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Discussion Starter #1
Woke up this morning to go to breakfast with a friend and had the Check engine light illuminated immediately upon start up. Pulled out my code reader and there were 7 codes. Cylinder 1-6 misfire and then a random cylinder misfire code as well. The car seemed to be running fine so I drove another 6 miles or so. When I started the car up to go back home, the light was still on. I plugged my code reader in and instead of cylinders 1-6, it was 1-3,5,6 misfire. I ended up clearing the codes and the light didn't come back on for the rest of my drive. Here are are some thoughts I had and I am asking for any assistance with trouble shooting this.

-Spark plugs were changed at 151,000 miles (I am currently at 184,000 miles)
-My first thought was the ignition coils, however I am wondering if it's possible that all 6 would fail at the same time? (Also this is kind of expensive)
-What does a misfire sound/feel like?
-Any other ways to be sure of what is causing this? I'm not really interested in throwing a bunch of different parts at it.
-Or should I just leave it be until the light comes on again? It did this at 172,000 miles, then my mechanic cleared the code and nothing happened again

I know there seem to be tons of misfire code posts on this forum, but I figured it would be best to explain my individual situation. In addition to all of this I have read a bunch of different posts on the matter. Still trying to determine what the best course of action is. Thank you in advance!
 

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Has the valves ever been adjusted? I had multiple random misfires and adjusted my valves and all went away and never came back. I tried changing my spark plugs then coils before that but neither worked.


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Discussion Starter #3
I have a little video of the engine revving and then idle. Doesn't sound any different to me. If the valves needed to be adjusted isn't there usually a ticking noise? I will look into that.

 

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You'd know a persistent misfire when you encounter it. The engine goes from stable purring into groups of purrs depending on how many cylinders fail to fire. Of course you'd feel engine shake more as well.
To me your engine sounds fine. Are your plugs still torqued properly?
 
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Discussion Starter #5
You'd know a persistent misfire when you encounter it. The engine goes from stable purring into groups of purrs depending on how many cylinders fail to fire. Of course you'd feel engine shake more as well.
To me your engine sounds fine. Are your plugs still torqued properly?
Hmm...I'll check the plugs. Another thing is the car is not sluggish at all. I actually drove it about 60 miles on the Natchez Trace Parkway on Friday and thought it handled it great!
 

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All 6 coils won't fail together, don't waste your money on those.

If it's on startup, it sounds like the car isn't getting enough air or fuel, check the tube above, then replace the PCV valve. Clean out the EGR valve, it's easy to do. Clean out the egr passages, pretty simple to do this too. On the 04-05's, there are very obvious pcv passages on top of the air intake plenum where you can remove the top plate, and clean out those passages. It gets clogged just like the tube above.
 

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Also check your spark plugs and see if you have oil on them, if you do, it's time for valve cover gaskets and spark plug tube gaskets
 

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I had oil on plugs 3 years back, before switching to high mileage oil. Since then engine is dry and clean and no more oil seepage anywhere. I was going to change seals and even bought them, but did not have to thanks to Valvoline MaxLife.
 

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I had the Problem - cleaned out my EGR path to each cylinder, easy to do, that clear up the misfire and codes. There are a couple of YouTube videos on the procedure. (search 2004 Honda Pilot EGR port cleaning)
 

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I have a little video of the engine revving and then idle. Doesn't sound any different to me. If the valves needed to be adjusted isn't there usually a ticking noise?
Just the opposite. Valves need clearance, and clearance means some clicking. A moderate clicking is normal. If the valves are quiet, then clearances are too tight, and the valves may not be closing fully, especially the exhaust valves. I bet that your Pilot has never had a valve adjustment. An adjustment will probably fix your misfire issue.
 

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Discussion Starter #12
Just the opposite. Valves need clearance, and clearance means some clicking. A moderate clicking is normal. If the valves are quiet, then clearances are too tight, and the valves may not be closing fully, especially the exhaust valves. I bet that your Pilot has never had a valve adjustment. An adjustment will probably fix your misfire issue.
Thanks...I am sure it hasn't been done. It's on my list of upcoming things that need to be looked at.
So I've driven about 40 miles since then, the code is cleared and hasn't come back. Engine does have the typical Honda V6 clicking. Sounds the same it always has. Not planning to do anything until it comes back. When my next timing belt service is due, I'll have the valves adjusted. As I said before, I've had this CEL misfire issue about 10,000 miles ago and it went away.
 

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I would echo STMech on the valve adjustment. This sounds a lot like how my issues started (see this thread for details). I swapped out multiple parts searching for an answer to what started as an intermittent CEL that progressively came on more and more often. Ultimately the valve adjustment was the answer.
 

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Discussion Starter #14
I would echo STMech on the valve adjustment. This sounds a lot like how my issues started (see this thread for details). I swapped out multiple parts searching for an answer to what started as an intermittent CEL that progressively came on more and more often. Ultimately the valve adjustment was the answer.
Thanks! I plan on getting a valve adjustment when I do my next timing belt. Haven't noticed a decline in performance but given that it has yet to be done, I definitely want to have them do it.
 

