when I would press the accelerator. I haven't added coolant(or needed to) since I re installed the engine after I completed the rebuild. Which is another reason why I'm kind of scratching my head on this. You would think that if this misfire was caused by or related to coolant in the cylinder and since the misfire has been happening for a while I would be consuming coolant. If it is/were in fact bore scoring, on my last used oil analysis(4000 miles ago), do you think I would've seen elevated levels of nickel, aluminum or silicon? I just looked at the report from Speediagnostix and the "wear per 1000 miles" was 7.5 and it was all green across the board. No signs of glycol in itl. Fuel dilution was low.

Yes, interesting ... We'll wait to see if the over the weekend pressure test is conclusive .... If not then the Compression, Leak Down, and Blow-by Tests will be in order along with the pictures from the other 5 cylinders for comparison. With the MIssfire Symptom not following a coolant leak in cylinder pattern,, it could be just the usual sticking intake lifter on the high lift and not related to the Smoking on start.. On the aftermarket pistons the second ring is not "pinned" and can rotate in the cylinder and if the ring gaps happen to line up and at the bottom, oil can seep in overnite put out smoke on start-up ..On the OEM pistons the second ring is pinned so it can't rotate..

Take my observations with a shaker full of salt -- I'm far from an expert. Those scratches look to me to be from debris of some kind, not the same as the typical M9x bore scoring due to failed piston coating. The fact that the scope is through the spark plug hole and the scratches run all the way up the bore is one of the things I'm basing that on. The question then becomes, what kind of debris might do that? Bits of carbon off the top of the piston maybe. Might that lend credence to the idea of coolant getting into the combustion chamber and "steaming" the stuff off the piston?

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Thanks for working through this with me. If no coolant in cylinder after being left pressurized over the weekend, then I will feel loads better especially with your prescription of testing leak down, compression and blow by as well as getting bore images of the other cylinders for comparison. Off the top of your head, what numbers should I be hoping to see for compression, leak down and blow by numbers to indicate good health? The more I calm down and think about this clearly, the less certain I am of the shops initial diagnosis of coolant leaking in to cylinder, washing the wall and scoring the cylinder. Though, that is not out of the realm of possibility. Having not needing to add any coolant in almost 2 years, used oil analysis reports all showing no presence of glycol, almost no presence of nickel, silicon or aluminum. Wear metal amounts all very, very low. I also went and looked at some images I took last summer of the bores and the cylinder walls look almost identical to what they are in these new images from the shop with 2 or 3 oil changes and UOA in between. Again, almost zero signs of wear metal in the UOA's. So, thanks a million Porschetech3 for calming me down from both my wife and I!

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Yeah, those scratches up at the top are really the only ones that actually like a scratch to me. The shop is, I think, interpreting the linear marks to be bore scoring. Which if you read my above response to Porschetech3, I remembered I had taken some bore images last summer and they look almost identical to what the shop took. That coupled with no consumption of coolant, oil consumption is the neighborhood of 1 quart every 2500 miles, and the used oil analysis reports showing no signs of wear metals,helps me to feel a bit more optimistic that this isn't catastrophic. But, as my wife can attest, I've been wrong in the past.

This is very late stage bore scoring (huge oil consumption, loud ticking noise, black soot on the left). You can see that it is more serious toward the bottom but the scratches go way up to almost the top of the cylinder too.

This is the "end of the beginning" stage of bores coring on a Cyl6. This car has zero oil consumption, no noise, and no black soot. It will probably get to the late stage in 20K miles.

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This was what my cylinder 6 looked like as well before I rebuilt with Nickies. I had audible piston slap, huge oil consumption and sooty bank 1 tailpipe. I just don't know enough about Nikasil to know what scoring looks like on that coating versus the streaking which millennium coatings says is normal and will eventually go away over time. I did every thing that was suggested by LN for block prep and assembly. Washed it a couple of times with warm soapy water, wiped cylinders with denatured alcohol and kimwipes until no more grey staining showed on the kimwipe. Cleaned the hell out of all the rings and pistons, inserted well lubed. Did my absolute best to make sure everything was as clean as possible. Followed Jake Raby's "Focus On M9X" series like the bible. I'm really trying to not let myself get too dejected yet, but it's an uphill battle at the moment! But for the time being, I am just going to have to wait to see if leaving the cooling system pressurized over the weekend results in coolant in the cylinder then go from there.

