Ideal Fuel Pressure For Road-Going Isuzu Engines

Isuzu Rodeo owners and enthusiasts often turn to online forums to discuss issues with their vehicles and seek advice. One common issue is low fuel pressure, which can cause hard starts, loss of power, and error codes. To diagnose this problem, it is recommended to test the fuel pressure at the rail. This can be done by disconnecting the fuel line and connecting a pressure gauge. The fuel pressure should be around 40-50 psi when the key is turned to the on position but the engine is not running, and it should hold this pressure for a long time. If the pressure is lower than expected, it could be due to a weak fuel pump, a dirty fuel pump screen, or a leaky fuel injector.

Fuel pressure gauge readings

To check the fuel pressure of a 1993-1995 3.2L Isuzu Rodeo, you will need a fuel pressure gauge. First, remove the plastic dust cap from the Schrader valve. Place a shop towel around the Schrader valve and fuel line to absorb any fuel that may leak. Connect the fuel pressure gauge to the Schrader valve. Ask your helper to cycle the key on and off but not to crank the engine. Check your connections for fuel leaks and resolve any issues before continuing. Then, crank the engine and check the fuel pressure gauge.

The fuel pressure specification with the engine running is 25-30 PSI (with the fuel pressure regulator connected to its vacuum hose). If the gauge registers a pressure less than 25 PSI, the fuel pump is failing.

If the fuel pressure gauge reads 0 PSI, you will need to check the fuel pump fuse. On the 1993, 1994, and early 1995 3.2L Isuzu Rodeo, this is fuse #9 in the underhood fuse/relay box. On the mid-1995 and later 3.2L Isuzu Rodeo, it is fuse EB-11 of the underhood fuse/relay box. Remove the fuse and check if it is blown. If the fuse is intact, you can conclude that the fuel pump is bad and needs to be replaced.

If you are using a 1996-2004 3.2L Isuzu Rodeo, the expected fuel pressure is 42-55 PSI. A reading of 25 PSI indicates a weak fuel pump.

Fuel pump failure

A faulty fuel pump can cause a range of issues with your Isuzu Rodeo, from difficulty starting the engine to poor fuel efficiency. If you suspect your fuel pump has failed, there are some initial checks you can perform to diagnose the problem.

Firstly, check your fuel pressure. The fuel pump is responsible for delivering fuel from the tank to the engine, and if it is not functioning correctly, the pressure will be low. You can test this by attaching a fuel pressure gauge to the fuel rail, which is located on the driver's side of the engine block. With the ignition in the 'accessory' position, the fuel pressure should be around 40 psi. If it is significantly lower, this indicates a problem with the fuel pump or another component of the fuel system.

Another way to check for fuel pump failure is to listen for a whining noise coming from the fuel tank when the ignition is turned to the 'run' position. This noise could indicate that the pump is faulty or obstructed.

If you suspect your fuel pump has failed, there are some potential causes you can investigate. One common issue is a clogged fuel filter, which can restrict the flow of fuel and cause the pump to work harder than usual. This can lead to premature wear and failure of the pump.

Another potential cause of fuel pump failure is a faulty fuel pressure regulator. This component maintains the correct fuel pressure in the system, and if it malfunctions, it can cause the pump to work harder, leading to overheating and potential failure.

Additionally, check the electrical connections to the fuel pump. Ensure that the pump is receiving power and ground, as a loss of power can cause the pump to fail.

If you determine that your fuel pump has failed, replacement is usually the best course of action. This can be a complex job, as the fuel pump is often located inside the fuel tank, requiring the tank to be removed or lowered for access. It is important to relieve the fuel pressure and disconnect the negative battery terminal before beginning any work.

When replacing the fuel pump, it is recommended to install a new fuel filter and pressure regulator at the same time, as these components can contribute to pump failure if they are not functioning correctly.

Finally, always refer to the manufacturer's specifications and a qualified mechanic when performing any repairs or replacements on your vehicle.

Fuel pump testing

Overview

Testing the fuel pump on your Isuzu Rodeo is a straightforward process that can be done in a few simple steps. This guide will cover the testing procedure, the symptoms of a faulty fuel pump, and the tools you'll need to get an accurate reading.

Symptoms of a Bad Fuel Pump

Your Isuzu Rodeo's engine needs three things to start: air, fuel, and spark. If the fuel pump fails, the engine will either not start at all or will start but run with a lack of power. Over time, fuel pumps can fail in one of two ways: they may stop working entirely, causing the engine to crank but not start due to a lack of fuel, or they may deliver just enough fuel to start the engine but not enough to keep it running optimally.

Some common symptoms of a failing fuel pump include:

• Engine backfires when accelerating
• Engine takes a long time to start
• Engine knock when accelerating due to a lean air/fuel mixture

Tools Required

• Fuel pressure tester (Actron CP7818 Fuel Pressure Tester Kit, Actron CP7838 Professional Fuel Pressure Tester, or OTC 5630 Fuel Pressure Test Kit)
• Shop towel
• Helper (optional)

Testing Procedure

Test 1: Fuel Pressure Test (Engine Does Not Start)

• Remove the plastic dust cap from the Schrader valve.
• Place a shop towel around the Schrader valve and fuel line to absorb any leaking fuel.
• Connect the fuel pressure gauge to the Schrader valve.
• Ask your helper to cycle the key ON and OFF but not to crank the engine.
• Check your connections for fuel leaks and resolve any issues before continuing.
• Crank the engine and check the fuel pressure gauge.

