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Discussion Starter #1
2006 MDX with 180k miles. Over the last 2 months, noticed some rough start specially when very cold outside. Engine runs smooth within a minute or 2. Then in the last 2 weeks, start getting P0305 CEL and VTM-4 ON sometime. These days it seems to misfire regardless of outside temperature. I can do it after sitting for an hour or a day. But it starts smooth if the engine is warm.

For background, timing belt and all plugs were changed at 100k, 9 years ago.

I've scouring the site and reading everything I could find on misfires and these error codes. So far I've tried:
  • Cleaning EGR valve and ports: Did not seem particularly dirty
  • Cleaned PCV valve: Some oil sludge on it. Blew some compressed air and re-installed
  • Swapped out plug and coil between cylinder 5 - 6. Reset code. Code came back, still P0305.
I have some mechanical skills but I'm now in guessing territories.

What I don't think it is:
#1 Coil or plugs: evidently, I swapped them and code stays with same cylinder so that seems to rule that out
#2 PCV or EGR: Since this is isolated to a single cylinder, seems less plausible
#3 Valves needing adjustment: again, single cylinder issue. Plus adjusted previously at 100k. Could that be needed again?
#4 Fuel pump: Less sure about that one but I've been taking the habit of leaving the ignition on for 2-3 seconds to let the fuel pressure build. Does not seem to make a difference.

Before I give it to a pro, was going to throw out what I think it could be in order of less costly to more costly:
#1 Injector: Could injector #5 be dirty or bad. Thinking about running seaform or techron
#2 Valve adjustment: Maybe still needed
#3 Head gasket: engine never overheated but I did add a little coolant recently. I have the transmission fluid bypassing the radiator for a while now.
 

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First off - thanks for posting a detailed, well-written request. It is a huge help in getting to the final solution.

I agree with all your assumptions above. If it was my vehicle, here's what I'd do...

1) Try a can of Seafoam in the gas (maybe adding it less than a full tank to get a higher concentration). If it's a "garden variety clogged injector", that just might clear it up. Plus, it's cheap and easy (a couple of my favorite adjectives).
2) Try swapping the injectors to see if the problem follows the suspect injector, or stays with the same cylinder.
3) Adjust the valves again. It's really just about due for that anyway (just 20k miles short), so there's really no big down side. If I were to guess, I'd suggest it's always possible that one cylinder might have been adjusted a little "tighter" than the others, so it would exhibit issues before the others. It certainly wouldn't be hard to make a fraction of a mm error on one cylinder when adjusting valves.
4) If none of that works, I'd take a very close look at the plug from the suspect cylinder to see if there's any indication that there might be a coolant leak (via a bad head gasket). From what you wrote, I doubt this is the case, but it couldn't hurt to check.
 

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Discussion Starter #3
Thanks for the quick reply. I did read all your post and saw your case. I looked at the plugs carefully and did not seem oily or wet.

Also, in the current condition, would it be better to stop driving it or is it safe and not harmful to keep driving?
 

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I’m no pro but from the description, work so far, and miles since adjustment, I suspect the valves. Our 06 which we bought new needed the first adjustment around 85K miles. #5 is the front middle so the front valves are much easier to check and if needed, adjust. However, if the fronts need adjustment, the rear bank will probably need adjustment too.

If it were the fuel pump, I think you would get random misfires. One note on your description - you said you leave the key on for 2-3 secs. You might try turning the key 2-3 times and waiting about 1-2 secs before each sequence. That pause allows the fuel pump to charge the line. If the pump is going out, the multiple charges gives the pump a chance to build pressure. Best way to determine its the pump is a fuel pressure test.

Hopefully it’s not the head gasket. A DIY test that could give you more info would be to get a loaner tool from Autozone or OReillys and check the coolant for exhaust residue. You have to buy the test fluid - about $10. It’s blue and turns orange if there’s exhaust residue. The test can be done in less than an hr if one of those stores are nearby.

You could try cleaning the throttle body - if it’s not been done, it won’t hurt but probably not the cause.

Looks like you’re being methodical and trying one potential “fix” at a time, starting with most probable. So from here suggest Seafoam, key test for fuel pump, throttle body clean, etc.

FWIW, here’s a link on valve diagnosis on an Odyssey. Long but really good explanation - skip to the 10 min mark. This shop uses a pressure transducer to diagnose before doing the job so a customer would be in it for a diagnosis fee. Part II (haven’t watched) is the adjustment.


Good luck!
 

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swap your injector from cyl 5 to 6 and also make sure the wires are good going to the injector and coils, southmainauto on youtube had a pilot with a bad connector on the injector.
 

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I wouldn't be concerned about driving it with a misfire, at least for a while. The only down side is putting too many miles with a totally non-firing cylinder is that the gas reaching the catalytic converter(s) can leave enough residue to clog it up. Driving a few hundred miles shouldn't cause any problems that a couple long pulls at full throttle won't clear up (the extra heat will tend to clear the residue).
 

