I have a 2008 Honda Fit. I'm the only owner and have been diligent about its upkeep. It as kept me moving through many a long haul trip. In the last year I've been chasing down a misfire issue with my (trusted) Mechanic and wanted to see if anyone here could confirm or suggest an issue which has us stumped because I'm about to try and sell it (family expanding and it's hard to get two car seats and a person in he back).

So we've have the 3 cylinder misfiring on and off for a year. We've replaced the plugs, the fuel coils, checked sensors, cleaned any potential gunk that might be causing a misfire. Essentially we've ruled out anything mechanical being wrong with the car.

In tracking it over time, we did notice it happens more in the winter, and the light stays off if the engine is allowed to entirely get to warm before putting it in gear. Until then it's stinky, and idles rough, but once it is warm you'd never know anything was wrong with it. My mechanic had another fit of the same vintage which he saw something similar on, but that car just wouldn't start if it was cold.

So we THINK it's the computer and that it's malfunctioned so that cold starts are not getting the right fuel mixture and that it's causing a misfire. So as long as we warm it up in the winter it behaves, but he thinks that if it is the computer and I wanted to fix it, that I should bring it to Honda. He doesn't want to take my money to do something which wouldn't be any cheaper than the dealer and thinks that doing anything with the computer shouldn't be done by someone who isn't a Honda tech. So we haven't touched it, and it ran fine all summer.

It's starting to cool off, and we're looking to sell, so its on my mind again. I want to address it instead of selling it and explaining this issue and having the buyer go through the process of isolating this issue again.
My question is this... does this theory (which we haven't tested, it's just all that's left really) make sense? Like I said, my mechanic is great and honest, and I'd imagine if he wasn't he'd be getting me to keep binging it in. But I also don't want to go through the whole issue with Honda as well.

Thoughts?

 

Anytime someone thinks the PCM is the problem, 99.99% of the time that's the wrong answer.

Compression test, hot first then again stone cold (hopefully cold enough it would be a problem).

Do valve adjustment. Cold.

Swap fuel injectors between #3 and another cylinder, see if misfire follows the injector.

 

What brand of ignition coils were used?
IMHO even Hitachi 0053 coils are not equal to Hitachi coils that are going to the dealership.
(I could be wrong on this)
There is a possibility of oxidized wire connectors in terminal blocks, or ignition coil relay itself (in the fuse box)

 

Compression test was fine, It stays at the three Cylinder. Plugs, Coils, injectors all checked and/or replaced. The issue can only be recreated below freezing. There is a slight under powered issue in reverse before warm the rest of the year, but it doesn't kick an error unless it has gone below zero. Mechanic checked at drop off and after leaving it outside overnight in Toronto in Feb and couldn't find anything that should mechanically cause the misfire.

 

Doctor J, I'd have to go back to check on brand. Electircal was all lean up after having to take out a POS aftermarket DRL module required for the import from the US to Canada. So that should all b good, but I can check it out.

 

I'd get the valves adjusted, for sure.

The clearances are surely different between a cold and warm engine, so that's when you see the issue.


++++++++++++

doctor J, what leads you to suspect this?

 

Checked the maintenance records. On April first all the coils were tested and swapped after being replaced the previous month (along with plugs). At that service the injectors, ect sensor, and compression test all checked out OK both warm on drop-off and first thing after the overnight. The injectors were also cleaned and we started using premium to avoid fuel additive build up (which came out as a $$ wash with improved milage actually).

So you're recommending to do a valve adjustment on a valve where there is no (measurable) compression issue?

 

Yes.

If the valve is closing properly (seat is sealing OK) the compression test result will be GOOD.

If the valve is too tight, it will open, but inadequately. As the engine warms, it expands, which is enough to eliminate the misfire (for now).

We have checked/adjusted the valves on our '07 twice (~ every 60K miles) and the exhausts have been out of spec (tight) each time.

PS, a tight valve is NOT noisy. (Just in case you have read in the Service Schedule to 'Adjust Valves Only If Noisy')

Honda recommends to check them every 100,000 - 110,000 miles, but on the 1.5L, this is not soon enough.

 

The car is not as fast at hard acceleration as it used to be with original coils before one started to miss. I saw it right after replacement of all four.
If my car will be over 150 kmi, I would probably not see the difference but at 68 k it shows.