Reusch

I've had a rough idle for quite a while now so took it to a Porsche specialist they've diagnosed it as a stretched timing chain.
Engine out job I've been told and between £1500.-££2000 to do the work anybody else had this problem (2004 3.2 petrol 112,456 miles)

ScootCherHienie

The timing chain never actually stretches. That's a description that's used by people who either don't know what they are talking about or who are "dumbing down" the explanation of what is going on because they have decided you aren't smart enough about cars or engines to understand the truth. What really happens is just plain wear. Contact surfaces on the chain wear. Pivot points along the chain wear. Sprockets the chain goes around wear. Idlers the chain goes around (if the idler is a metal sprocket) wear and idlers the chain slides over (tough plastic "shoes" that are flat) wear. All of that wear translates into the the worn timing chain being longer than the "new" timing change... but it's not because the chain stretched, it's because the 200 (or however many pivot points there are along the chain) all have a little extra wear compared to the new chain, the and because the sprocket teeth and contacting chain surfaces have all worn a little bit also. None of the stretch and wear from a single chain link or from a single sprocket tooth is significant, but when you add up the extra "length" in the chain because of all the wear, then you have a more significant issue. BUT, it takes the worn chain the same amount of time to make 1 full revolution thorough the chain path as a new chain because the sprocket teeth keep the chain "in time"... the variation in timing from the added slop in the chain, though, can cause valves to open and close a few degrees early or late. In theory a worn chain might cause a rough idle, but I'd think you'd see more issues at high rpm than at low rpm since degrees are more critical at high rpm. Put a conventional rubber timing belt in just 1 tooth off from the correct timing and you don't notice a problem until high rpm when you get a "fail" that sounds like wildly floating hydraulic lifters due to revving the engine higher than the hydraulic lifters can operate. Which begs the question about whether their diagnosis is right or not. A vacuum leak, IMO, would be more likely to cause a noticeable idle issue that might seem to disappear at higher engine rpm. Even spark plugs could be involved. Have you changed the plugs recently?

MisterMisfire

Apologies for waking up this zombie thread but my 2004 3.2 Cayenne S has just been diagnosed with the same 'stretched' timing chain. The engineer told me today that he somehow could see through a hole into where the cams were and lined everything up. He turned the crank shaft through a revolution and identified that the cam for cylinder 6 (the one that is always showing on the OBD II) was retarded in the cycle.

I asked about the wires in the footwell and was advised that this is definitely a timing chain issue.

I trust these guys because they actually told me to offload the car instead of doing the work - they basically talked themselves out of a couple of grands worth of work. The estimate was a grand (15 hours) to take the engine out and strip it down. Not sure what the cost of the chain is, but they said that if there was cam wear then they would recommend its replacement which they guessed at a couple of hundred pounds or more.

Any thoughts?

ScootCherHienie

Timing chains don't really "strech"... everything just wears over time and the wear results in slop that makes it appear that the timing chain is longer than it should be. When that happens, the chains can flop around and grind other nearby items... plastic tension shoes, plastic or metal chain covers (either of those result in contaminating the engine oil either with metal or plastic shavings... neither one is good for the engine. When the components wear, everything should be changed... new chain, new sprockets, new idlers, new chain tensioners, change the engine oil in case there is contamination in it. Are you sure the V-6 has to be removed to replace the chains? Seems like there would be a lot more space/access at the front of a V-6 allowing you to get in to change the chain, sprockets, etc. ALL the cylinders are going to be retarded with a worn cam drive system, but one cylinder can definitely be more problematic... depends on the engine design and firing order.

MisterMisfire

I read a puss earlier by a guy who replaced this timing chain in his V6 by removing the front bumper, radiator and associated pipes. He reckoned it took 30 hours in total. If this engineer can do the job in 15 them I'm all for removing the whole engine.

I think you're right about replacing as much as possible inside there. There's no point in putting a new chain in worn sprockets.

I've just got to get the money saved in order to get the job done...

Dilberto

True....chains really do not stretch. It's the chain rollers and pins wearing down to the point the diameters collectively are reduced. This is also a known fact, in the cycling world...

porkandbeans

I was given the similar speech from my independent. He gave me whatever degrees of stretch/wear/out of tolerance or whatever you want to call it. He said it is the timing chain tensioners that also wear and measure the difference, thus throw a code.
The chain kit couldn't be found for less than $800some.
Then EACH of the tensioners are another $800sum.
I'd be looking at ~$2600 in parts plus 15 hours labor.

