Cylinder 6 valve replacement questions

Well, after a spirited Sunday drive... I rounded the corner into the neighborhood and to my surprise a flashing check engine light appeared. I shut it down immediately and coasted into the driveway. OBII reader confirmed cylinder 6 misfire. Pulled coil and inspected plug, both new less than 12 months and a 1,000 miles on them. Just for kicks I swapped 5 and 6 coils, cleared ecu and fired her up. Rough idle and check engine light soon appeared with same PO306 code. Monday had her towed to shop. Today I am told that coil, plug and injectors all tested in spec. Compression down on 6 180lb. Mechanic suspects valves. Wants to pull motor and replace just 6 intake and exhaust. 16 hours labor plus parts 2,800.00 est. 10hrs for motor R&R. Background. 2004 996 AE w/ 31k mile car, oil changed 12 months for life of car. Blackstone oil reports all good. Car is 9.5-10 condition. I have three P cars. None of them daily drivers. Question Suggestions while motor out? I am not going to do IMS or clutch in less something shows its needed. Thoughts 1. AOS 2. Coolant 3. RMS (small weep) 4. Oil filler tube 5. 6. Last, do full right side valves or just 6? Mechanic said just 6 with low mile car in less after inspection something suggests otherwise. Positive helpful comments appreciated.

So your mechanic thinks the #6 valves are...??..bent? bad guides? what exactly? If it were me, engine out would be an opportunity to replace IMSB, RMS and AOS for sure. You seem resistant to this but that is what I would do. The coolant will be replaced, no doubt, since it will be drained. I would also replace the coolant reservoir since it is so easy with engine out and I think age affects these more than miles.

Shop said until they pull covers they wont know lifter stuck, valve bent broken etc... having ruled our coil, plug and injector, and testing low compression on 6 this is their best opinion. reservoir great idea. might do water plump too.

180 lbs should fire ....look for something else

He is right. What are the other compressions measured at the same time/conditions? Really should have done a leak down instead.

I asked for a leak down the shop owner said it wouldnt be helpful or reliable. Not sure what he meant. He stated its a lifter or valve and no way to know more until opened up. He said he ruled all other issues out. All other cylinders measured above 200lb on compression with 180lb on 6. I am starting to think I need a second shop opinion here.

If the lifter has collapsed it would make noticeable ticking noise from the cam cover . Lifters can be replaced with the engine in the car

180 psi of compression will absolutely NOT cause a misfire. There must be something else wrong.

After 4 plus hours he cant confirm the problem with any certainty. Except to say he ruled our coil, plugs and injectors. I am going to have a flatbed PU and take it to a recommended Indy for second opinion.

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Sometimes 996 3.6L valve seats are known to come loose.

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I assume a leak down wont tell you if its a bent valve, loose or stuck lifter etc... Maybe this shop is correct. Needs to be opened up to see what is going on.

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Need to have a borescope inspection thru the sparkplug hole. If the 1st shop didn't recommend this I would go elsewhere. Callas Rennsport in Torrance may be the best at diagnoseing this. You can go to their website & post a question.

So borescope inspection can determine valve or lifter stuck or bent or?

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Bore scope can't help unless the valve head is really bent and if it was it would probably have broken by now. The only way I know a valve can get bent is if one does a money shift. Do you money shift the car? If you tell me the misfires occur at low RPMs my WAG is it probably isn't a bent valve or stuck valve or a collapsed lifter. More than likely one intake valve lifter for the #6 cylinder has had its low/high lift feature fail. The lifters have to come out but the head can remain on the engine and the engine can remain in the car. The camshaft cover comes off and the cams come out. The factory manual has a section on trouble shooting / diagnosing misfires due to a bad intake valve lifter which should be used to ensure one doesn't replace lifters for no reason. Oh, and the factory guidelines are to if even one lifter on a bank is bad to replace all lifters. The problem can arise from "dirt" and this can affect more than one lifter. The concern is one cylinder misfires first and this gets fixed but after the engine is buttoned up then other cylinders can manifest a misfire due to the same problem and one is back under the camshaft cover replacing another pair of lifters.

