1987 BMW 325i Fuel Pump Relay Location: Your Complete Guide

The fuel pump relay in your 1987 BMW 325i (E30 chassis) is located inside the main power distribution box situated under the hood, near the driver's side strut tower. This black plastic box houses several important fuses and relays crucial to your car's operation. Specifically, the fuel pump relay is one of several identical-looking relays plugged into sockets within this box. Identifying the correct one is key, as they are not individually labeled inside the box itself.

Finding and understanding this small but vital component is essential for diagnosing and resolving fuel delivery issues, a common problem area in these classic cars. Knowing exactly where it is and how to access it can save significant time and frustration.

Understanding the Power Distribution Box Layout

The main power distribution box, often referred to simply as the fuse box or relay box, is positioned on the left-hand side (driver's side in left-hand-drive vehicles) of the engine bay. It's mounted vertically on a bracket attached to the inner fender wall, just behind the battery and close to the brake fluid reservoir and windshield washer fluid reservoir. It's a large, rectangular, black plastic box with a removable lid. This lid is usually secured by plastic clips or small screws on the sides.

Opening the lid reveals an array of fuses (small, colored plastic components with metal strips visible through the top) and several larger, cube-shaped components – these are the relays. The relays are typically black or dark-colored plastic cubes, roughly 1 inch square, with multiple electrical terminals (pins) protruding from the bottom that plug into sockets within the box. Each relay socket in the box might have a small label adjacent to it, often molded into the plastic base or on a sticker, indicating its function. However, these labels can fade, become dirty, or be missing entirely over time.

Identifying the Fuel Pump Relay (K5)

The critical step is identifying which of these identical-looking relays is the fuel pump relay. BMW designated this relay as K5. This designation is crucial. Here’s how to find it:

  1. Look for the K5 Label: Carefully inspect the plastic base inside the fuse box where the relays plug in. Look specifically for the socket labeled K5. This label is usually molded into the plastic or printed on a sticker near the socket. It might be small, so good lighting and perhaps a magnifying glass can help. The K5 designation is the most reliable indicator.
  2. Position: While the exact position can vary slightly depending on the model year and specific production date within 1987, the K5 relay is generally found in the row of relays closest to the front of the car (the radiator side) within the fuse box. It's often one of the relays positioned towards the outer edge (fender side) of the box.
  3. Relay Appearance: The fuel pump relay itself looks identical to several other relays in the box, such as the main relay (often K1 or K6) or the horn relay. They are typically black plastic cubes with four or five electrical pins on the bottom. There is usually no external marking on the relay itself indicating its function; identification relies entirely on its socket label (K5) within the fuse box.

Why the Fuel Pump Relay Matters

The fuel pump relay acts as an electrically controlled switch. It receives a low-power signal from the engine control unit (ECU or DME) when the ignition is turned on (and especially during cranking). This signal energizes the relay's internal electromagnet, closing a set of internal contacts. When these contacts close, they complete the high-power circuit that delivers battery voltage directly to the electric fuel pump located inside or near the fuel tank.

If the K5 relay fails – its internal contacts become corroded, burnt, or the electromagnet coil breaks – it cannot complete this circuit. The result is that the fuel pump receives no power and therefore doesn't run. This leads directly to a no-start condition: the engine cranks but never fires because no fuel is being delivered to the fuel injectors. A faulty fuel pump relay is one of the most common causes of a sudden no-start situation in an E30 BMW that was previously running fine.

Symptoms of a Faulty Fuel Pump Relay

Recognizing the signs of a failing K5 relay can help diagnose the problem quickly:

  1. Engine Cranks But Won't Start: This is the hallmark symptom. The starter motor turns the engine over normally, but the engine doesn't fire up or show any sign of ignition.
  2. No Fuel Pump Prime Sound: When you turn the ignition key to the "ON" position (before cranking), you should hear a distinct whirring or humming sound coming from the rear of the car (near the fuel tank) for about 1-3 seconds. This is the fuel pump priming the system. If you hear no sound at all when turning the key to "ON," a faulty fuel pump relay is a prime suspect (though a dead fuel pump or wiring issue could also be the cause).
  3. Intermittent Starting Problems: Sometimes the relay might work intermittently. The car might start fine one moment and then refuse to start the next, perhaps after being driven and warmed up, or after sitting for a short while. This can be caused by failing internal contacts within the relay.
  4. Relay Clicks But Pump Doesn't Run: You might hear the relay click when turning the key to "ON," indicating the electromagnet is activating, but the fuel pump still doesn't run. This suggests the relay's internal contacts are faulty and not passing current, even though the relay is receiving the signal to activate.

Testing the Fuel Pump Relay

Before rushing to replace the relay, it's wise to test it. Here's a basic method:

