Replacing The Fuel Relay Switch In A 1999 Jeep

If you're looking to change the fuel relay switch on a 1999 Jeep, you may be referring to the ASD relay or the fuel pump relay. The ASD relay is located in the power distribution center, on the right fender side shield. The fuel pump relay is located in the same power distribution box as the ASD relay. If you're experiencing issues with your Jeep not starting, you can try checking the relays with the ASD and fuel pump relay location in the diagrams provided in the source links. It's important to note that bypassing the relay is not recommended, as it can be a safety hazard in the event of an accident.

Check if the fuel pump relay is faulty

There are several ways to check if your 1999 Jeep's fuel pump relay is faulty. Firstly, if your engine is cranking but not starting, this could be a sign of a faulty fuel pump relay. The relay will typically fail in the open position, preventing voltage from reaching the fuel pump, resulting in your engine being starved of fuel. Another symptom could be that your fuel pump is running continuously, which could indicate that the relay is stuck in the closed position.

You can also try testing the fuel pump relay by swapping it with another relay from the power distribution box, such as the air conditioning compressor relay. If your fuel pump runs with the alternate relay installed, then you know the fuel pump relay needs to be replaced.

Additionally, if your Jeep is displaying an illuminated check engine light, this could be an indication that the engine computer, or powertrain control module (PCM), has detected a problem with the fuel pump relay or its circuit. However, not all vehicles will turn on the check engine light for a bad fuel pump relay.

Finally, you can refer to your Jeep's owner's manual to locate the fuel pump relay and check for any signs of damage or wear. The fuel pump relay is typically located in the power distribution box in the engine compartment.

Check the ASD relay for power

To check the ASD relay for power in a 1999 Jeep, follow these steps:

First, locate the ASD relay. The ASD relay is located in the power distribution center, on the right fender side shield.

Now, let's check for power. You can do this by measuring the voltage on the small ignition coil wires. To do this, simply connect a voltmeter to the coil wires and check for voltage. There should be voltage present both when you first turn on the ignition switch and during engine rotation (cranking or running).

If there is no voltage present on the ignition coil wires, this indicates that the ASD relay may not be functioning properly and could be the reason why your Jeep is not starting.

Additionally, you can try checking for any Diagnostic Trouble Codes (DTCs) that may be stored in the PCM. A scan tool can be used to read these codes, which will provide valuable information about any issues the PCM has detected.

By following these steps, you can effectively check the ASD relay for power and diagnose any potential issues with your 1999 Jeep's fuel relay switch.

If you determine that the ASD relay is not functioning properly, you may need to replace it or seek further assistance from a qualified mechanic.

Check if the PCM is faulty

The Powertrain Control Module (PCM) is a vital part of your vehicle. It is responsible for receiving information from the sensors and other control module units, as well as controlling various features, including ignition timing, fuel delivery, emissions, idle speed, throttle control, and more.

Check Engine Light Illuminates

The first sign of a bad PCM is often the Check Engine light on your dashboard. However, it's important to note that the Check Engine light could also indicate a bad sensor, wiring problem, or other issues. To verify that the PCM is causing the light to turn on, use a DIY scan tool to check your vehicle for trouble codes.

Poor Engine Performance

The PCM controls your vehicle's performance, so if it's not responding correctly, you may experience poor engine performance. A faulty PCM may cause issues with starting the vehicle, especially in colder conditions. In some cases, the vehicle may not start at all due to PCM-related problems with the ignition timing, fuel delivery, and other critical components.

Increased Emissions

When the PCM is functioning correctly, it minimizes your vehicle's emissions by optimizing engine performance. However, when it's not working properly, you may notice increased emissions and reduced fuel economy. This is because the PCM miscalculates and communicates incorrect values to the powertrain components, resulting in faulty combustion and reduced gas mileage.

Shifting Problems

If your vehicle is having trouble shifting gears, the PCM could be the culprit. Since the PCM controls both the engine and the transmission, any issues with the powertrain may be traced back to the PCM. Shifting problems can cause erratic handling and safety concerns, so it's important to address them immediately.

Other Error Lights

In addition to the Check Engine light, a failing PCM can cause other error lights to illuminate on your dashboard. As the PCM becomes unable to read the sensors correctly, your vehicle's performance may be affected, triggering various warning lights.

