i have a 2000 s10 blazer wit a motor out a 96 in it. It started making this weird thumping sound out of the exuast not like a back fire its a thump and when i was try to start it, it was doing some kind of back firing thing from the intake where it sucks air in i put a new fuel pump on it and a new rotor button i dont no what else to try?

 

Check the timing?

 

Cat converter, fuel pressure regulator, fuel filter, Injectors, bad gas? These could also be your problem.

 

I assume it ran good at some time then started acting up. Why did you change fuel pump? Was it for this problem?

Changed rotor but not cap? If the rotor was trash, the cap usually is as well. That can lead to crossfire with those symptoms.. as can installng plug wires wrong.

What happened at the time just before this started? It sounds like either timing or a more basic engine problem.

Seriously, at this level, I dont think you're going to be able to solve it without up close and personal help.

 

check the crank position sensor and the connector going to it, i mean the terminals inside the connector that is, the tend to spread apart slightly over time causing the socket to fail to make contact with the pin on the sensor, believe me i had the same exact thing happen to me, 3 hours of testing wiring all the way up to the controller and beyond ( IN THE RAIN!!! YEAAA!!!)