Car starts but won't stay running. 4.6 doc v8 didstributerless ignition fuel injected

May have drawn sediment up into the fuel system. Is it carb or fuel injection ?

run fault codes and check for MAF/MAP and VAF sensor problems

, like it ain't gettin fuel; probabley a fuel pump or fuel injecter, fuel filter, something along those lines. Start with the filter its cheapest

long shot guess, but a dam good one is your coil is bad. I'm 99.9 percent sure. Or coil wire bad

have alternator tested

Spray starting fluid into the air intake of the engine, if it starts and you have fuel pressure you have no injection or injector pulse as we call it. Check ECM fuse one and two for continuity if it starts with fluid..

It won't die when pulling the relay because it has another power path to the fuel pump through the oil pressure switch . Fuel Pump Electrical Circuits Description and Operation watch this video on fuel pump control , shows chrysler first , ford ,then gm . wait for gm an he explains the oil pressure switch . Plus when it won't start ,don't guess or theorize ! Test what's missing ? check for spark , no spark check ignition system , coil's , ignition module , crank sensor etc... has spark ,do a fuel pressure test etc... don't think computer , when it won't start does the check engine light come on with the key on run not start . If light is lit ,nothing wrong with the cumputer . If want to fix cars you really should take some automotive classes . Test don't guess .Watch some other videos crank no start videos etc...

It has nothing to do with ECU and immobiliser even if you turn your ECU OFF your car will start and will your but not properly without CPU your car will work in emergency mode. try finding Idle sensors and check them if they are ok

Sounds like the fuel supply through is inadequate. That is a Want-to-be fuel injection system that uses a relay to enrichen the gas mixture.

Solution could be a container of fuel system cleaner, and a spray or two of carb cleaner in the injector.

Other causes could be:
Failure of the "choke" to richen the gas mixture
Vacuum line leakage.
Fuel filter becoming clogged

These kinds of troubles should show as a fault on the engine computer. Rent your own scanner and have someone watch it while you try to drive the car. The primary thing you are looking for is whether it is a fuel or ignition problem--sudden stops point to ignition failures as fuel problems usually stumble to a stop. I'm assuming that the engine uses throttle-body fuel injection rather than direct multi-port injection. With throttle body injection, only one injector is involved, and it could cause sudden engine stoppage if the injector solenoid coil opens or loses operating signals when hot. An intermittent crankshaft position sensor or camshaft position sensor can cause these problems. I assume that the engine never exceeds the normal operating temperature. An ignition problem could involve any component of the ignition circuitry including 12 volt supply, but not the spark plugs or plug wiring.