Misfires diagnosis FAQ!

[bigBADbenny]

Misfires diagnosis FAQ

One cylinder misfire:

Check the coilpack loom plug barb isn’t broken, if the plug backs out it can cause continuity issues. Use a new coilpack or ziptie to hold the plug on.

Check spark plug tightness is correct and to torque or turns/angle spec.

Remove and check spark plug colour and gap.

Swapping the affected coilpack with one on a known good one, preferably from the opposite bank may be considered a blind test for a faulty coilpack.

Check coilpack plug boot for powdery white residue from shorting to the head.

Check for oil in the spark plug pocket in the head & cam cover area.

It’s possible for the spring to miss the top of the sparkplug on reinstalling the coilpack.

For non coil on plug engines, run the car in complete darkness with the bonnet open and look for arc sparks around the spark plug leads, boots and coils.

Follow the cel related FSM DTC (diagnostic trouble codes/CEL/check engine light) diagnostics.

viewtopic.php?f=6&t=34980

Log per cylinder misfire or roughness to find the conditions that trigger the CEL.
Iirc the CEL is triggered after a number of misfire events meaning a log will give you a more thorough idea of the exact conditions where misfires are happening.

Make a log with tuning parameters,
off boost is fine, unless you’re diagnosing load or boost related issues.
15minutes plus, street and freeway,
long part-throttle & vacuum pulls…

After ecu reset, some advise to “learn the car in” with an off boost drive with some traffic & freeway cruise.

*share* a link to the csv file using google drive, wetransfer, dropbox etc.

Learning parameters are generally FBCK, FLKC, Fuel Correction (STFT/short term fuel trims) and Fuel Learning (LTFT/long term fuel trim), Knock Sum.

Other essentials parameters for logging are referred to as tuning parameters, but generally vehicle speed, petrol afr, rpm, tps, manifold relative pressure and engine coolant are essential for log clarity.

How to log AP:
https://www.google.com.au/search?q=how+ ... ent=safari

When logging, use tuning parameters:

Logging Parameters for H4DOTC:
From Torqued Performance:
A/F Correction #1(%)
A/F Learning #1(%)
A/F Sensor #1(AFR)
Engine Load (g/rev)
Engine Speed
Feedback Knock Correction
Fine Learning Knock Correction
IAM
Ignition Total Timing
Injector Duty Cycle
Intake Air Temperature
Manifold Absolute Pressure (PSI)
Manifold Relative Pressure(corrected)(PSI)
Mass Airflow (g/s)
Mass Airflow Sensor Voltage
Throttle Opening Angle(%)
Vehicle Speed (mph)
Optional (but mandatory for health check):
VVT angles (L&R)

VVT specific parameters:
Engine Speed
Vehicle Speed (mph) (kph if not logging for a USA based tuner)
VVT angles (L&R)
OCV duty (L&R)
OCV current (L&R)

Logging parameters for H6DO:
From XRT

32bit ECU - H6 3.0R

A/F Correction #1 (%)
A/F Correction #2 (%)
A/F Learning #1 (%)
A/F Learning #2 (%)
A/F Sensor #1 (AFR)
A/F Sensor #2 (AFR)
Accelerator Pedal Angle (%)
Coolant Temperature (C)
Engine Load (Calculated) (g/rev)
Engine Speed (rpm)
Fine Learning Knock Correction (degrees)
IAM (multiplier)
Ignition Total Timing (degrees)
Injector Duty Cycle (%)
Intake Air Temperature (C)
Intake VVT Advance Angle Left (degrees)
Intake VVT Advance Angle Right (degrees)
Learned Ignition Timing (degrees)
Manifold Absolute Pressure (psi)
Mass Airflow (g/s)
Mass Airflow Sensor Voltage (V)
Oil Temperature (C)
Throttle Opening Angle (%)
Vehicle Speed (km/h)


Misfire codes are also generated from discrepancies in crank and cam position timing events plus AFR so bear that in mind during diagnosis.

Single engine bank misfire CELs: eg cyl 1 & 3 or cyl 2 & 3 may be related to AVCS, thus log VVT angles and compare them to rule it out as a cause or contributing factor.

viewtopic.php?f=6&t=36504

Misfires are also related to afr issues, system too rich/lean. As such an inlet pressure test may be a useful health check.

viewtopic.php?f=6&t=36513

These are a few easy tests to do before going deeper looking for issues.