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2005 Cayenne Turbo Cylinder 4 Misfire

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Hello All,

So, a brief history...

I have a 2005 Cayenne Turbo. I bought it used (coming off of a lease) with 17,000 miles. I now have 105,000 miles on it.

Several days ago, it started to exhibit a rough idle. Additionally, especially at low RPM's (2k and below) it would exhibit rough acceleration. About 2k RPM's it would smooth out a bit, but not quite right.

The next day, the CEL came on.

I did some research and found the many threads on here, and elsewhere, about the coil packs. I bought 8 new coil packs (suffix=20) and 8 new NGK BKR-6EIX spark plugs. I checked/gapped the plugs to 0.032".

I installed the new plugs and the new coil packs.

I really thought I had the problem solved. When I started the car, the rough idle was a little less, but remained. When I took a drive, the rough acceleration was less but remained.

I decided to bring the car to the dealer to have them read the codes.

They called at the end of the day today and told me that cylinder 4 was showing a misfire. I was not on the phone long enough to get the actual codes. But, I will be speaking with them in the morning and will get the codes.

They also told me that they pulled the cylinder 4 plug and it was wet, I assume with gas. I was told that they checked the compression in that cylinder and found it to be 40psi. I asked what the normal compression should be and was told around 180psi. They then said it could be broken rings, valves or a cracked piston and a new engine might be the solution.

Obviously, this was disheartening news. Also, note, I am an engineer and have been around cars my whole life. I know my way around them, from this plug and coil change to an entire K24 turbo installation on my 996TT.

I started reasoning this out and was looking for all possible options that could lead to the low pressure, the misfire code and the wet plug. I realize that the above suggestions could be true (rings, valves or piston) but I also thought it could be a head gasket problem.


I could swear that when I started the car, right after changing the coils and plugs, that I heard what sounded like a small exhaust leak..Pfft, pfft, pfft, pfft. I bent down to the ground and and it sounded like it was coming from the bottom of the firewall, presumably where the exhaust manifold connects with the exhaust pipes to head towards the back of the car. So, in my mind, I am thinking that cylinder four is at the rear of the right bank (correct??) and the head gasket could be expelling air through it while not necessarily interacting with with block/head coolant tubes. That would explain the lack of compression, the pfft, pfft sound and the lack of coolant in the oil/oil in the coolant.

I have attached a p[hoto that shows the OLD plugs and coil packs. I kept tham in the order removed from the car. I believe #4 is the right rear cylinder. You'll notice that OLD plug is black, while the others are tan. What does this typically mean?

Do you guys have any ideas or suggestions?

Your help would be very, VERY, much appreciated.

Thank you in advance.


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Hi Loren,

First off, thank you for responding. It is greatly appreciated.

Also, please note the photos are of the old plugs and old coils. That said....

The plugs and coils have been sitting there for 1 1/2 days, but with a good sniff I can detect a faint gas smell on #4 (That is #4, right?)


My mind says, ok, the old coil or plug wasn't sparking correctly, or at all, and the injected gas didn't burn thus leaving the gas residue on the plug. Seems to make sense based on my reasoning.

So, this raises several questions:

  1. Why would the new plugs and coils still show a misfire in #4?
  2. What would explain the low compression in #4?
  3. Why would the new plug and coil still be wet? This was told to me today by the dealer.

Thanks in advance for your continued help.


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Depending on how many cars you have and how much work you do (sounds like you do a bit), one of my greatest tools is my Snapon BK6000 Video inspection camera. It will fit down the plug hole where you can inspect the cylinders, and with the mirror attachment you can look backup at the valves. Slowly crank the engine by hand and you can see all of the valve seats. You can see imperfections, scrapes & scratches in the cylinder walls. It has telescopic capability and variable lighting. I have inspected the cylinders in all of my older vehicles. See if the dealer has something similar, I would think so.

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I spoke to the dealer a short time ago and the answer to the "wet" question is fuel, not oil. This agrees with the old plug which I smelled and reported on last night.

I am into the dealer for $300 at this point to pull the codes and the plug and perform the compression test. The car is buttoned up and ready for pickup.

I talked with the DEALER further and following is a recap of the important points of our discussion...

