i just rebuilt my 4.6 last week and i am having a misfire problem. during the rebuild i did all new bearings, rings, gaskets, heads milled, cylinders honed, crank polished, replaced a bent con rod and all lash adjusters. also all new plugs and wires from ford. the truck is idling rough and lacks power. it seems to run okay at around 2350 rpm and higher. i know i have some exhaust leaks around the flange where the manifolds connect to the y-pipe. i am working on fixing those. i also have an EGR pipe that seems to be broken off inside the fitting. i couldnt break the fitting free while i had it appart so it looks like i am going to be buying a new manifold for the drivers side. i am wondering if the exhaust leaks alone would be enough to cause the misfire. would the leaks cause the O2 sensors to tell the PCM to screw the mixture up bad enough to cause the misfire? the code i am getting right now is 0305 and 1000. i replaced the injector on #5 cylinder still misses. i am burning a decent amount of oil and i was also wondering if the rings are not seated yet and that was letting enough oil into the combustion chambers to cause a problem. it has about 200 miles since the rebuild. i am going to do a compression test this week... i had the IAC overspeed error code also but i cleared that and it has not returned. i dont dectect any obvious vaccum leaks but i am thinking of trying the old ether trick just to be sure. anyone got any ideas... thanks

 

I would suggest that you fix all the little mechanical problems first as they will only confuse the diagnostics. Can the leak in the exhaust cause the misfire? very unlikely. It could be the ignition, coil, plug, wire, etc or the injector. It could even be a valve sticking or the lifter . What year is the truck?

JMC

 

+1

or he used the same engine builder as neal

 

its a 97... i dont think a sticking valve is likely cause i had a valve job done also...

 

do a compression check. a ring could have been installed improperly. or a number of other problems