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Discussion Starter #1 (Edited)
Solved - misfire codes - 05EX-L

Need advice resolving a misfire code (P0300-P0306) on all cylinders on a ‘05 EXL. The current mileage is 96k. Here’s a quick background…

Valves adjusted at 91k miles due to loud tapping sound. The dealer said valves were significantly out of adjustment on the back bank and wanted to tear down the cylinder head to check the VTEC system. Due to my job status, I passed on the additional diagnostic work and just had the valves adjusted. The engine sounds great and the adjustment seemed to solve the problem.

At about 95k miles, the CEL started to come on intermittently. Dealer diagnosed code P0420 and replaced the catalytic converter. (This may be unrelated but threw this in just in case.)

Now, at 96k, the CEL comes on intermittently due to misfire codes. They want to tear down the cylinder head again thinking it may be the VTEC system on the back bank. I am not comfortable this is the best approach since misfire is on both banks. The engine runs well but is slightly rough when cold.

The job situation hasn’t changed so I can’t throw a lot of money at this but don’t want to ruin a new catalytic converter. We bought this new and the van is otherwise in fairly good shape.

Any advice on a course of action to pinpoint the problem or otherwise eliminate less expensive causes?
 

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Discussion Starter #3 (Edited)
Thanks mjody, I agree with your comment about VTEC. That's why I was leery of the dealer's recommendation.

Yes, the plugs were replaced with NGK IZFR5K-11 (which I think are Laser Iridium) at 65k miles.

I'm beginning to think its the EGR valve. After the dealer cleared the codes, the CEL came on again when I started the engine in cold weather (20 degrees) and quickly put it in reverse. So, I bought a scanner and cleared the codes myself. Since then, I let it warm up for a few minutes before driving and the CEL hasn't come on yet. I can't think of any other components which are impacted by a cold start and that would trip the misfire codes. But, before I replace the EGR, I want to give it a few more days.

I wish there were a way to definitively pinpoint the problem. Any thoughts?
 

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Unlikely EGR, it is only activated when the engine is warm and you are at a steady cruise.
 

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Discussion Starter #5
What if the valve was stuck open and prematurely dumping exhaust gas into the cylinder before the engine is warm enough? Could that cause the misfire code?

Also, how does the engine diagnose the misfire? It can't really tell if the cylinder is firing properly. Instead, it has to read the exhaust gas to see if its too rich. That is why I was thinking it may be the EGR.
 

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2ndODY said:
What if the valve was stuck open and prematurely dumping exhaust gas into the cylinder before the engine is warm enough? Could that cause the misfire code?

Also, how does the engine diagnose the misfire? It can't really tell if the cylinder is firing properly. Instead, it has to read the exhaust gas to see if its too rich. That is why I was thinking it may be the EGR.
Yes it could. It is possible a piece if carbon has jammed it open. Pull it off and see if the pintle is stuck open.
 

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Discussion Starter #7
I took the EGR off and visually inspected it…doesn't appear to be a problem.

I also went to the library and checked AllData for this code. Since there aren't any other related codes, the diagnostic sequence covers the following potential culprits...

1) Bad fuel
2) Spark plugs
3) Fuel pressure (too high = regulator, too low = pump and filter)
4) VTEC oil pressure switch

There is a VTEC possibility but probably doesn’t require the head to be disassembled.

Based upon a suggestion, I currently have the battery disconnected to see if resetting the ECU helps (beyond just clearing the codes).
 

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With the cables off, hold them together for a minute to erase the ECM codes. It is kind of like re-booting your computer at home.
(and no it does not damage anything ;) )
 

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What did the plugs look like? Possible the coils are failing causing weak spark. Anybody you can swap a set with to see if improvement?
 

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Discussion Starter #11 (Edited)
I checked the plugs this afternoon and they didn't look too bad. One had a slightly more gray color. As a reminder, the plugs only have 30k on them and are NGK.



Also, I think I have it narrowed down to a cold-start problem. The engine runs rougher (but not horribly) at first and the CEL came on again this morning. If I drive it enough during the day, the CEL will eventually go off by itself. When the engine is warm, it runs like a charm and is very smooth and quiet.
 

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First and third plugs look poor for only 30K. That is a lot of crap built up on them. Middle plug not much better.

I have seen plugs from a Honda V6 with twice that many miles and they look like new.
 

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Discussion Starter #13
Those plugs came off the back bank where the dealer said the valves were most out of adjustment. Maybe I'll go ahead and install a new set to eliminate an easy culprit.

Any other obvious cold-start issues? Would the performance of ignition coils degrade when the engine is cold?

By the way, here's a picture of the EGR valve and mounting plate. Any concerns with this?



 

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Bottom pic, the pintle is on the top with the hex cutout. It is not stuck open, would be obvious.
 

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Discussion Starter #15
Here's an update...

If I drive enough during the day, the CEL goes off on its own but comes on during the first cold restart.

Today I replaced all the plugs and coils. After the van sat awhile, I started it and the light came on again. I guess it wasn't a spark issue.

What other system related to cold starts could be tripping the misfire codes? Is there anyway to diagnose the engine when its cold?
 

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The dealer sounded incompetent, wonder if valves were adjusted accurately or even at all?
 

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Discussion Starter #17
In case anyone else runs across this problem and finds this post via a search, I thought I would post an update.

The misfire codes in our van were apparently caused by a bad valve adjustment...the valves were adjusted down too tightly.

I won't bore everyone with all the details, but if you get the P0300-P0306 misfire codes without any other corresponding codes, definitely consider the valve adjustments.
 

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2ndODY said:
In case anyone else runs across this problem and finds this post via a search, I thought I would post an update.

The misfire codes in our van were apparently caused by a bad valve adjustment...the valves were adjusted down too tightly.

I won't bore everyone with all the details, but if you get the P0300-P0306 misfire codes without any other corresponding codes, definitely consider the valve adjustments.
I WIN!!!!:D
 

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Same CEL / misfire code issue

I found this thread very helpful. Over the past year I've had this same CEL / misfire issue with my 2005 Odyssey EXL. I went through buying and replacing all the ignition coils - which didn't help.

Based on your recommendation I'm going to go back to my mechanic for a valve adjustment. It could be touchy telling him that he may have caused this problem with a poor job adjusting the valves the last time he serviced my Odyssey.

Any other updates would be appreciated. Has your CEL / misfires been resolved totally?

Thanks again for the great thread.
Al
 

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Discussion Starter #20 (Edited)
So far, the CEL hasn't come on. The only thing I can add is that I had the timing belt and water pump changed at the same time they re-adjusted the valves. The van currently has 98k miles, so this was a little early. But I didn't want to tear down the engine again. This was my call...not the dealers.

I suppose there is a small chance the new timing belt could have fixed the misfire. I've read that the belt could stretch or slip which theoretically could cause the misfire. However, the mechanic was fairly certain it was the valve adjustment. Their description on my service ticket read: "...checked the valve clearance. All intake and exhaust valves on the front and rear head were too tight...". I noticed it was a different technician on the second service order too.

I hope this is the end of the story. If not, I'll post an update.

Good luck with your van.
 
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