94 Camaro 3.4

Hello everyone,
I just discovered this sight and can't wait to get completely familiar with it.In the mean time, my son has a 94 Camaro with a 3.4 liter engine with a 5 speed manual that was running fine when he came in the house, then the next time he went out to start it it wouldn't start and repeatedly backfired. I suspected the ignition module, the ECM, or the timing chain. The ignition module test good and I replaced the ECM to no avail. Same results. No start and backfiring. I also can not get either the old or new ECM to flash any codes. They will not even flash the 12, 12, 12 codes.Before I get into tearing everything apart to change the timing chain, I need a trouble shooting flow chart of some kind to cover all of the issues that may be causing my problem so that I cover all other options that may be a simple fix but I am not thinking about. Any help will be greatly appreciated................Tom

well yer not gunna get the ses light to flash by jumping the aldl connector you wil;l have to get it scaned how many miles are on it and was any work performed befor it acted up