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I bought the car about a year ago. I knew she had problems when I got her, but it was waaaaay too good a price to pass up. I had to deal with a bunch of BS from the seller, but in the end I got a pretty sweet looking DB9. And honestly, she looked pretty great throughout the tear down. I found cylinders 1,2 and 3 of the left bank had no compression (20, 10 and 15 for 1, 2, and 3), but nothing major showed up on the bore scope, and the right bank seemed to be working just fine. Adding some oil helped a little, but still none of the numbers went above 40 PSI. Being that all the bad cylinders were in the front, I decided to try and do and engine-in repair (despite every repair in the manual starting with "remove the engine"). Anyway, with the help of a few amazing threads from the forum, I got the timing cover off, the exhaust manifolds disconnected and then the head came right up and out. And honestly, I'm kind of at a loss now.
It looks as if nothing is wrong, certainly nothing that would cause compression to be 10-20 PSI. There's some vertical scoring on the sleeves, but the pistons looks fine and so do the valves and head gasket. The only oddity is that there is a weird pink fluid in cylinders 1 and 2.
I drained the coolant, engine oil and transmission fluids, though, and all looked normal other than being dirty. I have no idea what this stuff is. Looks like strawberry yogurt or something.
Moving on, I realized a likely similarity for cylinders 1, 2, and 3 being problematic is that they share an exhaust manifold. In removing the left rear cat I found a ton of dust and busted up cat pieces.
After clearing the pipe, the cat actually looked fine, so I moved up the left front cold-start cat. The gasket looked undamaged and all I could see on the top of the cat was about a 3/4 inch hole. But in finagling the bore score up from the bottom, the insides were wrecked. Melted, broken and all in the pile I had dumped on the floor. Naturally I examined the left rear cold-start cat which looked perfectly fine from the top, but the bottom was pretty melty. Not nearly as bad as the front one, but definitely bad.
Anyway, that's where things stand as of now. Weird pink fluid, cold-start cats that have sustained major damage to the bottom, but look pretty good from the top, and a rear cat that doesn't appear to have sustained any damage.
Oh, I did forget to mention there was also oil in the airbox, so that's a possible contributor as well.
And everything else looks relatively fine. Honestly I'm shocked that the engine looks so good for not having compression in 1, 2 and 3. All I can think of now is to put a micrometer on the pistons to try to determine if there's a bent rod. Anyone else have any ideas? Any input would be greatly appreciated.
did you throw some liquid in the head chambers of the bad cylinders while the valve is closed to test for leakage? and did you pull the pistons to check the rings? i would suspect that the compression test was accurate but that the analysis WRT the cause has missed something. it's clear that the first three valve chambers are discolored and have suffered some sort of trama. i would thoroughly double check everything.
and i would, as strange as it may sound, taste that pink stuff. it won't kill ya.
Good call, the valve leak test is another item on my to-do list for tomorrow.
I haven't pulled any pistons. I do plan to drop the subframe and pull the oil pan tomorrow, so I'll see how tough it would be to do that work without pulling the engine. I haven't heard of anyone trying that, so I'm not optimistic. Hopefully the contents of the oil pan will shed some light, or one of the other tests will reveal something.
And I'll make sure to throw some of that pink stuff on my toast tomorrow morning
There is a strong possibility that your DB9 ingested the CAT pieces that were originally in the exhaust manifold. This would intern start the process of destroying the engine. This is a well known problem with the DB9.
If you have not done so, I would high recommend you watch the many Bamford Rose videos on this phenomenon. Below is just one of their videos.
I give you much credit in tackling this project and I hope you have it running soon.
CAT pieces bent a valve spring in my 2012 V12 Vantage...engine was replaced under extended warranty. I would examine the valve assemblies on the low compression cylinders very closely.
Best of luck.
Thanks,
JH
MAUMAU, great link and very helpful! This seems to explain all the issues (except maybe the pink stuff). Looks like I'll be pulling out the internals for inspection.
Bones 53, thanks for the input. I'll definitely be checking the springs and valves today.
I did a leak test on the valves today. No leaks at all. For good measure I pulled them all, cleaned them up and checked the runouts. All were below the .05 mm maximum.
The springs all looked good upon initial inspection. I'll do a proper test tomorrow to verify they are straight and still provide suitable resistance,
I also measured the pistons at TDC. Every one checked out fine.
Tomorrow I'll be dropping the subframe to check the contents of the oil pan and try to get at the pistons. All I can guess now is that the rings are bad. At this point I HOPE the rings are bad. I'm almost out of stuff check.
FWIW, i think you're on the right track. i wouldn't be surprised that all that grit has worn those rings down. a leakdown test would prove it, now that you are convinced the valves are not leaking. of course if you're getting 10 - 20 PSI compression it's pretty much a given that that is the problem assuming the block isn't cracked. which it may be. although three contiguous cylinders failing with one crack? that's a bit too much to believe, IMO.
if so, and you haven't drained and thrown away the oil and filter already, an oil analysis may show the remnants of a worn down ring or three. you may even find what looks like mud (a mix of oil, ground cylinder bores. rings and catalyst) in the bottom of the pan. and if the grit from the cats is fine enough the bores may not even look that bad, and yet the rings may still be worn, unusable and not hold compression.
I did cut open the oil filter a few days ago. I found some very fine metallic bits, but nothing chunky.
Also, I did leakdowns before I pulled the timing cover and head. The air was escaping behind the timing cover I think for all three, so looking more and more like the rings are the culprit.
i have no idea how one would go about specifically testing for worn rings. i don't know... maybe pour some kind of liquid in multiple cylinders and see how long each take to drain?
In one of Bamford Rose’s videos concerning this issue, they removed the remaining catalyst in the header itself which not only prevented it from happening again (which it will due to the design), but also improved the power and exhaust note a bit.
If if I remember correctly, it was a bit of a project removing the remaining catalyst, but yours looks so disintegrated that it may be an easier task.
Again, much respect in tackling this and look forward to your updates.
61mga: I had the same thought. I'll be giving that a shot today.
MAUMAU: I did see that one, and that's what I plan to do. As the car gets older, it seems only more likely that this will happen again if I keep the primaries. Right now I'm learning about the Lambda (O2) sensors and devising a way to trick the downstream ones into thinking there's less O2 present to avoid having to do an an ECU remap. Since it's just a voltage reading that's sent to the ECU, I figure I can put a resistor in to show the correct voltage. I imagine that would be 0.0V or close to it. Have you any info on that? I'm sure BR has that info so maybe I'll reach out to them. I suppose, though, that it's probably about the same for all cars.
ETA: I just watched a BR video that claims the V12's are factory mapped to run rich in order to quench the primary cats and keep them cooler. The optimal Lambda for maximum power is .89, but at higher (4000+) RPM's, Aston runs the engine extremely rich at a .72 Lambda. So a remapping might not be such a bad idea after removing the primary cats.
11-13-2022, 07:56 PM
although three contiguous cylinders failing with one crack? that's a bit too much to believe, IMO.