Misfire Battle
 

I have a 2007 Fit with 203K on it. All stock other then a K&N air filter.

Quick backstory:
Last July I had a one time misfire issue and it did occur when it ran very low on gas (was a oops). It threw a Cyl 1, 4 and random misfire (twice) codes in a short time. The plugs had about 70k on them at the time and I replaced them (Denso's) with Hitachi coil packs 1 and 4. I can dig out the part numbers on these if needed) The plugs were in good shape, some carbon, no oil, bad buildup or unusual wear. I am not 100% certain but I think this incident is not related to the mess below...

It ran fine (and constantly getting 36MPG) until late November when it started to misfire on #4 only. P0304 codes. It seems to misfire at around 2500 RPM and up. It will idle all day long just fine. The 2500RPM can be while sitting in neutral or going down the road. It's very consistant, always #4, no randoms. It will also start with a flashing CEL (reader says pending code at the time) then eventually it will set it and the light will stay on solid (confirmed code) I can clear it and it will come right back.

I have done the following (since Nov):
I have swapped around plugs and coil packs with other cylinders and the problem stays with #4. Plugs have some carbon but not excessive, in good shape otherwise.

New fuel injectors on all 4 cylinders

Checked/adjusted valve clearances

Checked compression, around 200psi while cranking.

Replaced intake/exaust valve springs with Honda springs (per 3 recommendations).

It still misfires the same.


On my to do list:
Thorough inspection of the intake and gaskets for damage (quick visuals didnt catch my eye for anything). (per a few recommendations)

Clean out the oil pressure/vtec solenoid and screen. No solenoid codes but wondering if it's theres just enough of a blockage to lower the oil pressure enough that one of the rocker assemblies wont activate, but not enough to trip a low vtec oil pressure code. I did unplug the solenoid to see if it coded any different. It gave the expected vtec codes, but still misfired on #4 only at 2500.

Take it to Honda with a 12pack sitting in the back. I called a dealer today and told him what I've done and he said that I've done about everything he would have tried and is stumped without the car being in front of him. He quoted me a reasonable rate to take a look at it so it may go in this week sometime if I dont get any further.


I'm looking for suggtions on what to do/check next. I have so far kept clear of common systems/areas due to no issues with the other 3 cylinders, and it running "too good" otherwise. It gets the same mileage it has always gotten, has all it's power when the light isnt on. Is there any weight to my weak oil pressure to the rocker assembly theory above?

Not a engine nut but good with research and finding my way around. Have a code reader available and access to about anything else.

Just for giggles, unplug the EGR valve wire connector....and drive it for a while and see if it still sets misfire codes.
It probably will set a code for EGR but ignore for the moment, just drive to see if misfire code still sets.

I unplugged the EGR (didnt giggle..sorry).

No egr codes. It still gave me a misfire in #4.. first one was pending, i turned off/back on to clear it and let it warm up more and it went to a confirmed code the 2nd time. Both were at around 2200-2300 rpms.

My short term fuel trim has been in the +teens to low +20's the whole time i've been fighting this. I did notice with the EGR unplugged it did go down to less then 1 after the engine warmed up. (is this anything?)

EGR error value (and command) were both always at 0 with it unplugged for obvious reasons. The EGR error would go into the high 90's alot with it plugged in. Today it stayed low until I revved it then went to 99-100. I didn't look at it closely before in the past but noticed it at 99 alot, not sure if it was at idle or revved. I do not recall seeing numbers in the EGR command line ever (but havent watched it closely). (and... is this anything?)

Thinking back... I did take the EGR off a while back when I changed out the alternator but it's been running good since that and I haven't disturbed the EGR since.

Just thinking out loud. When you say you replaced the plugs with Densos, you did use iridiums, right, and not some other type of plug?

And when you replaced two coilpacks with the OEM Hitachis, that means there were two that were older and not replaced, right?

It is possible that one of your Hitachi coilpacks is acting up and not firing properly. If you're swapping around older coilpacks, it might not make that much difference in the final outcome if those coilpacks are marginal to begin with. Don't know which set of coilpacks you're on, but at 203K, you might be inching up toward a third set.

Also if you car runs fine at idle, that doesn't mean much because you're essentially putting no stress on it. Rev it to 2500RPMs in neutral and still not much stress except RPMs. Put it under a load (driving) and the situation suddenly changes. 2500RPMs under a driving load is much more taxing than 2500RPMs in neutral or less at idle.

I'm thinking one of two things: bad coilpack (more likely) and bad ECM (less likely but still possible). Outside of replacing your ECM, not sure how I'd test the second.

Infant mortality on an injector.. ?? I've had it happen twice on brand new ones.

Ugly, but if you can't find anything else... Use a ohm meter and test from the injector to the matching ECU pin. Sometimes the connectors go wonky and you won't get a good connection to the ECU.

They are irradium and the same model plug that has been used in the car at least the past 100k miles. I just forgot the number. I think it's the 5358's but don't hold me to it.. need to find the receipt.

Correct.

I replaced the plugs and the #1 and #4 coil packs just after the first hiccup due to rough idle. It did not help the idle so I did not replace the other 2 coil packs. Swapping them around at the time did not change the idle either. The misfire problem that I am having now did not exist at the time either.

Since the misfire problem started I swapped coilpack #3 and #4 (old to the new) and it made no difference. I also grabbed one of my 'old' coil packs and tried it. No difference. I swapped #3 and #4's plug and it made no difference. It was always #4 that misfired no matter what I tried.