  1. He listened in the area of #4 cylinder while the car was running and also took it for a drive. He does not hear, nor does he believe, it is a head gasket leak. No Pfft, pfft, sounds or anything like it. So, he feels the head gasket is not the cause.
  2. I asked him about his choice of words during our previous conversation wherein he said you may need a new engine. I explained how I reasoned it out, being fuel and thus relating to a problem in the head, and thus suggested a valve job. He response was that regardless, the engine and transmission needed to be removed. It would need to be removed to pull the head and it would need to be removed in order to put a new engine in. He quoted $5000 for just pulling the engine and transmission. I am told it drops out the bottom similar to the 911. His/their reasoning is that a new engine can be warranteed and it relieves the liability of just repairing the head/heads (presumably you would do both if you are that far with a complete engine pull). If you just deal with the heads, there could be issues associated with the gas injected into cylinder #4 running down the bore and affecting the lubrication of the rings in the bore. Seems to make sense. It is dependent on the length of time the issue was present. I would expect to see a dilution of the engine oil.
  3. I asked for a quote on the engine (more out of curiosity than anything) and it was $20-something. When I heard $20.., my ears closed and I didn't hear the end of his sentence. So, $21k, or $28k, it is largely irrelevant.
  4. This is where I left it with them. I am supposed to get the car tomorrow.

I have also been speaking to a local INDEPENDENT that knows his stuff and I know through a friend. He has been helpful with knowledge and insight. His comments are:

  1. Recommended a leak down test of cylinder #4 at its TDC to see what was causing the compression loss. Listen at oil cap, at exhaust and at intake to isolate the loss. Sounds like sound advice.
  2. He seems to think it is a burnt valve, allowing compression to leak by.
  3. He also mentioned the possibility of a weak valve spring and/or sticky valve, again causing the loss.
  4. He has the Snap-on scope with the mirror and can look at the valves that way.

So, with mileage like this, and a residual value of $15-$20k at most, one has to question whether to cut losses and sell the car with the problem (disclosing the knowledge of course) or invest in it with the intent to hold onto it for awhile. Very difficult decisions, especially considering the ambiguity of not knowing what the actual problem is!! One thought is to throw a little more diagnostic money at this with the INDEPENDENT so that a true educated decision can be made. If I were to do that, the big question is whether to drive it to him (80-100 miles) or have it flat-bedded. Will driving it (like a granny) do any further damage? Does it make sense to detach the wire to the #4 fuel injector to drive it there so that fuel cannot wash down the cylinder bore?


That is a great idea. I know it is probably commonplace for something like this, but I never thought of that. I actually have Milwaukee's version of the boroscope (see below). It can only view straight ahead, as far as I know. But I am about to look and see if there are any mirror accessories available for it.


As always guys, I very much appreciate all of your help.


Edited by KPV
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I would go with the independent - sounds more spot on for what I would do.

Weak spring or bent valve sounds logical.

If the cylinder head needs to be removed (valve or valve spring) then (according to the Porsche service manual) the engine needs to come out. Porsche Book time 9.9 hours for engine and head removal.


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Thank you for the information.

So, two questions...

  1. Do you have any thoughts on the idea of pulling the #4 injector wire to avoid washing cylinder bore with fuel in order to drive it to his location?
  2. Can the valve train cover be pulled with the engine in place?


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I think the first thing I would do is to reconfirm the results of the compression test. 40lbs is SO low, it's amazing that you wouldn't notice serious drivability issues way before it got that low. You can buy a second hand Snap-on or MAC compression tester on eBay for about $60. I believe you will need a steel extension adapter (not just the normal hoses),because of the recessed plugs; I know MAC sells these, not sure about Snap-on.

What also makes me question the reliability of anything this dealer has to say is their $5,000 quote to pull the engine and head. If this is really less than 10hrs as quoted above, that's $500/hr. Which tells me they are thieves. Even if that price included reinstalling the motor, they are still padding the cost by $3k. So it's time to question their diagnosis and find a good Indy. Everything the Indy you went to made sense, but I would check the compression before going further.

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Also, worse case, and you do need a motor, you could ask the independent if the could get a guaranteed low milage motor from a junk yard. Probably under $6,500 for an insured junkyard motor; you could be on the road for somewhere under $9k. But I'd bet a bad valve or broken spring could be repaired for thousands less. Makes a hell of a lot more sense than 3x that for a new motor from the dealer. And if the bottom end is confirmed as bad, strain all the oil and cut the filter open to look for any metal bits. I'd want to be really sure it wasn't a piece of broken turbo that killed the motor. From a junkyard, there's not a whole lot of price difference for a turbo motor with or w/o turbos, so you may as well use the known good turbos from the replacement motor, but some come with them and some don't.

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The problem with the dirty spark plug (cyl.#4)looks more oil than fuel, the reason why i think that is based on the functioning of the used DME engine management system. After a preprogrammed number of misfires, the DME will proceed to closing the injector of the respective cylinder to protect the cats. for overheating, the plug is therefore (fuel) dry when removed from the warm engine after a drive. I'm curious for the result and solution, after disassembling.I hope it can be resolved at minimum cost.

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Hi Guys,

Thanks for the comments, feedback and suggestions.

Before I go on, I will say that I am always suspicious of the diagnoses and suggestions of any dealer. I have known this service tech for probably 10 years. He used to be the service manager at a different dealership before moving to this one. The previous dealer had a big shakeup of staff and he and the head mechanic both moved on. I have always valued their candor and professionalism. That said, I am still always questioning everything at all times.

