I have a 98 silverado with a 5.7. It is hard to start and backfires through the intake and exhaust. The fuel pump has already been replaced and im wondering if timing is an issue here. However a GM tech used the tech 2 to check for codes and no codes were shown about timing. Has anyone had this issue before?

I'm going to take a stab at it being your poppets are leaking/not firing off correctly. This is a common issue with the Vortec injector spider assemblies. Best and easiest course to take is to upgrade to the newer MFI kit. Not exactly cheap. Close to $300 for the entire injector kit.

another common issue is the dist gear wearing out "knife edging". if anyone has ever messed with the dist either it could be out of time because people just stab it in and go if there are no codes but it could be as much as 20 deg off before you get the 1345 code. they have to be set with a tech 2 or higher end scanner that does cam retard. i think the first thing i would check is fuel pressure, it should be 58ish and stay there, if it goes away its likely the fuel pressure regulator which is attached to the poppets that mike was talking about and the mpfi kit has the new FPR

Ok little history on this truck, its actually my father in laws he just bought it running as is. He replaced the fuel pump and i did check it with a fuel pressure gauge and pressure did hold. Checked the plugs and they were fouled out. Dont think anyone has messed with the distributor cause doesnt look like it has been taken out. And it does look like it is getting spark to the plug but still not firing off. Before the fuel pump was changed out the truck would run but would backfire, after the pump was changed truck wont start. Is their any way to check the poppets just to make sure?

when you get the problem with the poppets it leaks more fuel into the cylinders than supposed to. i was getting rich codes and it would stall if you were at a red light too long. if you have a live data scanner you can tell if the fuel trims are messed up or the timing advance but i dont know if you dont how to tell if the timing is off or the fuel. i just use a 5 dollar program for android called torque pro and a 25 dollar obd2/bluetooth adapter. best 30 bucks i have spent because it saves a ton of guessing

I'm with Justin. Having the ability or access to scan live data would be real helpful in this case. What your needing to do is scan for your Long Term Fuel Trims on both banks.