ScootCherHienie

Timing chain tensioners are $125 at Pelican Parts, I'm sure you can find the same parts elsewhere for much less than Porsche charges. The trick is finding someone selling the timing chain before it becomes a Porsche part. The chain manufacturer would have to sell the chain direct to parts resellers to get it cheaper. I've always spent 1/2 or less of the prices Porsche charges for replacement parts. I'm sure there must be specialist parts suppliers in Europe who resell parts the same ways some of the parts outlets in the US sell them (much much less than Porsche prices). You would probably find that Porsche pays maybe $50 for the timing chain. There is zero justification for them charging the equivalent of $800 for it, but they do it and people pay the cost when there's no reason to have to pay those prices. I replaced an alternator made by Hitachi (huge thing with water cooling). Porsche wanted something like $1600 for it. The shop that did the work for me doesn't markup the prices they pay for parts. Their "usual" wholesaler had the alternator for $1350. But I told them I'd seen a retail site selling them for $840. So they checked their backup wholesaler who had the same Hitachi alternator for $825. I didn't see any of the usual sites I checked who sell a timing chain, but I'm sure some are out there. Our prices don't include taxes though... if you are going to pay $800 BEFORE tax... wow! that is going to be a really expensive repair.

porkandbeans

Thanks for the info! I thought I checked Pelican, but maybe I missed something. (04 Cayenne Turbo)
I remember Pelican didn't carry the chain or chain kit, so we found the chain kit at FCP Euro for $763. I didn't find the tensioners anywhere at a discount price, but I'd definitely look again.
We priced the parts from Porsche for schiits and giggles... No kit, the chain alone was around 1000. Adding all parts together was around 4000 I think from Porsche. It's really the 15 hours the bugs me the most. Oh, also, my mechanic did say that it is possible that it is just seals (behind the tensioners, I think) that are bad. So, in theory, best case scenario would be 15 hours labor, plus (inexpensive) seals to solve the issue. But... after investing 15 hours labor, may want to pay for the chain too.
Thank you very much for your info! I'll look further.

markar

Hi I am bringing back old post.
My mecanic just tell me same think is this condision will fail the spark plugs it's just misfiring after new plugs?

J'sWorld

No need to resurrect a thread from the dead. This post is about the v6 which is a totally different design. You have a 4.5 v8 and I told you advice on the thread you started. There are not many people with experience of the inner workings of the 4.5. I am one of the few here who do. The most probable failure to the degree that would cause a problem on this engine is the upper U guide or the tensioner itself. The tensioner guide is not large or curved enough to illicit a change in timing that the tensioner itself cannot compensate for. The chain does not stretch. The rollers/pins do not wear. The sprockets do not wear. Up to probably 250+ k miles on a properly maintained engine these items do not wear enough to illicit a change that cannot be compensated for by the variocam actuators or the tensioner.

I told you what to do in your thread you started. I will add one more thing and tell you why. Check the cam deviation from bank 1 to 2. Bank 2 is the driven side. It is almost physically impossible to develop slack between the crank and bank 2. This is not likely. The large upper u guide is between bank 1 and 2. This U guide is the most likely to fail due to the design and how much load it carries. If there is an issue with this guide you will see a large deviation between the two banks. The deviation is only measured at each intake cam because this engine only has intake cam position sensors, not exhaust. Even if you have a large deviation between the two banks the ECU can compensate to a point by adjusting the variocam actuators via the variocam solenoids to make both banks equal while the engine is running. There is a large margian of adjustment built into the design and it is not all needed. This is so that the actuators can adjust for wear and make the actual intake camshaft angles match while the engine is running at idle and still be able to achieve full intake camshaft advance at speed or when the ECU desires it. The ECU calculates deviation by looking at several measurements.

Now that I have given the technical explanation of something that you will not understand I will refer you to the original advice of compression test and borescope. The reason for this is because it sounds like you have a case of bore scoring developing. You need to explore this and eliminate it as a variable right now because it is the cheapest and most important diagnostic expense you will incur and it needs to happen first in the work flow due to costs. You have not given us enough information to take a more educated internet guess because you do not work on the vehicle. I have taken this into consideration.

Listen carefully-

Your mechanic is not qualified to work on your Cayenne anymore. He is telling you to sell because he cannot figure out the problem and does not want to admit that to you. It looks bad on his part. A true timing issue would be not only fixable but very profitable for him.

Eliminate or validate the possibility of bore scoring before you move forward. Fuel fouls plugs more with soot than with deposits as oil does in the short term. Fuel fouled plugs are not likely to misfire after the mixture is corrected. Oil fouled plugs will.

markar

thank you for explaining this to me I am going take car to Porsche dealership to see what they are going to tell me .

J'sWorld

I wish you the best.

nodoors

^^^Listen to this man's advice. He spits Cayenne truth.

GTSeries1

Hello,
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GTSeries1