P0304 Misfire - SOLVED! Computer & Injector Fried
 

My 07 Fit has a consistent misfire.

I was out on a longish trip to pick up another old Pilot. I grabbed a tank of gas close to the destination. 10 minutes later I was there. Bought the car (wife driving pilot, fit running normally) and 5 minutes down the road I get the flashing CEL. Pull over, check fluids, everything checks out so I risk it and drive the 2 hours home with CEL blinking the whole way. Gutless, and noticeable misfire. I thought my EGR might be stuck as this happened recently. Ran the code at home and I got P0304 - misfire on cylinder 4. Checked the EGR just to make sure and it seems good?

My coil packs and plugs are 6 months old, less than 10K kilometers on them. I had a misfire 6 months ago and new Hitachi coil packs and plugs from Rockauto took care of the problem. I swapped coil packs and plugs between cyl 4 and 1 and still get the misfire on cyl 4. I can hear the misfire and the CEL starts flashing as soon as I start accelerating. It still gives me P0304 (Pending fault after only driving a couple of minutes).

I pulled it apart tonight and adjusted the valve lashes. It was very much as expected, with the intake valves being slightly loose and the exhaust valves being very tight. I took my time and got them all within spec. Reassembled and started the car and could hear it instantly. On acceleration the CEL starts flashing and I get P0304 as a pending fault again.

I'm not sure what to do next. Injectors? I haven't done a compression test yet but I can't see it going from perfect to completely F#$%ed instantly and it be a compression issue. Can't help but wonder whether it had something to do with the gas.

FYI - I like to think of myself as a little above novice when it comes to mechanics. I repair small engines and boat motors on the side and I have done a lot of work on vehicles over the years (no formal training). I've got a full shop less the hoist.

This has me stumped.

HELP!!!

You mentioned your next step: Compression test.

Tight valves can burn. Perhaps the longer trip put 'em 'over the edge'. :eek3:

Check the intake for cyl 4 to make sure there are no leaks. A leak could cause the code, misfire, loss of power.

If car passes compression or leak down test remove EGR plate from intake manifold and clean the ports.

Thanks everyone for the interest in my problem!

The compression test results are as follows:
Cyl 1: 180
Cyl 2: 152
Cyl 3: 150
Cyl 4: 205

The results are as disappointing as they are confusing. 50lbs between cylinders and the one with the best compression is misfiring??

Tomorrow I will try to clean the EGR channels, but I don't know how the EGR system could be the problem when it is misfiring on idle with a cold engine (it is my understanding that the EGR valve would remain closed in this situation). I'm willing to try anything!

Also: how do I check the intake for leaks? When I had it off I inspected gaskets and they were intact and pliable.

Assuming compression test is performed correctly (for me it never shows head gasket leaks) and cylinder 4 is the one closest to transmission,
Take it to the emission station with 5 gas analyzer.
A) if exhaust shows low hydrocarbons and high O2 content, injector #4 is not working for whatever reason
B) If exhaust shows high hydrocarbons and high O2 content fuel is getting into cylinder 4 but is not ignited
If EGR is niot fully closed and holes for cylinders 1-3 are plugged up all exhaust will go into cylinder 1 diluting the charge (will cause situation B

Thanks again for the continued attention to my problem.

I peeled the car apart again tonight. I cleaned the EGR channels out. They were very clogged but nothing was blocked completely. Next I pulled the injectors. They were quite difficult to retrieve and i cut myself on the aluminum intake gasket. I tried to clean around them first but some dirt still dropped down. After the first one I started pushing rags in below to catch the dirt. Lesson learned.

Visually the injectors and o rings looked good. I measured the resistance across the terminals and got the following:
Cyl 1: 10.2ohms
Cyl 2: 10.2ohms
Cyl 3: 10.2ohms
Cyl 4: 1.2ohms

Needless to say I was pretty pleased to find a significant difference on the cylinder that is misfiring. I'll pick up another injector tomorrow and pray my problems are solved.

Great finding!! Assuming the ohmmeter probes did not accidentally touched each other during the test, shorted injectors not quite that common! (they mostly getting clogged up or rarely open)
This is a second situation known to me that injectors are in fault (one user had high idle rpm and code P0172-rich- due to the leaking injectors
The car I was stripping on the junk yard had injectors removed. Too bad I could not open this low resistance injector to check.
PS I've recently fixed 2006 Acura with broken timing belt and valves were NOT bent despite interference design (I pulled valve covers and rocker arms and checked all valve heights)

Video how to change injectors is here

Another test for injectors is to touch them with screwdriver (or mechanic stethoscope) and listen for consistent clicking (ticking) sound

Wow.

