XC90 2.5t dead #3 cylinder

69ragtop · Post by **69ragtop** » 18 Sep 2018, 08:51

Hello, new member here although I've been lurking for a few months, this is a great site with lots of info. After doing some research on this and other sites I purchased a '06 XC90 2.5 AWD with 140k miles for my daughters last October. I had looked at several and the one I chose seemed the best cared for, no leaks, dents, scratches, rust, non smoker, ect. I was a little hesitant when the PO couldn't produce the service records, but the car drove nice and had no vices; four relatively newer Yokohama tires, idled smooth, good power, cold a/c, etc. ( I should note I used to be a mechanic years ago, worked in several private garages, was an Mercedes and Toyota tech, also worked in an automotive speed / machine shop doing all types of engine rebuilding, so I have a pretty good grasp of what I'm looking for in a used car.) After getting the car home I immediately did everything to bring it up to standard: Timing belt, water pump, tensioners, spark plugs, fluid changes, etc. The car ran well until earlier this spring when it developed a miss in #3 cylinder. Pulled the plug and the ground electrode was bent against the center electrode. Compression test showed 80#. Cylinder leak down test showed the valves were sealing and the leak was from the cylinder. I opted to replace the engine with one I found at a local yard with 90k miles and a 6 month warranty, but was and am still bothered by what caused the failure in the first place. I disassembled the original engine, #3 combustion chamber and piston looks as if someone took an ice pick to it, with a small depression on the piston head on the intake side where I suspect the ring is scorched and leaking. The only things that seem odd are the turbo shaft had roughly 1/4" of side to side play and there is some damage to the turbo blades on the exhaust side, maybe from the wheel hitting the housing due to the excessive play. To me, the damage to the head and piston looks like mild detonation. I should note that all the cylinders were very clean, no excessive carbon deposits. I have a hard time thinking something foreign was in the induction system, as the car ran fine for 6 months after I did the major service. The 2.5 was heralded as being bulletproof, which was a factor in my decision in buying this car, but I've since seen other posts where owners have had issues with #3 cylinder, and am trying to find some answers here for closure. Has anyone ever come to a conclusion on what's going on in that cylinder? I've done searches and still don't have a warm and fuzzy feeling. We like this car but I'm about the end of my monetary and time commitment with it. Sorry for the long winded post, and thanks for reading it.

Post by **oragex** » 18 Sep 2018, 09:18

Interesting reading, you say there is some damage to the turbo blades, could a small piece indeed have traveled into cyl. #3? Have you checked inside the intake manifold for other metal pieces? The 1/4" play is huge for a turbo.
On the other side I think that strong detonation can melt a spark plug electrode - or maybe there was an issue with the coil#3? Maybe test the coil and also the injector in that cylinder - and also look close at the coil wires near the coil, not unheard to have these crack

Side note, turbo failure is uncommon on these engines - some components may fail bur the turbo rarely - this coupled with no maintenance proof may be a rather good lead.. does the oil filler strain look clean or rather gummed up?

69ragtop · Post by **69ragtop** » 18 Sep 2018, 11:24

I installed new Denso coils during the major service along with new NGK Iridium plugs. I had also cleaned the injectors and installed new o rings. I checked everything related to the induction system for foreign objects or debris of any kind and found nothing. It's hard for me to believe that something would have been laying in the system, downstream of the air filter for almost six months of driving, with a few 3hr trips on the turnpike, only to decide to jump into the air stream on the way down my driveway on the way to lacrosse practice. Then it would have to get sucked into the combustion chamber, past the intake valve, dance around in the cylinder head, beat the top of the piston to the point of clamping the compression ring in the ring land, then exit out of the exhaust valve without damaging it, and chew up the turbo blades. And there was no debris in the cat either. The marks in the head and on the piston look alot like pistons that used to come out of hi performance engines I used to work on, which makes me think it was detonation. I'm thinking my girls, after driving a Subaru for their first car, were putting regular in the Volvo out of habit. I was hoping to hear back from others who have been through the #3 cylinder mystery in some degree would chime in with what they found or did to fix it.

69ragtop · Post by **69ragtop** » 18 Sep 2018, 11:28

Forgot to mention I had also dropped the oil pan and installed a new OE pickup screen (been down that trail before with a Saab) and cleaned the PVC passages and installed a new PVC unit and hoses. Engine had great oil pressure and minimal deposits.

Post by **SuperHerman** » 18 Sep 2018, 15:01

I ran my XC70 on 87 octane w/o issue for over 40k miles. I think that turbo blade may have found its way into the #3 cylinder. It could have gotten fused to the spark plug, and from there a mess consistent with what you describe. Any high spots from debris could cause ignition hot spots and cascade from there.

Can you post some pictures of the #3 piston top, spark plug and #3 cylinder head area?

If the cylinder head and #3 piston wall are undamaged it may be worth replacing the #3 piston with a used one and rebuilding the top end. New valve seals, valve lap, cam seals and head gasket. Set it a side or keep it as a spare - not a bad little winter project.

Curious to see the carnage.

69ragtop · Post by **69ragtop** » 18 Sep 2018, 15:23

Hope these turn out, trying to send them from my phone in the shop. First pic (from the bottom to the top) is the combustion chamber, second one is a close up of the damage. Third one is the Piston, fourth one is a closer view, last one is the damaged turbo impeller. This engine is totally rebuild able, not sure if I have the inclination to spend the time or money to do it again. Interesting theory about the impeller fragments being back drafted into the cylinder. Nothing was attached to the plug.

Post by **SuperHerman** » 18 Sep 2018, 20:54

Based on your photos something hard ended up in cylinder #3. I am seeing a combination of contact damage and detonation damage. What is odd is if you had an object in there it would have to have been fairly large - larger than the impeller fragments.

The bb holes appear like detonation, but some of the other marks look like impact. Curious that the exhaust valves have marks but the intake do not if I am seeing the head right.

I would guess something fell in there, found its way into #3 and took it out. Started on the intake side and once it was small enough it made its way around to the intake side. From there to the turbo and mangled it. When you worked on the PCV system did you remove the intake? That could be where it started. Bounced around a while and finally made it from the head to the combustion chamber. What does #3 intake look like looking in from the side?

Do you know if the intake opens further than the exhaust? That would explain the markings on one side. Overall I don't think the start to finish (death) took very long once the object entered the combustion chamber.

Usually the issues with the engines is the exhaust valve cokes up and burns out (very common on Subarus) - you do not have any signs of this in the pictures. Actually the engine looks really healthy, save for #3.

Interesting.

Post by **abscate** » 20 Sep 2018, 12:36

ISnt an XC90 specified for RON 91 gas (our 87 octane)??

Can you show the other four cylinders? Im amazed that only one would detonate - that in itself would make me think bad fuel injector or ????

Post by **SuperHerman** » 20 Sep 2018, 19:51

I believe you are right on the fuel requirement - either way I always used 87 and had no issues.

A bad injector would have had the car running like garbage and most likely thrown a code.

Are any valve guide keepers missing? I am of the theory something fell in there and let loose a storm.

Post by **mrbrian200** » 21 Sep 2018, 01:08

I bet if you disassembled the turbo further you'd find bits of metal scraped-flaked-broken away on the intake/compressor side either on the compressor wheel, housing, or both. With 1/4" play the center bearing might have also started breaking apart (isn't there a circlip used to retain the bearing/center shaft? also suspect), which would be a harder metals that would definitely do some damage. Metal bits would end up in #3 because they're heavier than air and momentum would carry them in a straight line into #3 instead of following air flow into a random cylinder.