Hey guys! Been a long time member but never posted before until now.

I drive a 2013 Honda Fit Sport Automatic Transmission with 125k miles on the clock.

I am posting because I am at my wits end with random misfires that usually come on when the engine is under load, when I am merging onto a highway, pulling away, etc... The engine seems to buck, lose power, stutter, shake, etc when regular acceleration is applied. It is quite annoying and sometimes dangerous. If heavy acceleration is applied the engine does not do this and car flies everywhere but I don't like to drive like a maniac all the time.

If I check the $06 with the Scanner, misfires are quite random and can occur on any and all the cylinders. NO check engine light or flashing of any lights on dash as the bucking or loss of power occurs or afterwards.

I followed the advice in this forum and replaced spark plugs and coils, using different high quality units. Currently running NGK Ruthenium plugs and NGK coils. When checking for misfires, they're almost always random and do not point to any cylinder in particular. Have tried 3 different sets of coils and problem persists.

I am at my wits end because of the many different things I have tried to no avail. I don't know what else to do. My dad suggested corroded grounds or corrosion at the ECU but I can't find any obvious signs of either of these. Battery is one year old and both it and the charging system have been tested.

The car has a somewhat comprehensive service history with some recent services.

Under my ownership the car has received:
-Fresh synthetic oil change
-Fresh synthetic AT oil change
-New Ruthenium NGK Spark Plugs
-New NGK Coils
-Throttle Body Clean and Idle Relearn with Scanner
-Valve Adjustment
-New Air Filter
-EGR Clean
-MAF Sensor Clean
-New Denso Upstream 02 Sensor
-Lots of injector cleaner, BG cleaner, etc...
-Premium gas tried as well.
-Checked and cleaned fuel pump filter, no obstructions.
-Checked injectors with Scanner, shutting them off individually.
-EVAP system tested, passed test.
-Ran Lambda Test, all cylinders passed.

Only things that have somewhat come out is that at idle, the engine runs slightly lean, thought O2 sensor was at fault. Replaced O2 sensor, no change. Engine still slightly lean at idle.

Other times when the engine will stutter will be if I make a turn and then try to accelerate coming out of the turn, the car will misfire, stutter, lose power, etc....
Engine idles more or less OK with only slight vibration.

Do any of you have any other suggestions or places to look? I can't get rid of the loss of power and it is driving me absolutely crazy. Any other tests I can try?

Thank you!!!!

 

The things I would start considering with random misfires would be bad gas, bad plugs, bad coils, bad valve adjustment or a faulty map sensor. After reading the things that you've checked/ and or replaced, the thing that comes to my mind is your fuel pump failing? The slightly lean condition at idle, the misfire after making a turn and then acceleration, and a loss of power in acceleration could be symptoms of a bad/ failing fuel pump.

 

Thank you so much, I wanted to figure out a way to check out the fuel pressure coming out of the pump with either live data or one of the modules but I wasn't able to. When I was taking apart the fuel pump I realized how easy it is to replace the pump itself so I might just do that. Thanks for the observation!

 

What kinda scanner are you using? I'm shopping for a mid grade one and looking at autels.

Has your car ever overheated or sat for a long period? Didja take a peek at the timing chain to see if there's any slack, or see any plastic when changing oil?
I know you can use the torque app to monitor throttle position, too!

 

I am currently using the Autodiag Bluetooth Dongle that I bought off Ebay for $79
Comes with a year of full access included, that includes all the bidirectional commands for most makes. I've used the throttle body relearn, the brake purge, EVAP test, Lambda test, EGR test, VTEC test and a few others. Has live data as well but not for fuel pressure.... not sure if it's not a Honda parameter.... Has the basic OBD2 functions as well, that's where I saw the $06 misfire data. You use your phone with it. It's cheap and powerful but once the subscription runs out you kind of have to throw it away because it's pricey.

Car hasn't overheated and has no signs of sitting for long periods. Car has had a pretty mellow life overall. I haven't looked at the chain but don't hear any rattles.

I ordered a new fuel pump which will hopefully be here in a few days so I can test and hopefully report back with positive results.

No plastic in oil when changing it.

Ran the Throttle Body test as well, matches consistently to most computer input, only 1 or 2 degrees difference in a few of the commanded opening settings but nothing major.

Will hopefully be fixed with a new fuel pump.

Thanks again!

 

That's. Actually a pretty good deal! Thank you.

It sounds like you're heading in a good direction and I'm looking forward to an update!

 

Sad to report back by saying that replacing the Fuel Pump has not fixed the problem.
Car is still losing power when accelerating and cutting back, etc, etc...
I have read someone who had similar problems and turned out to be a bad injector. Since replacing the injectors is somewhat time consuming on the Fit, I will probably be replacing all 4 injectors. Anybody have a spare set lying around? Half joking.

