Checking Fuel Pressure In A Mitsubishi Mighty Max Diesel

Checking the fuel pressure of a Mitsubishi Mighty Max diesel engine is important to ensure optimal performance and fuel efficiency. While the process may vary slightly depending on the model year of the vehicle, there are some general steps that can be followed. One method is to listen at the gas tank while someone turns the ignition key to the on position. If the fuel pump is working, you should hear a whirring sound for a few seconds. Alternatively, you can pull the fuel line loose where it connects to the injectors and observe if fuel pumps out when the engine is cranked. Additionally, checking the fuel pump fuse in the owner's manual and replacing it if blown can help diagnose potential issues. For a more comprehensive inspection, a certified mechanic can diagnose and address issues related to loss of power, including defective fuel pumps or filters, vacuum leaks, ignition system problems, and airflow sensor failures.

Listen for a whirring sound at the gas tank with the ignition on

To check the fuel pump electrical power and operation of a Mitsubishi Mighty Max pickup without draining and dropping the fuel tank, listen at the gas tank while someone turns the ignition key to the on position. You should be able to hear a whirring sound at the tank for a few seconds. This is a sign that the fuel pump is working.

If you don't hear the whirring sound, there are a few other ways to check the fuel pump. One way is to pull the fuel line loose where it goes into the injectors and see if any fuel pumps out when someone cranks the engine. Another way is to check your owner's manual for the location of the fuel pump fuse and see if it is blown. If it is, replace it, and if it blows again, you will need to track down the short in the wiring.

Check for fuel flow from the injectors when cranking the engine

To check for fuel flow from the injectors when cranking the engine of a Mitsubishi Mighty Max, there are a few methods you can use.

One way is to listen for the sound of the injectors. Put on safety gear, such as eye protection, and open the hood of your car to locate the fuel injectors. You can refer to the service manual for your specific vehicle to find their exact location. Once located, take a long metal rod or screwdriver and place it on one of the injectors. Bring your ear close to the rod and listen for a clicking sound, which indicates that the injector is functioning. Repeat this process for each injector. If you find one that is not clicking, there may be an issue with the injector or its electronic control.

Another method involves checking the voltage of the wires connected to the injectors. Turn the key to the "on" position without starting the engine to activate the vehicle's electrical system. Connect a test light to the negative terminal of the battery, and then locate the two wires going into each injector. One of these wires should be a 12-volt constant that is continuously receiving power. Use the test light to probe each wire, and if one of them lights up, the injector is receiving the necessary voltage. Repeat this process for all injectors to ensure they are all receiving power.

Additionally, you can check the trigger circuit for the injectors. Connect the test light to the positive terminal of the battery this time. Have someone attempt to start the engine or turn it over while you probe the opposite wire of the constants identified in the previous test. With the engine running at idle, the test light should flicker dimly, and when your helper presses the gas pedal, the light should flicker more brightly. This indicates that the ECU is transmitting a signal to the injector to spray fuel. If the test light is not lighting up, there may be an issue with the injector or the electronic control unit.

It is important to note that basic fuel system diagnosis should not only focus on fuel pressure but also consider fuel volume and flow. The fuel injectors are the last component in any EFI system, and the entire fuel system is designed to provide the proper injector flow rate. Therefore, when diagnosing fuel system problems, it is crucial to understand the components, fuel system design, pressure and flow theory, as well as diagnostic techniques.

Check the fuel pump fuse

To check the fuel pump fuse on a Mitsubishi Mighty Max, start by locating your fuse box. This is usually found under the driver's side dashboard, or sometimes under the hood or in the trunk. Once you've found the fuse box, look for the fuel pump fuse. It will be labelled, either with a picture of a pump or the words "Fuel Pump".

If you're having trouble locating the fuse box or the fuel pump fuse, refer to your owner's manual. This will have a diagram of the fuse box and will show you where the fuel pump fuse is located.