  1. Locate K5: Identify the K5 relay socket as described above.
  2. Swap with a Known Good Relay: The simplest test is substitution. Identify another relay in the box that is identical in appearance and known to be working correctly. Common candidates are the horn relay or the high beam relay. Carefully pull out the suspected K5 relay and the known good relay. Plug the known good relay into the K5 socket. Turn the ignition key to "ON" and listen for the fuel pump priming sound. If you now hear the pump prime, the original K5 relay is faulty. Important: Ensure the relay you swap in is electrically identical! Check the part number or the pin configuration (number and arrangement of pins).
  3. Basic Electrical Test (Requires Multimeter):
    • Remove the K5 relay.
    • Set your multimeter to measure resistance (Ohms Ω).
    • Identify the two control coil terminals on the relay (usually the two smaller pins or the ones connected to the electromagnet coil inside – consult a relay diagram for your specific relay part number if possible). Touch the multimeter probes to these two terminals. You should measure a resistance value, typically between 50 and 100 Ohms. A reading of infinite resistance (OL or overload) means the coil is broken and the relay is dead. A reading of zero Ohms means the coil is shorted and the relay is also bad.
    • Set the multimeter to continuity (beep mode).
    • Identify the two main switch terminals (usually the two larger pins that carry the high current to the pump).
    • Touch the probes to these two large terminals. There should be no continuity (no beep) when the relay is at rest (de-energized).
    • Apply 12 volts to the two control coil terminals (matching polarity if possible, though many relays aren't polarity-sensitive for the coil). You can use jumper wires connected to the car battery (BE CAREFUL) or a dedicated 12V power source. When 12V is applied to the coil, you should hear and feel a distinct click from the relay. Simultaneously, your multimeter should now show continuity (beep) between the two large main switch terminals. If it doesn't click or doesn't show continuity when powered, the relay is faulty.

Replacing the Fuel Pump Relay

If testing confirms the K5 relay is faulty, replacement is straightforward:

  1. Purchase the Correct Relay: Obtain a replacement relay. It's crucial to get the correct part. The original BMW part number for the 1987 325i fuel pump relay is often 61 36 1 373 319. However, confirm this using your VIN with a dealer parts department, a reputable online BMW parts catalog, or by matching the part number printed on your old relay. Bosch was the common OEM supplier, and equivalent Bosch aftermarket relays (like Bosch 0 332 014 406) are widely available and reliable. Ensure the replacement relay has the same pin configuration and electrical ratings.
  2. Locate K5 Socket: With the ignition OFF, open the fuse box lid and locate the K5 socket again.
  3. Remove Old Relay: Firmly grasp the faulty relay and pull it straight out of its socket. Avoid excessive wiggling or force that could damage the socket pins.
  4. Install New Relay: Orient the new relay correctly (match the pin configuration to the socket) and push it firmly and squarely into the K5 socket until it seats completely. You should feel it click into place.
  5. Test: Turn the ignition key to the "ON" position. You should hear the fuel pump prime for a few seconds. Attempt to start the engine. It should now start normally.

Troubleshooting Tips If the New Relay Doesn't Fix the Problem

If you've replaced the K5 relay and the fuel pump still doesn't run:

  1. Check Fuses: Inspect the fuses inside the main power distribution box. The fuel pump circuit is protected by a fuse. For the 1987 325i, this is typically Fuse 11 (15 Amp). Visually inspect the fuse wire – it should be intact. Replace it if blown. Check other relevant fuses too (e.g., main DME relay fuse).
  2. Check the Main DME Relay (K1/K6): The fuel pump relay (K5) gets its activation signal from the Engine Control Unit (DME). However, the DME itself requires power, supplied via the main DME relay (often labeled K1 or K6, located in the same fuse box). If the main DME relay fails, the DME won't power up, and it won't send the signal to activate the K5 fuel pump relay. Test or swap the main DME relay using the same methods described for the fuel pump relay.
  3. Listen for the Relay Click: Have an assistant turn the ignition key to "ON" while you listen near the fuse box. You should hear a distinct click from the K5 relay socket as the relay activates. If you don't hear a click, the problem lies before the relay: faulty DME, wiring issue between DME and relay, or a problem with the main DME relay/power supply to the DME. If you do hear the relay click but the pump doesn't run, the problem lies after the relay: faulty fuel pump, wiring issue between relay and pump, bad ground connection for the pump, or a problem with the fuse supplying power to the relay.
  4. Test Fuel Pump Power: This requires a multimeter or test light. Locate the fuel pump electrical connector (usually accessible under the rear seat or through an access panel in the trunk floor near the fuel tank). With the ignition turned to "ON," check for 12 volts at the pump's power wire (consult a wiring diagram for wire color, often violet/white or green/violet). If you have 12V at the pump connector when the ignition is on (and the relay clicks), the pump itself is likely faulty. If you don't have 12V, trace the wiring back towards the relay/fuse box, checking for breaks, corrosion, or poor connections.
  5. Inspect Grounds: A poor ground connection for the fuel pump can prevent it from running, even if it has power. Locate the fuel pump ground point (often near the pump itself or on the chassis nearby), clean any corrosion, and ensure the connection is tight.
  6. Consider the Fuel Pump Itself: If power and ground are confirmed good at the pump connector, the fuel pump motor itself is likely dead and needs replacement.

Preventative Maintenance and Reliability

While relays can fail unexpectedly, there are steps to improve reliability:

  • Use Quality Replacements: Stick with OEM (BMW) or reputable brands like Bosch for replacement relays. Cheap, generic relays often have shorter lifespans.
  • Clean Connections: Periodically inspect the fuse box and relay sockets. If you notice any corrosion on the relay pins or socket contacts, carefully clean them with electrical contact cleaner and a small brush. Ensure relays are fully seated.
  • Consider Carrying a Spare: Given the critical role of the K5 relay and its relatively low cost, carrying a spare relay in the glove box is excellent insurance against being stranded by a sudden failure.

Conclusion

Knowing the 1987 BMW 325i fuel pump relay location – specifically identified as relay K5 inside the main power distribution box under the hood – is fundamental knowledge for any owner of this classic car. This relay is a common failure point leading to frustrating no-start conditions. By understanding its location, function, symptoms of failure, and how to test and replace it, you empower yourself to quickly diagnose and resolve a significant percentage of fuel delivery problems. Remember to always confirm the relay socket label (K5), test before replacing, and use a high-quality replacement part. With this knowledge, you can keep your E30 running smoothly.

Back to blog