Mitsubishi Triton MK 2005 – 6G72 V6 3.0L Petrol – Miss firing

Vehicle Symptoms – Miss firing and check engine light on.

The vehicle was driven into the workshop and the vehicle was miss firing, sure we found that when cyl 2. spark plug lead was removed from the coil the engine would not change its roughness and that by removing that coil lead from that coil that was the cylinder that was not pushing the piston from a firing event.

the scan tool was set up and codes checked just to check what fault codes could be submitted by the engine ecu for data that may help
Code 41 – Injector Fault
Other Code Tps Fault. live data checked closed position was 0.258 volts where 0.45 volts is the target.

We scoped the cylinder 2 injector wires and found that the injector is operating from the ecu. This engine to do any thing is a mission to remove the inlet manifold, so you want to make sure you know what your getting into before you remove it

Compression Testing

No problem we decided to carry out a relative compression test to rule out a cylinder miss fire due to compression loss.

that rules out main source of missfire there is no way i can explain how an engine feels by reading this post but the missfire was all the way through the rev range.
However comp is good on to next issue.

Checking Secondary ignition waveform

A comparision wave form was taken from a good cylinder and cyl2 bad cylinder to show the difference between good and bad, i have read about this type of waveform before but never seen it, So we had to do some digging in ignition wave form books to help with the memory loss.

left side is bad right side is good (left is high resistance)
the main thing i learned here is that once the initial high voltage spike goes up it must also come right back down and oscillate if no there is not a constant connection from spark plug to coil. ( hence high resistance)

After taking a history lesson on what i had learned years ago, i looked and looked at this, and the only reason i could come up with is either shorting out of the spark plug tube or a faulty spark plug.

Now we had a reason to open up the inlet manifold and delve into the many bolts

with the passengers bank leads and spark plugs out, The images show Cyl 2 as having a partial misfire even though the cylinder was completely dead. (explanation will come)

cylinder 2 spark plug and cylinder 4 spark plug bad/good

This is something i have not done in a very long time measured the resistance of spark plugs,

a good cylinder
A bad Spark Plug

I remember something back from aircraft days if the spark plugs where over 5000 ohms they need to go,
all of the other 5 measured 4.64 K Ohms and the bad one 5.27k Ohms, this is not a huge difference but it might be the high resistance im looking for………

I sat over night and pondered the thought, there has to be something more……

High Voltage spark leakage through spark plug tube.

I had looked the end of the spark plug and there was no mark, the end of the ignition lead had a white short marks to say it is tracking, i had put the spark plug into the lead and the lead did not click onto the spark plug,
This was the high resistance i was looking for…………
The HT Lead was not fixed in the spark plug tube and was being pushed up inside the tube not clicking onto the spark plug.

Spark Plug Boot

Refit and Test

Inlet manifold refit with new leads set and 1 New Spark,
The engine started and had a slight hesitation and then started to pick up and smoothen out the ignition waveform was checked and spot on no misfire coudl be heard, the throttle body and TPS adjusted codes cleared and test driven with sucess.

This is Far from a code 41 injector fault. This fault coming in this vehicle was due to the high voltage spikes going into the ecu and tricking the ECU’s logic as it could not work out the affected cylinder, being a Waste spark ignition system it could not assign cylinder misfire fault code.

Comments for this post are closed.