Honda Odyssey 2005 – 176000 miles. Cylinder 4th Misfire – check engine light

Honda Odyssey 2005 – 176000 miles. Cylinder 4th Misfire – check engine light
Honda has about 176000 miles. When cold – before warming up – it acts like nothing is wrong – as it gets warmer – to the middle of the temperature gauge – it misfires.And runs rough.
Evaluation: Honda Dealership thinks it is a cracked Valve or needs adjustment – they have replaced a spark plug and swapped coils. Not for sure.
They think if that is not the case then there could be additional problems.
Why does it act normal when cold ? How can we confirm if it is the valve and not cracked head ?
Please advise any suggestions .

Could be an intake or exhaust leak. Either of those will change with temp change.

Using your email address as a screen name is not real bright.
@cdaquila you might want to help this person.

My first guess would be some kind of electrical problem in the ignition system. Coils, plugs, wires, igniters, cam or crank timing sensors, something like that. But it sounds like the shop has already tested for that. Did they put it on their fancy electronic ignition system tester to see if any spark pulses are missing when they should be firing on that plug? I presume they already did that.

Since it only occurs on one cylinder, if it isn’t spark related, then I’d have to concur w/your shop, it is probably valve related. Compression and leak down tests might provide a clue, as would measuring the valve clearances. Unless you are aware that some routine engine maintenance item has been postponed a really long time, those tests are probably what I’d do next. Best of luck.

Edit: One more thing, it could be a faulty or plugged fuel injector or fuel injector pulser. Shops usually have tools to test the pulser without it taking too much time. And the shop could do a test to compare the injector fuel spray amount against each other, one by one. Still, probably best to do the above testing first, before considering a fuel injector problem.

Thank you all for your feed back.
The service adviser did checked compression and it was at 120 PSI and I am told it should be 175.
I have kept up regularly with all my maintenance. Thanks .
I am lost -

PS: how do I change my user name- I tried Editing but it did not work

120 is pretty low. Probably low enough to cause an occassional misfire. Is that reading only for cyl number 4? What do the other cylinders measure? If my Corolla had this problem I’d be measuring the valve clearances.

Go to your inbox and send a private message to @cdaquila . She will edit your screen name and send you a email telling you what it is. I also recommend you read up on internet security as far as passwords and such.

Thanks- Yes according to them it was 120 in the 4th. I am not sure if they checked all.
do you think I should change the engine ?

A 120 is low. The dealer had the spark plugs out. That was the time that a proper diagnosis should have been done with a dry/wet compression test or leakdown test.

A tight valve can cause a problem like this. However, if the tight valve is an exhaust valve an adjustment may only be a temporary cure if it helps at all. Generally speaking, a valve face will suffer some damage in a short time if it is too tight and even if properly adjusted that damage will continue to worsen.

This means a valve job. Whether that is justifiable in your case I do not know. A lot depends upon the compression readings of the other cylinders, whether ring wear is an issue, etc.
Ring/cylinder wear is much more major and means either a rebuild or replacement.

My guess is valve job also. A valve clearance inspection is normally done around 100k by Honda recommendation but mostly not done as they are rarely off then.

You can hope it did not burn a valve and require an adjustment.

If it has a burnt valve is this a bid job ?

I meant, will it take a lot of labor and $

Burned valve involves removing both heads and send out typically for machining outside a shop or dealer.

If it comes to that I would suggest getting a few quotes as it will range $1000-$1500 as sheer guess. I spent double that on Subaru however the motor had to be removed in order to access the valve heads due to flat-4 layout. Honda luckily the heads are at top of motor although minivan is tough accessibility to work on back side.

Don’t assume it is a burned valve at this point. Some more testing is required.

The dealer should have clarified all of this during their diagnosis and parts swapping expedition.

Diagnosing a problem like this is very easy to do. If the cause is a valve issue then whether it’s worth doing it or not is dependent upon compression readings on the other cylinders.

You do not want to spend X dollars having the cylinder heads redone and end up with a weak engine due to low compression caused by piston ring issues.
I would hope that they ran a full compression test on all cylinders and not just the one that is acting up.