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Sorry I didn't catch this thread until now. I rarely have time to hop on the forums other than on the weekends when I can come to the office and work without interruption. We pressure test each and every block to 40 psi and blocks are surfaced after sleeve installation as well to ensure the deck is perfectly flat. I'm leaning towards some sort of contamination from initial start that led to the visible scratching. Considering the UOA looks good, you haven't had to add any coolant in years, and the oil consumption if far less than the typical 1 quart in 1000 miles, I think you're good to go, especially since the bore photos look the same as after initial run-in. For sure you need to take care of the vacuum leaks and get the fuel trims corrected. As Skip said, the lack of pinned second rings (something that no aftermarket piston manufacturer offers, even Mahle Motorsport), can allow the rings to rotate and have the end gaps line up at the bottom of the bore. This can result in a puff of smoke at startup. However, a leaky injector also can cause this, as fuel will pool in the cylinder and wash the lubrication away. If the injectors were not replaced at time of engine installation, I'd recommend that, but that said, we had to buy an injector tester to check new injectors even, as we've seen many of the new Bosch injectors be bad out of the box, ever since manufacturing switched to China for these. If you send your UOAs over, I'd be happy to look at them. Lastly, I want to add that we've seen scratches from FOD for decades now. We decided to change our manufacturing process to include deep cleaning of the bores post-honing, something that previously was up to the engine builder, as we were seeing more and more instances of even professionals messing this up. https://lnengineering.com/ln-enginee...deglazing.html After years of taking profilometer traces and inspecting cross hatch with a microscope, I can guarantee you our process for scrubbing the bores is hands down the best process out there for this. To Jake's credit, he's the one who first noticed this years ago when he did this by hand. Thankfully, this process can now be improved on with only 2 minutes a hole. We ship these tools worldwide and have tested its effectiveness on even shelf Mahle cylinders.

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The shop sent a note via their online client portal system that they did NOT find coolant in cyl 1 after leaving cooling system pressurized over the weekend. they did however find a tiny coolant leak from the little coolant console just below that alternator. Charles, no worries. I greatly appreciate you and everyone else who has offered there experience, expertise and thoughts. I could be off about oil consumption, I just know that I haven't had to add more that 2 or 3 quarts with a 4000 mile oil change interval. So still less than the typical 1qt per 1000 miles. I replaced all six injectors with new from LN as part of the rebuild as that was best practice as well as MAF and all 4 O2 sensors. I had ordered another new injector a couple of months ago from LN with that being the next thing to replace after I had replaced coil and plug on cyl 1 then finally got around to replacing the cyl 1 injector the weekend before bringing the car to this shop. Misfire did not go away but knew that I had some vacuum leaks because I smoke tested after my work and was still showing some leaks, I just couldn't easily identify them. I had gotten frustrated (I don't make good decisions when I'm frustrated lol) and gave in to have the pros look at it in hopes of getting it corrected with out spending loads of my time and money just throwing parts at it. They sent a video this morning (4/21/2025) starting the vehicle up, I'm assuming cold, and it did puff smoke out of both banks, but slightly more from bank 1 exhaust but cleared up after 5-10 seconds or so. Again, replaced injector on cyl 1. If you could shoot me your preferred email address I'll send those over, would love to get your thoughts. I am going to ask them to do compression and leak down tests as well as get images of the other 5 cylinders and go from there. I have an additional oil fill cap that I am going to fit a bulkhead to and measure crankcase vacuum with a manometer as well. I believe the correct reading should be around 5 in H20, does that sound correct? If lower than that, that would indicate that I have a crankcase vacuum leak(oil filler tube, dipstick tube etc.), is that correct? What numbers should I be looking for in the compression and leak down tests? Thanks again to all who have replied, I really appreciate the help.

