29 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCH996 3.4 running rough, on 5 cylinders
Leading reported evidence
Check plug (not
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
They checked the plug (not that), then did a compression test: 0 bar on cylinder 2.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I'll be in for around 5 grand with tax (engine in / out, head off / on, lapping the valves, changing half of the valve stem seals, plug tubes, 24 lifters, AOS, variocam chains / pads, gearbox check, oil change, AC refill, etc.).
Leading evidence: 'Check plug (not' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check oil' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
Since the exchanger was replaced in the past, the shop thinks it probably failed and led to oil in the coolant before being replaced, which damaged the lines.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
-being the engine is out and a head is off, my indy wants to replaced the variocam chains (i.e.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Check oil
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I'll be in for around 5 grand with tax (engine in / out, head off / on, lapping the valves, changing half of the valve stem seals, plug tubes, 24 lifters, AOS, variocam chains / pads, gearbox check, oil change, AC refill, etc.).
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I'll be in for around 5 grand with tax (engine in / out, head off / on, lapping the valves, changing half of the valve stem seals, plug tubes, 24 lifters, AOS, variocam chains / pads, gearbox check, oil change, AC refill, etc.).
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
29 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T165820Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Hey everyone,
My 996 started acting up this morning, right as I was pulling off the highway. It started with a stutter as I was putting gas in 5th, then a check engine light, then a rough idle.
I limped it home and read the codes a couple of times on the way: P302 appears immediately, sometimes followed by either P301 / 303.
The car had a strong lifter tick a few months back on bank 1 (cylinder 2 or 3) but that went away after an oil change, and even this tick isn't back. But the misfire's on the same bank, so that might be relevant info.
Any thoughts ? I would hope this is a coil but the misfire developed all of a sudden and it feels as though the car "lost" a cylinder.
Also, oil pressure & temps are good, no other codes (well P300, but who's counting).
Yeah I don�t have the tools to do any of that.
Was hoping swapping coils would be a good start but it�s likely I�ll just limp it to a local specialist a few miles away. He knows the car and is well reputed (as well as terribly expensive).
Had the shop on the phone who recommended I swap the coils before having the car towed, just in case. Swapped cylinders 1 & 2, still have P302.
I'm not mechanically inclined enough (or too risk-adverse, probably) to try the ATF trick.. Will have the car towed shortly. My guess is it needs a set of lifters.
So, car's in the shop. They checked the plug (not that), then did a compression test: 0 bar on cylinder 2.
After putting an endoscope in the cylinder, it turns out one of the exhaust valves doesn't close properly by maybe 1mm. There's also what might be water in the oil in that cylinder. That rules out timing, a lifter or the variocam solenoid (which were my main suspects). No bore scoring to be concerned of.
They will drop the motor and remove the exhaust cam. Maybe a broken spring? Or a sticky valve? More news early February.
If that motor isn't dead, it'll be the opportunity to do the AOS.
I'm in France so that's not an option I'm afraid. There's a shop a few hundred miles from here that specializes in M96 rebuilds and does a couple hundred a year. They should be able to handle rebuilding a head.
Just hope I can have the car back for spring.
Here a couple of low-quality pictures showing the intake valves (closed), and the exhaust valves (one stuck open):
Looks like the head is going to have to come off.
They apparently do around 250 engine rebuilds / year (mostly M9x I believe). So at least twice as many heads, plus whatever volume of heads they refurbish outside of full engine rebuilds.
Finally an update. The engine was pulled out last week and torn down this morning. What the shop found was... unexpected.
Apparently, someone had mounted the exhaust gasket on bank 1 the wrong way around, which meant some of the gasket was protruding in the exhaust's air path. With time, heat and airflow, those protruding bits tore off, and some got sucked back into the cylinders. The small bit in question (probably 10mm in length) was pinched between and exhaust valve and its seat, as well as between an intake valve and its seat, meaning it was never going to go away on its own.
Interestingly, the same gasket material is missing on all bank 1 cylinders but only #2 seems to have gotten its gasket stuck in a way that prevented compression.
