Car will run sometimes then at other time it will not crank. I have replace computer, ignition module, fuel pressure regulator, and fuel pump. Do you have any suggestions.

the problem is crank ( as in turning over off the starter ) but will not start ( as in continuing to run)
that would mean that there is a problem with the following systems
broken timing belt/ chain
crank/cam position sensors,
no fuel pressure / insufficient fuel pressure ---no fuel, pump , problem pressure regulator ,injector controls
ECM
ignition control module
immobilizer inoperational
try to get closer to the fault area by running the fault codes

ignition components are heating up from resistence caused by age--worn coil is common-havit testd--ignition module 2nd--the injector drivers in the computer 3rd

Something is definitely wrong with this picture. It should only take 2 or 3 seconds for the pump to make correct pressure. Just turning the key to on turns the pump on to pressurize the system, then pump will shut off, maintaining pressure, until the computer gets an engine cranking signal, at which time pump should come back on, and stay running when engine is running.
The only way to check fuel pressure is with a fuel pressure gauge hooked onto the fuel rail. If you check and pressure is correct and doesn't drop right away, the problem is elsewhere, not in the fuel delivery. You said takes a long time before car will crank-is there a problem with the engine cranking over with key in start? That would be an ignition or starting circuit problem, not having anything to do with the fuel pressure.

install pressure gauge and watch when key is turned off to see if pressure drops to zero if so bad drain back valve in fuel pump replace it or deal with it or could be cheap aftermarket pump and has hard time building unnecessary pressure to open poppet valves between before fuel injectors

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This is how your problem is researched in my shop. Out of the box, I'd say that you have a problem with the fuel management system. However, there's a good chance that it's something simple and inexpensive like a clogged fuel pressure regulator or water in the fuel tank.

My second area of concern would be the manifold pressure sensor which is located under the hood, center, rear engine area, above valve cover, mounted in bracket. However, you must remember that these are nothing more than starting points and not guaranteed solutions at this preliminary stage.

First a little background for your edification. You may be aware of all this but we've never done business before and all assumptions are off the table.

For an engine - make that any engine and irrespective of manufacturer - to run, you need three things to happen inside the engine, compression, fuel and ignition, without any one of these components the engine will not run.

• Compression - Engine compression caused by crankshaft rotation and pistons moving up and down inside the engine block. If the timing belt or timing chain fails it will cause the camshaft to become out of correlation with the crankshaft or allow the camshaft to stop rotating. Either of these conditions will cause the engine to lose compression and sometimes cause internal engine damage.
• Fuel Delivery System - The fuel system includes: fuel pump, fuel injectors, pressure regulator, fuel filter and pressure lines. This system is used to supply fuel under pressure to the fuel injection system, the lack of fuel pressure or volume will cause the fuel delivery system to fail and the engine to stall or not start. The fuel pressure regulator has screen that can be removed with a small pick if it is dirty and appears to be clogged. Removing the screen will not affect the operation of the regulator.
• Ignition Spark Delivery System - The ignition system components include: spark plugs, spark plug wires, distributor (if applicable), crankshaft angle sensor, camshaft angle sensor, ignition coil, ignition module, knock sensor and PCM (powertrain control module). The engine relies on the ignition spark to be delivered to the combustion camber at the correct time. If the ignition spark stops or is delivered at the wrong time the engine will not run or run poorly.


Whenever your engine cranks but does not start, runs rough, staggers, sags or cuts off, follow this Troubleshooting Guide. Some of these steps require a code scanner. They are costly but AutoZone will loan you one for FREE.

Most vehicles operate by the same principle; basic troubleshooting procedures apply to most cars.

• Step 1: Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If all fuses test okay continue to the next step.
• Step 2: To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) and the fuses test okay a trouble code scan - borrowed from AutoZone - is needed to identify any system trouble. Use this easy-to-use simple scanner tool to retrieve trouble codes and see if they relate to the specific problem, like a crank angle sensor failure code. If the trouble code present does not pertain to the immediate problem like an EVAP code ignore it until a later time, after the car is running.


NOTE: Scan the system again after the vehicle is running. The reason is that non-related codes can be detected after the engine is running because sometimes false codes can be triggered by the engine not running. Once the engine is running again the code present might cycle and turn itself off. You might say "if the engine doesn't run shouldn't it have a trouble code?" Sometimes conditions occur that will not be detected by the computer, example: if the fuel pump fails the computer cannot detect the failure, so the engine doesn't start and the computer thinks everything is okay with no codes. If no trouble codes are present proceed to the next step.

If you have trouble using the code scanner or interpreting the codes click on the following link and use my access code (carrepair): Free Automotive Repair information for Users of a Code Scanner

All the best

Ben

I would check the ignition module and crank sensor.

If it runs on start fluid and nothing else its obviously a fuel concern fuel pump ,fuel pump relay ,check fuel pressure at the regulator that you replaced.

I have a 90 chevy k1500 350 tbi with same problem! I have traced problem to... after turning on key fuel pump kicks on when u crank it over injectors shoot gas and truck starts! After few seconds injectors stop spraying and truck dies! This can happen many times over and over! Eventually sometimes truck stays running and all is great! I changed ignition module, oil pressure sending unit (which i was told controls gas after vehicle is running) fuel filter, computer, fuel pump relay, I am at a loss now! Hope this helps and hope someone can help me!

You have mentioned that you replaced the O2 sensor. The oxygen sensor is completely ignored by the engine computer while the car is starting, and doesn't come into play at all until the engine warms up completely. Are you sure you have a fuel pressure problem? If so, replacing the O2 sensor would not have any affect.

To be sure you have a fuel pressure problem, you need to measure it. This car does not have a fuel pressure test port, so you need an inline fuel pressure test gauge. To test the pressure, connect an in-line gauge and switch your ignition switch to the "run" position. (Do not start the engine.) The fuel pump should run for two seconds. During this time when the engine is not running, you should have between 41 and 47 PSI of fuel pressure. If you start the engine, the fuel pressure should drop somewhat at idle (maybe somewhere closer to 28-35 PSI). Fuel pressure is regulated according to intake manifold vacuum, so at idle, it should be fairly low, while at higher throttle settings, it should be higher.

From what I gather, your car cranks for a long time before starting. If you suspect low fuel pressure, a defective fuel pump relay could cause that condition. The relay is located in a relay/fuse box under the hood on the driver's side of the car. If the relay fails, the fuel pump can still be energized by the engine oil pressure switch. This switch closes when engine oil pressure reaches ~4PSI. If your engine is not producing 4PSI of oil pressure while cranking, or if it takes a while to reach 4PSI, that would explain your problem.

may not be fuel related,replace crank shaft sensor,if it isnt that ,,,ignition module