Stopped firing on one cylinder (again!) - ECM Issues
 

Hi Fit Freaks, long time listener, first time poster here.

My 2010 Fit has 130k miles on it. Always well maintained and never any problems. I recently had an issue with a rough (cold) idle and poor gas mileage. Brought it to my mechanic who swapped spark plugs which were already not old, checked the valve clearances (said they were all within spec), and a few other little things which resulted in the idle and MPG issues going away.

Fast forward a week and it suddenly stops firing on one of the cylinders. Engine code thrown confirms this and after checking the coil, injector and continuity to the source of the impulse my mechanic thinks its the ECM. We swap in a used ECM and have the dealer flash it and we're firing on 4 cylinders now :wiggle:.... BUT the rough idle is somehow back and the dealer's diagnosis is a high MAP reading and probably tight valves.

I agree to take the car back for a little while because we've been without it for 3 weeks now and we need to return my father's loaner car. The idle even gets a little better. BUT today, a little over a week later, my wife was out driving and AGAIN it suddenly drops down to firing on 3 cylinders. :mad:

I'm ready to take it straight to a dealer or someone who specializes in Hondas but before I do I'd like to be armed with a little knowledge. What could this be? Can something cause repeated damage of an ECM that just affect the impulse to one cylinder? Is there a separate problem that the replacement ECM just masked? HALP!

Try moving each of your coil packs one over (or just the one affected if you know which one) to see if the misfire changes cylinders. Coil pack failures are fairly common.

If that does nothing try the same with injectors.

Replacing the ECM is just goofy, that's an exceptionally rare failure and even when it does fail it tends to be all or nothing.

Thanks for that advice.

As it turns out, the dealer is saying the #3 injector was bad and was causing a short which was in turn frying the PCM. Now that they determined that and replaced the injector we have to replace the PCM yet again (now on third one) and that should in theory sort it all out. I sure hope so. This is starting to cost a lot.

Ouch! Sorry for your troubles!

Even injector failures are rare AFAIK.

If you're not already, I suggest only running top tier fuel.