Car is still running somewhat lean at idle but no other data is showing any obvious problems, using the scanner. Still having misfires on random cylinders, I will keep an eye out on those now that I have replaced the fuel pump to see if there are any changes.

Thank you guys for helping me out!

 

You can bench test the injectors But none of yours should have an issue if the misfire is random. I suppose it would be possible if the wiring for all 4 was somehow not good. Or if they had obstructed spray holes. I've tested this by putting a few drops of fuel or fuel cleaner in their port, energizing via jumpers to the battery, and blowing through them. You can also set the engine to idle and wiggle the harness at varying points.
I'll look at some troubleshooting procedures in a sec..

You can still check for vacuum leaks, and you can remove or disconnect sensors individually for intake/exhaust to see if the car runs better.

​​​​​​Sorry this isn't the best written response.. I've had a fair bit of experience chasing weird faults, and totally get the feeling that comes with it. I wanna help, so I'll see what I can dig up or make up.

 

Have you checked the speed sensor?

 

If I'm going to get to the point of being able to remove the injectors might as well replace them with an OEM flow matched set that I have already purchased. That way I am not guessing, and I hope it restores some MPGs and some power. I am running out of time and don't have a good bench to test the injectors. I'm in Minnesota and my outside working days are counted.

I am not sure why the engine continues to misfire.

I have taken your advice and have tried unplugging various sensors to see what happens.
Unplugged the MAF and the car started bucking like crazy, so it probably is not that.
When I am into the injectors I will look at the MAP sensor as well.
Can't find a vacuum leak, have done the carb cleaner spray with no results.

I don't have the expertise to read the data to find faults.

How do I check that the vehicle speed sensor is working or not? Would it throw a code?

I'm expecting the injectors in next week and will post here accordingly.

Thanks again!

 

Camshaft sensor?

 

You would think that these major sensors would throw a code when malfunctioning? I think I can check the Camshaft Sensor with my scanner so I'll make sure and check that and the VSS the speed sensor too!

Thanks!

 

Installed new fuel injectors today, not super complicated now that I've removed the intake a few times now.....

Drumroll.......

Car is still running horrible. Stumble, cutting power, misfire, etc felt often between 1,800 and 2,200RPMs.
A little hard to start in the morning, crank maybe 2-3 seconds.

Out of ideas.

Any ideas???

 

Another thought, the O2 sensor?

Usually will throw a code, but not always.

https://www.700r4transmissionhq.com/bad-oxygen-sensor-symptoms-honda-fit/

https://www.wheelsjoint.com/honda-fit-bad-o2-sensor-symptoms-causes-and-diagnosis/

 

Upstream O2 sensor is a brand new Denso unit. No change in behavior after replacement.

Thanks!

 

Sorry, I looked at your list that you have done, but missed that Seems like you have done everything.

 

One last thing, have you checked your pcv valve?

 

Attached to this post is the troubleshooting procedure for random misfire. If you want me to upload any other sections, just ask.

Potential causes listed are:

• Bad Fuel
• Bad Spark Plugs
• Fuel Pressure Regulator
• Fuel Pump
• MAF/IAT Sensor
• VTEC Rocker Arm
• Poor Connection/Loose Terminals at Ignition Coils, Injectors, ECM/PCM

This is assuming that you have Honda's scanner and it can read and test all other relevant systems. If you still have your old spark plugs or recall what condition they were in you may be able to get an idea of the conditions in the combustion chamber.. Apologies if that's kinda basic, I don't mean to be insulting. I believe I've still got my most recent set for comparison. I don't think vacuum leaks will be springing up any time soon unless the hoses are exposed to harsh chemicals or somethin'. Honda used some mighty fine rubber. But if something got left disconnected or poorly connected.. you know. That does sound super unlikely though given the consistency of the fault and how many times you've visited the valve cover now. The fault hasn't changed at all between services rendered, right?
You might try jiggling/inspecting the above mentioned wire connections. How long has your car had a misfire? If this has been going on for a long time, you may have a damaged exhaust catalyst that could restrict exhaust gasses escaping from the engine. If significant though, this could impact engine temp, which should be observable on your scanner. Only bringing up that last bit because of recent experience.

 

Isn't that the procedure for specific codes? He's not getting any codes, unfortunately. And, it sounds like he has replaced almost everything on the list already.

 

@JDFit I dunno what the $06 thing is from his scanner, but I figure these procedures are useful for thinking of some odd stuff, and it matches the fault! Like hey, high fuel pressure caused by an aging regulator was not something that came to mind 😂
If I were this far along, I'd drink a beer, take a hydroxyzine, and get a second opinion from the dealer.