1990 Acura Integra Fuel Pump Relay: Location, Testing, and Replacement

Diagnosing and fixing a faulty fuel pump relay is often the critical step to restoring your 1990 Acura Integra when it cranks but won't start, especially if you hear the fuel pump prime when you first turn the key to "ON." Located in the under-dash fuse/relay box, relay K6 (or "Main Relay 1") controls power to the fuel pump and fuel injectors. Symptoms include sudden no-start, intermittent stalling, and inconsistent fuel pump operation. Testing involves checking for audible clicks, verifying power and ground signals at the relay socket using a multimeter, and performing a jumper wire test. Replacement with a compatible Honda/Acura relay is a straightforward, relatively inexpensive fix costing between $25-$70 for a quality part, typically taking under 30 minutes for a do-it-yourself repair.

The inability to start your 1990 Acura Integra, particularly when the engine cranks over strongly but refuses to fire, can stem from various causes. However, a surprisingly common culprit, especially in vehicles of this age, is failure within the Main Relay assembly. Often referred to specifically as the Fuel Pump Relay (F/P Relay or PGM-FI Main Relay – part number 39400-SH3-003, 39400-SH3-A01, or equivalents), this single integrated component houses two crucial relays in one housing: one controlling the Engine Control Unit (ECU) and fuel injectors, and the other dedicated to powering the fuel pump. When either relay inside this box fails, your engine loses vital components needed for combustion. Recognizing the signs, knowing its location, and understanding how to test and replace it are essential skills for any '90 Integra owner.

Recognizing the Symptoms of a Failing 1990 Integra Fuel Pump Relay

Don't ignore these warning signs pointing towards relay trouble, often manifesting intermittently before complete failure:

1. Engine Cranks But Won't Start: This is the most frequent symptom. The starter engages and spins the engine normally, but the engine never catches and runs. This happens because neither fuel pressure is being generated (due to the fuel pump not activating) nor are the fuel injectors receiving their activation signal if the ECU relay section fails.
2. Intermittent Starting Problems: You might experience no-start conditions occasionally, perhaps after the car has been driven and warmed up, or after sitting in hot weather. Later, sometimes after the car cools down, it starts normally. Heat-related failure of internal relay solder joints is a classic pattern.
3. Sudden Stalling While Driving: The engine might abruptly die while driving, potentially leaving you stranded, only to possibly restart after cooling down for some time.
4. No Fuel Pump Priming Sound: When you first turn the ignition key to the "ON" position (before cranking), you should hear a distinct whirring or humming sound from the rear of the car (near the fuel tank) for about 2 seconds. This is the fuel pump priming the system. The complete absence of this sound is a strong indicator the fuel pump relay is not activating the pump.
5. Absence of Check Engine Light at Key ON: When you turn the ignition key to "ON," the Check Engine Light (CEL) on your dashboard must illuminate briefly (usually for about 5 seconds) as part of the ECU's self-test. If the CEL does not illuminate at all, it points strongly towards the ECU/fuel injector section of the Main Relay failing, as the ECU isn't getting power.

Locating the Fuel Pump Relay in Your 1990 Acura Integra

Finding the relay is straightforward:

1. Position: Sit in the driver's seat. Look down to the lower left of the steering wheel, towards the very left edge of the dash panel.
2. The Fuse/Relay Box: You'll see a rectangular plastic cover. This is the access panel for the under-dash fuse/relay box.
3. Opening the Cover: Remove the cover by gently prying at its lower edge and pulling it straight out towards you.
4. Identifying Relay K6 / Main Relay: Inside the box, you'll find numerous fuses and several larger, cube-shaped relays. The critical component you need is typically labeled as K6 on the inside of the cover diagram or sometimes stamped on the relay box housing itself. It is very commonly referred to as the PGM-FI Main Relay or simply Main Relay 1.
5. Visual Identification: The relay itself is black, cube-shaped (approximately 1.5" x 1.5" x 0.75"), and plugs directly into the socket at position K6. It's often located near the upper right corner of the fuse/relay box area, usually surrounded by other relays and fuses.

