Finding Fuel Pressure Problems In Your '87 Bronco

If you're experiencing issues with your 1987 Ford Bronco II, such as poor acceleration, lack of power, or a weak fuel pump, you may need to check the fuel pressure. To do this, you'll need a fuel pressure tester kit, which you can usually borrow from auto parts stores with a deposit. You'll also need a jumper wire or paper clip and a wire with alligator clips on both ends. Connect the tester kit to the fuel rail's Schrader valve, which is usually covered with a black plastic dust cap. With the engine off, turn the key to the 'run' position and check the fuel pressure gauge. It should be within the range specified in your service manual. Repeat this test with the engine idling and then again with the engine running at wide-open throttle. Compare the PSI readings at each stage to diagnose any issues with your fuel pump or regulator.

Check the fuel pressure gauge with the key in the 'run' position, engine off, and pump running

To check the fuel pressure on a 1987 Ford Bronco, you'll need a fuel pressure tester kit, which you can borrow from most large auto parts stores with a deposit. You can also use any 0-100psi gauge if you have the right adapters. You'll also need a jumper wire (or a paper clip) and a wire with alligator clips on both ends.

First, locate the EEC test connector, which should be near the driver-side hood hinge. Connect the jumper wire to the lower right terminal of the EEC test connector, and then use the wire with the alligator clips to short the jumper wire to ground.

Next, locate the fuel rail fuel pressure test port. This is usually covered with a black plastic dust cap and is attached to the chrome fuel rail. On the 460 engine, it's on the passenger side, and on the 4.9L, it's on the driver side.

Connect the gauge to the adapter. Then, turn the key to the 'run' position but don't start the engine. With the jumper wire connected to the EEC test connector, the fuel pump will run constantly.

Now, with the key in the 'run' position, the engine off, and the pump running, check the fuel pressure gauge. It should be within the 35-45 psi range specified in the service manual. If the pressure is lower than expected, it could indicate a problem with the fuel pump, fuel filter, fuel pressure regulator, or fuel lines.

Check the fuel pressure gauge with the engine idling

To check the fuel pressure gauge with the engine idling, you will need to start the engine and check the fuel pressure gauge. It should show 5-10 psi lower than the 'engine-off' test, which verifies that your fuel pressure regulator is working correctly.

• Park your Bronco on a flat surface and engage the emergency brake. This test is for in-tank fuel pumps only.
• Locate the pressure port on the engine fuel rail and remove the cap. If your vehicle doesn't have a pressure port, you will need an adapter from the test kit, which can be attached at the fuel filter or fuel pressure feed line headed to the engine's fuel rail.
• Take the fuel pressure test gauge from the kit. Most gauges have quick-disconnect couplers that allow for different adapters. Find the correct adapter for your vehicle and connect it to the gauge.
• With the engine off, attach the pressure gauge to the pressure port or adapter. A small amount of fuel may come out, so have a shop towel ready.
• Without starting the engine, turn the ignition key to the 'on' position. The gauge should read between 45-58 psi for direct port injection systems and 13-17 psi for throttle body injection systems as the system primes.
• If there is no pressure, recheck the hose or adapter connections. Recycle the ignition switch to recheck. If there is still no pressure, suspect a faulty fuel pump, fuel pump relay, or fuse.
• Now, start the engine and check the fuel pressure gauge. It should show a reading of 5-10 psi lower than the previous reading, indicating that the fuel pressure regulator is functioning correctly.
• The final check is the load test, which determines how the pump performs under load. You can do this by putting the transmission in reverse (for automatic transmissions) and holding the brake while gently giving the engine throttle. Alternatively, you can close the hood to the first safety catch and drive the car at a safe speed while keeping the gauge visible through the windshield. The pressure should hold continuously throughout the test.
• If the fuel pressure is low under load or while idling, it could indicate a clogged fuel filter or a failed fuel pump that needs replacement.

By following these steps, you can effectively check the fuel pressure on your 1987 Ford Bronco, including checking the fuel pressure gauge with the engine idling.

Stand by the side of your truck and have a helper power-brake your truck for no more than 3 seconds

To check the fuel pressure on your 1987 Ford Bronco, you'll need to be standing by the side of your truck for safety reasons. You don't want to risk getting run over by your own vehicle while performing this test.

Ask a helper to power-brake your truck. This is when the transmission is put into second gear, the brakes are held, and the accelerator is pushed to the floor. This should be done for no longer than 3 seconds.

