Rajan Wilcox
To get power to the fuel pump on a 1987 GMC Jimmy, start by verifying the fuel pump fuse and relay in the under-hood fuse box, ensuring they are intact and functioning properly. Next, check the fuel pump wiring harness for any signs of damage or corrosion, as this can disrupt the electrical connection. If the fuse and relay are good, test for power at the fuel pump connector using a multimeter; if there’s no power, trace the wiring back to the oil pressure switch or inertia switch, as these components often control power to the pump. Additionally, ensure the ignition circuit is sending the necessary signal to activate the fuel pump when the key is turned to the on position. If all else fails, consult a wiring diagram specific to the 1987 GMC Jimmy to diagnose and resolve any remaining issues.
| Characteristics | Values |
|---|---|
| Vehicle Model | 1987 GMC Jimmy (Gimmy is likely a misspelling of Jimmy) |
| Fuel Pump Type | In-tank electric fuel pump (common for this model) |
| Power Source | 12V DC from the vehicle's electrical system |
| Fuse Location | Typically under the hood in the fuse box, often labeled "Fuel Pump" or "ECU/ECM" |
| Relay Location | Usually under the hood near the fuse box or on the firewall, labeled "Fuel Pump Relay" |
| Wiring Diagram | Available in the 1987 GMC Jimmy service manual or online resources (e.g., Haynes, Chilton) |
| Common Issues | Blown fuse, faulty relay, corroded wiring connections, or a bad ground |
| Diagnostic Tools | Multimeter to test voltage, continuity, and resistance |
| Safety Precautions | Disconnect battery before working on electrical system, avoid sparks near fuel tank |
| Recommended Parts | OEM fuel pump relay, high-quality fuses, and dielectric grease for connections |
| Troubleshooting Steps | 1. Check fuse and relay, 2. Test for power at fuel pump connector, 3. Verify ground connection, 4. Inspect wiring for damage |
| Professional Help | Consult a mechanic if issue persists or for complex electrical diagnostics |
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What You'll Learn
- Check Fuses and Relays: Inspect fuse box for blown fuses and relays for proper operation
- Test Wiring Connections: Verify all wires to the pump are secure and undamaged
- Inspect Fuel Pump Ground: Ensure the pump’s ground connection is clean and intact
- Use a Power Probe: Directly test power supply to the pump at the connector
- Check Inertia Switch: Reset or replace the inertia switch if tripped or faulty
Check Fuses and Relays: Inspect fuse box for blown fuses and relays for proper operation
Fuses and relays are the unsung heroes of your 1987 Gimmy's electrical system, acting as gatekeepers that protect circuits from overloading. When your fuel pump isn’t getting power, a blown fuse or faulty relay is often the culprit. Start by locating the fuse box, typically found under the dashboard or in the engine compartment. Consult your vehicle’s manual to identify the specific fuse and relay associated with the fuel pump circuit. This step is critical because a blown fuse or stuck relay can mimic symptoms of a failed pump, leading to unnecessary replacements.
Inspecting fuses requires a keen eye and a simple tool: a fuse puller or a pair of needle-nose pliers. Remove each fuse related to the fuel pump circuit and examine it for visible signs of damage, such as a broken filament or discoloration. A blown fuse is a clear indicator of an electrical issue, but even a slightly discolored fuse can suggest a weak point in the system. Replace any suspect fuses with ones of the same amperage rating—using a higher-rated fuse can cause more harm than good by allowing excessive current to flow.
Relays, on the other hand, are more complex and require a different approach. A faulty relay may not show physical damage but can fail to switch properly, interrupting power flow. Test the relay by swapping it with another of the same type in the fuse box (e.g., swapping the fuel pump relay with the horn relay). If the fuel pump engages after the swap, the relay is likely the issue. Alternatively, use a multimeter to test the relay’s continuity and ensure it’s functioning as expected.
While checking fuses and relays is straightforward, it’s easy to overlook subtle issues. For instance, corrosion in the fuse box can cause poor contact, leading to intermittent power loss. Clean the fuse box terminals with a wire brush and dielectric grease to ensure a solid connection. Additionally, if you’ve recently installed aftermarket accessories, they may be drawing too much power, causing fuses to blow repeatedly. In such cases, address the root cause rather than simply replacing the fuse.