Thoroughly Testing the 1990 Integra Fuel Pump Relay

Testing involves a multi-step approach to accurately diagnose both internal relays:

Initial Audible Check:

1. Have an assistant turn the ignition key to the "ON" position (do not crank).
2. Simultaneously, place your fingers on the relay (or listen closely).
3. You should feel and hear a distinct "click" sound the instant the key is turned "ON". This click confirms at least part of the relay coil is receiving the signal and the main relay is attempting to engage its internal switches. Note: A click doesn't guarantee both internal relays are functioning correctly. Listen for a second faint click when turning the key back "OFF".

Multimeter Testing at the Relay Socket:
This requires accessing the relay socket terminals. Ensure you know the terminal numbering! Use the diagram on the box or cover. Terminals are typically labeled with numbers:

• PIN 1: Output terminal for the Fuel Pump relay section (+12V to pump when active).
• PIN 2: Input voltage (+12V from battery) for the fuel pump section's coil (comes active with Key ON).
• PIN 3: Control Ground for both relay coils (- Signal controlled by ECU during crank/run).
• PIN 4: Input voltage (+12V from battery) for the ECU/Injector section's coil (comes active with Key ON).
• PIN 5: Output terminal for the ECU/Injector section (+12V to ECU and Injectors when active).
• PIN 6: Input voltage (+12V) for both relay output circuits (Main battery feed).
• PIN 7: Not usually used (or specific function varies, often unused in earlier models).
• PIN 8: Input voltage (+12V) for the fuel pump section's coil (sometimes constant feed).

1. Preparation: Turn the ignition OFF. Locate and carefully remove the relay from its K6 socket.
2. Check Power Inputs (PIN 6 & PIN 8):
   • Set your multimeter to Volts DC. Connect the negative (-) lead to a clean, unpainted metal grounding point under the dash (like a bolt).
   • Turn the ignition key to the "ON" position.
   • Touch the positive (+) meter probe to socket terminal PIN 6. You must see a constant +12 Volts (battery voltage).
   • Touch the probe to socket terminal PIN 8. You should also see a constant +12 Volts.
3. Check Power to Coils (PIN 2 & PIN 4):
   • Key still ON, probe socket terminal PIN 2 (fuel pump coil feed). Should show +12V.
   • Probe socket terminal PIN 4 (ECU/Injector coil feed). Should show +12V.
4. Check Control Ground (PIN 3):
   • Key still ON, switch multimeter to measure continuity (Ohms) or Volts relative to ground.
   • Voltage Check: Probe PIN 3 with the meter positive lead (negative lead still grounded). It should read very low voltage (close to 0V) indicating a good ground path is present. Crucially, while an assistant cranks the engine, PIN 3 must still show low voltage (~0V) to indicate the ECU is providing the ground. If it goes high (near 12V) while cranking, the ECU ground signal is missing (problem elsewhere).
   • Continuity Check: If possible with tools/access, probe PIN 3. With Key OFF, there should be no continuity to ground. With Key ON, and especially while cranking, continuity to ground (or very low resistance) should be present.
5. Check Output Behavior (PIN 1 & PIN 5):
   • Key OFF. Connect meter positive lead to socket terminal PIN 1 (FP Output). Negative lead grounded.
   • Turn Key ON: Within 2 seconds, PIN 1 must show +12V for approximately 2 seconds (during the prime cycle), then drop back to 0V if the engine isn't cranking/running. This verifies the fuel pump output channel is triggering.
   • Connect positive lead to socket terminal PIN 5 (ECU/Injector Output). Negative lead grounded.
   • Turn Key ON: PIN 5 must show +12V constantly as long as the key is ON. This verifies the ECU/Injector output channel is functioning.

The Jumper Wire Test (Critical Safety - Pinpointing Failure):
THIS BYPASSES THE RELAY. PERFORM CAREFULLY TO ONLY TEST CIRCUITS. DO NOT RUN ENGINE LONG OR DRIVE WITH JUMPER WIRES INSTALLED.

