I have a 92 mustang of which i just rebuilt the engine and have gt40p heads. The engine only had about 1200 miles on it when a fuel injector o-ring went out and began leaking onto the block. I pulled the upper intake, closed all the vacuum leaks and replaced all the injector o-rings. Now that everything is put back together the engine misses on the lower RPMs under a load. I replaced all spark plugs and the wires are all brand new... before i touched the injectors the car was running fine so I'm wondering if its a faulty injector or not... I would think that if i had a bad injector that the engine would miss all the time and not just on low RPMs. Any advice would be great!! thanks

 

you have a vaccum leak

 

just replaced all vacuum hoses, intake gasket and pcv valve with gromet with no effect... I have no idea what could be causing this