Checking Fuel Pump Pressure: 89 Ford Guide

Checking the fuel pump pressure on an 89 Ford is a straightforward process that can help identify any issues with the fuel pump. The fuel pump is responsible for delivering fuel to the engine, and when it fails, the engine will not start or will exhibit performance problems. By connecting a fuel pressure test gauge to the fuel injector rail, you can measure the fuel pressure and compare it to the factory specifications. This will indicate whether the fuel pump is delivering the correct amount of pressure and volume to the engine. Additionally, checking the fuel pump inertia switch, which cuts off power to the fuel pump in the event of a collision, is important to ensure it is not activated and causing issues.

Check the fuel pump relay

To check the fuel pump relay in your 89 Ford Bronco, follow these steps:

• Locate the fuel pump relay in the power distribution box, typically found near the battery.
• Remove the relay from the box and inspect it for any signs of damage or corrosion.
• Using a multimeter, set it to read DC voltage.
• Test for voltage at the relay's power input pin with the key in the "on" position.
• If there is no voltage, check the relay's control circuit for any breaks in the wiring or damaged components.
• If voltage is present, jump the relay's power output pins with a jumper wire to determine if the fuel pump runs.
• If the fuel pump runs, the relay is likely faulty and should be replaced.

The fuel pump relay is typically located in the power distribution box under the hood, on the driver's side inner fender, or possibly tucked into a plastic bracket on the back of the coolant/washer fluid reservoir.

Check the wiring and connections to the fuel pump

To check the wiring and connections to the fuel pump on your 89 Ford, you'll need to locate the fuel pump relay in the power distribution box, typically found under the hood near the battery.

First, inspect the relay for any signs of damage or corrosion. Then, using a multimeter set to read DC voltage, test for voltage at the relay's power input pin with the key in the "on" position. If there's no voltage, check the relay's control circuit for any breaks in the wiring or damaged components.

Next, turn your attention to the wiring and connections. Over time, the wiring may become corroded or damaged, causing problems with the fuel system. Ensure that all connections are clean and tight.

Additionally, check the small black wire with a green stripe connected to the NEG (-) post of your battery or the body near it. Make sure the body is grounded, as a proper ground connection is crucial for the fuel pump's operation.

If you find any issues with the wiring or connections, address them and retest the fuel pump to ensure proper operation.

Test the fuel pump inertia switch

To test the fuel pump inertia switch on your 89 Ford, you'll need to locate the switch first. On some Ford models, the inertia switch is located at the far left part of the toe board. On others, it's on the passenger side cowl panel, just forward of the right front door.

Once you've located the inertia switch, check the red button on top of it. If the button is raised, the switch is in the open position and is not supplying power to the fuel pump. To reset the switch, simply push the button in (or down). This will allow voltage to flow to the fuel pump.

If your Ford won't start and you suspect the inertia switch may be triggered, you can try resetting it. The inertia switch is a safety feature that cuts off power to the fuel pump in the event of a collision. However, it can also be triggered by other occurrences, such as a blown tire or hitting a pothole.

If resetting the inertia switch doesn't solve the problem, there may be other issues with your fuel pump or electrical system that will need further diagnosis.

Check the fuel injectors

To check the fuel injectors on your 89 Ford, you can perform a listening test, a power test, and a trigger circuit test.

Listening Test

Put on safety gear, such as eye protection and gloves, and open the hood of your car. Locate the fuel injectors, which are usually found on the intake manifold, with one injector between the fuel rail and the intake manifold. Place a long metal rod or screwdriver on one of the injectors and bring your ear close to listen for an audible clicking sound, indicating that the fuel injector is functioning. Repeat this for each injector. If you find one that isn't clicking, there may be a problem with the injector or the electronic component that controls it.

Power Test

Turn the key to the "on" position without starting the engine to activate the vehicle's electrical system. Connect a test light to the negative terminal on the battery, and locate the two wires going into each injector. One of these wires is a 12-volt constant that should be continuously receiving power. Test each wire for voltage using the test light. If neither wire makes the light turn on, there is an issue with the power reaching the fuel injector. Repeat the process for each injector.