In conclusion, checking fuses and relays is a low-cost, high-reward step in diagnosing fuel pump power issues. It’s a task that combines observation, basic tools, and a systematic approach. By ruling out these common electrical faults, you’ll either resolve the problem or narrow down the search to more complex issues, saving time and frustration in the process. Always keep spare fuses and relays on hand—they’re small investments that can get your Gimmy back on the road quickly.
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Test Wiring Connections: Verify all wires to the pump are secure and undamaged
Loose or damaged wiring is a common culprit behind fuel pump power issues in 1987 GMC Jimmy models. Before diving into complex diagnostics, a thorough inspection of the wiring connections is essential. Start by locating the fuel pump wiring harness, typically found near the fuel tank. Visually examine each wire for signs of wear, corrosion, or fraying. Even a small crack in the insulation can lead to intermittent power loss or a complete circuit failure.
To test the connections, use a multimeter set to the continuity or resistance mode. Disconnect the wiring harness from the fuel pump and check for continuity between the corresponding pins on the harness and the pump. A reading of zero or near zero indicates a good connection, while an infinite reading suggests an open circuit. Repeat this process for each wire, ensuring all connections are intact. If any wire fails the continuity test, it must be repaired or replaced to restore power to the fuel pump.
Another critical step is verifying the security of the wiring connections. Over time, vibrations from driving can loosen terminals, leading to poor contact. Use a small screwdriver to gently tighten any loose connectors, being careful not to overtighten and damage the terminals. Additionally, inspect the ground wire connection, often located on the vehicle’s chassis near the fuel tank. A poor ground can mimic a power issue, so clean the grounding point with a wire brush and ensure a tight, corrosion-free connection.
For added reliability, consider applying dielectric grease to the terminals after cleaning. This non-conductive lubricant protects against moisture and corrosion, extending the life of the connections. If the wiring harness shows significant damage, such as melted insulation or multiple broken wires, replacing the entire harness may be more cost-effective than attempting repairs. Always consult a wiring diagram specific to the 1987 GMC Jimmy to ensure correct reconnection of the harness.
In summary, testing and securing the wiring connections is a straightforward yet critical step in troubleshooting fuel pump power issues. By systematically inspecting, testing, and tightening each wire, you can eliminate common electrical faults and ensure a reliable power supply to the fuel pump. This approach not only saves time but also prevents unnecessary replacement of expensive components.
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Inspect Fuel Pump Ground: Ensure the pump’s ground connection is clean and intact
A weak or corroded ground connection is a silent killer of fuel pump performance. Even if power reaches the pump, a poor ground prevents the circuit from completing, starving the pump of the full voltage it needs to operate efficiently. This can lead to symptoms like hard starting, stalling, or a complete loss of power, often misdiagnosed as a faulty pump itself.
Diagnosis: Begin by locating the fuel pump's ground point. On a 1987 Jimmy, this is typically a bolted connection on the pump itself or a nearby chassis point. Visually inspect the connection for corrosion, rust, or loose wires. Use a multimeter to test continuity between the ground point and a known good chassis ground. A reading significantly above 0 ohms indicates a problem.
Remedy: If corrosion is present, disconnect the ground wire and clean both the wire terminal and the grounding surface with a wire brush and electrical contact cleaner. For stubborn corrosion, sandpaper can be used. Ensure a clean, bare metal surface on both sides. Reconnect the ground wire securely, using a torque wrench if a torque specification is available.
Prevention: Regularly inspecting and cleaning the fuel pump ground during routine maintenance can prevent future issues. Consider applying a thin layer of dielectric grease to the connection to inhibit corrosion, especially in areas prone to moisture.
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Use a Power Probe: Directly test power supply to the pump at the connector
A power probe is an indispensable tool for diagnosing electrical issues in your 1987 Gimmy’s fuel pump system. By directly testing the power supply at the pump connector, you eliminate guesswork and pinpoint whether the issue lies in the wiring, the pump itself, or elsewhere in the circuit. This method is straightforward, efficient, and minimizes the risk of misdiagnosis, saving time and frustration.