The problem always seems to start in the lower 2000's no matter what the situation, sitting or driving. The freeze frame info when it sets a 'confirmed' misfire code is always between 2100 and 2400. It hasn't varied. It will either set a code or flash the CEL when i get to that range for more then a second or so. Quick mash of the pedal wont set the code if I allow it to spin back down below that range.

Hoping not ECM. going to take it in tomorrow night to have it looked at. I have some pinched nerves in my neck and carpal in my hands.. It's been really tearing my hands up.

Since my last post......

I pulled off the EGR valve and it had it's usual carbon caking. I cleaned it off and was able to move the valve by hand now. It's nice and free.

I pulled off the EGR passage cover on the intake and started digging for diamonds. I did not see any blockages but it was nice and dirty inside. Half a can of carb cleaner and a nice black stain on my driveway later it's all cleaned out. I put it back together.. Much smoother idle now, fuel trims are much lower (getting into single digits finally). Still misfires the same. Was really hoping passage #4 was plugged.. oh well.


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dwtaylorpdx:
I had no change of symptoms from old injectors to the new. Quite a long shot but, I've seen worse.

Bummer that new injectors didn't help. Hope it's something simple, and let us know if you get a final diagnosis.

I'm kidof having same probs I have a 2007 Honda fit and last night check engine light came on and started flashing so new sum thing was bad had auto zone hook it up and its misfireing on all cylinders but number two it only has 108000 miles on it anyone no what it could be

Well... This sucks.
 

Update on the misfire...

I took it to a independent shop that is a import specialist.
They determined that the ECU messed up #4's injector and both should be replaced. No ground pulses coming from the ECU for #4 when it does misfire. They also said they see this fairly often on this era. I would need to do this through the dealer.

I called my local dealer and they said $600-800 for a new ECU (depending on my VIN) and about a hour to install and program it. I did not ask about the injector (already know how much). They too have said they see quite a few of ECU failures.

So....

Is there such a thing as a place that repairs these?

The dealer is willing to install junkyard pulled ECU's at my risk and they do see DOA ECU's from the junkyard. Worth a gamble if I can find one? (Anybody got a functioning ECU sitting in a closet collecting dust?)

I see alot of mention of aftermarket ECU's. I'm not looking for a performace car. It's my long trip car (about 700 miles a month shuffling my kid around). Is there any advantage to look that way?

Time to send it out to pasture?

pull the center console out and physically remove the ecu yourself. open up the case and see if there is any burnt or hot spot. Look for any bad soldering.

If you have the patiences, look at the ecu pinout for the injector signals and trace the pins in the ecu to see if anything is out of place.

Another option is the wiring to the injector may be bad. Look at the injector plug itself and see if the pins have come loose. Check the wiring to the pins to make sure you have a solid connection.

I had to order new pins when I swapped injectors in my fit. (went to rdx injectors)

I did get a chance to open it up tonight. The injector driver is bad. It's 1 chip that drives all 4. There is visible damage on the case of it. It's a 4 layer circuit board and I am having trouble finding the part so, it is probably going to be sent out.


I can't tell what took what out first, but I dug out the old injectors that I replaced. 3 of them have a 12 ohm resistance across the terminals and the 4th had a 2 ohm resistance.

I haven't pull the new injector out yet but I did a quick resistance check and it seems to have a lower resistance then the others.

Bottom line of this... if you can't find the misfire issue, check your injector resistance. If one is really low, your ECU is probably damaged too. Hope this helps someone. Thanks for your replies.

If you run long enough with a bad injector it will ruin the driver chip in the ECU if its shorted, or too low resistance.. On cars over 5 years old injector service might be considered a Preventative maintenance item... ?

Well, if I add a valve adjustment to my list, that's pretty much what I am doing. I added seafoam to the gas and oil. Doing an oil change soon. With my commute being about a quarter mile, it'll take a while to get through my tank of gas.... i really do live my life a quarter mile at a time...

I checked the front o2 and there is no spacer. I will pull it off and inspect it.

I also need to find a better way to fasten my k&n filter on. It's just a zip tie. A regular hose clamp wont work the way they did it.

Also, anyone know what to call the little removable panel just under the parking break handle? Mine is missing and I'd love to find one.

And then keys... I just found out how expensive the keys are for the 07. What a pain! This was after spending $80, only to find out that the keys I bought did not have the right chip. I didn't read the fine print. Even though it said it fit a 2007. Jist not the H code keys. I guess I'm stuck with the dealer.

Search for "cheap keys" on this forum there is a whole writeup on how to switch the car to another package that uses the another setup. Yea the EWS not eh 07 is a one hit wonder..

Really? Maybe the car needs taken out and driven once in a while...Super short trips is hard on everything from the oil to the spark plugs. Carbon buildup would be expected after a very short while....especially if you never get the engine all warmed up to operating temperature and keep it there for an extended period of time.


A good bit of high speed freeway driving is beneficial, along with an occasional "floor it and hold it there" acceleration runs to 'blow out the cobwebs' as they used to say (yes it really does help get rid of carbon deposits and clean off the spark plugs) https://cimg2.ibsrv.net/gimg/www.fit...56821a1678.png

Honda online store : 2007 fit console parts

You're welcome. My Fit (now my GFs Fit) was literally the guinea pig we used before the author mcnoople wrote the thread:

https://www.fitfreak.net/forums/1st-generation-gd-01-08/90854-2007-sport-cheaper-factory-key-how.html