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2001 w/ 404,967 miles - rough idle and misfire codes

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Hello all. Original owner looking for help diagnosing misfire codes:

Codes: P0300, 0301, 0304, 0305, 0306, 1399.
Symptoms: Intermittent rough idle, low power, struggling up even gentle slopes at highway speeds. Runs fairly smoothly on level highway. Seems to be worse when engine cold.

Recent relevant maintenance history:
337,476 mi: new IAC
366,445 mi: new EGR valve
384,909 mi: cleaned EGR port, new valve cover gaskets, NGK plugs and coils, PCV valve,
398,744 mi: new timing belt, water pump, idlers, and tensioner (Aisin kit)

This trouble started all of a sudden.

Troubleshooting:
1. I have cleared codes and swapped coils with inconsistent results.
2. Engine still runs rough and triggers codes with open exhaust (catalytic converter removed and rear O2 sensor unplugged). (Every few months was getting a low cat efficiency code so thought maybe the cat had failed.)
3. Unplugging EGR valve made no difference.
4. Measured vacuum at motor mount port. 17" @ idle, 19" @ 2000 rpm (no load)
5. All plugs pulled and inspected and looks ok. (Not something I have lots of experience with but check some spark plug pics on the internet.)
6. Verified 12v to all coils.
7. All coils have same resistance between corresponding terminals (though I have no idea the spec).
8. Disconnected battery for a bit and did the idle re-learn procedure. Still had codes come back after driving.

My mechanic took a brief look at it and couldn't find anything obvious. Said the catalytic converter was good. Also said might be running slightly lean but not sure what he based that on.

Just finished compression test tonight with cheap tester from O'Reilly. Cranked for about 3 seconds 3x/cylinder and averaged the readings.

1: 143#, 2: 154#, 3: 148#, 4: 141#, 5: 146#, 6: 160#

So at this point not sure what else to look at. The injectors are original but I wouldn't expect so many to fail at once. The O2 senors are a bit old.

Very prompt at changing oil/filter every 5000 mi and running Lucas upper cylinder lubricant and injector cleaner in tank every oil change.
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Discussion Starter · #3 ·
"Open exhaust" means that I ran the engine with the catalytic converter removed and nothing in its place (my sons want me to straight pipe it but not going there). So there could not have been a clogged exhaust system since it was out of the picture. There is only one cat on this van. I suspected clogged exhaust, which is why I removed the cat. The atmosphere where I live is not clogged. :)

Besides troubleshooting, one reason for the compression test is to see if the car is worth additional investment. The high numbers indicate that I am doing ok and can spend some money without wasting it. Not sure what's up with cylinder 6 at 160# - seems a bit high.

Late last night as I was rechecking the OBD codes (trying to) I found the battery pretty much failed (only 11.36 V). So time for a new battery. Hopefully a failing battery was dragging down the electrical system and causing weak fuel pump and/or injectors. This would also explain my mechanic saying he thought it was running lean.

I can only hope it will be this easy. Will post later with results.
 

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Misfire Codes. On all cyl. Only a few things could produce those.

Timing - skipped ?
Timing Belt
Valve clearances
Bad/worn cams
OEM Coils?
Head gasket

Others - thin;
Air intake hose cracks.
IAC?
MAF?
Clogged PVC / passages

? ? ?

Sounds like you are all over it.

Good Luck
 

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Discussion Starter · #5 ·
Thank Bear 3142.

Not all cylinders. "Only" 1, 4, 5, & 6. I believe 2 & 3 are closest to the fuel pump. Coincidence?

Compression seems to rule out head gasket.
NGK coils with only 20k miles.
I checked valve lash when I replaced the valve cover gaskets. A few of the valves needed a little bit of tweaking.

Vacuum of 17" - 19" might be a little low (couldn't find spec) but a propane check did not reveal a vacuum leak.

Still working on the theory of a single common cause.

I new battery doesn't fix problem, probably check timing marks.
 

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Discussion Starter · #7 ·
Let the drama continue ...