1. Goal: To determine if bypassing the internal relays makes the car start.
2. For Fuel Pump Circuit (Confirming Relay Failure Causes No Fuel):
   • Remove the relay. Insert a fused jumper wire (10A fuse minimum) or a heavy-duty paperclip ONLY between socket terminals PIN 6 (Input) and PIN 1 (Fuel Pump Output).
   • Turn Key ON: You should definitely hear the fuel pump run constantly now. If you didn't hear it before and do now, the fuel pump relay section was bad.
3. For ECU/Injector Circuit (Confirming Relay Failure Cuts ECU/Injectors):
   • Crucially, try starting first: Attempt to crank the engine normally (without jumper wires). Does it start? If it cranks but doesn't start, proceed.
   • Remove relay. Insert a fused jumper wire between socket terminals PIN 6 (Input) and PIN 5 (ECU/Injector Output).
   • Do not install jumper for fuel pump (PIN 1 to 6) yet.
   • Turn Key ON: Check Engine Light should now illuminate on the dash (if relay was at fault).
   • Now insert a second fused jumper wire between PIN 6 and PIN 1.
   • Attempt to start the engine. If the engine starts and runs normally while both jumpers are installed (PIN6->PIN5 and PIN6->PIN1), this is definitive proof that your Main Relay (K6) has failed internally and needs replacement. The car started because you manually provided the power outputs the relay was failing to deliver.

Replacing the Faulty 1990 Acura Integra Fuel Pump Relay

Once diagnosed as faulty, replacing relay K6 is one of the simpler DIY jobs:

1. Acquire the Replacement: Purchase a new or quality remanufactured Main Relay (PGM-FI Main Relay) specifically compatible with the 1990 Acura Integra (part numbers 39400-SH3-003, 39400-SH3-A01, or a confirmed cross-reference like Standard Motors RY134 / Bosch 0332019150 / BWD R3128, etc.). Expect to pay $25-$70. Avoid the cheapest generic relays – reliability matters. Verify the pin configuration matches exactly.
2. Prepare: Turn the ignition OFF. Locate relay K6 in the under-dash fuse box (as previously described).
3. Remove the Old Relay: Firmly grasp the relay and pull it straight out of its socket. Avoid excessive side-to-side rocking. If stuck, gently wiggle while pulling straight. Inspect the socket terminals for any corrosion or damage; clean if necessary using electrical contact cleaner and a small brass brush or toothpick.
4. Install the New Relay: Orient the new relay correctly by aligning the terminals and the relay's locking tab with the socket. Push it firmly and evenly into place until it seats completely and you feel the locking tab engage. Ensure it's fully seated.
5. Verify Operation: Turn the ignition key to "ON". Listen for the fuel pump's 2-second prime cycle hum. Check that the Check Engine Light illuminates. Attempt to start the engine.

Cost Considerations for Replacement

The primary cost is the relay itself:

• New Genuine Acura (Honda): Less common now, typically $50-$70+ if available.
• New Aftermarket (Quality Brands like Standard, Bosch, Genuine Gemini, etc.): $35-$60. Offers good reliability.
• Remanufactured / Economy Aftermarket: $25-$40. Quality and lifespan can vary; read reviews. Best for temporary fixes or tight budgets.
• Professional Installation: If you choose a mechanic, labor is typically 0.3 to 0.5 hours, adding $30-$75 to the cost depending on shop rates, plus the relay cost. DIY installation clearly saves this labor expense.

By understanding the vital role of the Main/Fuel Pump relay (K6) in your 1990 Acura Integra, recognizing its failure symptoms, knowing exactly where it's located under the dash, confidently performing methodical testing procedures, and safely completing a replacement, you empower yourself to resolve one of the most common causes of a frustrating no-start condition. This critical component, once restored, ensures your fuel pump and engine management system receive the stable power they need, getting your classic Integra back on the road reliably.