Will not start

What is the symptom? What parts were replaced, and what led you to them?

You have a crank/no-start problem; not a starter system problem. That correlates with the parts you listed.

The first concern is with the new flywheel or flex plate. I suspect that is where the crankshaft position sensor sits. If your engine uses notches on a ring, those are what are detected by the sensor. It is common to use different numbers of notches, or with different spacing, for different years. If the Engine Computer does not recognize the signal pulses, it will not know which spark plugs to fire.

The first thing is to determine if you have spark and fuel pressure. Fuel pressure can be misleading because the fuel pump should run for one second when the ignition switch is turned on. That should be enough to get the pressure high enough. What is harder to tell is if the pump resumes running during engine cranking. Instead, start with spark. If that is missing, the best suspect, after the crankshaft position sensor, is the pickup assembly in the distributor. (Be sure the distributor is turning too).

Replacing the Engine Computer, or disconnecting the battery, erased any diagnostic fault codes in the computer. You might want to check them anyway, but often fault codes related to the crank sensor or distributor signals do not set just from cranking the engine. They have a better chance of setting while a stalled engine is coasting to a stop.

The fuel pump must not run when the ignition switch is on if the engine is not rotating. The pump should run for one second when the ignition switch is turned on, then not again until the engine is cranking or running. Does that agree with with what you are finding?

The fuel pump relay is in the fuse box under the hood, left side of engine compartment. The twelve volts to run the relay's coil and contact comes from the PCM power relay. The fastest way to determine if that relay is turning on is to back-probe the white/red wire feeding either bank of fuel injectors. You should find twelve volts there when the engine is cranking.

I found your fuel pump circuit is a little different than most and should be a little easier to work on. There is no reference to the relay being turned on for one second, as I previously stated. The Engine Computer still turns the relay on when the engine is running. It knows that from a signal from the ignition coil. Instead of running for one second to insure pressure is up for starting, your pump relay is turned on by the ignition switch when it is in the "crank" position. That gives us two different conditions to look for.

If the problem is related to the Engine Computer or ignition system, the pump will still run while you are holding the ignition switch in the "crank" position. If the pump never runs, it is not the fault of the computer, because it would still run during cranking.

First verify you have spark. If you do not, we need to see if the PCM power relay is turning on. That sends the twelve volts to supply the fuel pump relay. If the PCM power relay is not turning on, we cannot expect the fuel pump relay to turn on either. Next, I cannot find on the diagram where the ignition switch enters the circuit. The first thing I would try is disabling the starter system, then see if the fuel pump relay turns on when you hold the ignition switch in the "crank" position. If it does, we will have to regroup and think this over some more. You can disable the starter by removing the starter relay, or by placing the gear shift in "reverse" or "drive". I would prefer you remove the relay, just in case the fuel pump is not supposed to run when the transmission is in gear. Basically all we are looking for here is if the fuel pump relay ever turns on, or if you ever find twelve volts at the pump's connector.

Does your car have the optional factory-installed anti-theft system? If it does, that is part of the starter relay circuit and the PCM power relay circuit. Feel the PCM power relay while a helper turns the ignition switch, either to "run" or to "crank". If you do not feel it click, check the "Engine" fuse, number 10, a 15-amp in the "Joint Box". (Not sure where that is). If it does click, check for twelve volts at either white / red wire at the two groups of injectors. If twelve volts does not show up there when that relay clicks, either that relay is defective, or check the "Engine/Injector" fuse in the same main fuse block as the PCM Power relay is in, under the hood. That is a 30-amp fuse that should have twelve volts on both sides all the time.

I realize I am jumping around between circuits. Once we know what is working and what is not, I will be able to focus on one circuit. At this point, until testing proves otherwise, I am leaning toward something related to things being taken apart, like connectors with a push-out or bent terminal, pinched wires, and things like that. I do not suspect a failed computer or sensor problem, at least not yet. Do not overlook wires that were chewed up by a vicious mouse!