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Discussion Starter #1
Hi all,

I have a 2009 EX-L with 180K, bought in 2017 with 120K. Just recently, I've gotten reports from the wife that the CEL has come on and off a couple times, and she's felt some occasional hesitation in reverse.

Took a trip last week and on the way home Saturday the CEL came on, then starting blinking, with rough running while slowing down and at idle. Went to the closest dealer to get the codes, but they couldn't get us in that day for anything beyond codes... P0301, P0174, & P0400. Oil level was fine. I thought a quick/easy initial attempt would be the EGR valve. The VSA light came on during the 2 mile drive to NAPA.

As a side note, it ended up taking much longer than the expected 5-10 minutes to replace the EGR valve. The socket set I had with me ended up not being sufficient for the left nut. I went through a lot of the NAPA loaner socket pieces before finding success with a 1/4" drive with a few extentions and universal joint (thinner than the 3/8" pieces) and a hex socket (because the nut got stripped earlier)... gotta love honda engineers.

Anyway, got back on the road, and the slowing/idle vibration seemed better, though still there, the CEL still blinking, and VSA light still on. Everything felt normal driving up to highway speeds, with the exception of a lack of pickup when trying to merge into faster traffic to pass. I know driving with a blinking CEL is strongly discouraged, but we were able to get home with no symptoms worsening... and hopefully not further harming the engine.

So now I'm left with trying to figure out the problem. As far as I'm aware, until I get the PCM reset, I can't be certain that the EGR valve wasn't part of the problem... so the reset is on my list of things to do. After doing a bunch of reading here and on other sites, and talking to a couple friends, here's my current list of things to investigate/try:

0) PCM reset, then wait to see if symptoms/CEL returns,

1) get compression tester loaner (a friend found a problem here after dumping a bunch of $ into plugs, coils, multiple valves/sensors, etc.

2) check for vacuum leaks (I have already spotted 2 big cracks in the intake hose)

3) o2 sensors (i'm finding conflicting info online about this... some say if I'm getting these codes, the van has already run tests to confirm the o2 sensors are working properly... others say o2 sensors resolved their problem)

4) spark plugs and/or coils

5) fuel injectors

6) clean throttle body (I don't think this could be part of the problem but I'll make sure to clean while it's open if I replace the intake hose)

7) VCM issue (I didn't know about the VCM issue until now): my impression is that it's too late to get the extended warranty work. Has it been extended further, or is going to corporate successful? Should I get VCMuzzler II or VCMTuner?

Any thoughts on what's most likely, what to try, and what order would be appreciated.

Another option obviously is to pay the $140+ for a dealer diagnosis... or likely less at an independent mechanic. I like to do as much car work as I can, especially if the extra time it takes for something new will keep paying off, but if it's likely I'll be chasing this for weeks while wasting lots of money on unnecessary parts, I might rather hit the "easy" button.
 

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A blinking money light suggests that you have a steady misfire. Confirm if cylinder 1 is indeed misfiring. Yank the plug to see if there is any change, if not, it's indeed dead. Then swap plug and coil from a working cylinder.
 

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Discussion Starter #3
Thanks Klondike.

Am I correct to assume that once I have confirmation of the cylinder and that swapping plugs/coils changes which cylinder is misfiring, then I would try both plug/coil combinations to identify which is bad? In other words, in C1, I'd try the C1 plug with C2 coil, then C2 plug with C1 coil.

OTOH, if the misfire stays in cyl 1, then I'd go to a compression test?

edit to add... obviously I'll look at the plugs as I pull them in case they're shouting something by appearance.
 

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Thanks Klondike.

Am I correct to assume that once I have confirmation of the cylinder and that swapping plugs/coils changes which cylinder is misfiring, then I would try both plug/coil combinations to identify which is bad? In other words, in C1, I'd try the C1 plug with C2 coil, then C2 plug with C1 coil.

OTOH, if the misfire stays in cyl 1, then I'd go to a compression test?

edit to add... obviously I'll look at the plugs as I pull them in case they're shouting something by appearance.
Engine needs spark, compression and fuel to fire.
Yes, if C1 is not firing with know good plug and coil combo, then I would check compression. If compression is good, I would then check injector 1, and the injector harness. Unfortunately, you have to remove the intake plenum to gain access to the injector on a J35 engine.

Edit: You may want to do a leak down test if you have access to compressed air and a leak down tester. I remember one YouTuber demonstrated a Honda engine can hold 180psi but it's got a severely leaky piston ring or valves that's causing misfiring, which was caught only in leak down test.
 

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Discussion Starter #5 (Edited)
ok, I think I have a good flow chart going.