Once you've found the fuel pump fuse, you need to check if it is blown. This can be done in a few ways. One way is to visually inspect the fuse for any signs of damage or discoloration. If the fuse is blown, you may see a broken wire or a burnt mark on the fuse. Another way to check is to use a multimeter to test for continuity. This will involve removing the fuse from the fuse box and using the multimeter to check for electrical resistance. If the fuse is blown, you will need to replace it with a new one of the same type and rating.

If you find that the fuel pump fuse is blown, replace it with a new one and see if that solves the problem. A blown fuse could indicate a larger issue, so it's important to identify and address the root cause to prevent it from happening again.

If the new fuse blows, there may be a short circuit in the wiring that needs to be addressed by a professional mechanic.

Check for power in the fuel pump circuit with a multimeter

Checking the fuel pump circuit with a multimeter is a straightforward process, but it does require some care and attention to detail. Here's a step-by-step guide on how to do it:

Step 1: Locate the Fuel Pump Relay

Turn off your vehicle and remove the key from the ignition. The fuel pump relay is usually located in the fuse box under the hood or under the steering column. Refer to your vehicle's manual if you're unsure.

Step 2: Remove the Relay

Pull the relay straight out from the fuse box. If it's stuck, try rocking it gently back and forth to loosen the connection. Removing the relay will prevent the fuel pump from working, so your engine won't start.

Step 3: Clean the Relay Prongs (If Necessary)

If the relay prongs show signs of rust or corrosion, clean them with a wire brush. Alternatively, you can use an electrical contact cleaner and a cloth to remove any residue. This step ensures a solid connection when you plug the relay back in.

Step 4: Understand the Relay Circuit Diagram

Look for a diagram printed on the relay's body. This diagram represents the circuit that the relay controls. Identify the power prongs, usually labeled 85 and 86, and the prongs to be tested, typically labeled 87 and 30.

Step 5: Set Up the Multimeter

Set your multimeter to the ohm (Ω) setting to measure the resistance in the circuit. If your multimeter has multiple ohm ranges, choose the lowest one for accuracy.

Step 6: Connect Jumper Wires to the Battery

Use jumper wires with alligator clips to connect one wire to the positive terminal and the other to the negative terminal of your vehicle's battery. Ensure the wires don't touch each other to avoid creating a spark.

Step 7: Connect Jumper Wires to the Relay

Clip the jumper wire from the negative battery terminal to the terminal labeled 85 on the relay, and connect the wire from the positive terminal to the pin labeled 86. Listen for a clicking sound, indicating the relay is still functional.

Step 8: Test the Relay Circuit

Hold the multimeter probes against the remaining prongs, 30 and 87. The multimeter will measure the resistance in the internal circuit. If the circuit has power, the multimeter should display a reading of 0, indicating no resistance. A reading greater than 0 indicates a faulty circuit.

Step 9: Additional Testing (If Necessary)

If the relay and circuit test show no issues, you may need to perform additional checks. Test the fuel pump fuse using the multimeter, or perform a voltage drop test to check for high resistance in the wiring. You can also test the fuel pump itself by removing it and using the jumper wires to test for voltage.

Scan the computer system for trouble codes

To scan the computer system for trouble codes in a Mitsubishi Mighty Max, you will need to locate the diagnostic port. This is usually found under the dashboard, behind the fuse box. Once you have located the diagnostic port, you can use a suitable tool to read the trouble codes.

For the 1989 model, you can use a +12V LED and about 48" of 26H wire. Connect the LED across the diagonal pins in the diagnostic port. The LED will light up in one direction. The long pulse is "10" and the short pulse is "1", so, for example, LONG LONG SHORT equals code 21.

For the 1991 model, you will need a 12V LED with a built-in resistor and a pack of small alligator clips. Crimp a clip onto each of the LED wires, then hook them up to the pins in the diagnostic port. Turn the key in the ignition and the LED will flash a code. As with the 1989 model, a long flash equals "10" and a short flash equals "1".

If you have a 1990 Mitsubishi Mighty Max, you can use old software and OBD1 cables to datalog and read trouble codes. You can also use software such as tmolog or ALDL Droid on your Android phone to read the data.

It is also worth noting that if you live in the US and have an AutoZone nearby, they will read the OBDII error code for free.

Frequently asked questions