I've been trying to get my Fit going for a little while now, first I had po301 and po304 so I checked the compression, and all four tested good, I then replaced the spark plugs and Coils which removed the po301 code but still the same misfire on the fourth cylinder, I'm wondering what I should do next, any help would be greatly appreciated.

 

There is a thread somewhere about a part on the ECU that could go bad and throw the misfire code. Sorry, don't have time right now to find the thread about it.

 

I was trying some simple testing like flipping my injectors around just to be certain that I didn't just have a bad one or something simple, first when I started It, Everything was fine no codes, bad sounds nothing that made me nervous so I let it run it got to temp at idle, went to take it for a test drive and almost instantly it went into limp mode and threw three code, this time po300, po301 and, po304, As far as I'm aware the problem could be like you said the ECU/PCM, the Throttle Body, Valves need adjustment or are damaged or potentially stripped out spark plug threads. Either way entire Ecu is around $60 which I would be willing to try, just would like to have a way of finding out where the problem area is rather than just buying parts until something sticks if that's what I have to do then so be it but again any advice is appreciated.

 

good afternoon I’m the one who figured out the ecm issue.

here is how you can test it it

With the injectors unplugged you should have around 10.3ohms of resistance on the injectors themselves. If your injectors read out of this margin by more than .2-.3 you have a bad injector. The bad news is if your injector is bad so is your ecu, the good news is its repairable. Every injector you swapped into that circuit will also likely be bad or will fail soon and fry the ecu power mosfets.

The injector clips should read 7.3v with key on engine off. More or less means the ecu is bad and the Mosfets need to be replaced the Mosfets themselves are cheap SSD103 is the number of them.

 

Here is a link of how the ecm is tested and repaired. This is the actual ecm from my car repaired by a local electronics repair guy. if you repair the ecm like this then you won’t need to pay Honda to reprogram a new one for you. Getting it open is the hard part, but once you do it’s forever serviceable.