My s-10runs ok but when in idle or park but sometimes ( not al the time) when I am driving it likes to backfire and in a sense sounds like a dog growling!!!! (best way toput it) I have done a complete tuneup as well as the fuel filter, I dont know how to test the fuel pressure but someone told me my fuel pump is bad, which i don't know how to change) so how can I tell if it is indeed the fuel pump???????? please help!!! is there a way to tell without test the pressure????