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YOUR RESEARCH996 Engine low compression in one cylinder Smoke on initial startup
Leading reported evidence
Install short block seems like a good deal
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Performed · outcome unconfirmed
9k for an installed short block seems like a good deal.
996 Engine low compression in one cylinder Smoke on initial startup
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Leading evidence: 'Install short block seems like a good deal' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'compression test results' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Install short block seems like a good deal' (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.
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Performed · outcome unconfirmed · Original poster
so Cylinder 4 had a fouled plug and it was the one with the scoring, it's the only one they used the borescope on since the plug was fouled while the others were ok....makes sense since it's on the passenger side bank.
996 Engine low compression in one cylinder Smoke on initial startup
Use there is essentially no torque transmitted at any time
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Performed · outcome unconfirmed
Also, some sets of winter wheels/tires are such that the speed difference between the sets of tires is very small so when these winter wheels/tires are used there is essentially no torque transmitted at any time.
996 Engine low compression in one cylinder Smoke on initial startup
compression test results
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Suspected cause
Frankly with no CEL I want to suspect the compression test results.
996 Engine low compression in one cylinder Smoke on initial startup
Replace air oil separator
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Suggestion · Original poster
Had leak down compression test done to make sure before replacing the AOS.
996 Engine low compression in one cylinder Smoke on initial startup
Run approved oil
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Suggestion
My opinion is if you decide to live with the scored bore -- and I am not convinced there is truly scored bore -- you should do so running an approved oil with the viscosity ranges suitable for the ambient temperature where you live/drive.
996 Engine low compression in one cylinder Smoke on initial startup
Use borescope
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Performed · outcome unconfirmed · Original poster
so Cylinder 4 had a fouled plug and it was the one with the scoring, it's the only one they used the borescope on since the plug was fouled while the others were ok....makes sense since it's on the passenger side bank.
996 Engine low compression in one cylinder Smoke on initial startup
Use there is essentially no torque transmitted at any time
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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
Also, some sets of winter wheels/tires are such that the speed difference between the sets of tires is very small so when these winter wheels/tires are used there is essentially no torque transmitted at any time.
996 Engine low compression in one cylinder Smoke on initial startup
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17 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261026T135432Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Need some advice... I have a 99 996 C4 100k miles. Runs great. Bought the car knowing it smoked at start up, suspected an AOS. Had leak down compression test done to make sure before replacing the AOS. Found compression down 22% in one cylinder. Borescope showed scarring on one cylinder. Smokes for about 30 seconds at first start up then it goes away. Does not seem to consume oil. Again, other then initial smoke on start up runs great. Does have CEL for secondary air pump fault. What should I do? Dealer says replace engine (way too expensive), Indy says live with it. Thoughts???
eh, some guy here drove with scored cylinders for like 30-50k miles or more and aside from burning some extra oil and the occasional smoking, it seemed to have no ill effects. Car will likely be down on power but I'd probably keep driving it for now.
I've owned a number of 996 and currently have another 99 with only 70k miles that is pristine. The c4 runs just as strong... can't see dumping 15k+ into it as i bought it to throw some snow tires on and run this winter. I bought the car CHEAP so I know you get what you pay for...
Scoring can't be that bad if the oil consumption is ok, if there is no noise, if there is no CEL.
Frankly with no CEL I want to suspect the compression test results. The DME constantly checks each cylinder for proper operation and a cylinder truly down on compression should have triggered a CEL and one or more misfire error codes.
So in this case I'd agree with your Indy: Live with it.
But maybe not before possibly taking care of the AOS. It would be the AOS that accounts for the smoking. The AOS doesn't have to be completely bad just sub-par and letting excesisve amounts of oil vapor through which collects as fluid on the intake walls and this then can oil maybe just one cylinder and you get a bit of smoking upon startup.
Oh and take care of that secondary air pump problem.
Which cylinder had the low compression? Is it the same cylinder that showed scarring? What are the exact compression numbers for each cylinder? Did they do a leak-down test on the cylinders? What did the spark plugs look like from the cylinders? What weight oil is in it? What is the CEL code for the secondary air pump fault? At 100K your AOS should be replaced. Have you pulled the TB to see how much oil is in the plenum?
That's pretty much what I want to do with one, ideally with scoring too so I can get it cheap. From there all I care about is the 4 wheel drive somewhat working.
=)
Unless it's the AOS I'd run it and take it a little more easy on warming up. Unless you have or want to spend the money to fix it.
I'm talking to the service manager in an hour and I am going to get the answers to the questions posted...there was a compression and leak down done. Stay tuned for his response. I also talked to 3 Indys, all of which I know from PCA and all of which know their stuff. All said live with it. One suggested using a higher viscosity non synthetic oil and add some Lukas oil treatment...
The AWD works great, heated seats, back up sensors, nice side skirts... Just smokes on initial start up. Once warmed up it's fine.
Should have mentioned the smoke on start up is from the driver side... passenger side has the normal puff but the bulk is from the drivers side pipe...
so Cylinder 4 had a fouled plug and it was the one with the scoring, it's the only one they used the borescope on since the plug was fouled while the others were ok....makes sense since it's on the passenger side bank. I've attached a pic of the cylinder scoring. results of compression/leak down showed falsely high compression in cyl 4. 1- 155, 2 - 140, 3 145, 4-160, 5 - 165, 6-170.
$9k aprox for a new Porsche short block installed or sell it as is.
Or re-sleeve the cylinders...depending on how much you like the car. Or just deduct a re-sleeve job from your asking price and provide full disclosure to a new owner willing to take that on.
Main reason I bought it was to keep from driving my 07 Targa 4....
Thinking of dumping some Lucas into it and driving it...
here are some pics of the 996...
While it is nice the AWD is working it will be of little to no value in bad weather.
The AWD system requires a speed difference between the rear wheels/tires and the front wheels/tires. The rear wheels/tires need to make more revs/mile than the front wheels/tires so torque is transferred from the rear axle to the front axle.
The range of torque transferred is between 5% to 40% with the 40% coming in at around 150mph.
If you find you have the car "stuck" and the rear tires are just spinning the front tires will get no torque and if you keep spinning the rear tires you'll just ruin the viscous coupling/front diff.
Also, some sets of winter wheels/tires are such that the speed difference between the sets of tires is very small so when these winter wheels/tires are used there is essentially no torque transmitted at any time.
As for the non-synthetic oil recommendation I can't see subjecting the rest of the engine to probably sub-par lubrication in order to accomodate a suspected bore scoring problem.
My opinion is if you decide to live with the scored bore -- and I am not convinced there is truly scored bore -- you should do so running an approved oil with the viscosity ranges suitable for the ambient temperature where you live/drive.
I see I have another thread to add...
here's my 1 of my scored cylinders (4&6 were the same)
smoke on startup. wicked knocking, Consumed 5L of oil in 1000km of driving.
here's my plugs, guess which ones are 4 & 6
20150301_205856_zpsmv4wvdre.jpg
never once had a cell.
smoke went away after 10-20 seconds of idling. car pulled hard all day long at the track. was on Tesla's *** all night.
never once had a cell.
drive it to the ground. or spend 18k and DIY to fix it or send to a known builder and probably drop 20k +
There's a member here who has put quite the number of KM's on his car since finding out about his scored cylinders. Just adds oil and drives it.
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