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I apologize if I am posting this in a the wrong section over all I am new to the site and stuck for ideas of what to do with my mom's car.
Back story:
The car was purchased second hand and ran fine for the longest time. The vehicle was taken to Honda dealer for routine oil change. The car developed a misfire and they spend many monies and time trying to fix it ultimately they gave up and pushed my parents to take the car back broken. The car was driven the way it was for some time.
After some additional testing was done at a 3rd party shop and some basic parts swapped coils, plugs etc no change, eventually my mother thought it might be a good idea to purchase a new used engine so that was done a local (But different) Honda dealer swapped the two engines we are still getting misfires.
I can replicate the problem on command really easy I just don't know what the issue is.
I have an Autel MK808S so I can run some diag if anyone has any suggestions.
Codes/Faults that come up when scanned:
P0300
P0304
P0405
P0306
The way it replicates is you are driving down the road accelerating at a basic/normal rate then the rpms will hang ever so slightly between 2 to 4th. You can feel the engine has some loss of power and almost feels like it wants to bog, if the engine shifts into 5th then the problem seems to disappear altogether and you get a surge in power all of a sudden and you can feel it for sure. but it if hangs too long or if you try and accelerate your way out of it the misfires happen.
The car also feels like it idles rough, not sure if that would be related to the problem
Doesn't really matter how slow or quick you speed up it seems to want to do it regardless.
This we have replaced on the replacement engine (Wrecker says the engine ran fine before they sold it):
New Spark plugs
New Coils
Test results and things I have done to try and isolate the problem.
Ran it cold no difference, Ran it after a good amount of time to warm up no Diff.
I have run with Bank 1 sensor 1 unplugged to force the system to stay in open loop no difference problem still happens.
The reason I ran it in open loop was to see if the main control board is fine (Still not sure at this point) This was not taken from the doner car but still the original one.
I looked at AF readings for bank 1 and bank 2 simultaneously. Bank 2 tends to deviate somewhat from bank 1 but will deviate a lot while the engine rpms seem to hang right before it shifts gears, and you get that final surge of power then it falls back into line. While I don't doubt that the o2 sensor may be bad it doesn't explain why the problem occurs in open loop when the system is not taking commands from the various sensors.
I know that these accord tend to have a Eco mode issue where they foul the plugs etc etc it have a VCM muzzle on it to keep the Eco from coming on, Problem occurred before the muzzle was installed and happens if it's on it or not.
ST fuel trim and long term fuel trim on bank 2 don't deviate all that much from bank 1. Bank 2 tends to dip short term from a 1.0 reading to as low as 0.77 when the AF reading is high V reading right before it will misfire. (Only way to get it to not do it is either to hope it upshifts soon, or to back off the throttle all together and to get back on it and off and on until you see the AF reading start to oscillate again.
Not sure if this is too much info or if anyone has any thoughts but I'm not sure what to do at this point. The Wrecker is willing to sell the Main control board (Brain) to us, but we don't want to keep sinking more and more money into an 08.Thanks,
Nandor
*Update* The rpms will tend to hang in between 1,500-2,000 rpms while accelerating and it isn't until you gain speed that the rpms stop hanging and you get this feeling of a surge of power. Not sure if that info helps at all.
*****Update***** I did some additional driving of the car to see if I can figure out the problem. About 5 minutes away from our house I had the speedo drop out completely and the RPM go wild. I Nursed the car home and before shutting down the car scanned it for fault codes as the CEL was on.
Ended up getting a P0722 Output Shaft (Countershaft) Speed Sensor (No Signal Input) Called the Honda dealer and ordered the part, cost around $60 swapped out the part in the driveway. Car is now driving great. It also shifts a lot smoother than it used to. All of the previously listed RPM issues are gone.
Problem is solved. I hope this post helps others that may end up having a similar issue.
Thanks,
Nandor
The following user(s) said Thank You: Noah, Chad, Speedy01, Lupe
Well after some much enjoyed time with the car working the problem is back. And back with a vengeance. The car still had the same codes and doesn't have any additional codes at the moment. We originally replaced the countershaft sensor which not only made the code for it go away but also seemed to fix our misfire issue. The problem returned about 3 or 4 months after we thought it was fixed, We have since replaced the input shaft sensor as well thinking it might also be bad. Made no change. We are stuck at this point on what the issue may be.
Just refresh our collective memories here, exactly what codes is it setting now?
I have seen quite a few V6 Honda products with "misfire" like symptoms and no actual misfire codes because of converter shudder. It's weird that changing a input speed sensor would have fixed a misfire that presented with p030x codes
Codes/Faults that come up when scanned:
P0300
P0304
P0405
P0306
We are taking the car to get Honda service to see if there is a possible ECU/PCM Software update as the issue may be software related as the issues has in the past gone away for months at a time. If there is no software update I'm leaning towards getting a used ECU/PCM from a junkyard.
The P0405 may be a bad EGR valve, but could also be the cause of the misfires. I have seen that generation engine with the EGR ports restricted or with the top plate plenum gasket installed upside down. The EGR is then directed to only a couple of cylinders and causes misfires.
I wanted to say thank you to everyone that reached out and offered advice and recommendations. I ended up buying a used ECU from a used 08 accord, swapped it out, programmed in the VIN, the keys and the car is now running like it did when it was first purchased. The original Honda dealer that damaged the car during a routine oil change must have shorted out the ECU in some way as this is the only part that was never changed by anyone that worked on solving the cars issues.
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