Trigger Circuit Test

Connect the test light to the positive terminal of the battery. Have a friend start or turn over the engine. Probe the opposite wire of the constants identified in the previous test with the test light. With the engine running at idle, the test light should flicker dimly, and more brightly when your helper applies throttle by pressing the gas pedal. This light represents the signal being transmitted by the ECU to the injector to spray fuel. If the test light is failing to light up, the injector may be bad, or there could be an issue with the electronic control unit.

Additional Notes

• Fuel injectors can get clogged and sensors can go bad, causing the fuel injectors to malfunction.
• Fuel injectors usually last between 50,000 and 100,000 miles, but they can wear out sooner.
• Fuel injectors can be cleaned by pouring fuel system cleaner into a full tank of gas, or by removing them and spraying them with fuel system or carburetor cleaner.

Check the fuel pump pressure with a fuel pressure test gauge

Checking the fuel pump pressure with a fuel pressure test gauge is a straightforward process and can help you identify issues with your Ford's fuel pump. Here's a step-by-step guide on how to do it:

Step 1: Understand the Symptoms of a Bad Fuel Pump

Before you begin, it's important to know the signs of a failing fuel pump. Typically, a faulty fuel pump will exhibit one or more of the following symptoms:

• Engine backfires through the intake manifold when under load.
• The check engine light illuminates, indicating lean air/fuel mixture codes or a MAP sensor issue.
• Lack of power when accelerating the engine under load.
• Engine stalls when accelerated under load.
• The engine cranks but does not start due to a lack of fuel.
• The engine starts but runs poorly and may shut off after a few seconds.
• Stalling when accelerating.
• No power when driving.
• Backfiring.
• Check engine light is illuminated, indicating lean air/fuel mixture issues.

Step 2: Purchase a Fuel Pressure Test Gauge

You will need a fuel pressure test gauge to accurately measure the fuel pump pressure. The following kits are recommended and include the Ford Schrader valve adapter:

• Actron CP7838 Professional Fuel Pressure Tester
• OEMTOOLS 27167 Fuel Pressure Test Kit
• Performance Tool W89726 Master Fuel Injection Test Kit
• Actron CP7818 Fuel Pressure Tester Kit
• OTC 5630 Fuel Pressure Test Kit

Step 3: Check the Fuel Pump Inertia Switch

The fuel pump inertia switch is a safety feature that cuts power to the fuel pumps in the event of a collision. Even a minor impact, like jumping a curb, can activate this switch. Resetting it is simple:

• Locate the fuel pump inertia switch behind the passenger-side plastic kick panel.
• Push down on the red button on top of the switch until you hear a "click".
• Crank and start the engine.

If the engine starts with either tank selected (front or rear), the fuel pump inertia switch was activated, and you can move on to testing fuel pump pressure.

If the engine does not start with either tank selected, the issue may lie with the fuel pump relay, fuel tank selector switch, or the fuel pump inertia switch itself.

Step 4: Perform the Fuel Pump Pressure Test

Now, you can proceed with testing the fuel pump pressure:

• Locate the Schrader valve on the fuel injector rail.
• Remove the dust cap from the Schrader valve and place a shop towel underneath to catch any leaking fuel.
• Connect the fuel pressure gauge to the Schrader valve.
• Ask an assistant to cycle the key on and off without cranking the engine while you observe the fuel pressure gauge.
• Check for fuel leaks at the Schrader valve connection and tighten if necessary.

Step 5: Interpret the Results

Your fuel pressure gauge should read between 35 to 45 PSI with the Key On Engine Off (KOEO) for a functional fuel pump.

Case 1: 0 PSI

If the gauge reads 0 PSI, this confirms a lack of fuel as the cause of the no-start issue. To be absolutely sure, you can perform an additional test by attaching a multimeter in Volts DC mode to the wire supplying voltage to the fuel pump. During cranking, verify that the fuel pump is receiving this voltage. If it is and the fuel pump is still not functioning, the fuel pump requires replacement.

Case 2: 35 to 45 PSI

A fuel pressure reading between 35 to 45 PSI indicates that the fuel pump is operational and delivering sufficient fuel to the fuel injectors. Therefore, the reason for the no-start issue lies elsewhere, and the fuel pump is functioning as expected.

Frequently asked questions