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Discussion Starter #1
Verdict is in on my now constant “misfire” and it’s not good. Cyl no. 5 (center in rear bank, anyway) shows only 25 lbs compression. Fuel pressure, injectors and spark all great. New injector and ignition coil tested and installed just to rule it out formally.

Mystery Oil poured into plug well and left alone for about a week. No improvement.

Conclusion: broken or stuck compression ring(s).

Before I drop huge coin to replace cylinder, rings, liner etc., is there anything else I can try?

One thing that started contemporaneous with the misfire going from intermittent to constant is a speedometer that jumps on idle and acceleration but not on overrun. I don’t see how each could connect to each other but would love some instruction about fixing the speedometer.
 

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Rear cylinders are 1-2-3 so #2 not #5.

Mystery Oil no improvement, it could be valve(s) or lifter(s) issue.
 

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Discussion Starter #3
Rear cylinders are 1-2-3 so #2 not #5.

Mystery Oil no improvement, it could be valve(s) or lifter(s) issue.
Thanks for the clarification! Is there a specific compression test (like leakdown vs max compression) that would point one way or the other, or is that the wrong direction.

I would pray the issue is valve/lifter rather than rings!
 

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Thanks for the clarification! Is there a specific compression test (like leakdown vs max compression) that would point one way or the other, or is that the wrong direction.

I would pray the issue is valve/lifter rather than rings!
I think since oil trick did not raise compression it is the valve(s).

leak down pressure test through sparkplug hole with #2 intake chrome runner removed you maybe be able to tell if it is one of the two intake valves.
 

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I would think that a smoke machine test could help pinpoint what component is causing the low compression. Engine in position so that all valves on affected cylinder are closed ( is there a sweet spot on those engines where ALL valves are closed for all cylinders on that head?), smoke pushed into cylinder through spark plug hole. If smoke migrates up through dipstick hole - then rings. If through exhaust pipe - then exhaust valve(s). If through air intake - then intake valve(s). Escaping air pressure may even be detectable in one of those locations during a leak down test.
 

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Mystery Oil poured into plug well and left alone for about a week. No improvement.
Lets not jump too quickly to the valves, although that's my guess as well. If you let it sit for a week the oil will seep past the compression rings, thus giving you the same reading you had before the test.

To test the rings specifically you want to get them to seal up temporarily with a table spoon of 20w50 oil down the spark plug hole then immediately do the compression test. If you get over 25 psi that means the oil has filled the gaps in the rings and raised the compression a bit pointing the finger at rings. If there is no change and you still get 25 psi then the rings are doing their job and you have a valve that is bent or a lifter sticking. Its all sorta moot; either way your head is coming off. As its the rear head the engine is probably coming out. Glass half full says now is a great time to do a Q2 diff and clutch, so ya got that going for you!
 

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Good point Jake. Oil in do test right then.
 

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Discussion Starter #8
Thanks to all. To be clear, which I wasn't in my first post, I'm certain my mechanic tested the compression before adding Mystery Oil. This being the case, I'll speak to him about testing immediately after dropping engine oil in as described and using the smoke test.

In an effort of faith, I added another bottle of Techron about 20 miles ago with 10 gallons of fresh Shell high octane. The engine feels a tiny bit more smooth, but that impression may be a product of my wishful imagination.

Luckily, the car has already installed the Quaff LSD and fairly new clutch. Otherwise, is it then time to change timing belt and water pump as conventional? Any other do-it-while-out parts and service suggestions?
 

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Discussion Starter #10
Not yet. I hate to admit a common reality, but finances and spousal enthusiasm for dropping serious coin on a likely rebuild keeps me driving it as I can. That said, I do plan on taking your sage advice to my trusted and hopefully trustworthy mechanic.

My garage has the tools; I certainly lack the acumen and can't muster the courage. I mean, we all know the answer to the questions, "How bad could it be? After all, what could happen?"

I've Christmas presents to buy and tuition payments soon to make. Dreams of sugar plums and hot chocolate certainly means Santa will come through, right? ;)

Apologies to Dave Pratt of the AROCNE!

Jingle bells, hot oil smells, Alfa's on its way
Oh what fun to hear the noise of 24 valves all day.
Oh! Jingle bells, hot oil smells, where is my mechanic?
Why did I buy what I cannot fly? We all know the answer to that!
 

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Discussion Starter #11
Update: Franco Marcantonio of Prospect Foreign Car Garage in West Hartford, CT reminded me that several months ago he performed a leak-down test on that pesky cylinder. His method used a CO detector placed in or on the coolant or radiator tank (not sure which, not sure it matters), and a sensor at the tail pipe The coolant sensor did find CO in the coolant, but did not find a funky mix from the tail pipe, which together he says confirms that the exhaust ring is malfunctioning, either stuck, broken or both. I forgot to ask wether he poured oil down the plug hole first.

The CO sensor makes sense to me and seems to achieve the same as a smoke test. I will get a second opinion before opening my wallet, of course.

What might the list of activities include when doing a ring job on the middle rear cylinder?
  1. Replace piston, rings and liner. These come together in a kit, or used to, right?
  2. Change timing belt and tensioner etc. Should I change the water pump because it's there, like is conventional practice on conventional cars?
  3. Should I avoid or seek out the OEM-type head gasket? I think this gets changed, right?
  4. The engine will be pulled. Any other things to consider with my beloved's guts spilled across the floor?
What might a retail shop charge for this surgery? Should I draft Multicam Frank to operate?
 

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You can certainly ask him for advice I would think, as he is a very nice guy, familiar with the 24V car since he has one.
 

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Discussion Starter #13
You can certainly ask him for advice I would think, as he is a very nice guy, familiar with the 24V car since he has one.
Yes, Frank is a peach. He kindly invited me over a few years ago when this saga began, in the midst of a timing belt change occurring 2 days before the AROC convention in PA. I sent him a PM just now. At least I think that's what I did in this newfangled platform. ;)
 
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