No money shifts. Misfire at idle occurred. 10-4 on right bank replace all lifters if one has failed. This seems more likely than a valve based on opinions I have been reading and your comments. I spoke with a second shop owner and based on my description he said same thing. More likely a lifter problem. They are a race shop and specialize in 996. He said he rarely sees valve issues but lifters are much more likely after ruling out coil, plug and injector and their connections. The lower compression leds him to think lifter but he wants the car of course to test. Flatbed PU for second opinion tomorrow. 5 hours from first shop and no firm diagnosis. Bummer. I will ask the second shop about testing bad intake valve lifter procedure due to misfire before opening up to inspect. More later in the week. Thank you all for your comments.

Picked up a car and had it flatbed delivered to second shop for opinion. Conclusion; valve spring or bad lifter four hours at 130.00 an hour. Did learn new code besides PO306. P1360 and P1371 valve lift control. "No way to know more without dropping motor or opening valve cover and removing cams" according to shop 1. Should know more today. Second shop estimated 3 hours at 140.00 an hour to determine what going on.

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A bit of a long shot but if your engine has a bracket that holds the solenoid in place be sure the bracket is ok. Sometimes these can fracture and cause all sorts of problems. P1371 Valve Lift Control Checksum Error This is I believe a code indicating a non-specific error of the valve lift control system. P1360 Valve Lift Control, Cylinder 6 is a more specific error code pointing to the well, the specific cylinder. These errors combined with the misfire error code sure points to #6 cylinder and its lifters. I have one of the VarioCam Plus lifters at my desk. Not sure if one could tell the lifter was bad, was say unable to switch from high lift to low lift, unless the thing was obviously showing signs of some damage/wear or ? My concern would be that an inspection would find nothing amiss and the lifter or lifters would be reused and the problem persists. If one is at the point the two lifters can be removed for inspection then thoroughly clean and inspect them. If you spot some signs of problems that's great. But if you don't I'd be very reluctant to reuse them. As far as I'm concerned once removed from the engine they are only good for paper weights. Were I in your shoes I think I'd drop in two new intake lifters (make that 6 new intake lifters) and as I mentioned in a previous post the SOP is to replace all intake lifters on a bank if even one is suspect. (As an aside while the exhaust lifters don't play a role in the low/high lift feature they of course play a critical role in the proper operation of the cylinder, so I would believe the exhaust lifters should be removed and inspected as well.) The shop/tech should know this but it is important to keep the lifter with the bore it came from and do not use a magnet to pull the lifter out of the bore. Do not scratch the lifter's face -- where the cam lobe contacts it -- nor nick or scratch it anywhere. Be sure the lifters before they are installed are worked in a clean pan of engine oil to thoroughly charge the lifter with oil and to ensure no air pockets remain. The last thing you want to hear is a ticking lifter after the engine is buttoned up and fired up for the first time afterwards. There will be some noise but it should go away very very soon after engine start.

Great points. Second shop seemed to believe that they can determine what is going on without opening the cover and removing cam. More to follow.

Both 1360 and 1371 point to one or more of the valves are stuck at LOW lift in cylinder #6. If the shop has PIWIS, there is a test they can run to determine if it's just one lifter or more than one lifter. It's all described in the Porsche diagnostic manual in details.

The lifters on these cars don't collapse. They expand... Very common issue... Replaceable in the car btw

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Yes, expand = LOW lift

No. Expanded means too much lift. Valve stays open

Second shop is talking your language. Said with confidence his PIWIS tool will provide the details along with leak down results. To be thorough he wanted to do a full work up so 3 full hours estimated. Seems like shop number 2 is on the right path.

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Forgive an amateur question - perhaps we are misunderstanding ? When I dismantled all 24 lifters in my 2001 Variocam M96(not Variocam Plus) to inspect the tappet inside each bucket - I found several were 'hammered' or collapsed.They were jammed tight, compressed to their smallest size. They could be separated only with Vise grips. The remaining tappets were normal -you could compress them manually.As you know there is a ting spring and ball valve inside each tappet. So how do they fail in an expanded condition? And would that not cause excessive valve lift - not insufficient ? I had understood that this 'hammered' condition was the usual Mode of Failure and the cause of valve clatter or ticking.