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With a factory AOS, the manometer reading should be 4-6 inches of water column. With regards to the startup smoking, if the shop started the car up to move it and shut it down without driving it and getting it fully up to temperature, that's a guaranteed recipe for startup smoking. The best way to send the photos is to send them to [email removed] .

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No measurement is ever 100% accurate but we try to do our best, and be as precise as possible.. 1: Compression Tests : In Compression tests there can be a number of variables ...Gauge accuracy, starter RPM , compression ratio , cam profile, cam timing ,.human error, whether the TB is open or not ..( TB should be blocked open ) .. all these things can/will effect the Compression Test results .. In a perfect world ;;;;;Compression ratio X atmospheric pressure = PSI .ie... 11.3 X 14.7 = 166 psi ..... So on this engine the optimal number is 166psi...but with so many possible variables we are mainly looking for less than 10% variation from high to low cylinder readings.. 2: Leak Down Test :: In Leak Down Tests we have less variables...No Starter RPM ....not effected by Compression ratio , not effected by Cam profile or Cam timing.. Doesn't matter whether the TB is blocked open or not ... In Leak Down Test we can also hear where the air is leaking in a severe loss of sealing IE air going out exhaust valve or out Crankcase ect... Leak Down Test can be very helpful in tracking down the source of a Low Compression Test on a particular cylinder .. Very meticulously built Race Engines will have less than 3% Leak Down, and normal engines less than 10% ..again we are looking for evenness in cylinders ..or if a cylinder is low we look for where the air is escaping to ... 3 : Blow-by Test :: Blow-by Test has zero variations so is the most accurate for engine health assessment ( not for diagnosis of a low compression on a cylinder)..I developed a very simple and easy to do Blow-by Test for the M96/97 ... It is the most accurate because it is dynamic not static, and with no variables ...All the air leakage is forced to go through a calibrated orifice and the residual pressure in inh2o is used to calculate the LIters per min of air that gets parts the compression rings in real time as the engine is running... In fact the Blow-by Test is so accurate the results will vary quite a lot even on "normal" engines that are still considered good enough to perform a task of getting from point A to point B With a idle speed of 800rpm and .110 orifice the Liters per MIn of Blow-By should be about 12LPM....... at 4500rom full throttle and .221 orifice the Liters per MIn should be about 80 LPM ...... As an example an M97 bore scored #6 cylinder we tested had a blow-by of 170 LPM ....

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Skip! This is exactly what I was looking for. Thank you! Just as an update of where I am at with this at the moment. I picked the car up Tuesday, they had pressurized the cooling system for well over 48 hours. They pressurized to 18 psi on a Friday and some point on Monday the cooling system was at 13 psi and zero coolant found in the cylinder. They had found a tiny external coolant leak (a drop coming from the console directly below the alternator but no pool on the ground or other signs of leakage). My thought was 18 psi --> 13 psi over a couple of days is nothing to be alarmed by. They claimed that the puff of smoke on start up smelled like coolant. When I collected the car, I did observe a smoke cloud coming from both banks exhaust pipes but it only smelled like fuel and no sweet coolant smell. And have not observed smoke on start up since then, which I think validates Charles comment about not letting the engine get to op temp before shutting it off being a recipe for smoke on startup. I have since fixed the vacuum leaks, performed a hard reset of DME(disconnect battery, touch pos & neg cables together then let sit for a couple hours). Misfire is still present. I've ordered a compression tester and leak down tester and plan to carry out both of those tests as well as scope other cylinders for reference. I also measured the AOS health with a manometer, AOS health readings were -4.12, -3.87 and -3.94 in/H20. I also performed Skip's blow by test(read every post of that thread, fascinating stuff and I learned a TON). Test at idle with .110 orifice, AOS tube to intake plugged both on intake side and AOS side readings were -1.90, -2.21 and -2.34. Average of -2.15 in/H20 = ~40 lpm/4 = ~10 lpm with the .110 orifice. At some point I'll do one at WOT and the larger orifice for the blow by at peak torque. Leading me to believe, with the info I have so far, is that my overall health is okay. Again, I still plan to do compression and leak down as well as scope inspection. Now that brings me back to the initial issue here, the misfire. I have read several general misfire as well as cyl 1 specific misfire threads and had been working my way through the likely causes by swapping coils and plugs, smoke testing and repairing vacuum leaks, replaced cyl 1 injector. The last common/likely cause that I had read about was what Skip had mentioned/suspected, a lifter stuck in high lift. Being the most invasive, I had left this for last. Skip, I would love to get your thoughts on this. Based on what info I've shared here(happy to fill any blanks you think I may have missed) what would you say would be my next best step? Again, thanks to both Skip and LN/Charles for help and the insight! PS. One other thing that didn't really sit well with me regarding the shop I brought the car to, not once did they mention any sort of DME investigation. No reading of MAF, fuel trims, O2 sensor voltages. I would think that I would want to at least see what the engine is doing aside from looking at the DTC the car threw when investigating a misfire. I know that isn't the only thing to look at, but wouldn't you want as much information as possible?