The head surface is a little worse for wear, but nothing terrible. Cylinders seems intact and so do the valves. Hoping I can avoid a full rebuild... more news soon.
I�m trying to figure out in my head how that can happen. I would think that�s almost impossible? Sure, there�s a bit of valve overlap, but still. Unless the engine was spun backwards?
I have seen similar once on a 3.2 Boxster where a small piece of the Catalytic Converter broke off and was blown back into and under the exhaust valve...( under warranty) . The Porsche Field Engineer and Porsche Hot-Line Engineers argued that it was not possible....But the evidence spoke for itself.....That is "exactly" what happened.....It is much easier to see how it can happen on a Boxster engine where both banks exhaust are connected to each other at the main muffler so that exhaust pulses from other cylinders can blow back into open exhaust valve ports, but on the 911 where the banks are separated all the way, it only has two other cylinder pulses to blow back to the open exhaust valve port...
On said Boxster all I had to do was remove the piece, lap the valve, and replace the failing cat....return to customer....( under warranty)...
Good catch and call by your shop !!!
I just got the time to speak a little longer with the indie. The diagnosis is confirmed and no rebuild is needed. That's the good news.
On to the not-so-good news. They are:
-several coolant pipes look bad. Since the exchanger was replaced in the past, the shop thinks it probably failed and led to oil in the coolant before being replaced, which damaged the lines. They want to replace all the ones that can only be accessed with the engine out. Seems reasonable.
-at least one lifter looks like crap and isn't coming back on. This might explain my start-up tick. The question is : should the 23 others be replaced as well? Also, isn't there a BMW reference that is identical & a lot cheaper?
-being the engine is out and a head is off, my indy wants to replaced the variocam chains (i.e. the chains between cams) & pads on both sides out of precaution. Is this necessary? Should be under a grand with labor.
AOS will be done, flywheel checked, and the engine mounts appear good so they're staying.
Alex
The BMW part # is 11-32-1-748-884. Can't verify it's exactly the same, but if you enter the Porsche part # 996-105-041-72 on FCP Euro they return the INA part # 420-0104-100 (that's what I used on my build). The INA part is currently showing as backordered, and the link for equivalent part from other suppliers takes you to the BMW parts. So looks like they're all cross-referenced to each other.
Since the engine is out and has been "torn down", I'd replace as much as I could afford. Do it
right
or do it twice!
Replace all lifters. Again, you're talking a 20+year old engine.
Definitely necessary. They do "stretch" from years in operation and will cause camshaft deviations even when the engine is properly timed. I would replace all chains but that would require a full rebuild. And definitely replace the VarioCam wear pads. Perfect time to do those! I would also replace the chain tensioners.
In addition to the AOS, perfect time to replace the following proactively:
1. LN Engineering IMS bearing
2. OEM Rear Main Seal
3. Crank Postion Sensor
4. OEM Oil Cooler
5. OEM Coolant Expansion Tank
6. SACS clutch kit
7. LuK dual mass flywheel
8. Oil pressure sensor
9. Oil filler tube
10. OEM water pump with composite impellers
It runs! On all cylinders ! I'm picking it back up this weekend.
I'll be in for around 5 grand with tax (engine in / out, head off / on, lapping the valves, changing half of the valve stem seals, plug tubes, 24 lifters, AOS, variocam chains / pads, gearbox check, oil change, AC refill, etc.). Not cheap, but I was afraid it could be worse.
It's back home!
You Tube
The next expenses -and hopefully the last for a while- will be a Rennline phone mount (the one that goes next to the center vents, already ordered), and set of new tires. The current ones are P Zeroes (which I don't like), and they're getting very close to 10 years old. They're in good visual condition and have plenty of tread left, but wobble a bit and I don't want to spend on balancing a set of 9.x years old tires.
A few rattles to sort as well, I'd forgotten how much a 996 rattles compared to a modern car.
This is a source reference. Confirm exact model applicability in the original material.