It never ceases to amaze me what cars look like in parts of the world where they are not soaked in saltwater for half the year. Is that your video? Imagine every single bolt on the car has enough rust that sockets are hard to fit over the head. Now imagine trying to remove those bolts! Oh, the joys of road salt.

At any rate, thanks again for your help. I've already got the injectors out, I'm just waiting on the new part coming in. I'm not really sure why I even took them out when I could have just confirmed the #4 injector was faulty without removing the other 3. Ah well. And yes, I'm certain the probes didn't touch as I tested them all several times to ensure I wasn't hallucinating out of desperation.

I've had misfires in the past on this vehicle and others, but they have always intermittent. This one is very clearly a dead cylinder. A faulty injector is a good explanation for this and I'm hoping all goes well after reassembly and I'm back on the road.

Also: interesting to hear the interference head did not result in valve damage. Was it an MDX? My wife drives a Pilot. We recently (last week) bought another Pilot due to blow-by on one cylinder resulting in extreme oil consumption (and a grocery list of other issues). I tried to drive the old Pilot to work yesterday (since my Fit is apart in the garage) and it seized before I got there. Probably should have checked the oil before I left!!!

No I found this video on YT. The dealer's mechanic (!) told him to replace injectors because car was dying cold (this most likely caused by tight valve clearances) so instead of checking the valve lash like you did , he swapped injectors...
The car was 2006 TL with high mileage. The belt was eaten away and snapped during cranking, causing no start condition .I posted the article attached below (with some sarcasm in the text) on AcuraZine forum with skeptical replies, probably from the people who never fixed something challenging by themselves

A very thorough and detailed report. This is why I always consult the internet hive-mind prior to undertaking new work. I'm sure your post will prove helpful for any backyard mechanic looking to do timing work. Do you want a Pilot?? I have one cheap, might have motor issues ;)

I wish I could cut defective injector open and see how it can short out. The next thing to hope that the shorted out injector did not fry switching transistor inside of the PCM . Open injector will only mess up the fuel delivery while shorted one increases the current trough the circuit (1987 and older Toyotas) had "power resistor" in series with injectors for this reason

Oh fantastic. I was hoping there would be further problems. Perhaps this is why the car didn't throw a code related to the injector?

I could cut the injector open for you but I'm afraid I've damaged it further already. I thought I would hook it up to 12V and listen for the clicking noise. I put alligator clips on the leads and hooked the pos side to a battery. I then tapped the wire from the neg side on the neg pole of a battery. I saw a spark but heard no click. The next time, there was no spark and no click. The ohmmeter now shows an open circuit between the two leads.

Maybe it doesn't receive 12V or maybe I somehow reversed the polarity? I'm not sure.

Again, I'm just praying that when the new injector is in, the car runs normally!!

For future testing of automotive solenoid valves and even cooling fans, fresh alkaline 9 volt battery should be sufficient and safe. For testing gas pumps, electric windows, power seats and wiper motors 9 volt battery pack from cordless drill is good enough. One time I tested 87 Cressida gas pump power source with cordless drill (the drill did not run , turned out to be bad connector on the ground wire).

Remanufactured injector came in today. Showed 10.0 ohms across terminals. It did not help.

After installing it I got P0113 and P0108 instantly. I cleared them and wiggled connections to intake and throttle body. Started car again and they did not reappear. Misfire did not change.

Test light shows both sides of injector plug grounded on cyl 4 with key off. One side grounded on good cylinders. Cyl 4 shows 12v across cyl 4 plug with key on vs 0v on good cylinders.

with key on cyl 4 plug shows one side grounded one side hot. Good cyl shows one side hot and nothing grounded.

ECM or wiring?

With motor running, screwdriver stethoscope gives audible click on functioning cyls but cyl 4 is silent

P0113 and P0108 were set when connectors got unplugged (if removed within an hour after turning engine off) no problem is here.
The less time consuming test is to locate signal wire near PCM for injector 4 and unplug it
If this makes test result same as the rest of injectors the PCM has shorted switching transistor (I wish, I'll know where to find it on the circuit board)
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