My 1996 Chevy Surburban 1500 5.7l 2wd will turn over ok when trying to first start, but will not completely engage the full start. But, when I jump My vehicle with another vehicle's battery it will start ok, then. Also, earlier this year some of the wiring which included the STAR system and an over-ride switch had to be taken out. The mechanic said that wiring was causing the initial starting problems. And it was starting ok untell just recently. Is this a mechanical or electrical problem, possibly pertaining to several components. These components or parts might be the ignition control module, the ignition coil, starter or solinoid, distributor cap and rotor, or even a bad battery cable. But I'm not sure which ones, if any are possibly bad since I don; t have any electronic-checking equipment to test with.
Make sure the battery has a full charge. I like to use a digital multimeter to do testing. If the vehicle cranks good but won't start, have a helper crank it while you visually check for spark at the spark plugs. If you have spark everywhere, use a gage and check fuel pressure. Some of the national brand autostores will loan out a fuel pressure gage. You may have to put up a deposit, you get it back when take the gage back.
Check applicable trouble codes. To check codes yourself, you need an obd2 code reader. Your local autostore should sell a code reader. Some of the national brand autostores will check codes for free.
With engine cranking, your system gets battery voltage. Engine running, the system gets alternator voltage, several volts difference.