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

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

P0304:Cylinder 4 misfire detected – Implausible signal, test conditions arenot-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

Alsowith Durametric connected I can only see misfires in cylinder 4 whenlooking at actual values no other cylinders show any misfires. Thismisfire 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.

Edited by RLHornbeck
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Well the problem has been found. I tried the injectors but that was not the problem. The intake manifold gasket had blown out right at cylinder 4. This was a very small break in the gasket which did not give the normal loud pop and bangs but rough idle and low power.

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It was found by accident. While swapping injectors I broke the vent line that runs across the front of the engine and then behind the intake manifold. In order to fix the vent the manifold needed to be removed, which allowed this to be found. I do not think it would have been found if the vent line did not break.

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  • 5 months later...

RL Hornbeck, and others responding,

About finding the issue

Had Cyl 8 and sometimes 1 missfire codes set (P0308/1), and my CTT idled rough. Suspected coils/plugs, but swapping did not help.

Problem got worse and worse. also seemed to notice increased hissing sound while idling... hence gently sprayed Brake Cleaner along intake manifold (near to injector rail) and noticed significant increase in RPM near Cyl 8. this gave me the clue about the intake manifold gasket being blown. Sure enough, after removal of "intake Distributor" it showed missing end corner on Cyl 8....

Wondering: Was this a mistake on my side some 5000 miles ago when I did the coolant line Job?

thanks again to all who share / and donate :-)

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