To begin, ensure your vehicle is turned off and the ignition is in the "off" position. Locate the fuel pump connector, typically found near the fuel tank or along the chassis. Connect the power probe’s ground clip to a solid metal surface on the vehicle’s frame to establish a reliable ground. Insert the probe’s tip into the power wire terminal of the fuel pump connector. Turn the ignition to the "on" position but do not start the engine. The probe should light up or emit a tone if power is present, indicating the circuit is functioning up to that point.
If the probe fails to detect power, trace the wiring back toward the fuse box or relay. Test each connection point along the way to isolate the break or fault. Common culprits include corroded terminals, blown fuses, or a faulty relay. Replace any damaged components and retest the circuit. If power is present at the connector but the pump doesn’t operate, the pump itself may be faulty and require replacement.
Using a power probe offers a clear advantage over traditional multimeter testing by providing both visual and auditory feedback, making it easier to work in tight or poorly lit spaces. However, exercise caution when working near the fuel tank, as fuel vapors can be hazardous. Always disconnect the battery before making any repairs to avoid accidental shorts or sparks.
In summary, a power probe is a reliable and efficient tool for diagnosing fuel pump power issues in your 1987 Gimmy. By systematically testing the circuit at the connector and tracing faults, you can quickly identify and resolve the problem, ensuring your vehicle runs smoothly. Always prioritize safety and precision when working with electrical systems.
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Check Inertia Switch: Reset or replace the inertia switch if tripped or faulty
The inertia switch is a critical safety feature in your 1987 GMC Jimmy, designed to cut power to the fuel pump in the event of a collision. However, it can also trip accidentally due to rough terrain or even a hard bump, leaving you stranded with a non-responsive fuel pump. Before assuming the worst, checking and resetting this switch should be one of your first troubleshooting steps.
Locating the inertia switch is straightforward: it’s typically mounted in the passenger compartment, often near the kick panel or under the dashboard. Refer to your vehicle’s manual for the exact location. Once found, inspect the switch for a small button or reset mechanism. If the switch has tripped, this button will be popped out. Simply press it firmly until it clicks back into place, restoring power to the fuel pump.
While resetting the inertia switch is often a quick fix, repeated tripping or a non-responsive switch indicates a deeper issue. A faulty inertia switch can fail to reset properly or may not engage at all, posing both a safety risk and a reliability concern. If resetting doesn’t resolve the problem, replacement is necessary. Fortunately, inertia switches are inexpensive and widely available at auto parts stores. Installation is typically a plug-and-play process, requiring no specialized tools beyond a screwdriver. Always disconnect the battery before replacing the switch to avoid accidental short circuits.
Comparing the inertia switch to other fuel pump issues highlights its simplicity and importance. Unlike diagnosing a faulty pump relay or clogged fuel filter, checking the inertia switch is a low-effort, high-reward step. It’s a prime example of how modern safety features, while essential, can sometimes cause unexpected headaches. By understanding its function and knowing how to reset or replace it, you’re better equipped to keep your 1987 GMC Jimmy running smoothly, even when the road gets rough.
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Frequently asked questions
Locate the fuel pump relay under the hood, usually near the firewall. With the key in the "on" position, check for power at the relay's input and output terminals using a multimeter. If power is present at the input but not the output, the relay may be faulty.
The fuel pump fuse is typically located in the fuse box under the hood or near the driver's side kick panel. Consult your owner's manual or a repair guide for the exact location and fuse rating (usually 15-20 amps).
Yes, a poor or corroded ground connection can prevent the fuel pump from receiving proper power. Check the ground wire connected to the fuel pump (usually near the fuel tank) and ensure it's clean, secure, and making good contact.
Use a multimeter to check for continuity in the fuel pump wiring harness. Disconnect the fuel pump connector and test for power at the pump side of the connector with the key in the "on" position. If power is present, the issue may be with the pump itself. If not, trace the wiring back to the relay and fuse to identify any breaks or shorts.
