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Disconnect the cable on the negative terminal of the battery to avoid starting the engine accidentally. Remove the filler cap for the fuel tank to relieve the pressure in the fuel tank. Wrap a shop towel around the fuel pressure fitting on the fuel rail and attach a fuel pressure gauge to the fitting. Connect the bleed hose to the pressure gauge and place the open end of the bleed hose into a container approved for gasoline. Open the fuel pressure gauge to relieve the pressure in the fuel system. Remove the fuel pressure gauge from the fitting.

Place one end of a hose into the filler tube of the fuel tank and place the other end into the gasoline container. Siphon as much fuel as possible from the fuel tank into the container.

Disconnect the filler pipe and fuel lines from the fuel tank. Support the fuel tank with jack stands and remove the bolts for the fuel tank straps with a socket wrench. Disconnect the fuel tank straps and lower the fuel tank slightly so you can disconnect the harness clip from the cross member and the electrical connections from the fuel tank. Lower the fuel tank completely and remove it from the vehicle.

Turn the retaining ring for the fuel sender assembly counterclockwise with a fuel tank sending wrench. Remove the retaining ring, and detach the fuel sender assembly from the fuel tank. Discard the gasket on the fuel tank. Pull the fuel strainer from the fuel sender assembly and discard the strainer.

Detach the electrical connector for the fuel pump. Release the retaining clip for the fuel sensors electrical connector and detach the fuel sensors electrical connector. Release the retaining clip for the fuel level sensor and remove the fuel level sensor.

Install the new fuel pump and gasket by reversing steps two through five. Tighten the bolts for the fuel tanks retaining straps to 30 ft. lbs. with a torque wrench. Tighten the bolts for the cross member to 37 ft. lbs. Fill the fuel tank and replace its filler cap. Connect the cable for the negative terminal on the battery with a socket wrench. Turn the ignition on for two seconds, then turn it off for 10 seconds to pressurize the fuel system. Turn the ignition back on and check for fuel leaks.

Map out the serpentine fan belt, noting how the belt wraps around each pulley. The serpentine fan belt is located between the engine belt and the radiator fan. Sketch out a diagram on a piece of paper. A diagram is also printed on the underside of the engine hood or on the fan shroud, but it may be missing.

Locate the tensioner pulley. On the 3.8-liter engine, the pulley is located between the alternator and the power steering pump. On the 2.8-liter engine, the pulley is located between the alternator and the air conditioner pump. The pulley has a square hole in the center of it. The diagram on the underside of the hood also shows the location of the tensioner pulley.

Place a 3/8-inch ratchet drive into the square hole and set the ratchet setting counterclockwise.

Pull up on the handle to release pressure on the serpentine belt then slide the bottom of the belt off the tensioner pulley.

Remove the belt from the rest of the pulleys then place the new belt onto the pulleys. Follow the belt routing diagram to ensure each pulley turns in the correct direction.

Pull up on the handle of the ratchet and slide the belt under the pulley. When you release the ratchet, the tension pulley applies tension to the belt.

View the Quick Stop Speed Shop manual (see Resources). The manual includes information on Chevrolet engine casting numbers. Locate the "CID" column and scroll down to find "327." The other columns provide information such as the model year, casting number, type of vehicle and special notes.

Go to the Chevy-Camaro website (see Resources). This website provides engine casting number information for Chevrolet vehicles. Select "327" from the "Select Block Casting Group" drop-down menu. The results include casting numbers, horsepower and notes specifying relevant vehicle types.

Review the Chevelle manual (see Resources). This manual provides casting numbers and related information for various Chevrolet engines. The first section includes details for small block engines. Scroll down the page or use the PDF "Search" to locate "327" and relevant information, such as horsepower and vehicle type.

Drive the 2002 Chevrolet Blazer up onto two car ramps, and then apply the parking brake.

Place a wheel block behind one of the rear tires.

Put the safety glasses on, and crawl underneath the Blazer with the remaining items.

Locate the oxygen sensor(s) you intend to replace. The two front ones are located in the front Y-pipe of the exhaust system towards the front of the engine. There is one per side of the Y-pipe. The other two are located before and after the catalytic converter (which is just behind the Y-pipe towards the center of the vehicle on the passenger side).

Spray the threads of the oxygen sensor with penetrating lubricant, and allow it to soak in for a few minutes.

Follow the wire harness from the oxygen sensor to the plug connection. Use a small forked pry tool to unseat the retaining tab of the plug connection from the frame or undercarriage of the SUV. Disconnect the wire harness plug.

Place the plug of the sensor through the box-end side of the 22-mm or 7/8-inch wrench, and then place the wrench onto the hex-headed portion of the sensor.

Turn the sensor counterclockwise using the wrench. A quick jerking motion of the wrench should loosen the sensor effectively, but if necessary, start the engine for a couple of minutes to warm up the exhaust system and expand the binding metals of the pipe and sensor. Be careful that it will not heat up the front Y-pipe sensors because they can become hot enough to burn you.

Thread the new replacement sensor into the exhaust port by hand as far as it will allow. Tighten the sensor to 30-foot pounds with a torquing hand wrench. Do not over-tighten the sensor, or you will damage the threads.

Reconnect the wire harness of the replacement sensor to the plug connection, and then push the retaining tab back into its respective hole in the frame or undercarriage.

Use the socket wrench to remove and take out the fuel pump relay. Its attached on the engine compartments right side near the fuse panel. Turn on the engine. Let it run until it stops so that the fuel pressure will be relieved.

Take out the trunk liner. Remove the cars spare tire. Youll now see the cars access panel which will allow you to access the pump. Take of the bolts which hold the pump in place. Take off the panel.

Inspect the pump assembly. Clean out any dirt or debris from around it. Unsnap the fittings which keep the lines in their place. Disconnect the electrical connector. Unlatch and remove the large ring which holds the pump assembly.

Take off the pump assembly. Replace it with the new one. Put the latch back into its original place. Carefully plug the electrical connector back in. Put the spare tire back in and reinstall the access panel.

Turn the key in the ignition and listen for any sounds coming from the engine. If you hear "clicking" then a technician should test the alternator on a diagnostic machine.

Turn the ignition halfway to turn on the instrument panel. Look over the instrument panel to make sure you have enough fuel to start the engine (if not, add about 1 gallon of gas).

Open the hood of the vehicle and look over the battery connections. If you find the battery connections loose, tighten them with a pair of channel locks or pliers. Try to restart the car. If the car will not start, the charge might be low.

Use a voltmeter to test the battery. Connect the positive and negative leads of the voltmeter to the positive and negative leads on your battery. Look over the reading. If the reading is under 11 to 12 volts, you need to charge the battery.

Connect a battery charger to the positive and negative terminals on the battery. Plug the battery charger into an electrical outlet and let the unit sit for about 12 hours. Try to restart the vehicle after 12 hours. If the vehicle does not start, you need to replace the battery.

Get under the vehicle and look for the starter. The starter is a small black box on the right side of the engine. With the emergency brake engaged and the car in "Park," have a friend turn the ignition and listen for a "buzzing" noise coming from the starter. If you hear the buzzing, you need to have the starter replaced by a service technician.