Basically, first confirm the misfiring cylinder. Then, for that cylinder, check whether it's the plug and/or coil that are bad. If so, replace where bad, ensure no longer misfiring, reset PCM, and drive to see if problem resolved. If plug and coil are good, check compression. If compression bad, do leak down test to quantify loss and locate where the air is going... findings dictate next steps. If compression good, check injector/harness, and clean/replace as necessary.

Does that sound right?

Assuming all these steps are done correctly, is it possible to find good plug/coil, good compression, and good injectors?

I can confirm later (if I get to this point) all the locations to check for escaping air during the leak down test, but this would be independent from a vacuum leak, correct? ie, compression can be good, but if too much oxygen is getting in through the intake for example, that can cause a lean condition and misfiring, correct? Sorry if this should be obvious... my prior diagnostic/repair work hasn't gotten this invasive, and I'm not 100% clear on how all the internals work.

edit to add... might be worth asking, assuming I'm correct that vacuum leaks would be a separate issue, should I do a quick vacuum leak check with carburetor cleaner (on a cool engine) before all of the above?
 

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Nice name . If you get through this unscaved buy the vcmtuner2 .

Is the intake hose you speak of from throttle body or does it go to back of intake plenum?

If its from the throttle body . Mine was cracked/split and didn't cause any problem or cel .

158221
 

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Discussion Starter #7
I'm referring to the intake hose that connects the throttle body to the air filter box.

Thanks for the input. Seems I'd be more likely to find something impactful at or past the throttle body.
 

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ok, I think I have a good flow chart going.

Basically, first confirm the misfiring cylinder. Then, for that cylinder, check whether it's the plug and/or coil that are bad. If so, replace where bad, ensure no longer misfiring, reset PCM, and drive to see if problem resolved. If plug and coil are good, check compression. If compression bad, do leak down test to quantify loss and locate where the air is going... findings dictate next steps. If compression good, check injector/harness, and clean/replace as necessary.

Does that sound right?

Assuming all these steps are done correctly, is it possible to find good plug/coil, good compression, and good injectors?

I can confirm later (if I get to this point) all the locations to check for escaping air during the leak down test, but this would be independent from a vacuum leak, correct? ie, compression can be good, but if too much oxygen is getting in through the intake for example, that can cause a lean condition and misfiring, correct? Sorry if this should be obvious... my prior diagnostic/repair work hasn't gotten this invasive, and I'm not 100% clear on how all the internals work.

edit to add... might be worth asking, assuming I'm correct that vacuum leaks would be a separate issue, should I do a quick vacuum leak check with carburetor cleaner (on a cool engine) before all of the above?
Yes, that is a good flow. You sounded like a computer guy/gal as you used 0 as starting index:).

A vacuum leak will cause lean condition, but it will be more pronouncing at idle and lower RPM. It is not likely to cause a steady misfire. However, if you have a bad misfiring cylinder, the O2 sensor of the problematic bank will see high o2 content and try to dump more fuel to it -- high fuel trim. If the fuel trim is higher than +25%, you will get a "too lean" code on that bank. In your case, if this is the theory, you should be getting P0171(bank 1 too lean) but you have P0174. It's a mystery. If you have a scanner that can monitor fuel trim, you want to see if the fuel trim change at different RPM to begin.

If you find out you have a leaky cylinder, I would first confirm if timing is dead on, is there any chance you have a loose tensioner such that it jumped tooth on you?

Keep us posted on your findings please.
 

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Discussion Starter #9
I was finally able to find some time to do some testing of the cylinders, but I'm getting inconsistent results. With all plugs/coils in their original spots, I was getting no impact from pulling the cyl 1 coil, and some impact from other cylinders, but pulling cyl 6 coil repeatedly made engine significantly struggle. So I swapped coils between 1 and 6, still got significant change in 6 and no change in 1.

Then I pulled the plugs. Cyl 6 plug is a normal tan, with a small white spot (not built up) on the gap side of the ground electrode. Cyl 1 plug electrodes are black, including black residue into the threads. Not sure if this is carbon or oil fouling. I'll try to upload photos in a bit.

Anyway, in my attempt to confirm the cyl 1 plug is bad, i swapped plugs with cyl 6. This is where things got confusing. Initially there was significant change in cyl 6 when I pulled the coil, which suggested that the plug is still working ok though appearing fouled. Cyl 1 still had no change when pulling coil. Then after repeating the cyl 6 pull a few more times, there wasn't much change. Could it be that the cyl 1 plug is going bad but can still work on occasion, explaining the noticeable impact on first check after putting it in cyl 6?

After getting back on the computer and looking around, I realized that I probably should've checked the plug ceramic insulators and the inside of the boots for burn marks... the photos I took don't show the insulators.

Thoughts?
 

