I have been working on a misfire in cylinder 4 but can not seem to find the cause. The truck runs rough at idle and seems to have a bit less punch. The DTC light is on and my 05 CTT is showing 2 fault codes.



P0300: Random / Multiple cylinder misfire detected – Implausible signal, test conditions are not-completed, fault is active and is causing a DTC light



P0304: Cylinder 4 misfire detected – Implausible signal, test conditions are not-completed, fault is currently active and is not causing a DTC light



I have done a few things but none have fixed or moved the problem to anther cylinder. What I have done:



Moved the coil from cylinder 4 to 3: misfire still in cylinder 4



Moved spark plug from cylinder 4 to 3: misfire still in cylinder 4



Also with Durametric connected I can only see misfires in cylinder 4 when looking at actual values no other cylinders show any misfires. This misfire also only shows up when at idle, any application of throttle and the misfire stops until idle is reached again.



Any thoughts as to what to check next? I have tried a search for P0300 and P0304 but nothing beyond coils shows up.

 

I went through something similar.. clearly the code is misleading if you tested the coilpacks and plugs. Next, I would unplug both MAFs and see if the misfiring goes away (Yes, you can drive it in this state in open-loop). If so, then replace the MAFs.

 

Compression test cyl 4.