So, battery is ok, not at spec CCA (725A) but good enough for now (660A). The fact that it keeps going weak/dead when installed remains a puzzle. When I reinstalled it used ammeter and only measured 170mA of draw with everything off. I assume that's ok but not sure. Don't feel like playing the pull-one-fuse-at-a-time game right now.

Found out that OBD won't connect with fuel pump fuse pulled. OBD reader did not work until fuse reinstalled.

Started engine and unplugged ignition coils one at a time at idle. Idle was rough. No codes thrown until I started unplugging. Unplugging cylinder 1 coil had no effect on rough idle until the engine warmed up. All other cylinders affected idle all the time when unplugged.

Turned off, cleared codes, and took for short test drive and still have no codes. Sigh ... Not that I WANT codes but would rather fix permanently.

So my latest extremely tenuous theory is that removing the battery reset the ECM and that the cyl 1 fuel injector (still original) is intermittently failing but especially when engine is cold. Think I've read elsewhere that one cylinder misfire can trigger code on other cylinders (my theory kind of depends on that).

If anyone has any better ideas I'm listening ...

Thanks ahead of time.
 

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Can't always trust the codes to tell you which cylinder is misfiring- especially with multiple codes. The testing you just did is often referred to as a coil-drop test.

When testing the coils- if the rough idle is unaffected, that coil is misfiring. (wasn't firing before unplugging, still not firing when unplugged)
Unplugging cylinder 1 coil had no effect on rough idle..
If the idle get rougher when you unplug the coil- that coil is ok. (was firing before unplugging, now idle is rougher when unplugged)
All other cylinders affected idle all the time when unplugged.
So your test shows that cylinder #1 is misfiring.. (it could be the coil or the plug that causes the misfire).
..no effect on rough idle until the engine warmed up.
So the idle is ok when the engine is warmed up?

swapped coils with inconsistent results.
If you are just relying on the codes to find the misfire, I'm not surprised. Now that you did the drop test- if you swap coil 1 with coil 5 for example, and the drop test now shows cylinder 5 is the culprit- it's definitely the coil that's bad. But if cylinder 1 is still misfiring- probably that spark plug or injector is the culprit.
 

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Are the intake/exhaust valves in-spec? It can be those or the injectors. Right?
 

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I'm no professional, but good compression numbers leads me to think that they're OK.
I am not an expert either unfortunately. Its the blind leading the blind, deaf and mute here. :D
 
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Discussion Starter · #14 ·
Another update ...

Mentioned last time that I couldn't get the codes to come back. So today, with engine cold, started up and couldn't reproduce previous results with the "coil drop" test. Engine still sounds intermittently rougher than normal at start.

I let the engine warm up and checked the fuel trims using my Autel 539B. No graphs but does capture live data.

I tracked the following data at idle (730 rpm), 1500 rpm, and 2500 rpm under no load:

LONGFT1 (this was pegged at zero all the time so thinking its meaningless)
SHRTFT1
SHRTFT11
SHRTFT12
O2S11
O2S12
MAP

My observations:
Once warmed up, the SHRTFT fuel trims all bounced around 0 as expected at all three rpms. Changing rpms produced expected transients.
MAP showed 7.4 mmHg at idle and 6.5 at 1500 & 2500. Guessing that's ok.
O2S11 voltage was all over the place between 0.155 and 0.820 volts at all rpms. (O2 sensor going bad ???)
O2S12 voltage was very steady at 0.055 volts at 1500 & 2500 rpm. At idle it was all over the place like O2S11.

When I disconnected the motor mount vacuum line the fuel trims all hovered around +5.5%, which would be expected. With vacuum line reconnected, trims went back to 0.

Will try looking at the data under load when I get a chance - might be a few days and not sure what else to do at this point.

Lack of any CEL and smooth running when warm beginning to look like I had a problem that has resolved itself. (until ???)

Might just put new injectors on next years' budget anyway.
 