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The problem with those values (MAF, fuel trims, o2 sensor voltages) is that they affect the entire bank, not a specific cylinder. Therefore, they are either inconclusive or un-informative to what is ailing just one cylinder.

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Ah, got it. That makes a lot of sense. Thanks. Aside from replacing coil & plug, replacing injector, checking for vacuum leaks, what are the standard diagnostic steps used for a single ailing cylinder? Is there a prescribed test for checking if a lifter is stuck in high lift like Skip suggested?

The problem with diagnosing your misfire is two fold.. One is that the missfire is intermittent ... any symptom that is intermittent increases the difficulty in determining the root cause......As a Factory Dealer Top Troubleshooter I had some Problem Symptoms that would only occur "once a month" under certain circumstances..... A big part of the Troubleshooting is to actually figure out exactly what are the circumstances when the Symptoms appear .. The other problem with diagnosing your misfire is that there are no definitive tests for an Intermittent Lifter sticking on high lift......When a Lifter sticks on high lift it causes a Volumetric Efficiency Deficiency in that cylinder due to the increased valve over-lap of the Cam Timing .... The only thing that can detect this is the Cylinder Smoothness or Cylinder Balance which is what modern DME's monitor constantly and where the fault code comes from ... So in cases like this the "best" you can do is the "process of elimination" which you have already started to do .ie.. swap plugs, coils, injectors ..... that leaves only Internal possibilities of valve spring, valve seat, or the two-stage Lifters.....You can eliminated the valve spring because it would not be so intermittent......That only leaves the valve seat and the two-stage Lifter.....Although either one is possible, the two-stage Lifter is the much much more plausible and the least costly ....... PS :: the two-stage lifter is always at low lift on start-up and low RPM, it switches to high-lift at higher RPM and when it RPM comes back down it "Should" switch back to low lift ....This is normally when the Symptoms of missfire occur when the two-stage lifters stick ....So the "circumstance " is the most important part of the proper theoretical diagnosis ... PS2 :: The Missfire Monitor is actually a program in the DME that measures the acceleration speed of each tooth on the 60 minus 1 flywheel because after each cylinder fires the crankshaft will speed up then slow down as the next cylinder is on the compression stroke....These patterns are checked for evenness and are "learned" in the DME...This "learned function" is earased when fault codes are cleared and the Missfire Monitor is less sensitive during the "re-learning process" as it learns any irregularities in the flywheel teeth..Note :sometimes the MIssfire Monitor can be too sensitive and actually set "false missfire codes" when hitting potholes in the road that causes a slow down of the crankshaft speed momentarily...This is not a ususal problem but there were some instances that required an updated DME Software....I just though I would throw that in here while I was rambling ....

If a sticky lifter is suspected, don't put any flush product in the engine. That will likely make the problem worse. What you might try is using Valvoline's new Restore and Protect oil. I had an engine with a stuck lifter (not a Porsche) and used the 5w30 and it cleared up the issue coupled with an Italian tune-up. https://www.valvolineglobal.com/en/restore-and-protect/ High Performance Lubricants makes a similar product These guys are local to me. https://www.advlubrication.com/colle...engine-cleaner