Check for spark

To check for a spark in your 1999 Jeep, you'll need to perform some diagnostics on your ignition system. Here's a step-by-step guide:

Step 1: Check the Basics

• Ensure you have enough fuel in your Jeep.
• Check your battery by turning on the headlights. If they're dim or not turning on, you may need to jumpstart your Jeep.
• Inspect your fuse box for any blown fuses, which usually have a black or burnt spot in the middle.

Step 2: Prepare for Diagnostics

• Park your Jeep in a well-lit area with enough space to move around it.
• Gather the necessary tools, such as wrenches, a multimeter, a test light, and a spark plug tester.
• Disable the fuel system by removing the fuel pump fuse or relay to prevent fuel from entering the cylinders while the ignition is off.

Step 3: Check Spark Plug Wires

• Insert a spark plug tester into the plug boot and ground it on a clean, unpainted metal part of the engine.
• Crank the engine and observe if there's a spark. If there's no spark, you may have an electrical issue.

Step 4: Locate the Distributor Cap

• Remove the distributor cap by unscrewing or unclipping it.
• Crank the engine and check if the distributor is turning. If it's not, you may have a broken timing belt or chain.

Step 5: Test the Ignition Coil

• Turn the ignition key on without cranking the engine to power up the electrical components.
• Locate the ignition coil, which has three wires attached: a thin positive wire from the ignition switch, a thin negative wire to the ignition module, and a thick coil wire to the distributor cap.
• Use a test light to check for power in the positive and negative wires. If there's no power in the positive wire, check for breaks in the wiring from the ignition switch to the coil. If the negative wire doesn't light up, trace the length of the wire and repair any breaks.
• Crank the engine and observe if the test light flickers. If it does, trace the negative wire to the ignition module for any breaks. If there are none, use an Ohm meter to test the resistance of the ignition coil.

Step 6: Check the Distributor and Ignition Module

• Locate the pulse generator on the distributor, where the wiring from the ignition module comes in.
• Connect an A/C voltmeter to the wires at the pulse generator and crank the engine. If there's no current, the pulse generator may need replacement. If there is a current, the ignition module may be faulty.

If all the above checks don't reveal the issue, consider taking your Jeep to a professional for further diagnosis.

Check for a ground problem

To check for a ground problem, you will need to test the fuel pump relay. This can be done by swapping it with another relay from the power distribution box. If the fuel pump runs with the alternate relay installed, you know the fuel pump relay needs to be replaced.

Step 1: Park your car on level ground and engage the parking brake. Put the transmission in Neutral or Park. It is preferable to perform this test inside a garage, as it will be easier to listen for the buzzing or clicking noise of the fuel pump.

Step 2: Turn the ignition key to the "ON" position but do not start the car. Listen for the fuel pump to activate as you turn the key.

Step 3: If you cannot hear the fuel pump, raise the hood and locate the fuel pump relay. It is usually located in the large fuse box in the engine compartment. Refer to the wiring diagram or the owner's manual if you need help finding it.

Step 4: The fuel pump relay will emit a clicking or buzzing sound when the key is turned to the "ON" position. If you cannot hear this sound, proceed to the next step.

Step 5: Disconnect the negative cable from the car battery. This will disable the power to the fuel pump and all related circuits.

Step 6: Remove the fuel pump relay. If it is difficult to remove by hand, you can use a pair of needle-nose pliers.

Step 7: Set a multi-meter tool to resistance mode. Connect the probes of the multi-meter to the load and battery pins in the relay. You will need to use a 12-volt power supply or voltage regulator to feed power to the relay. Connect the ground of the power supply to the ground pin in the relay.

Step 8: Feed power to the input voltage pin. The multi-meter should beep to indicate continuity. If there is no continuity, the relay is broken, busted, or burned out.

Step 9: Replace the bad fuel pump relay with a new one that is compatible with your vehicle. Install the relay in the fuse box and put back the fuse box cover.

Before starting the car, open the fuel door and remove the fuel cap, then put it back on to ensure a tight seal. Start the car and take it for a short test drive.

Frequently asked questions