Checking Fuel Pressure: 91 Suburban Diy Guide

If you're experiencing issues with your 91 Suburban, it could be related to fuel pressure. To check the fuel pressure, you'll need to locate the fuel pump relay, which is typically found on the firewall in the engine compartment, towards the passenger side. Once you've located the relay, you can use a fuel pressure gauge to measure the fuel pressure at the fuel rail. With the ignition on and the engine off, the fuel pressure should be within the specified range, usually around 60-66 psi. If the pressure is below this range, there could be an issue with the fuel pump, fuel lines, or fuel pressure regulator. It's important to consult a repair manual or a mechanic to properly diagnose and address any issues with your vehicle.

Testing the fuel pressure

There are a few ways to test the fuel pressure of a 91 Suburban. One way is to use an Actron fuel pressure tester kit, which can be ordered online. To use this kit, you will need a 3/4" open-end wrench and a 3/8" or 7/16" line wrench. Remove the air cleaner and stand on the driver's side of the truck. Locate the fuel line nut on the back of the throttle body (TB) closest to you and place the open-end wrench on it, then place the other end of the wrench on the actual fuel line. Screw the fuel line adapter from the Actron kit into the TB first, then connect your fuel line, being careful not to over-tighten the connections. Connect your fuel gauge before starting the truck, as the fitting can leak while connecting the gauge. It is recommended to tuck the gauge under the hood and hold it by the door while standing outside the truck and cranking it. This way, you can observe the truck prime and the pressure after it is running. Acceptable fuel pressure readings are between 9 and 13 PSI, according to General Motors. Turn off the truck before disconnecting the fuel pressure gauge.

Another method is to use a generic OTC brand fuel filter adapter, which requires purchasing the OTC 7665 fuel pressure adapter or a similar product from another brand. For this method, you will need a fuel pressure gauge, penetrating oil or lubricant, a line wrench, and possibly other wrenches to hold the fuel filter. It is recommended to have buckets and rags or paper towels handy, as the fuel lines may leak during the process. The fuel filter is typically located on the frame rail just underneath the driver's seat. Hold the fuel filter while trying to loosen the line nuts with the line wrench. Do not use any other type of wrench on these nuts to avoid stripping them. Take your time, as the fuel lines may be rusty if the filter has never been replaced. The goal is to remove the fuel filter and install the adapter in its place. If you break the fuel line, it will need to be repaired before testing the fuel pressure. Connect the fuel pressure gauge before starting the truck and observe the pressure while the engine is running. Turn off the truck before disconnecting the fuel pressure gauge.

Additionally, you can test the fuel pressure by blocking off the return line. This will cause the pressure to increase and remain constant. If the pressure does not hold when the system is shut off, you may need to rebuild the FPR (Fuel Pressure Regulator).

Checking the fuel pump relay

To check the fuel pump relay on a 91 Suburban, you'll first need to locate the relay. It is located on the firewall in the engine compartment, on the passenger side, towards the centre.

Once you've found the fuel pump relay, you can perform the following checks:

• Check for power to the pump: Use a multimeter to verify if there is power reaching the pump. If there is no power, the problem may be a bad ground, bad connection, or bad wire.
• Bypass the relay: There is a single red wire hanging off the fuel pump relay. By applying 12V directly to this wire, you can bypass the relay and the oil pressure switch. If the pump runs when you do this, then the problem is likely with the relay or switch.
• Check the oil pressure switch: The oil pressure switch is a backup in case the relay fails. If the relay is faulty, it can result in abnormally long cranking times with a cold engine.
• Check the wiring: Ensure that all wires are connected properly and securely. A loose wire could be the cause of the issue.
• Check the fuel pump voltage: You can check the fuel pump voltage at the ADAL plug. The exact port to check may vary depending on the model.
• Check the ground: Verify that the ground connection is clean and secure. A dirty or loose ground can cause issues with the fuel pump.

Troubleshooting the fuel pump

Step 1: Check for Power to the Pump

First, ensure that power is reaching the fuel pump. You can do this by using a multimeter to verify the voltage at the pump's electrical connector. If there is no power, check the fuel pump relay, fuses, wiring, and ground connections. A common issue is a faulty or dirty ground connection, so make sure to clean and inspect all ground points.

Step 2: Listen for the Pump Priming

When you turn the key to the "on" position, listen carefully for the sound of the fuel pump priming. It should run for a second or two. If you don't hear this, it could indicate a problem with the pump itself or the fuel pump relay.