No valve clatter or ticking. Rough idle, check engine light and codes.

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Variocam+ 101. Image borrowed from Dharn55 When you said expanded, I assume you mean the top diagram, which is low lift.

UPDATE Second shop ran full diagnostics. leak down number within spec, no signs of valve or lifter problem. Computer testing showed intermittent issue on six. Shop added ATF to engine oil and said drive car 200 miles.Then, get the 5w50 Mobile one out and revert back to 0w40. They are a large shop and maintain many 996 race cars. They see this often. They cleared codes and have done several test runs with no issues. All test within specs and no new codes or errors being recorded. Did I dodge a bullet? Only time and mileage will tell. Second opinion may have paid off. Hopefully I wont be writing again soon with "she's back in the shop". Thank you all for your opinions and helpful comments.

Well, I completed 100 miles post PU from shop. Car running great. Smooth idle and no lights. ATF and 5W50 coming out this morning. 0W40 going in with new filter. Of course magnetic drain plug will be inspected and oil filter cut open. I will run a few hundred miles on 0w40 and change again. I really want to be sure I clean out all the ATF and any debris.

ATF in the crank case ? you have found an old schooled wrench....probably knows how to use a dwell meter and timing light..........tip him well if it fixes the car

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Boy, those were the good old days! There wasn't a computer in sight on the cars! No CEL either! No codes to read or reset! A much simpler time..indeed. I miss it.

They said they have done this many many times. Only after full diagnostics to confirm nothing bent or broken and no other issues they will go with AFT. Apparently our 996 motors have some very small oil passenages that can easily clog even with annual oil changes. Nothing on magnetic plug after 100 miles and oil filter looked new. Probably because it was. 0W40 Mobil one back in. This shop only runs 0W40 which includes many race cars and insisted I do the same. I dont want to turn this into an oil thread. Only sharing my experience. Plan to make a high speed run Saturday morning and will do another oil change after a few hundred miles.

Great fix ! A mark of smart mechanics to resolve a threatening problem so unobtrusively and inexpensive. " Shop added ATF to engine oil and said drive car 200 miles.Then, get the 5w50 Mobile one out and revert back to 0w40. " Do you know how much ATF they added ? Just 2 qts. or more ?

5W50 had zero miles on it. They said they drained two quarters out and added two ATF. Owner of shop said 100 miles minimum and suggested to run 200. Just no red line but dont baby it either. I opted for the 100 mile minimum. I have annual oil change history for the life of the car and the oil test at blackstone have all been good. Just finished oil change. Started, idle smooth. So far so good.

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I have the same issue with my 04 C4S. I get a check engine light and the codes P0300 and P0306, I clear the codes with my durametric and the check engine light comes on right away. If a leave the car running long enough then I also get codes P1371 and P1360 in addition to P0300 and P0306. Did the ATF solve your check engine light and misfiring problems? Or, did You have to do something else in order to fix? TIA.

Sorry havent seen this tread in a while Yes, after AFT 100 mile treatment and fresh oil 0-40 no issue Seems my mechanic was right. Car didnt like the 5W50 All good 1k mi and a year no issues

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Thanks! I�ve tried the ATF method as well but no luck. The misfire is intermittent and only in low rpm�s, I can go weeks without check engine light on and then suddenly it just comes back, misfire only on cylinder 6 and only in low rpm�s, misfires stop @2000 rpm�s. I�ve swapped the variocam solenoids from one bank to the other and same thing. At this point everything points to a sticking lifter. I will soon attempt to replace the lifters in cylinder 6 without completely removing the engine. 😬

That's hard to do on number 6, but you should try it for your own education.

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It�s hard to do on any of them I believe. Do you think it�ll be harder on 6? And why?

New coils, sparks, checked grounds, gas treatment and ATF. Not sure which one fixed it but it hasnt come back in 1k mi and a year Oh, I had new injector too! Pull 6 injector and have it cleaned or swap.

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Did you only replace injector on cylinder number 6?

Bumping this thread. We have a 987.2 with the P1360 and P0306. Was this "ATF cleaning" a lasting fix? We have products now, like Valvoline Restore & Protect that might accomplish the same thing.