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Well, glad to know I'm somewhat going down the right path. Compression tester and leak down tester are slated to arrive tomorrow. If compression and leak down don't show any glaring issues, that would further point to the lifter issue, do I have that correct? For performing the compression test and keeping the TB "open" would just putting the pedal to the floor be sufficient? I would think jamming something in there to block the plate open could potentially cause damage to the motor/actuator on the TB. Based on Charles suggestion of trying that valvoline product, I have a case of Driven DI40 sitting here as the cars is due for an oil change(sitting at just about 4k miles on this oil), so I was going to perform an oil change and see if that has any effect as well and he has me thinking of running and grabbing some of that valvoline and giving that a shot first. I think the misfire issue has been more noticeable/prevalent as the oil ages, but I don't have any solid evidence to back that up, purely anecdotal.

A little update, compression gauge and leak down tester arrived yesterday afternoon so I was able to get cyls 1-3 tested. results as follows compression: 1 - 242 2 - 248 3 - 246 leak down: 1 - 90 psi supply, 88 psi cylinder pressure delta of 2.3% 2 - 90 psi supply, 88 psi cp for a delta of 2.3% 3 - 90 psi supply, 88 psi cp for a delta of 2.3% All three I could hear the little bit of leakage coming through the oil fill tube, nothing out of the intake or exhaust. Regarding the compression test, I pulled the fuel pump fuse, kept my foot on the accelerator to keep the TB open and cranked the engine over for about 8-10 pulses on the compression gauge. Obviously the number I got is way higher than what Skip detailed with the CR*14.7 formula, but understand the it's not necessarily the number we're concerned with the variability or delta between each cylinder. So, I'm taking the fact that the three I tested were all within 3% of one another my main takeaway here. If I missed something or for some reason should re test those cylinders, I'm happy to listen. Really trying to better understand the "why" with all of this. I also resampled the AOS health and blow by tests as I suspected I wasn't getting accurate readings due to how I made the test oil fill cap. Re made the cap and, turns out, the results were different. AOS health reading was -4.7 in/h2o and the blow by measurement was 15.25 lpm at idle. I have yet to make a WOT blow by measurement.

Yes this is the problem when diagnosing an "Intermittent " symptom.. Had you done the compression test when a #1 lifter was stuck in high lift, the compression would have been considerably lower at that moment on that cylinder But sine the symptom comes and goes and is only present for a short amount of time, testing at that moment is almost impossible... Also FWIW ::: 240-250 psi compression at starter speed makes for a very snappy quick responding engine at low RPM ..... FWIW 2 :: also the Formula CR X ATM = PSI is for " Absolute Pressure " and not " Gauge Pressure " ...and doesn't include the exponent for the air temperature increasing due to the air compression in the cylinder to a factor of ~ 1.4 so the 166 psi x 1.4 = 232.4 psi ( absolute ) ......absolute pressure and gauge pressure differ by 1 Bar ( or 1 ATM ie 14.7 psi) ......This is the reason we use the 10% difference from high to low across all engines due to the numerous variables .....but if working on one type engine all the time with the same specs and gauge...you can look closely at the actual numbers from each engine.....but otherwise the 10% from high to low is the most meaningful ..

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Would that be due to being on a "different" cam profile(lift and duration) changing the the flow(cfm) of charge air entering the cylinder? Good to know! That is definitely characteristic I have noted and enjoyed since the rebuild. This is the stuff that I find fascinating and that makes the most sense to me as it has overlap with my day job. I work as an ME technician for a small company that manufactures pressure and flow measurement devices used in measuring building performance. The leak down test is pretty much exactly what we do for houses and HVAC systems, but instead of using compressed air we use a fan as our flow generator and measure the delta P across its flow sensor to determine the leakage of the system under test. And it is measured in pascals not in/h20, or as we often joke "mouse farts". Skip, what would be your next recommended step be here? I'm thinking that lifter replacement is in order based on all that I have read as well as what you have suggested here and in other threads. I would be replacing all six lifters in this bank because I think it would be dumb not to. Again, thanks for taking your time to walk a dummy like me through this , greatly appreciate it!

