Hi I have a 03 Navigator 5.4 w/125k and the engine light came on P0308 misfire cylinder 8, it had been running rough at idle only! and somtimes is hard to start after being warm. Replaced the COP and plug on #8 and reset the codes, now a day later the same code is showing and is still rough on idle, also when its periodicly hard to start it smells like gas coming from the exhaust when it starts- Any ideas? Mabye fuel injector?
Thanks

I also pulled the vaccum line from the FPR and didnt see any fuel.

 

Yes, it sounds like the #8 fuel injector is leaking.

 

Is it worth doing an ohm test on that injector? Also would an ohm test even tell if it was leaking?

I'm guessing I'd have to remove the intake manifold to get at the injector or is it possible without.

 

Would a leaking injector throw the P0308 misfire code?

 

Yes, anything that causes a miss in a cylinder will throw a code.

I would agree the injector is likely leaking. There are a couple ways to test for it. Run it, let it get warm. Then let it sit for a while. Pull the plug, and look in the cylinder, if it's wet you know. If you can't get an angle to see. Have someone crank it over and watch and see if fuel sprays out. Please, don't be right over the hole though... (I know, but if I don't say it someone will whine about it)

Other thing is to put a fuel pressure gauge on it. Turn the key on, it will build pressure. Shut it off. If it bleeds the pressure down, that is a possible sign of a leaking injector.

 

Try the vacum tube elbow ... it causes all kinds of codes ..

 

Which vacuum elbow is that

 

He means the one on the back of the intake. Its the pcv tube. However, that would provide a random cylinder misfire, and lean codes. Not a cylinder specific code.

 

Ok, ill do the fuel pressure test and see if it leaks down.
Do you have to remove the intake manifold to access the injectors?