Hello,
I have a 04, 5.4, 194k miles and recently developed the "expected" intake coolant leak. The intake is the one that is mostly plastic but aluminum across the front of it. The leak is found mostly at the fwd LH side (looking aft) of the engine.
My question is the engine has started a miss (soft jerking) when under a low to moderate load in the last few days but the leak has been there for 2-3 months. It runs fairly smooth at idle and if you step on it, you don't notice it either. Could the rough running be caused but the leaking Manifold or is it most likely something else causing it?

Engine history:
194k miles
Torque converter replaced at 99,500 miles (not engine but more info)
1 park plug and coil replaced around 135k miles. All others are original.
The check engine light is NOT ON.

Thanks

 

If the plugs and coils are original it would be a good time to replace both the plugs and coils. What usually happens, one coil starts to break down and gets replaced then shortly after another coil goes and on and on . If you can, it is usually better if you stick with genuine Motorcraft plugs and coils. It may cost a little more, but in the long run it's worth it !

 

Thanks for the reply Hanky. So your thinking is, the intake manifold leaking coolant (externally) is most likely not the reason for the rough running? Ie: Two different issues.

Thanks

 

If the engine shows no signs of overheating, coolant is probably not getting into the combustion chambers although it could be getting into the intake system. Spark plug appearance should show some indication if that is the case. Usually coolant getting into the intake will cause the plug to have a white coating from anti-freeze. If the plug is black with fuzzy carbon that cyl might be running a little rich possibly due to a misfire condition. Best to take one step at a time and see what you have before drawing any hasty conclusions.

 

Thanks hanky. I replaced the intake manifold to stop the leak and did have a bad coil on the #1 cylinder. She seems to be back to running good again.
Your assistance is greatly appreciated.