Step 3: Check the Fuel Pump Relay

The fuel pump relay is typically located on the firewall in the engine compartment, usually on the passenger side. You can try jumping power directly to the fuel pump relay to see if the pump operates. If it does, the relay may be faulty and needs replacement.

Step 4: Measure Fuel Pressure

Use a fuel pressure gauge to measure the fuel pressure in the system. With the key turned on, the fuel pressure should be within the specified range (typically around 9-13 psi). If the pressure is low, it could indicate a faulty fuel pump, a clogged fuel filter, or issues with the fuel pressure regulator.

Step 5: Inspect the Fuel Filter and Lines

A clogged fuel filter or restricted fuel lines can cause low fuel pressure and fuel delivery issues. Replace the fuel filter and inspect the fuel lines for any signs of leaks, blockages, or restrictions.

Step 6: Check the Fuel Pressure Regulator

The fuel pressure regulator maintains the correct fuel pressure in the system. If it is faulty or leaking, it can cause low fuel pressure and affect engine performance. Inspect the regulator for leaks and ensure it is functioning properly.

Step 7: Verify Spark and Fuel Delivery

Check for spark at the spark plugs. If there is no spark, it could indicate issues with the ignition system or the engine control module (ECM). Additionally, ensure that fuel is being delivered to the injectors. If there is no fuel, it could be due to a faulty fuel pump, a clogged fuel filter, or electrical issues with the injectors or ECM.

Step 8: Pull Trouble Codes

Use an OBD scanner to pull trouble codes from the ECM. These codes can help identify specific issues with the fuel system, ignition system, or other components. Diagnose and address any trouble codes that appear.

Step 9: Inspect the Ignition Module

A faulty ignition module can cause spark issues and affect the ECM's ability to trigger the fuel injectors. Replace the ignition module if necessary and ensure all connections are secure.

Step 10: Check the Coolant Temperature Sensor (CTS)

A faulty CTS can affect engine performance and fuel delivery. Test the CTS and replace it if necessary. A common issue with older Suburbans is a failing fuel pump, so if you've gone through the above steps and are still experiencing issues, replacing the fuel pump and sending unit may be the solution.

Locating the fuel pump relay

The fuel pump relay in a 1991 Suburban is typically located in the engine compartment, specifically on the firewall. The firewall is the wall that separates the engine compartment from the rest of the vehicle's interior. This relay is usually positioned on the passenger side of the firewall, towards the center.

To access the fuel pump relay, open the hood of your 1991 Suburban and look for it on the firewall. It may be a bit challenging to locate, so take your time and carefully inspect the area. The relay should be clearly labelled, and you may also notice a 3" red wire coming out of it, as mentioned by a Chevrolet enthusiast.

It's important to note that the fuel pump relay is different from the fuse panel, which is usually located under the hood as well. If you don't find the relay on the firewall, it's worth checking the driver's side firewall as well, as some Chevrolet models may have it located there.

Once you've located the fuel pump relay, you can proceed with any necessary diagnostics or repairs related to your fuel system. If you're experiencing issues with your fuel pump, it's always a good idea to consult a certified mechanic or a Chevrolet specialist to ensure proper diagnosis and repair.

Replacing the fuel pump

To replace the fuel pump in a 1991 Suburban, you will first need to locate the fuel pump relay. This can be found on the firewall in the engine compartment, on the passenger side, towards the centre.

Once you have located the relay, you can then proceed to replace the fuel pump. It is recommended that you also replace the harness on the sending unit at the same time, as this can prevent issues with the new fuel pump.

Firstly, drop the tank and replace the fuel pump. You may also choose to replace the entire fuel sending assembly, although this is not necessary. Ensure that you also replace the hose between the pump and sender.

After replacing the fuel pump, check that you are getting power to the pump. If you are not, check the ground, relay, and fuses. You can test for power to the pump by putting 12V directly into the red wire hanging off the fuel pump relay. If the pump runs, then your problem is likely on the fuel tank end, such as a bad ground, bad connection, or bad wire.

If you are getting power to the pump, the next step is to check for fuel pressure. If you have at least 60psi but no more than 75psi, then your fuel pump is functioning correctly.

If you are still experiencing issues with your fuel pump, it may be worth checking the fuel filter, as a clogged fuel filter can prevent fuel flow.

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