Checking Fuel Pressure In Your Chevy Blazer: Diy Guide

If you're having problems with your Chevy Blazer, it could be down to fuel pressure issues. The fuel delivery system should be the first thing you check if your vehicle has a driveability issue. Testing fuel pressure and leakdown will tell you if there's a problem with the fuel delivery system. If you have a 1996 through 2005 (or a few late production CSFI-equipped 1995s) 4.3L Central Sequential Fuel Injection (CSFI) engine, you can refer to the GM dealer issue shop manual for guidance on how to correctly test the fuel delivery system.

How to check fuel pressure on a 1998 Chevy Blazer

To check the fuel pressure on a 1998 Chevy Blazer, you'll need to test the fuel delivery system. This involves checking the fuel pressure and the leakdown.

Preparation:

• Confirm fuel pump activation.
• Check the fuel filter is not clogged or restricted.
• Inspect the 3/8" fuel pressure line and the 5/16" fuel return line for any kinks, restrictions, or external fuel leaks. These lines run between the fuel pump module and the connections at the fuel metering block.
• Connect a fuel pressure tester to the service port in the 3/8" steel fuel pressure line located at the rear of the plenum, near the distributor.

Checking Fuel Pressure:

• Activate the fuel pump and check for leaks at the service port connection.
• The pressure indicated on the tester should be between 60-66 psi while the pump is running. This is the regulated fuel pressure.

Performing a Leakdown Test:

• Activate the fuel pump to pressurize the system, then deactivate it.
• Fuel pressure must remain above 55 psi for at least 10 minutes.

If the leakdown test fails, you will need to perform the fuel pump maximum output pressure and leakdown test to determine if the issue is in the plenum or the fuel tank.

Fuel Pump Maximum Output Pressure and Leakdown Test:

• This test is most easily performed at the fuel filter outlet. An adapter is required between the filter and the pressure tester.
• Disconnect the fuel filter outlet line from the filter and connect the adapter and pressure tester.
• Activate the fuel pump. Pressure must be between 73-108 psi.
• Deactivate the fuel pump. Pressure must remain above 55 psi for at least 10 minutes.
• If this test fails, there is a leak inside the fuel tank.

If the leakdown test passes at the fuel filter but fails at the service port, there is a leak in the plenum.

Fuel pressure regulator problems

If your Chevy Blazer is experiencing driveability issues, you should check the fuel delivery system. Symptoms of fuel delivery problems include excessive cranking when hot or cold, a fuel odour, failure to start, stalling, hesitation or stalling on acceleration, running rich or lean, misfire, induction (backfire through the intake), lack of power, and harsh transmission shift points.

If the fuel pressure or volume is insufficient, or there is too much leakdown, you will experience these issues. However, fuel pressure, volume, and leakdown are not directly monitored by OBDII, so no Diagnostic Trouble Code (DTC) will be set, and the Service Engine Soon (SES) light will not be illuminated.

To check the fuel pressure, you will need to connect a fuel pressure tester to the service port in the 3/8" steel fuel pressure line located at the rear of the plenum, near the distributor. Activate the fuel pump and check for leaks. The pressure indicated on the tester should be between 56 and 66 psi while the pump is running. If the pressure is lower, you may misdiagnose the problem as a faulty fuel pressure regulator. To avoid this, you should also check the maximum fuel pump output pressure.

If your Chevy Blazer is experiencing issues with the fuel pressure regulator, it is likely that it is leaking fuel into the engine, causing the fuel pressure gauge to fluctuate erratically and flooding cylinders 4 and 6. This can be confirmed by checking the plugs, which will be wet if this is the case.

If you have determined that the fuel pressure regulator is faulty, you will need to replace it.

Fuel pump and pressure regulator issues

The fuel delivery system should be the first thing to check if your Chevy Blazer has a driveability issue. Correct pressure and the ability to hold pressure are critical. Testing fuel pressure and leakdown will tell you if there is a problem with the fuel delivery system.

If the fuel pressure or volume is insufficient, or the leakdown is excessive, you will experience driveability issues. Symptoms of fuel delivery problems include excessive cranking hot and/or cold, fuel odour, cranks but will not start, starts and stalls, hesitation or stalling on acceleration, running rich, running lean, misfire, induction (backfire through the intake), lack of power, and harsh transmission shift points.

If the fuel pressure or volume is low, the oxygen sensors could detect a lean fuel mixture and set diagnostic trouble codes. However, malfunctions in the fuel delivery system can affect other systems that can set a DTC.

The fuel pump relay should be replaced if the engine will not start after a period of idling or after the engine gets to operating temperature. It is also recommended to replace the fuel pump wiring harness and screen when the fuel pump is replaced. The better fuel pump kits include a new harness and pump screen.

The fuel pressure should be steady between 60-65 lb with the engine running and should not drop below 55 lb for 5 minutes after the engine is shut off. If the fuel pressure is not steady or it drops rapidly after the engine is shut off, the pressure regulator is bad.

The fuel pump must be capable of supplying sufficient pressure and be able to hold it after the pump shuts off. This is most easily tested at the fuel filter outlet.

If the fuel pressure regulator is leaking, you do not have to replace the entire fuel "spider assembly". The regulator is a separate and much cheaper part.