Let me address your comments as best as I can at this point...


As for the compression test, I agree, it sounds very low. I spoke with another friend of mine in the indy business, albeit not Porsches, and he asked whether they did a dry and/or wet test. I wasn't sure what that meant and he explained that dry was with the car as-is and wet was after squirting oil in the spark plug hole, to presumably provide a better compression ring seal. Performing these two tests would yield results that show whether the compression rings are suspect (if the wet test jumps up in value) or it the compression loss is through the head (valves). It sounded like a great idea and I agreed with his mindset. This came about after I spoke with the dealer, but I will ask this question on Monday morning.

As for the cost of engine removal, I totally agree that the cost was excessively high. I can't recall their labor rate, but at $120/hour, the $5,000 works out to 42 hours to remove, and possibly reinstall the engine. I will question this on Monday too, more for my own edification and curiosity than anything else.

Regarding your second post comments, remember this is a $100k+ car. I am not, in any way, shape or form, considering a new motor. There are too many other 100k mile systems on the car that could be costly failures in the near future. I would rather move to a new vehicle than start dealing with a new engine (either new or reconditioned) in this car. I really don't want to throw more money at a bad situation, if it is something like the head, valves and/or potentially the rings. If it was something easier, simpler and cheaper overall, I would think about investing in the repair to get some additional mileage out of the car. There is a blurry line of worthwhile-ness that I am reasoning out.


Regarding the oil vs. fuel, I smelled the old #4 plug. It was out of the vehicle for 1 1/2 days, but smelled like gasoline, not oil. I was told the new plug, which I have not seen since I installed it, was wet and the wetness was fuel. This is strictly what I was told by the dealer after they pulled the plug and inspected it. Your information about the DME shutting down the #4 fuel is interesting and that sounds like an expected Porsche failsafe design. But, that does not explain the low compression. In your last sentence, you say that the plug is dry after removal from a warm engine after a drive. The plug is wet, as was told to me by the dealer and smelled of fuel.

These comments and my own reasoning has made me raise a new question...

Could I have a leaking injector? Follow my logic here....If the injector is leaking, the air/fuel mixture would be very rich. The excess fuel could wash the cylinder bore and reduce the oil film lubrication. This would create a weak compression seal. This would produce low compression. Low compression would not allow the A/F mixture to compress enough, thereby reducing its volumetric efficiency. The end result is a less powerful burn of the A/F mixture. This would explain the rough idle, since the #4 cylinder is just getting by without adding much power to the overall combined effect of the other 7 cylinders. This would also explain the lower compression due to cylinder wash and reduction of oil film sealing.

Can anyone address the validity of this idea?

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The injector has continuously power, is operated (open) by a ground impulse switched by the DME. The injector can permanently remain open when the DME is defective or when the injector ground wire is permanently attached to the ground for some reason. However this is not common when the car is still with knowledge maintained or repaired. A ordinary leaking injector is in this case more common. Keep us informed.

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As I was doing my internet search for additional knowledge on this malady, I came across this...


Several people say that the coating on the pistons comes off and wreaks havoc on the aluminum cylinder bore. This causes low compression. The thread also has two videos in it. They show removal of the engine in the "conventional" way up and out through the front....


Is coating wear a known issue for these engines?

I also found this thread about scored cylinders being a somewhat prominent problem...


Edited by KPV
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You are correct to ask if they tried a wet compression test after the dry, sounds like they didn't. That is a time tested way to determine if an engine needed just a valve job or rings/bore. As far as the injector wetting down the cylinder walls, on a Turbo it is slim since the block has cylinder mounted oil squirters that squirt oil on the bottom of the pistons and the cylinder walls. The non-Turbo V8 doesn't have this.

Redo the compression test before anything else, and/or use your borescope and inspect that cylinder right away.

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Thank you for your input. I am picking up the car today from the dealer. After I get it, my hope is to do a compression test and also look inside the cylinder with my boroscope.

This brings me to several questions about getting the best results when looking into the cylinder....

  1. My goal is to look at three things, the top of the piston, the cylinder walls and, of course, the valves. To do this I will use it with and without the the mirror attachment. In order to see the valves, does anyone have a a diagram of where the valves are in the head? When I insert the boroscope with the mirror, especially since #4 is a little hard to get to at the firewall, I would like to see a diagram as to where the valves are. In other words, at 12 o'clock, 3 o'clock, 6 o'clock or 9 o'clock. That way I will know the right clocking of the mirror to see what I need to see.
  2. In order to see the top of piston, cylinder walls and valves, it makes sense to have the piston at bottom dead center (BDC). Is there a way to accomplish this other than trial and error?

Thanks in advance for contributions.

Edited by KPV
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