The power-braking method is used to check the fuel pressure of your truck. This is done by multiplying the force out of the booster to create more force than was initially used to push the brake pedal. This is done by pulling the air out of the booster chamber with a pump or vacuum source, creating a low-pressure system inside. When the brake pedal is pushed, the input rod on the booster is pushed in, letting atmospheric pressure into the booster and pushing the diaphragm toward the master cylinder.

This test is best done with two people, and you should always set the parking brake and chock all four tires before beginning.

Check the whole fuel delivery system

To check the whole fuel delivery system of your 1987 Ford Bronco, you'll need to perform a series of tests and inspections to ensure that all components are functioning correctly. Here's a detailed guide on how to do it:

Conventional Fuel Delivery System Check:

Firstly, identify if your Bronco has a conventional fuel delivery system. This system is controlled by the Powertrain Control Module (PCM), which applies 35-65 psi of fuel pressure to the injectors. The PCM activates the fuel pump when the ignition switch is turned on to prime the fuel injectors.

Two-Line System:

If your Bronco has a two-line system, excess fuel is returned to the tank using a separate return line. Fuel pressure is controlled by an external, vacuum-modulated fuel pressure regulator. Most two-line systems include a Schrader valve at the fuel injector rail for mechanical pressure testing.

Single-Line System:

On the other hand, if your Bronco has a single-line system, excess fuel is released into the tank itself. These systems use an internal, non-modulated fuel pressure regulator mounted inside the fuel pump module assembly.

Pulse-Modulated Fuel Delivery System Check:

Pulse-modulated fuel delivery systems are less common, but if your Bronco has one, you'll need to check it differently. These systems control fuel pressure by changing the fuel pump speed and are usually diagnosed with a scan tool.

Direct Injection Fuel Delivery System Check:

Direct injection systems are the most fuel-efficient and require specific safety precautions due to high-pressure fuel. Direct injection systems use a low-pressure fuel pump and a high-pressure mechanical fuel pump mounted on the engine. Repairs to these systems may require specific procedures, such as replacing fuel lines and using a scan tool to relieve pressure before disassembly.

Basic Checks:

Before performing complex diagnostics, it's essential to rule out some basic issues. Hard-starting issues can be caused by stale gasoline, using the wrong type of fuel (e.g., E-85 in a non-flex fuel engine), or a clogged fuel filter. Always check for pending trouble codes and evaluate sensor data streams with a scan tool before condemning the fuel pump. Additionally, ensure the fuel level sensor is working correctly by adding a few gallons of gasoline, and inspect the fuel tank for dents or damage that might affect pump operation.

Cranking, No-Start Testing:

Connect a scan tool to identify the type of fuel delivery system and poll for error codes. Some PCMs may not activate the fuel pump if certain conditions are not met, such as a missing ignition key or a deployed airbag. If the fuel pump doesn't activate, check for available voltage and a clean ground at the fuel pump tank connection.

Fuel-Related Loss of Power:

For fuel-related loss of power issues, record short- and long-term fuel trim numbers with a scan tool while road-testing the vehicle. If the short-term fuel trims exceed about 20% at wide-open throttle, it indicates a fuel delivery problem. However, a faulty Mass Airflow (MAF) sensor can also cause high positive fuel trims, so be sure to check the calculated engine load.

Fuel Pressure and Volume Tests:

While fuel pressure and volume tests can be informative, they are not always conclusive. Some fuel pumps may pass these tests but still cause intermittent starting problems due to a worn commutator bar on the armature. Using a lab scope to analyze the fuel pump waveform can provide more accurate insights into the internal condition of the fuel pump.

Remember to refer to your Bronco's service manual for specific procedures and specifications, and always prioritize safety when working on your vehicle's fuel system.

Check the fuel lines to ensure they aren't pinched or crimped

Checking the fuel lines for any pinching or crimping is an important step in ensuring your 1987 Ford Bronco is running smoothly. Fuel lines can become pinched or crimped in a number of ways, from poor installation to wear and tear, or even off-road obstacles.

To check for this, you will need to get under your Bronco and inspect the fuel lines. These are often made of stainless steel, but can also be rubber. You are looking for any signs of damage or wear, such as cracks or brittle sections. Pay particular attention to bends in the line, as this is a common place for crimping or pinching to occur.

If you find a section of the fuel line that looks restricted, take a photo and compare it to an undamaged section. If it looks significantly different, you may need to replace or repair that section of the line. This can be done by cutting out the damaged section and replacing it with a new piece of tubing, using compression fittings to ensure a tight seal.

It is also worth checking the fuel pressure with a fuel pressure tester kit. This will help you determine if the fuel line is indeed restricted and affecting the performance of your Bronco.

Frequently asked questions