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Discussion Starter #7
swap your injector from cyl 5 to 6 and also make sure the wires are good going to the injector and coils, southmainauto on youtube had a pilot with a bad connector on the injector.
Good tip. Only thing is, with a bad connector, I'd imagine the misfire would be going on no matter what. Mine goes away after about a minute of idling.
 

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Discussion Starter #8
Was able to spend a little bit of time on this yesterday. Swapped out injector #5 and #6. Still, this morning, same misfire code on cylinder #5. Plus can't remember which youtube video comment I was watching but in the comment, he answered back to someone saying something along the line that an injector related issue would not cure itself when the engine warms up.

So I'm down to either valve adjustment or head cover gasket. I'll try to do the valve this week.
 

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It's not impossible for a bad connection to be intermittent, and for the failure to be "heat-related" (i.e., starts or stops working when it gets hot / cold). I'd guess it isn't the plug, since pulling and swapping the injector would have most likely either "fixed" (by re-setting the contact) or "broken" (by causing a very flaky connection to fail completely).

FWIW, it might be interesting to listen to the individual injector when the idle is stumbling, with a mechanic's stethoscope. You MIGHT be able to hear something odd - or not - depending on the failure mode.

I'd do the valves. ;-)
 

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Hope I'm not going backwards. Decided to adjust only the front of the engine cylinder 4-6. Totally doable BTW without taking the intake manifold out. After done, fired up and got P0300, P0301, P0303 and P0305.

Getting a little closer to taking it to a shop

Sent from my ONEPLUS A3000 using Tapatalk
 

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Discussion Starter #11
Also intake were almost all good. Exhaust a little tight.

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Just an update. Adjusted all the valves. Overall not much off but did it anyways. Unfortunately, still seeing same misfire with P0305.

I've already swapped the injector on cylinder 5 and cleaned the EGR. Did the fuel pump priming 2-3 times for 2 seconds.

So getting pretty desperate here. Top 3 suspects are:
1) head gasket coolant issue. Coolant level not dropping too much but may also be a very small gasket leak
2) Maybe still and EGR issue. But why would I only get 0305 all the times and not another one
3) some fuel related/injector. Maybe some kind of blockage on the fuel rail?



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Well, sounds like the valves needed adjusting and at least you’ve ruled that out. (The engine was cold or less than 100 F when you adjusted the valves, correct?)

There’s a filter inside the fuel pump so seems improbable that there would be a large enough obstruction in the rail just at #5.

As Habby indicated, maybe the injector is malfunctioning, not the injector since you swapped them but the wiring or controls.

Still think you would get random misfires with a bad pump but you could get a loaner fuel pressure test kit from AZ or OReillys. You’ll have to T into the fuel line feeding the fuel rails.

It sounds like you are losing some coolant. As mentioned above, you could get a loaner kit to test the coolant for exhaust residue.

Good luck!
 

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I almost hate to bring it up, but have you done a compression test on cylinder 5? It seems like you've done nearly everything you can to eliminate the fuel and spark. The only thing left is compression. Or, of course, something odd going on somewhere in the wiring to the #5 coil, or to the #5 injector. You could use a mechanic's stethoscope on the #5 injector to see if it sounds different than its neighbors when the engine is stumbling.
 

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Discussion Starter #15
Just about to pickup the car. Mechanic did a compression test and found compression good on all cylinder. They ended up spraying carb cleaner on the coils connections. Said they had not seen the issue since but to pickup the car and drive it a few days see if the problem reoccurs. Will see...
 

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Intermittent problems are no fun at all - hopefully your mech found and fixed a flaky connection to that coil. But you really won't know until you live with it for a while. In cases like this, I'll usually just remove, clean, lubricate and re-set the connections that COULD be causing the problem(s), which is what it sounds like your mech did (assuming they did the same with the #5 injector).
 

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Discussion Starter #17
Well that did not take long. Drove it back from the shop no problem. Then 2 hours later, get in the car and misfires again. Same code P0305.

While this is all happening, been in private conversation with jeffbMDX who has a similar problem. His is at the dealer and just came back with the diagnostic that it's a leak in the head gasket. I'm now pretty sure that is what it is.

At this point of the car's life, I'm not sure I'm willing to put that much time/money to fix it. I've been reading about these head gasket sealer you can put in the coolant (Bar's Leak Head Gasket Fix, Steel Seal, etc). Anyone thinks I should not do that?
 

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I'd do some research on the products (that's one thing Amazon tends to be good for - you can usually find hundreds of legit reviews for pretty much any product). And heck, yes... if it's a question of scrapping the vehicle (or just selling it for chump change), or spending a few bucks on some potential snake oil, I'd go with the snake oil. FWIW, it does seem that there are a few products out there that seem to take car of the relatively minor kind of head gasket issue you're having (assuming that's what it is, of course - and I have to say it doesn't sound unlikely).
 
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