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Discussion Starter #12
just FYI, according to dealer record I got from prior owner, plugs were last changed at 102k, along with timing belt, tensioner, water pump, drive belt, and PS pump. I bought it at 120k, and it's now at 180k.

Unless there are problems not worth fixing in this engine, I'm thinking it's time to replace the plugs anyway. Also, there's been a PS fluid leak for awhile... I was able to replace one o-ring, but couldn't get the other one off at the time, and the leak continued, so we've just been adding fluid on occasion. I haven't tried PS stop leak, so I was thinking I'd do that. There is a lot of PS fluid around the left side of the engine bay though, including on the timing belt, so once I resolve the PS leak, might be time to replace the timing belt, etc again too.

Anyway, lots going on, but I want to get to the bottom of the misfiring and whatever else is going on right now before worrying too much about the other stuff.
 

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Just a point of information, are you related to the other 09ody?

Now, get yourself an inexpensive OBDII adapter from Amazon, and buy the Torque App Pro or Car Scanner App, with which you can read and clear you own codes.

If cylinder #1 is being shut down by the van's computer, just turning the car off/on will allow the cylinder to run until the code is set again. You can do this as many times as you want. Does the code immediately come back?
 

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If you have a split tube anywhere after the mass air flow sensor (MAF) it will set lean codes (P0171 and/or P0174.) Even if it's before the throttle body. Be 100% sure you don't have a split tube.

Also, if you don't have a bidirectional scan tool DO NOT clean the throttle body. You will only add more misery to your situation as you'll end up with a high idle and/or a new code for an idle problem. If you have a way to reset the throttle position data using a scan tool then, by all means, clean the throttle body. Generic OBDII adapters from Amazon or anywhere else, will not do this.

As mentioned already, the easiest thing to do is swap coil and plugs with a known good and go from there. Be sure and stick with NGK Iridium plugs, the same as the originals. Using other brand or types of plugs can cause issues.
 

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Discussion Starter #16
Just a point of information, are you related to the other 09ody?

Now, get yourself an inexpensive OBDII adapter from Amazon, and buy the Torque App Pro or Car Scanner App, with which you can read and clear you own codes.

If cylinder #1 is being shut down by the van's computer, just turning the car off/on will allow the cylinder to run until the code is set again. You can do this as many times as you want. Does the code immediately come back?
I'm not related... just random similarity on name choice.

I have the MS300, though for some reason I thought it couldn't erase codes... looking at the details again it appears it can, so I'll try that. I'm fairly certain the same codes would return. During all the coil/plug pulling/swapping I did, the CEL stayed on and blinking. Each time I started the van, the light came on solid... and then a few seconds later started blinking.
 

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Discussion Starter #17
If you have a split tube anywhere after the mass air flow sensor (MAF) it will set lean codes (P0171 and/or P0174.) Even if it's before the throttle body. Be 100% sure you don't have a split tube.
Here’s the intake tube...
8B189CB7-EB18-431D-BCBA-F0A4212D8DE9.jpeg


Also, if you don't have a bidirectional scan tool DO NOT clean the throttle body. You will only add more misery to your situation as you'll end up with a high idle and/or a new code for an idle problem. If you have a way to reset the throttle position data using a scan tool then, by all means, clean the throttle body. Generic OBDII adapters from Amazon or anywhere else, will not do this.

As mentioned already, the easiest thing to do is swap coil and plugs with a known good and go from there. Be sure and stick with NGK Iridium plugs, the same as the originals. Using other brand or types of plugs can cause issues.
Thanks for the tip on the throttle body. I’ll make sure to check in there but not clean yet.

New NGK plugs are on the way. I figure $60 isn’t too bad for a first step to see what new plugs do... considering they’re due anyway. Hopefully other existing problems won’t Immediately foul any of them.
 

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Here’s the intake tube...
View attachment 158345
Holy moly! That needs to be replaced. You'll have all kinds of issues and codes with that tube. The dealer likely has them in stock as they harden and crack all the time.

The MAF sensor, mounted to the air cleaner right up stream of that tube, measures the air flowing in and the computer uses that to know how much fuel to add. With all that pirate air coming in, it will add fuel to compensate for all that extra air, and set your lean codes. It may also be enough to make it misfire.

So, new plugs and replace that tube, clear the codes and see what comes back.
 

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Not sure where you're getting your spark plugs from but they should cost you near $90. If you ordered from Amazon or eBay do NOT use those. They are fakes and will damage the engine. Get them from RockAuto or your local parts store.
 

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FWIW, I had very similar cracks on my inlet duct recently and replaced it with a new Honda part from Majestic.

Ditto on making sure you buy your new plugs from a reputable place - lot's of counterfiet NGK spark plugs out there.
 
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