Okay guys I have stumped a mechanic and myself with this one. I have a 1989 gmc sierra c1500 5.7L. It has brand new fuel pump, fuel sending unit, and tank. I put a working throttle body on, used old injectors since they seemed to work. I also changed oil before hand turning then engine. (It set up for six years) I also replaced spark plugs with Bosch plugs. The ignition cylinder was missing and we used needle nose pliers to crank till we put one in. The distributor had a bad reluctor so I had it replaced by a auto shop after having trouble with changing it, it now has a accel distributor. I changed the battery terminal cables after old ones were dry rotted. I replace the hose running next to the radiator water hose running into the firewall, (hose replaced ran from firewall to top of engine next to distributor housing) I checked oil after distributor change to make sure it was good and then fired it up it ran good till it got hot and shut off I replaced another hose and put water back into radiator solved the heat problem. Now it cranks up runs for a few minutes while quietly back firing and it does this rather it'* idling or giving gas. I checked to make sure I didn't have a blown head gasket and I didn't. To no prevail the spark still look brand new no water, but the oil was now pitch black (wth type of moment lol) I couldn't find out what was wrong with it after this, but it does the same thing everytime. I have no idea what'* wrong. Please help!!!