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Here are the usual suspects:
stuck fuel valve/float valve in the carburetor.
clogged fuel filter. or fuel line.
defective fuel pump.
electric fuel pump may be just a blown fuse, or wiring problem. good hunting.
No kill switch. You may have a fuel pump pressure issue, it may being losing pressure after shut down due to a faulty fuel pump check valve. Do a fuel pressure leakdown test, start the engine with a fuel pressure test gage hooked to the test port on the fuel supply rail to the fuel injectors, looks like a tire valve. Start the engine and run it and check for leaks at the pressure port to the test gage, repair as needed, once you are sure the test gage is leak free shut the engine down, if the fuel pressure bleeds down very quickly then you need to replace the fuel pump.
You should have a test port on the Fuel Supply rail, use a tool from a local auto parts "Tool Loaner program" where you can borrow tools for free,w/a deposit of course,then follow the steps provided;
MPI Fuel System Pressure Test
The MPI fuel system used in vehicles equipped with a 4.OL engine employs a vacuum balanced pressure regulator. Fuel pressure should be approximately 55-69 kPa (8-10 psi) lower with the vacuum line attached to the regulator than with the vacuum line disconnected. System fuel should be 214 kPa (31 psi) with the vacuum line connected to the regulator and 269 kPa (39 psi) with the vacuum line disconnected. CAUTION: Some fuel may be discharged when connecting fuel gauge to fuel rail.
Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail (Fig. 7).
Remove vacuum line from pressure regulator.
Start the vehicle.
Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi).
Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi).
If fuel pressure is not approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage. CAUTION: Fuel pressure will rise to as much as 655 kPa (95 psi) when the fuel return tine is pinched shut, shut engine down immediately after pinching oft fuel return line.
If fuel pressure is low, momentarily pinch shut the hose section of the fuel return line. If fuel pressure remains low, inspect the fuel supply line, fuel filter, and fuel rail inlet for blockage. If fuel pressure rises replace fuel pressure regulator.
If fuel pressure is above specifications, inspect the fuel return line for kinks and blockage.
Remove the cap from the pressure test port in the fuel rail.
Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to the pressure fitting on the fuel rail (Fig. 7).
Start the vehicle. Pressure should be approxi- mately 214 kPa (31 psi) with the vacuum hose connected to the pressure regulator and 269 kPa (39 psi) with the vacuum hose removed from the pressure regulator.
If the pressure is not to specification, check the following before replacing the fuel pressure regulator:
4a - Inspect the fuel supply and return lines/hoses for kinks or restricting bends
4b - Check the fuel pump flow rate. A good fuel pump will deliver at least 1 liter of fuel per minute with the fuel return line pinched off. If the fuel pump does not pump adequately, then inspect the fuel system for a plugged fuel filter or fuel pump inlet filter (sock). Fuel pump flow rate can be done by connecting one end of an old A/C gauge hose to the fuel test port on the fuel rail and inserting the other end of the hose into a container of at least 1 liter capacity. Run the fuel pump by installing a jumper wire into diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the fuel return line or most of the fuel will be returned to the fuel tank.
It could be either one, if the fuel pressure is too low.
Try this, as a rough test of fuel pressure. On the engine on the fuel rail is a test port to connect a fuel pressure gauge. It looks like a tire valve, may have a cap on it that unscrews. Follow your fuel lines to the top of the engine-they will connect to the fuel rail -where the injectors are. If you find the test port, use a small screwdriver or little punch type of thing: be careful of gas spraying out, don't hold your head over the test port: you want to press in the center little valve and see if gas spurts up out of the valve, with the ignition key in on, not start. If gas spurts up, you know the pump is working well enough to get gas up to the engine. The fuel pressure on multi port injection is quite high, about 50 psi. You would need to check what Isuzu calls for. It really would be best to rent a fuel pressure tester, if possible, and connect it at that test port, turn the key to on, and see what pressure you have. If the pressure is as called for, then you know the pump and filter is okay, and can look elsewhere for the problem.
"...tries to start, but turns off..." you mean it does fire and try to run for a second? That does sound like it may be a fuel problem.
Do a fuel pressure leak down test, the test port is located on the fuel rail that supplies fuel to the injectors on the top of the engine, the pressure should not drop more than 5 PSI after the engine is shut down, make sure the fuel gauge (special tool) is not leaking at the schrader port connection. If the fuel pressure leaks down right away you need to replace the fuel pump inside the fuel tank, it has a defective pressure check valve. I understand you can buy a universal test gauge from most parts stores for about $20.00 that hooks up to the above mentioned test port.
By what your stating, that it starts and dies every time, It seems to be fuel related. You need to perform a fuel pressure check. You will need a pressure tester, one that would at least be able to read pressure to a maximum of 150 lbs of pressure. Although you really only need about 50-60 pounds of pressure to maintain proper fuel injector operation. There is a test port located on the fuel rail where you would conect the pressure tester. The test port is usually located on the drivers side of the engine near the rear section coming up from the firewall. Unscrew the pressure port cap if its still there and connect your tester. But also keep in mind you may have fuel pressure of some sort in the rail so be careful. While the tester is screwed to the test port you want to cycle the ignition key on and read pressure, you may want to repeat this several times. You must have at least 50 pounds of pressure, if so it should start. If you are losing pressure while your maintaining a visual check on the tester it could also be a faulty pressure regulator/fuel pump or even a rubber hose connection inside the fuel tank that connects the fuel pump to the fuel line. If you have any questions Im here to help. Thanks for using FIXYA
get a fuel injection pressure test gauge, it hooks up to the fuel pressure test port on the top of the engine near the injector, in the fuel supply line to the injector, hook up the gauge to the test port valve (looks like a tire valve) and run the engine, verify you have no leak at test port connection to gauge, make a note of the fuel pressure PSI with the engine running, then shut it down, the fuel pressure shuld not drop off more than a 2 PSI, if it does the fuel pump is defective.
The fuel pump is in the fuel tank. There is an access port that resides under the back seat (drivers side). It can be use to replace and inspect the fuel gauge sensor. You can replace the fuel pump through this access port.
To access the port.."flip the rear seat cushion up and forward, then remove the inspection hole cover."
Before disconnecting the fuel lines you can remove the fuel pump relay or the fuel pump fuse and run the engine till it dies. Then crank the engine a few times to release any pressure in the lines.
You can test the physical function of the fuel pump by attaching a fuel pressure gauge to the front fuel line under the hood.Turn the key on but don't start the engine and the fuel pressure should rise to 40lbs. Start the engine and let it idle, there the fuel pressure gauge should read 35 give or take a few pounds. As you rev the engine the pressure should fluctuate between 30 and 45. If this all works as such then the fuel pump and pressure regulator are good.
You can also apply an Ohms meter across the fuel pump leads and test the electronics of the pump. Should be .2 to 5.0 Ohms