Fuel pressure test

To check the fuel pressure on a Chevy Blazer, you will need to test the pressure and perform a leakdown test. This will indicate whether there is a problem with the fuel delivery system.

Preparation

• Confirm fuel pump activation. If the pump runs when the ignition is turned to the "RUN" position, or if you bypass the relay, move on to step 2.
• Check the electrical connector at the fuel pump module:

• The grey wire must show battery voltage when the fuel pump relay is activated.
• The black ground wire must show less than 5 ohms resistance to the chassis ground.

• Make sure the fuel filter is not clogged or restricted.
• Check for and repair any kinks, restrictions, or external fuel leaks in the fuel pressure line and the fuel return line between the fuel pump module and the connections at the fuel metering block.
• Connect the fuel pressure tester to the service port in the fuel pressure line located at the rear of the plenum, near the distributor. Activate the fuel pump and check for leaks at the service port connection, repairing if/as necessary.

Testing

Pressure Readings at the Service Port

• Activate the fuel pump to pressurise the system.
• The pressure indicated on the tester is either regulated fuel pressure or maximum fuel pump output pressure, whichever is lower.
• Regulated fuel pressure must be 60-66 psi while the pump is running.

Leakdown Test

• Activate the fuel pump to pressurise the system, then deactivate the pump.
• Fuel pressure must remain above 55 psi for at least 10 minutes.
• If this test fails, you will need to perform the Fuel Pump Maximum Output Pressure and Leakdown Test to determine if the cause is in the plenum or in the fuel tank.

Fuel Pump Maximum Output Pressure and Leakdown Test

• The pump must be capable of supplying sufficient pressure and be able to hold it after the pump shuts off.
• This is most easily tested at the fuel filter outlet. It requires an adapter between the filter and the pressure tester.
• Disconnect the fuel filter outlet line from the filter.
• Connect the adapter to the filter outlet and connect the pressure tester to the adapter.
• Activate the fuel pump. Pressure must be 73-108 psi.
• Deactivate the fuel pump. Pressure must remain above 55 psi for at least 10 minutes.
• If this leakdown test fails, there is a leak inside the fuel tank. If leakdown is within specs on this test, and leakdown at the service port is excessive, there is a leak in the plenum.

Notes

• If the fuel pressure or volume is insufficient, or leakdown is excessive, you will experience drivability issues.
• Symptoms of fuel delivery problems include excessive cranking hot and/or cold, fuel odour, cranks but will not start, starts and stalls, hesitation or stalling on acceleration, running rich, running lean, misfire, induction (backfire through the intake), lack of power, and harsh transmission shift points.
• Fuel pressure, volume, and leakdown are not directly monitored by OBDII, so it can't set a Diagnostic Trouble Code (DTC) in memory and illuminate the Service Engine Soon (SES) light.
• Malfunctions that occur in the fuel delivery system can affect other systems that can set a DTC.
• Fuel pressure and leakdown must be tested with the engine off.
• Checking fuel pressure and leakdown at the service port is only a "quick check". There are things that the "quick check" does not test for.

Fuel pump replacement

Step 1: Disconnect the battery

Before starting any work on your Chevy Blazer, it is important to disconnect the negative battery cable to prevent any electrical accidents.

Step 2: Prepare the vehicle

Place a container to collect any fuel that you will bleed off from the system. Then, raise the vehicle to gain access to the fuel tank. Start by removing the filler tube hose and the straps holding the tank in place.

Step 3: Remove the fuel tank

Before lowering the tank, remove the protective shield. Once the tank is partially lowered, finish removing the tank filler hose and vent pipe. Then, lower the tank further to access the fuel line fittings and electrical connections. Remove the fuel lines, disconnect the electrical connection for the fuel pump, and disconnect the return and emissions lines.

Step 4: Clean the fuel tank

Remove the fuel tank from the vehicle and clean the outside thoroughly to prevent any debris from entering the tank when you remove the fuel pump module.

Step 5: Remove the old fuel pump

Remove the fuel line retainers to reuse them on the new fuel pump module. Then, remove the tank blocking ring, which is a snap ring design and will require a set of snap ring pliers. As you remove the module assembly, be aware that there is a reservoir that will retain fuel, so capture this to dispose of it properly.

Step 6: Prepare the new fuel pump

Drain the remaining fuel from the tank into a safe container and clean the inside of the tank thoroughly. Then, install a new fuel pump module, ensuring that the tank seal is in place.

Step 7: Reinstall the fuel tank and connect the fuel pump

Reinstall the tank underneath the vehicle and reconnect the fuel line retainers to the ends of the fuel lines. Reconnect the filler tube, vent tube, and emissions line. Reconnect the electrical connectors, ensuring that the safety retainer is in place. Finally, reattach the pressure line and the return line, tightening the hose clamps on the filler hose.

Step 8: Final checks

Reinstall the tank straps and the shield, and reconnect the negative battery cable. Cycle the key a few times to start the vehicle and monitor your fuel pressure gauge to ensure it is within the vehicle's specifications. Once you have confirmed this, shut off the engine and relieve the pressure from the system using the pressure relief on the gauge, capturing any fuel in a safe container.

Frequently asked questions