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Why not try some injector cleaner like Techron Concentrate Plus or another highly rated one?
Lots of miles on those injectors etc?
I might have missed it but did you ever pull the spark plugs immediately when it was running roughly???
If so, were they all equally wet or dry or?
Good job doing your diagnoses, overall.
Best of luck.
Buffalo4
PS: Have an enjoyable holiday weekend.
 

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another "cheap" "remedy" - fuel injectors cleaning by professionals: Remove all injectors and send them to nearby injector cleaning businesses. They usually charge between $18 to $25+ per injector and some even repaint them. You pay shipping to and from. These businesses usually give you a printed report on the flow pattern, amount for each injector, indicating which ones are faulty. Then, you can replace the bad ones. Cheaper than replacing all. Google/search "fuel injector cleaning business". Most Porsche owners use these services. Here's one Fuel Injector Cleaning and Flow Testing Service.
You mentioned that you checked Voltage on O2 sensors. If the voltage is NOT within the specs, they could be replaced (about 40-50 bucks on Rockauto, but only Denso brand). Listen to the others opinions about O2 sensor correct voltage range, etc. (Especially Upstream O2 sensor).
Carbon build-up inside the cylinders (combustion chambers)? Have you considered using a cleaning solution for this purpose only? Can you look inside the cylinders with borescope?
Another thought - I recently had a misfire, too. To fix it, I replaced one coil with a good used one (good - meaning impedance is close to those of other coils), and did a valve job (was not perfect - one valve is noisy, but noise is almost indistinguishable after 70 miles trip). The spark plugs are new. I also poured in valve/FI cleaner (Barryman's) with fresh gas.
 

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Discussion Starter · #18 ·
Happy Thanksgiving!

Thanks to everyone for your suggestions. Answers to a few questions posed:

Replaced coils and plugs with NGK about 20k miles ago. Swapping coils during troubleshooting didn't reveal anything. All coils have the same resistance between corresponding terminals.

I really like the idea of having the injectors cleaned. New o-rings wouldn't hurt. I very consistently run FI cleaner (Lucas) in a tank of gas every oil change and burn at least 3/4 tank before refill. I know this won't fix/prevent everything.

Thanks for the info about O2 sensors. I've heard about using Denso only and that's what I would get if I decide to replace. (I do my part to keep Rock Auto in business.) I believe the first O2 sensor is still original.

I don't have a borescope.

I adjusted valve lash when I replaced the valve cover gaskets. Only a few needed minor adjustment. I've considered pulling the heads and getting them redone at some point. Good compression indicates this is not necessary though might be "nice to have".

Did find a place selling used engines for $600. No idea the shipping. Not ready to bite that off.

As for carbon in the cylinders, this year I used the Seafoam upper cylinder treatment. That should keep carbon down but I have no way to inspect results.

I have not visually inspected the plugs immediately after the issue. Can't do that now anyway since the problem is not occurring.
 

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You can purchase a borescope for 60-70 bucks on ebay or amazon, or even on craigslist with dual cameras - one looking straight, another - at 90 degrees. BUT, get the smallest diameter - I think it was 8mm or so, the older version have thicker diameters and will not fit through spark plug hole. Don't get borescope that plugs into your cell phone - keep tools and entertainment separately.
Below is a picture of my #2 cylinder, which exhibited misfire (before fuel treatment):
Water Astronomical object Tints and shades Road surface Space


After 2 or 3 tankfulls of treatment, I will re-examine the same cylinder and compare conditions before and after.
Borescope is also very useful in inspecting valves, if you think, that they were damaged due to a broken or slipped timing belt.
Happy Thanksgiving!
 

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Discussion Starter · #20 ·
Added about 100 miles of mixed driving today while monitoring fuel trim and MAP.

Under load, fuel trim tended to hover above 0, bouncing between 3-8 or so. The interesting thing was MAP. On level highway with cruise control, MAP fluctuated between 10-22 mmHg. MAP tended to rise with increasing load and fall while coasting. I saw it as high as 28 and as low as about 3.

Anyone know if MAP should fluctuate that much? If not, maybe intermittent vacuum leak; will inspect for that (again) soon.
 
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