Interpreting Your Results:

• Case 1: If the fuel pressure gauge reads 0 PSI, this confirms that the fuel pump is not functioning. This usually means the fuel pump needs to be replaced, but first, check that the fuel pump fuse isn't blown (see Test 3).
• Case 2: If the fuel pressure gauge reads 41 to 46 PSI, this is the correct and expected result.
• Case 3: If the fuel pressure gauge reads less than 41 PSI, the fuel pump is failing and may need to be replaced.

Additional Notes:

• Testing the Fuel Pump Fuse (Test 3): Check the fuse box for a blown fuse. If the fuse is blown, replace it and retest the fuel pump as described above.
• Using Starting Fluid to Confirm Lack of Fuel (Test 4): If you don't have a fuel pressure gauge, you can use starting fluid to check if the engine is getting fuel. Spray a small amount of starting fluid into the throttle body with the engine cranking. If the engine starts and runs momentarily, this confirms that the engine is not getting fuel, indicating a problem with the fuel pump or a lack of fuel in the tank.

Community Tips

Some Isuzu Rodeo owners have shared their experiences and tips for fuel pump testing and troubleshooting on online forums. Here are some additional insights gathered from these discussions:

• The fuel pressure on a 2002 Isuzu Rodeo with a 3.2L V6 engine should be 38 PSI with the ignition on and the engine not running, and 35 PSI with the engine at idle.
• If you're having trouble locating the Schrader valve, look for a plastic cap covering it. It will resemble a large tire valve.
• If your Rodeo doesn't have a Schrader valve, you may need to install a T-fitting in the rubber fuel line to connect the fuel pressure gauge.
• One owner reported resolving a low fuel pressure issue by replacing the entire fuel pump assembly instead of just the pump itself.
• Another owner experienced a fuel pressure issue caused by a corroded wire and a loose hose connection to the fuel pump.

Fuel pump replacement

Overview

The fuel pump is a critical component of your engine's fuel system, drawing fuel from the tank and delivering it to the carburettor or fuel injectors. It is usually powered by an electric motor and located inside the fuel tank.

When to Replace

A high-quality, OEM fuel pump can last indefinitely under the right conditions. However, as with any electro-mechanical component, a fuel pump will eventually degrade and fail. Some signs that your fuel pump may need replacing include:

• Car won't start or unexpectedly stalls
• Check engine light is on
• Whirring noise from the fuel tank

The Replacement Process

• Park your car on level ground and engage the parking brake.
• Turn the key to the 'On' position and listen for the fuel pump, which should hum for 2-3 seconds.
• Locate and verify the fuel pump relay and fuse. If the fuse is damaged, replace it with a new one of the same amperage.
• Check the fuel pump's operation. If it is functioning correctly, the issue lies elsewhere. If not, check for power and ground at the pump. If these are fine, the pump is faulty.
• Relieve the fuel system pressure and disconnect the negative battery cable.
• Drain the fuel tank. Disconnect the filler fuel hose and electrical connection to the pump.
• Support the fuel tank with a jack stand and block of wood. Remove the pump assembly and lower the tank.
• Remove hose clamps and disconnect the fuel line/tank hose. Extract the old pump.
• Compare the new pump to the old one to ensure you have the correct part.
• Install the new pump, connecting all fuel lines.
• Reinstall straps and bolts. Reconnect the filler fuel and electrical connector, then reconnect the negative battery cable.
• Refill the tank and test the vehicle to ensure the new pump is functioning correctly.

Additional Notes

• Get the fuel filter changed when replacing the pump to avoid further issues.
• Always exercise extreme caution when dealing with gasoline due to its high flammability.
• Whenever the fuel pump is replaced, the fuel filter should also be replaced unless done recently.
• Keep your gas tank at least a quarter full to maximise the life of a new fuel pump.

Fuel injector issues

Fuel injectors can fail in a number of ways. Here are some common symptoms of a bad fuel injector:

• Hesitation when you accelerate your Isuzu Rodeo down the road.
• Misfire trouble codes (for OBD II-equipped vehicles): P0300, P0301, P0302, P0303, P0304, P0305, P0306.
• The fuel injector's internal winding suffers a short-circuit or open-circuit problem, causing it to stop injecting fuel.
• The fuel injector is clogged and does not inject enough fuel or does not inject at all.
• The fuel injector turns on and doesn't turn off, spraying a large amount of fuel when the ignition is turned on.

If you suspect a problem with your fuel injectors, you can test their internal resistance using a multimeter. Here's a step-by-step guide:

• Disconnect the fuel injectors from their harness connectors.
• Set your multimeter to Ohms (Ω) mode.
• Measure the resistance of each fuel injector across its two male spade terminals.
• Write down the resistance value for each injector.
• Compare the recorded resistance values to the factory specification for Isuzu fuel injectors, which is 11.8 to 12.6 Ohms.
• If all the injectors have similar resistance values within the specified range, it confirms that their coil windings are functioning correctly.
• If one of the injectors has a significantly different resistance value, it indicates that the injector is faulty and needs to be replaced.

It's important to note that on 1993 to 1997 Isuzu SOHC 3.2L engines, the upper intake manifold plenum must be removed to access the fuel injectors.

In addition to internal coil problems, fuel injector issues can also be caused by a faulty fuel pump or a clogged fuel filter. If you suspect a problem with your fuel pump, you can test it by using a meter to check for good battery voltage at the pump. A weak fuel pump may result in low fuel pressure, hard starts, and loss of power.

If you're experiencing fuel injector-related issues, it's recommended to consult a qualified mechanic or refer to a factory service manual for specific instructions and safety precautions.

Frequently asked questions