Glad you found the problem. I saw an Acura technician replace the rings on an MDX J37 in 5 hours. Amazing how quickly the pros can do it.

 

Call me a nerd. I have watched many videos of J32s, J35s, and J37s torn down. Commonly, the front head looks dark and cooked while the rear head looks cleaner and light. I am referring to the valvetrain when the valve covers are removed. The constrast in oil "staining" is very strange.

 

Not strange at all. It's entirely normal due to the way the PCV system works on these engines. Some earlier model J series engines have it reversed so the rear head ends up looking darker.

 

Maxud and John Clark are two of the most respected contributors on this board, and they have real experience to back it up. Only fools would blow them off.

 

I just found a good example of front head from another thread

Now compare it to the image you posted


Besides the burned exhaust #6 valve, do you see a difference in these pics?
I asked if you cleaned the valves in your pic and you ignored me.

Your pistons and valves are getting steam cleaned.

 

I just found a good example of front head from another thread
View attachment 170248

Now compare it to the image you posted


Besides the burned exhaust #6 valve, do you see a difference in these pics?
I asked if you cleaned the valves in your pic and you ignored me.

Your pistons and valves are getting steam cleaned.

That is interesting that my cylinder head looks very clean compared to this head. I did not clean anything. Oh, I replaced this cylinder head 2/3 years ago, so it is relatively new; I am sure that partly explains the cleanliness difference.

 

I took some pictures of the piston rings as I was taking them off, the top 2 were pretty stuck.

The catalytic converter underneath the vehicle is not plugged, it allows air to pass through it.

 

Seems like every word that Max has said has gone right over your head.

 

Your understanding is mostly incorrect.
The amount of gasoline injected is measured relatively to the amount of air ingested. Look up stoichiometric combustion.
In naturally aspirated engine, like J series, there is no forced induction, so the amount of gasoline depends on readings of MAF/MAP sensors,
and fuel trim adjustments based on O2 sensor outputs, but not based on whether its working in 3 or 6 cylinder mode.
The VCM activations are not arbitrary, but happen when demand from the power plant is at lowest, like coasting on straight roads or downhill.
The 3 cylinders are NOT doing the work of 6 cylinders, they are doing the work of 3 cylinders, that's why van feels laggy coming out of VCM.
The instant more power is needed, VCM is deactivated and different cylinder configuration is activated, deemed necessary by the ECU.

 

I measured the cylinder head for flatness and there is section with a 4 mil gap. Thoughts?

 

Here is the spec, 2mil (aka thousands of an inch). You are twice over the limit.

 

Sounds warped.

 

I don't know what a mil is, but the Honda service spec for "warpage" is 0.05 mm.

 

👏 👏 👏 excellent diagnostic!
I learned something.

 

I think you'll have to go to Amazon to find ones that'll tell you they work with 1/4 inch gaps. Or maybe Flex Seal.......

 

This head was either overheated or installed/removed incorrectly. Either way, it won't work long (if at all) if you install it that way. It needs to be machined.

The last head I did, was on a 09 Toyota Corolla. I removed it and checked it myself and found no warpage. I was careful when I removed it and followed the book procedure. I still took it to a machine shop to have it checked. They checked it for flatness, agreed with me that it was flat, pressure tested the valves, used a sanding block on it for just a few swipes and told me to bolt it back on. 4-5 thou of warpage in the right place will cause a huge compression loss. Usually it's in the center and the loss will be between cylinders.

One thing is for certain, if you bolt it back on that way you WILL have compression problems. You're already this far apart, tear it the rest of the way down, check the cylinder bores, and re-ring it.

 

@Odyssey3425, your plan sounds like genius. Please update us on results in a month or so.

 

You only assume it was sudden. Had you checked compression right before this happened? It's pretty safe to assume it didn't suddenly happen. It likely happened over time until it finally started to misfire due to compression or coolant intrusion. When the MIL starts flashing the computer will shut off injectors on those cylinders to save the catalytic converter. My guess is by then you had the coolant intrusion and took a bit to get it pumped out. This is all theory, of course, but I think you need to look beyond it being a "sudden" compression loss.

 

Update: after replacing the 2nd bank piston rings the compression is fixed. The compression test for cylinders 1-6 were 190, 195, 248, 180, 180, & 177 psi. The 248 psi on cylinder 3 had a faster crank because of the battery; it seems to high to be real.

I also replaced the front catalytic converter.

Once I got it running I had misfires on cylinders 4-6. I swapped the fuel injectors between the first & second bank, then all the cylinders were misfiring. I swapped them back and wasn't able to start the vehicle, one of the pistons was full of fuel and wouldn't compress. I took out the spark plugs to air it out. Then I cleaned the fuel injectors with a can of throttle cleaner and a 9v battery. Afterwards the vehicle ran but continued to misfire on all cylinders. I removed the ERG valve and it was stuck open with a chunk of carbon; after removing the chunk, it was able to close fine. The vehicle continued to misfire on all cylinders. I reset the throttle position and ECU many times throughout the process.

Eventually after letting it run for a while it started sounding better. I drove it around the neighborhood a few times and no misfires. It feels weak though, that is, it doesn't accelerate fast. It is also loud when accelerating; I think the inlet manifold gasket needs to be replaced, I have taken that on and off so many times without replacing it.

 

Good job. Glad to hear you replaced the front bank rings and the compression is better. I am wondering what happened to the 4 mil gap. You mentioned throttle and ECM/PCM reset but you did not mention CKP relearn. Possible the 3rd cat is clogged. The engine oil might be contaminated with too much gas so an oil change would not hurt.

 

CKP relearn

Nothing was done about the 4mil warped cylinder head. The oil was changed during the piston ring replacement.

I will try the CKP relearn. I think you could be right about the 3rd cat being clogged/restricted; that would explain the low power. Would that also explain the excess carbon build up that caused the piston rings to seize?

 

Wow. If you bolted a head back on with 4mil of warp it will not last. Of that I am sure. All the trouble to replace rings but bolted on a warped head to save a few hundred bucks at the machine shop.... Smh.

 

Smh

Can we move on from the warped head? I will let you know if it becomes is a problem in the future, but right now it is not.

 

Update:
3rd catalytic converter was clogged. After removing debris from the front catalytic converter; it was still in good shape so I just put it back on.

The car now has good power and is much quieter. The idle RPM is ~700.

My conclusion is that the clogged catalytic converter must have caused the piston rings to seize. I don't know the mechanism, but before the vehicle died it had power and obviously good compression. This is also the same situation that happened in the forum I shared earlier: Van shut off on the highway

 

My Friend, I think you have it backwards. The rings got stuck causing excess oil to pass into the combustion chambers and into the cat. Over time the engine oil damaged the cat.

 

When that cat clogs it's usually because the upstream cat disintegrated and sent its guts downstream. And guess what usually causes the upstream cat to disintegrate?