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My Comments are above in bold letters, is easier than breaking the whole thing apart ..... ​​​​​​​

I said I am an ME TECHNICIAN ! You can tell that I am not an actual engineer because I actually know how to put tools back where they came from. I have a 10th grade "education".(Long story short, like a good country song, I got sober for the second time when I was 16, dropped out and got my "Good Enough Diploma") Everything else I've learned comes from working a wide variety of jobs, fairly high mechanical aptitude and pretty high level of curiosity.

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Big respect. I'm a Technical Fellow at Boeing and let's just say my path was not direct

WOW Sammy, You have done everything right in your rebuild and following maintenance... This is a huge disappointment. You are very fortunate to have a couple of 996 engine experts advising you. I am just a newbie, but, I would swap cyl 3 plug and coil (and injector?) to 1 (see if the misfire follows... hopefully!) As for those marks, my first thought was FOD stuck in between the piston and cylinder (carbon?). It is very localized, and as high as the top ring?? (ie: not the base of the piston galling the bore, causing FOD that gets into the rings and then causing higher scoring, as those other pic show... in my un-expert opinion) I hope this turns out to be "nothing"... But keep doing what you are doing! Paul

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Thanks! I can almost guarantee that the more direct path is not likely to be the most interesting one. I wouldn't want it any other way. I feel pretty lucky to have gotten to where I am today.

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Thanks Paul! I had indeed swapped/replaced coil and plug. That was the first thing I tried. At this point, it is almost certainly going to be that one of the two stage lifters is sticking in the high lift position. I plan to give the Valvoline product that Charles from LN recommended a shot then if that isn't fruitful then it will be to replace the bank 1 lifters. Skips comment about how the lifter fails and the very low likelihood of it causing any collateral damage gave me a good bit of peace of mind. And for the "bore score", based on all my used oil analysis results indicating wear metal levels where they should be, not seeing any sings of glitter in the filters, compression, leak down and blow by tests all showing good engine health I am pretty confident it is not, in fact bore scoring. The reason I initially raised that question was because the shop I brought the car too was suggesting that the misfire was due to coolant leaking in to the cylinder and washing the cylinder wall down and causing bore score. When they pressure tested the cooling system over a weekend, it only dropped 5 psi(from 18 psi to 13 psi) and no coolant was found in the cylinder. Another factor was that I have bore scope images from last summer showing almost, if not identical, markings on that cylinder wall. I will definitely monitor this but my initial fear of cylinder failure seems to have been proven wrong and that I just won't bring my car back to that shop.

I just wanted to say thanks to everyone who chimed in on this both with insight and expertise as well as with kind words. I greatly appreciate it all! But especially Skip and Charles, you guys rule!

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I love your comment about putting the tools back where they came from, but you also probably know not to touch my tools in the first place!

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"Keep your dirty d**k beaters off of my tools".

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The sign I had was "Like hell they're yours, put 'em back." I started working in a machine shop (what are those? the kids ask) when I was 14 and it was legal. Was highly rated machinist at 18. Missed buying my first Porsche (356C) at 19 due to inability to add $50 to my $300 offer. Detour through college and career on Wall Street and here I am back doing much of my own work on a 996. Still have all the tools. How's that for a non-traditional path?

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The High Performance stuff comes up, easy to order online. The Valvoline is a rabbit maze to find who has it where/cost, etc. Forgive if dumb question: Do you mean to do complete oil change + filter with all of either of these products? Or do you just add 1 or X qts. to oil change? Also, how long to leave in engine, common use or higher revs/load, miles, time, whatever? I have a case of dt40 waiting for oil change, but would do this "Engine Clean" thing as a preventative-just-do-it bc engine has 108k miles. Car new to me, had "sketchy" service records, had been in my garage doing rad cleaning, brake pad/service, CV boots/axles, front diff oil, Tip fluid/filter change, engine mounts, and a bunch of other stuff. Warmer weather means I can actually do some of the cosmetic "paint correction"- cleaning, ceramic this or that, and maybe fix the seat backs. (2004 C4S). I am making a simple plastic tube manometer for AOS testing, but will get UAOS + (possible) Track Drain in the next few months. Also, which IMSB is useable? - Possibly not the oil fed one? Some well known engine builders do not use the oil-fed. Any reasons guesses as to why? TIA for any replies.