1987 Chevy Fuel Pump Relay: Complete Guide to Location, Diagnosis, and Replacement
If your 1987 Chevy truck, Suburban, or Blazer cranks but won't start, the fuel pump relay is likely the first component you should check. The fuel pump relay on a 1987 Chevy is a small electrical switch that controls power to the fuel pump, and when it fails, you get a classic symptom: the engine cranks for a long time before finally starting, or it won't start at all. This guide will show you exactly where to find the relay, how to test it, and what to do when it needs replacement.
The fuel pump relay in a 1987 Chevy R20, C10, K5 Blazer, and most other GM trucks of this era is typically located on the passenger side of the firewall in the engine compartment, mounted on a relay bracket. Some sources also report finding it under the dashboard on the driver's side near the firewall. The relay is a standard Bosch-style rectangular unit, usually black or gray in color, with four or five pins.
How the Fuel Pump Relay Works in a 1987 Chevy
The 1987 Chevy fuel system uses a relay-based design with a backup circuit. Understanding this helps you diagnose problems faster.
The ECM controls the relay. When you turn the key to the ON position, the Engine Control Module (ECM) energizes the fuel pump relay for about 2 to 3 seconds to prime the fuel system. This is why you should hear a brief whir from the fuel pump when you turn the key before cranking.
The oil pressure switch is the backup. If the relay fails, the engine will still start after extended cranking—but only once oil pressure builds up to roughly 4 PSI. At that point, the oil pressure switch closes and directly powers the fuel pump, bypassing the relay entirely. This is why a failed relay often causes the engine to crank for 10-15 seconds before firing up.
The circuit has two power sources. The ECM B fuse (usually a 20-amp fuse) provides constant battery power to the fuel pump relay and the ECM. The relay then sends power through the tan/white wire (circuit 120) to the fuel pump. The dark green/white wire (circuit 465) from the ECM triggers the relay to close.
Step-by-Step Guide to Locating the Fuel Pump Relay
Step 1: Check the passenger side firewall first. Open the hood and look at the firewall on the passenger side. The relay is usually mounted on a metal bracket with several other relays. On many 1987 models, it shares this bracket with the air conditioning relay and fan relay.
Step 2: Look for a rectangular plastic relay. The fuel pump relay is typically a black or gray rectangular box about 1 inch wide and 1.5 inches tall, with a 4- or 5-pin connector on the bottom. It may be labeled "Fuel Pump" or "FP" on the fuse box cover, but don't count on it—labels often fade or fall off after 35+ years.
Step 3: Trace the wiring if you're unsure. If multiple relays look the same, follow the tan/white wire from the fuel pump harness. This wire leads directly back to the relay. You can also look for a red wire with a green connector end sticking out of the relay harness—this is the fuel pump test wire.
Step 4: Check the under-dash fuse box as a secondary location. Some 1987 models have the relay under the dashboard on the driver's side, near the firewall. If you don't find it in the engine bay, check there.
How to Test the 1987 Chevy Fuel Pump Relay
Method 1: The listening test. Turn the ignition key to the ON position (don't crank). Listen near the fuel tank for a 2-second buzz from the fuel pump. If you hear it, the relay is working. If you don't, the relay or its circuit has a problem.
Method 2: Use the test wire. The red wire with a green connector end that sticks out of the relay harness is a factory test lead. Apply 12 volts from the battery to this wire using a fused jumper wire. If the fuel pump runs, the relay is bad because the pump is getting power when bypassed.
Method 3: Swap relays. If your truck has multiple identical relays (like the A/C relay or fan relay), swap them. If the fuel pump starts working after swapping, you've found the bad relay.
Method 4: Check for power at the relay. With the key OFF, you should have 12 volts at one terminal of the relay connector. With the key ON, you should see voltage at the control terminal (dark green/white wire) for about 2 seconds. If you don't get that control signal, the ECM or wiring to it is the problem.
Common Symptoms of a Failed Fuel Pump Relay
The engine cranks for a long time before starting. This is the most common symptom. The relay isn't energizing the pump during the prime cycle, so the pump only runs once oil pressure builds up during cranking.
The engine cranks but won't start at all. If both the relay and the oil pressure switch fail, the pump gets no power. This is less common but happens.
The engine starts fine when cold but stalls after driving. A failing relay can work intermittently when cold but fail when it heats up from engine heat.
No fuel pump prime sound. If you don't hear the 2-second whir when turning the key to ON, the relay or its power supply is suspect.
Troubleshooting Beyond the Relay
If replacing the relay doesn't fix the problem, check these components in order:
The ECM B fuse. This 20-amp fuse powers the relay and the ECM. If it's blown, the pump won't prime. Check for shorts in the tan/white wire that could cause the fuse to blow.
The fuel pump itself. Use the red test wire to apply 12 volts directly to the pump. If the pump doesn't run, the pump motor is dead.
The oil pressure switch. This switch is wired in parallel with the relay. If it fails, the pump won't get power through the backup circuit either. However, this usually only matters if the relay is also faulty.
The ground connection. The black ground wire from the fuel pump connects to the frame rail. Corrosion at this point causes voltage drops that can make the pump run slowly or not at all. Check for clean, rust-free connections.
Replacement Options for the 1987 Chevy Fuel Pump Relay
Genuine GM parts. GM part numbers for the fuel pump relay on 1987 Chevy models include 14078915, 10026187, and 10034222, depending on the exact model and engine. These are direct OEM replacements.
Aftermarket relays. Standard Bosch-style relays found at AutoZone, NAPA, or O'Reilly Auto Parts will work. The NAPA Echlin AR229SB is a common replacement. Wells WVE also makes a compatible relay for 1987-1995 GM trucks.
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Final Tips for Working on Your 1987 Chevy Fuel System
Disconnect the battery before working on electrical components. This prevents accidental shorts and sparks, especially near the fuel tank.
Use a fused jumper wire for testing. Never use a solid wire to bypass the relay for more than a quick test. A short circuit can melt wiring and cause a fire.
Replace the relay even if it tests good intermittently. Relays can fail when hot but test fine when cold. If you have symptoms and the relay is 35 years old, replace it. It's a cheap part.
Check the wiring harness for chafing. The 1987 Chevy's wiring harness runs along the frame and can rub against metal edges. Look for worn spots, especially near the firewall and the fuel tank connection.
The fuel pressure for a 1987 Chevy TBI system is 9-12 PSI. There is no test port on the throttle body; you must check pressure at the fuel line or back of the throttle body.
Getting your 1987 Chevy's fuel pump relay sorted is usually a straightforward job. With the right location information and a few simple tests, most owners can diagnose and replace the relay in under an hour. For a complete, guaranteed replacement, visit https://www.kemsoracing.com/ to find fuel pump components backed by a lifetime warranty and designed for lasting performance.