Replacing Fuel Pump In 1988 Gmc: Step-By-Step Guide

If you're looking to change the fuel pump on your 1988 GMC, you may be experiencing issues with your current fuel pump. Common problems include a faulty relay, a shorted wire, or a malfunctioning switch. Before attempting to change the fuel pump, it's important to diagnose the issue and understand the steps involved in the replacement process. This may involve checking fuses, testing wires for power, and verifying fuel pump operation. It's recommended to refer to a repair manual or seek assistance from a qualified mechanic to ensure a safe and proper fuel pump replacement.

Check the fusible links from the starter to the ignition switch

To check the fusible links from the starter to the ignition switch of your 1988 GMC, you will need to locate the fusible links in the wiring harness near a main harness connection. Fusible links are usually thinner than the rest of the wires and have a rubbery feel.

Once you've located the fusible link, check it for damage. You can do this by gently pulling on each end of the fusible link. If the insulation stretches, it means the wires have melted and the link needs replacement.

You can also use a voltmeter to determine the fusible link's available voltage. Check both ends. If one end has voltage while the other has none, the link might be open, which means you need to replace it.

Another way to check if the link is fine is by doing a light test. Attach a test light to the battery's output terminal and attach the other end to a good ground. If the test light illuminates, it means the link is still functioning.

If you suspect that the fusible links are burned out, you can replace them by following these steps:

• Identify what damaged the fusible link and resolve the issue.
• Check the size of the old link and look for a replacement with the same dimensions.
• Replace the bad fusible link by following the instructions in the service information.

Check for power from the ignition switch to the starter

To check for power from the ignition switch to the starter of your 1988 GMC, you will need to perform the following steps:

Firstly, locate the ignition switch. This is typically found in the steering column, and you may need to remove a cover to access it. Once you have located the ignition switch, identify the wiring. The wiring will include a red wire, which provides power from the battery to the ignition switch, and a yellow wire, which carries power to the crank fuse.

Next, you will need to check for voltage at these wires. Ensure that the ignition key is in the start position. Use a multimeter to check for voltage. The red wire should have battery voltage (at least 12 volts) at all times. The yellow wire should also have voltage (12 volts) when the key is in the start position. If there is no voltage on the yellow wire, you may need to check the red wire for voltage. This red wire is powered by fuse 34 in the fuse box.

If there is no voltage on the red wire, the issue may lie with the fuse box or a break in the wiring. Check the fuse box for any damaged or corroded connectors. If the fuse box and wiring appear intact, the ignition switch itself may be faulty and require replacement.

It is important to note that working on vehicle electrical systems can be complex and potentially dangerous. If you are unsure about any part of this process, it is recommended to consult a qualified mechanic or automotive electrician.

Check for power at the harness at the fuel tank

To check for power at the harness at the fuel tank of your 1988 GMC, follow these steps:

Firstly, locate the harness at the fuel tank. This is where you will find the plug for the fuel pump.

Now, check for power at the harness. You should find a grey or orange wire here. This wire should have power when cranking.

Check for a short in the steering column

To check for a short in the steering column of a 1988 GMC, you will need to consult a wiring diagram for your vehicle. This will help you identify the specific wires and components involved in the steering column circuit.

First, locate the steering column plug, which should be close to the steering pump. You will then need to check for power going to the steering pump when cranking the engine. Look for power on the tan wire going to the driver's side fuel tank. Ensure that the ground wire is also tight.

You can also check for power going from the battery to the ignition switch (red wire at the ignition switch) and then to the starter. Make sure there is at least 12 volts going to the fat cable at the starter, as this cable comes directly from the positive terminal of the battery.

If there is no power on the tan wire or the red wire, you may have a short in the steering column circuit. This could be caused by a blown fuse, a faulty ignition switch, or a broken wire. Further troubleshooting will be needed to identify the exact cause.

Check the oil pressure switch

To check the oil pressure switch, you can perform the following steps:

• Turn the key to the "run" position without cranking the engine. The fuel pump should run for a few seconds. If it does not, the fuel pump relay circuit may not be functioning correctly.
• Check the oil pressure gauge to ensure it is reading accurately. If the gauge is not working or the reading is incorrect, the oil pressure switch or its wiring may be faulty.
• Locate the oil pressure switch. It is usually found near the distributor or on the firewall on the passenger side.
• Unplug the oil pressure switch while the engine is running. If the engine shuts off, the oil pressure switch or its wiring is defective.
• Check the resistance of the oil pressure switch using a multimeter. The switch should be closed when there is sufficient oil pressure and open when there is no oil pressure.
• Inspect the oil pressure switch for any signs of damage or corrosion.
• If the oil pressure switch is not working properly, replace it with a new one.

Frequently asked questions