[FIXED] Cylinder 1 misfire, but car seem to work as usual

Hi!
Car: European Honda Accord 2002 (6th gen., made in UK, 1998-2002)
Engine: F18B2 (1.8 gas), 136 HP, 4 cyl., 16 val.
I have this car 4 years.

I recently started having issues with "misfire on 1st cylinder" and check engine light (CEL) - P0301 (current) and P1399 (pending). It sometimes appears when I start my car while the engine is cold. I live in Poland so recently the temperatures are (0-8 Celsius degrees). The Accord starts easily and the RPMs go to 1500 (as usual) and are steady. Then, of course, after some "heating up" they gradually lower to 750 RPM. But the issue is that the CEL appears just after starting up the engines - in 1-2 minutes. It does not flash. The car in general accelerates very well and have no other issues. The issue started to appear when I changed the air filter and noticed small vacuum leak (one metal band was not screwed in). I did everything very carefully, but after that I've noticed that the engine does not run "evenly" as it did previously after cold starting up (that could be an accident). No issue with RPMs or with acceleration as I mentioned, but during the cold start I sometimes can also notice that the engine is a *little bit* more shaky than usual, it gradually/smoothly goes off after 5-10 seconds. It's hard to say if this "shakiness" is related to CEL and this misfire, because I sometimes think that it runs more steady, but the CEL appears anyway.

What I did recently in general:
- checked shortly vacuum leaks,
- changed spark plugs (especially on 1st cylinder, I changed this one 2-3 times, Denso K20TT),
- checked spark plug wires (I have NGK RC-HE73, mounted 2-3 years ago, quite expensive, internally look as new, the wire for 1st cylinder has ~7kOhm resistance), all have sparks, but I felt (not sure about that) that this one on 1st cylinder had less change in RPMs/steadiness after disconnecting (is it normal?),
- changed distributor cap and rotor,
- fueled some better fuel and added fuel injector cleaner (tonight),
- changed oil, oil filter, air filter,
- disconnected battery for some time, twice,
- cleaned ground wires (using alcohol, then screwed in and then I applied special "grease for high conductivity"),
- the valves adjustment was done about 15-20k km ago.

Could you tell me do you have any ideas what is the cause?
I've heard that P1399 might be related to valves, so I will try to do valve adjustment tomorrow (this time - personally).

I have to mention that this engine was rebuilt a 2 years ago and the head was also rebuilt (including valves).
I have multimeter, OBD scanner and some other tools. I have a friend with a car shop, so I can ask him for more special tools.
I hope I wrote my post correctly (in terms of English language ). I'm a student and a mechanic novice.

Hey croocheck! Your English looks good to me. I'm always a little bit jealous of other vehicle markets, 'cause we never got the F18 in any of our Honda models in the US. Figures. :silly:

This screams valve adjustment issue to me, but you say it was done recently. I don't mean to insult whoever did the adjustment, but it's possible they didn't get it right. Coming from someone who's gotten valve adjustments wrong before. :blush:

The other thing I can think of would be a leaking intake gasket, specifically on the #1 runner. I'm not sure if this has a plastic or metal intake, but a plastic one will use rubber rings for sealing, and are more prone to temp changes. A cracked paper or fiber gasket will usually leak all the time.

One of the quick checks you can do for valve adjustment (or vacuum leak) issues is to watch the MAP sensor voltage at hot idle with no loads. I'm not positive about the F18, but the usual rule of thumb around here is 1.0V or less, preferably .9V. Higher than that suggests a vacuum leak or a tight valve.

So I adjusted all the valves. I'm not sure, but they were VERY tight (at least two or three that I checked). I double checked first cylinder valves. I started the car and it runs on idle a little bit better. For me (as owner for longer time) I think I see the difference, but it is so small that it might be placebo - I think that small vibrations on steering wheel are harder to notice now. So I have to admit that it is better or at least same as before. That's a good sign for me as it was my first valve adjustment. After that adjustment, I also took off ECU fuse to reset it. After that car started pretty well, but to be sure I have to check it at least twice or three times. I hope the check won't reappear.

Thank you for your support and detailed answer, Tyler!

About engine... F18B2 got some "engine of the year" award, but based on my experiences and internet forums, this engine is very prone to oil leaks, high oil consumption. Many people also complain about small vibrations on idle that couldn't fix (there were users that changed many parts, did many things and vibrations still were noticeable). Although I have to say that it's quite dynamic in terms of acceleration (for such big car).

croocheck wrote: Thank you for your support and detailed answer, Tyler!

No problem! Definitely let us know if the PCM is happy. It's my experience (with US market models, anyway) that the code set criteria for the P1399 code is VERY tight. Idled a bit low? P1399. Driver sneezed? P1399. :silly:

About engine... F18B2 got some "engine of the year" award, but based on my experiences and internet forums, this engine is very prone to oil leaks, high oil consumption. Many people also complain about small vibrations on idle that couldn't fix (there were users that changed many parts, did many things and vibrations still were noticeable). Although I have to say that it's quite dynamic in terms of acceleration (for such big car).

I saw the Engine of the Year thing on Wikipedia, very cool. Doing those kind of searches really opens my eyes to how many engines/drivetrains are out there in other markets.

Hi Tyler,

Just reporting that problem is fixed for sure. I haven't done anything after that.

To sum up,
1. Adjusted valves.
2. Reset ECU (again, to be sure).
3. Added some gasoline injector cleaner (yeah, sounds funny) to fuel tank and tanked some better 98 fuel.

I think valves were the issue. In addition to CEL, also small vibrations disappeared immediately after that.

Thanks for help and greetings from Poland!

Sweet! Glad to hear it, sir. I'm slapping a [FIXED] on this one.

Again, I'm unfamiliar with your engine, but it's been my experience that Honda engines of this era were very prone to valve seat recession problems. There's been no fix for it that I'm aware of, other than to keep up on valve adjustments, and replace the head when the adjustment can't compensate any more.

Unfortunately something is still going on... As I mentioned, now my car runs smoothly on idle, but before that I could feel constant (yet a bit irregular, uneven), small vibrations on steering wheel and seat.

Current issue is not very noticeable... Car runs fine, accelerates nicely and MPG is great. I've noticed lately that on (hot) idle I can feel the vibrations (very similarly or same as I used to).

What's more confusing, it runs nice after cold start and the issue itself does not show up every time. To confuse even more: I have noticed that when I rev it up (on idle) for a 2-4 seconds, the small vibrations are gone.

I think these small vibrations are related to slight misfire or bad compression, but I have no ideas what to do now. My intuition tells me that is wrong valve adjustment (after revving the temperature goes higher and the valve clearance is different-better? On the other hand - engine is already hot when it appears). I will probably change spark plugs again or consider changing coil (does it make sense when it runs fine on higher RPMs?).

The most confusing thing is that it (vibrations) stops after revving, ECU does not throw any CEL. I couldn't find same case in the internet. I will try to leave it for 5 minutes with those vibrations and maybe then the CEL will appear.

Could you tell me do you have any ideas?

My two friends also could feel those vibrations (when I asked them) and told that maybe they are not very noticeable, but they could feel it, so that's not just my imagination.

Hot idle in park:

Fuel trims (ST/LT)?
MAP voltage?
Misfire counter?

Bad engine mounts can cause vibrations. If all the data looks good, it's a possibility.

Totally agree with Eric about the mounts. If your Honda's are anything like ours, then the mounts like to tear and cause this kind of vibration. A quick visual of the rubber inserts in the mounts themselves would be the first step.

If you do end up changing mounts, go with the best quality you can find, or OE. Cheap mounts are not worth it!