Humm....can't say that I've seen that cause a miss fire....but I learn something new every day.

What happens if you pull the hose that leads to the intake and plug it, run the car?

 

I took the hose between the intake manifold and the EVAP purge solenoid off and capped both ends. When I ran the engine, I had the noise. I then turned the engine off and also removed the electrical connection on the EVAP purge solenoid and started the engine. No noise. I did not disconect the other vacuum hose connecting the solenoid to EVAP service port and whatever else is downstream on that line. After the tests, I reconnected everything and cleared the codes. After driving, the misfire codes are now back.

While I am not certain of it, it now seems to me that this is likely related to whatever is causing the misfire codes, but is probably not what is causing them. At least now we know that the noise isn't caused by a valve or a fuel injector.

Now what?

 

I just removed intake manifold on my Acura MDX (3.5L V6) to replace knock sensor and harness. Yours should be similar. Knock sensor harness looked to be chewed up by rodent camping in the space between engine banks. It was not too difficult to remove intake manifold. Removing the fuel injectors on front and rear is moderately difficult. I removed front injectors for access. Rear would have been slightly more difficult.

More tests before cleaning injectors would be to check Long Term Fuel Trim for any imbalance (hi or lo).

You might also clear the check engine code and see what happens. You never answered my question about missing; all the time, cold and clears when warm?

good luck

 

How do you check the fuel trim?

I reset the codes today and the misfire codes returned.

The missing doesn't seem too bad. I can't really say that there is any noticeable pattern.

 

The reason I ask is that multiple misfires on all cylinders would generally prevent any use or even starting. If it's missing all the time, the misses must be intermittent to allow use.

Many obd2 scanners allow monitoring of key sensor inputs/outputs. LTFT is one of those. LTFT will show if there is any trend in fuel supply; either adding fuel or subtracting fuel to try to balance fuel/air ratio. A simple obd2 code reader will not do this.

EGR system is another possibility, but absence of any codes related to EGR makes this less likely than fuel problem.

good luck

 

For code P0305 here is some data (mostly related to fuel trim since this is what you asked about): 2258 rpm; Inlet Air Temp 141 degrees (doesn't this seem hot?); Short Term Fuel Trim1 8.5%; Long term Fuel Trim 1 0%; Short Term Fuel trim 2 25%; Short term fuel trim 3 -100.6; Long term fuel trim 4 -100.6%; Short term Fuel Trim 4 -100.6%. The car was traveling 20 mph when the code was happened.

On the Emissions log since the las t clearing the only thing noteworthly is that the EVAP system monitor shows incomplete.

There is a lot more data there. I can pull whatever pieces you feel are useful.

 

Are there any event data captured for the DTC? Usually same parameters as monitored.

LTFT & STFT of 100 % is confusing. I've never seen this high. I would have thought this would set a lean code (adding lot's of fuel to balance air/fuel ratio).

good luck

 

Actually the 100%s have a negative sign in front of them.

After seeing this data, I'm not sure which direction to head now. What direction does it tell us to go?

 

The bulletin for the ECM

04-042 V6 03-04 misfire MIL. - Drive Accord Honda Forums

says that it only applys to codes which occured at engine speeds above 4,000 rpm. So for this misfire at least it doesn't apply.

 

Are there LTFT's for each cylinder, 1-6. I'm only familiar w/ single LTFT for all 4-cylinders. It might be possible to manage individual LTFT's for each cylinder. Perhaps these a sequential values at a time step?

This amount of LTFT (-100%) would suggest large non-commanded (not from FI's) fuel entry. I've heard of this from fuel pressure regulator diaphgram leaking allowing fuel to be pulled into intake through the vacuum reference line.

However, the V6 Accord pressure regulator is in fuel pump assy in fuel tank and does not have a vacuum reference. Excess fuel pressure might cause this symptom. Fuel pressure measurement would be required. Frankly this seems unlikely.

Perhaps a leaky or sticking FI might cause excess fuel.

Have you listened to exhaust and can hear misses regularly or intermittently?

good luck