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The engine should have a slight subtle tick to it. The valves don’t get loose over time, they get too tight, messing with the timing of the engine. I did my valves and like all of the forums say, they were all too tight on the intake side.
 

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+1 on the valve adjustment. As I understand it, it is just a matter of time before these engines will need this work, and this is the most common symptom.

I had the same problem, cylinder misfires (you could hear it from the exhaust on cold startup) and random misfires. CEL would come and go with similar codes to what you have, usually came on if I let it idle while cold for any length of time. It definitely seemed worse at idle, but otherwise ran just fine.

While adjusting the valves, I noticed that the intake valves were almost all within specifications, but every single one of the exhaust valves was much tighter than the specifications, with a couple having no clearance whatsoever.

These engines have a tendency for the exhaust valves to tighten up over time, so I adjusted them to the upper end of the spec. Problem solved, no more misfires. You should be able to clean the EGR ports easily while you have the intake off as well if that is needed. This is where I would start before throwing any parts at it, as it most likely needs to be done anyway.
 

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My exhaust valves might have been the tight ones, come to think of it...it's a tedious process, so I probably got that wrong. It's not a hard process though, most people act like it's rocket science, but with a basic youtube video, anyone can do it.
 

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My exhaust valves might have been the tight ones, come to think of it...it's a tedious process, so I probably got that wrong. It's not a hard process though, most people act like it's rocket science, but with a basic youtube video, anyone can do it.
The exhaust valves are the outer ones, far front and far rear, intake valves are the inner ones closest to the intake.

You're right, it's not rocket science, but it's certainly a bit more complicated than an oil change or replacing spark plugs if a person hasn't done anything more complex than that. It was a bit tedious and time consuming, but in just a few hours, I was able to save a few hundred dollars by doing it myself and I couldn't be happier with the result.
 

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You might want to adjust your valves sooner than later since it is a common problem on the Honda 3.5 liter engines..

What's happening is that your exhaust valve clearance gets tight due to wear on the metal contact. This causes the valve to open sooner and close later than it should. Closing later allows a small amount of unburned fuel to go into the exhaust. It won't always trip the P0300 Check Engine light because it's such a small amount of unburned fuel passing through.

The tight exhaust valves will cause your fuel trim will be around 14% where it should be close to 0%. The check engine light turns on when it reaches passed 20%. So you'll usually see the light come on when the engine is cold or is at idle for a good amount of time. I recommend you get a good scan tool to check the live data and see where your fuel trim is reading at when the engine is at operating temperature.

This unburned fuel causes carbon build up to go through your EGR and back into your intake. The carbon affects your intake valves to have a looser clearance because of the carbon build up. The unburned fuel will also affect your catalytic converter and you'll see that go out and get the P0420 code if you continue to run the car like it is.

If you want a quick fix, then you can run lacquer thinner in your fuel or change the oxygen sensors. The oxygen sensors is what's telling your check engine light to come on and it's probably really dirty at this point because of the unburned fuel going into your exhaust.

If you want to fully fix the problem, then adjust the valves, clean your intake and throttle body from the carbon, clean the EGR ports, and replace your oxygen sensors. You might also want to run Seafoam before adjusting the valves to get rid of any loose carbon off the intake valves.
 

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I bought mine with all the lights on and the previous owner's mechanic said it was the computer.

My scanner told gave me random misfires and the Honda Specific code suggesting valve adjustment. It wasn't bad for about a year, and then it ran like crap at idle, to the point it would stall when cold.

I bought my Pilot with over 300k so I didn't want to jump right into the valves - so instead I cleaned the plenum passages, cleaned the EGR ports, replaced the EGR, changed the coil boots and seats, replaced plugs, and ran 2 cans of Seafoam. I then knew the valves needed to be done, so I ran 2 more cans of Techron through over the course of a few weeks and used a can of Seafoam intake spray.

Adjusted the valves and changed the valve cover gaskets and grommets, which were beyond brittle. I needed to adjust all but one intake valve and all the exhaust valves were too tight. Took me 4 hrs but could have been done quicker - I was using up vacation time and let each valve cover soak for 30+ min to get the old gaskets off. Immediately purred when I was finished.

Do yourself a favor and adjust the valves - Honda calls for them to get inspected and/or adjusted every 100,000 miles and when changing the valve cover gaskets. If you go the DIY route it's about $50 for the gasket kits - my local dealers quoted me $600. I'll also add that I had feeler gauges but due to some comments on the forum bought a set of offset gauges and glad I did, I'm not sure I could have done the job without them. If you go the DIY route get the gauges off Amazon, they're ~$10 (or less).

EDIT: Don't be intimidated if you haven't adjusted valves before. Watch a few of Eric the Car Guy's videos, he does a nice job of demonstrating how the feeler gauge should slide when the valves are/are not adjusted properly, then just get a decent set of gauges. I bought the special tool for the valve bolts, but actually found it was easier with a small wrench and screwdriver, largely because the tool doesn't have the clearance needed for all the bolts anyway. If you DIY be sure to have access to an air compressor and (I swear to god) about 10 cans of brake cleaner to remove all the gunk from the valve covers and the carbon buildup from everything else (plenum, etc.).
 
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