I have a 92 Jeep xj 4.0. It's been running fine, but there is a long crank and I have to press the gas to get it to start fully. Since May the fuel pump had been replaced twice, the CPS twice, fuel injectors twice, ignition switch, vacuum lines, ECU, fuel filter twice, new battery (May 2022), IAC motor, and throttle body cleaned. I could never get it to start right up without the extra effort. Now though, it's not starting at all. When I hit the gas sounds like it turns over but then immediately stalled/turns off. I'm probably not using the right terminology so I included videos.
I have an engine code of 17 and 12 (haven't touched the battery though). (Video included in case I'm counting wrong)
Try jumpering the fuel pump ballast resistor. It's the white ceramic block on the drivers fender. Stick a volt meter on there and see if it has any voltage when it stalls.
If jumpering ballast resistor doesn't help (good idea to try for sure from lawson and you can safely do this with no worries as it is there only to reduce noise on the fuel pump), then you are back to basics of how to diagnose a "crank but no start" condition.
You basically need 3 components for the engine to run. You can assume you likely have good compression. That leaves fuel and spark. You need approximately 31 psi of fuel for your 93 4.0 liter engine to start, must be tested with a fuel pressure gauge. I know you replaced the fuel pump but you have to test your way to a solution and never assume anything. A quick and dirty way to test fuel delivery is to put a splash of fuel into the intake; if it starts and runs for a few seconds you have identified a "fuel delivery" problem. Have you ever replaced the fuel pressure regulator? On a 93, it's under the hood, not part of the fuel pump assembly in the gas tank like later model XJs.
For spark, remove a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground and have a buddy crank the engine. You are looking for a strong BLUE, snapping spark. Yellow/orange/white indicates a weak spark which may not be strong enough to start the engine.
For that code 17, (engine staying cold too long), you would likely be looking at a faulty thermostat OR possibly the coolant temp sensor that tells the computer what the coolant temp is. Not impossible that a faulty coolant temp sensor may result in an improper fuel/air mixture making the engine hard to start.
