Hi folks - I've gone far down the rabbit hole on this one...

I bought a high mileage fit with misfires, replaced all coils and plugs and the random misfire/mult cyl misfire codes went away for a few thousand miles then returned. I then performed a valve adjustment to exact factory specs and it went away for a few thousand miles... then just cyl 4 (P304) returned.

I swapped coils & plugs between 1, 4 and it stayed on 4. I figured something is off on that specific cyl. I replaced all four fuel injectors (why not, they had 200k+ on them) and noted smoother running overall, and gas mileage stayed steady at around 28/35.

With new fuel injectors, coils, plugs, and valve adjustment only cyl 4 continues to misfire occasionally - this tends to happen at idle or coming off idle. Freeze frame info pasted below... any thoughts on where to go next ?

Vehicle Calibration ID: 37805-RME-A140
37850-RCA-A100
UUUUUU Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Load = 91.765 %
Engine Coolant Temperature = 165.2 °F
Fuel Trim Bank 1 Short Term = -0.781 %
Fuel Trim Bank 1 Long Term = -19.531 %
Intake Manifold Pressure = 11.603 psi
Engine RPM = 1,648 rpm
Speed (OBD) = 0 mph
Timing Advance = 3.5 °
Intake Air Temperature = 100.4 °F
Throttle Position(Manifold) = 22.353 %
Run time since engine start = 174 s
EGR Commanded = 0 %
EGR Error = 99.219 %
Fuel Level (From Engine ECU) = 92.941 %
Barometric pressure (from vehicle) = 14.359 psi
Voltage (Control Module) = 12.4 V
Engine Load(Absolute) = 86.275 %
Commanded Equivalence Ratio(lambda) = 0.982
Relative Throttle Position = 14.902 %
Absolute Throttle Position B = 38.039 %
Accelerator PedalPosition D = 36.863 %
Accelerator PedalPosition E = 18.431 %

 

Poor terminal contact within a connector can cause miss.... While the engine is running, try gently wiggling connectors like for the coil and fuel injector on that cylinder?

Compression test?
Decarbon treatment for the valves?

EGR intermittently sticking open, and has some clogged ports in the manifold?


The FF data has a few items that look unusual for sitting still. Were you blipping the gas pedal when it set?

 

EGR error is minimal (100%-99.2%) is caused by wear mark on the EGR valve head (the valve still is not leaking , it just not sitting in its default factory position) so it is not a factor here. I would check the connection for injector harness (under the air box) C-103. On my car it was PLENTY of dust under rubber!
Otherwise the roller on the rocker arm on one of 4 valves can be out of round creating "variable" valve clearance

 

Yeah the FF data looks funny and I honestly can't recall the exact moment, but most of the time when I see the flashing CEL (encountering misfire, getting ready to set code) it's at idle at a light or coming off idle in first. So it's a low RPM issue. Thanks for the new suggestions! Any way to check on the rocker arm? Are they hard to replace on these engines (as a last resort down the road).

 

Set cylinder in question at TDC compression stroke
using permanent marker put a dot on the rocker arm roller
measure the clearances, remove the feeler gage
push on the valve end of the rocker (you gonna hear a click, this will lift the roller of the cam lobe)
using rubber eraser or equivalent device rotate the roller about 180 degrees (marker dot will face down) and re-check the clearance,
If it is "too small" re-adjust the valve
also look for flat spots on the rollers

 

Why haven't you done a compression test yet?

 

Because if compression is known bad, I have to replace some expensive parts. If it's unknown bad I can keep chasing cheap problems .

 

Joking aside, I am a recent transplant to CLT and did not have many/any of my tools for a while. I recently picked up the rest, and will be doing a compression test as part of my upcoming plug gap check/change.

 

Spoken like a true "value shopper".


What's the cost of that cheap price?

 

The 02 sensors on a fit last about 67K miles. Have you replaced them? I like Denso ones, cheaper and better than the NTK OEM ones. Order from sparkplugs.com.

 

Compression test came back consistent across 4 cylinders and the suggested connector was dusty and showed no changed after disconnecting, cleaning and reconnecting... running out of ideas.

 

Try a leak down test, My 07 turned out to have a blown head gasket, and I had a very slight stubble at idle when cold.

Cylinder to TDC, and put about 100PSI through the spark plug hole, radiator cap off, if it bubbles... Life sucks.