Checking Fuel Pressure On A C1500: 1989 Edition

Checking the fuel pressure on a 1989 C1500 is a complex process that requires specific tools and knowledge. The first step is to identify the type of fuel system in your vehicle, which will determine the testing method. For a TBI fuel system, you need to tie into the fuel supply line, and for an MFI fuel system, there should be a Schrader valve on the fuel rail. In both cases, it is important to ensure there is no pressure before removing any components, and to exercise caution when working with flammable gasoline.

Using a TBI fuel system

To check the fuel pressure on a 1989 C1500 with a TBI fuel system, you can use either the Actron fuel pressure tester or a generic OTC brand fuel filter adapter.

Actron Fuel Pressure Tester

The Actron kit costs around $38 and can be purchased on Amazon or by calling them directly. You will also need a 3/4" open-end wrench and a 3/8" or 7/16" line wrench.

First, remove your air cleaner and stand on the driver's side of the truck. Look at the back of the throttle body (TB) and put your open-end wrench on the TB's fuel line nut closest to you, and the other on the actual fuel line. Next, take the fuel line adapter and screw it into the TB first, being careful not to over-tighten as the adapter is made of brass and can easily strip. Connect your fuel line, again being careful not to over-tighten.

Connect your fuel gauge before starting the truck. This fitting was used on old R12 air conditioning systems and leaks quite a bit while connecting the gauge, so be cautious of leaking gasoline on top of your engine. It is recommended to tuck the gauge under the hood and hold it by your door while standing outside the truck and cranking it. This way, you can watch the truck prime and observe the pressure after it's running.

Acceptable readings, as per General Motors, are between 9 and 13 PSI. Anything lower than 9 will impact performance, but a little higher than 13 PSI is acceptable.

OTC Brand Fuel Filter Adapter

For this method, you will need to order the OTC 7665 fuel pressure adapter, which costs around $53.95. You will also need a fuel pressure gauge, penetrating oil/lubricant, a line wrench, and possibly other wrenches to hold the fuel filter. It is also recommended to buy a new fuel filter, as you will need to remove the old one.

Have buckets and rags or paper towels handy, as your fuel lines will leak while you work on the filter. The filter is located on the frame rail just underneath the driver's seat. Hold the fuel filter while trying to loosen the line nuts with your line wrench. Do not use any other kind of wrench on these nuts, as they can easily strip. Take your time, as the lines may be rusty if the filter has never been replaced.

Your 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. This adapter has a quick-disconnect fitting that doesn't leak fuel, so you can leave it connected with the truck running.

Testing Fuel Pressure

Regardless of the method chosen, you should check your fuel pressure at idle, under load (brake torquing), and momentarily with the fuel return line blocked.

If you are uncomfortable with this type of work, it is recommended to consult a professional, as gasoline is highly flammable and the fumes are dangerous.

Removing the fuel filter

To remove the fuel filter from your 1989 C1500, you'll need to locate it first. The fuel filter is usually found on the frame rail just underneath the driver's seat.

Before starting, ensure there is no pressure in the fuel system.

Now, gather the necessary tools: you will need an assortment of wrenches, including a line wrench, and possibly some penetrating oil/lubricant. It is also recommended to have a new fuel filter on hand to replace the old one. Have buckets and rags or paper towels ready to catch any spilled fuel.

Once you have located the fuel filter, the next step is to loosen the line nuts that secure it in place. Use the appropriate size line wrench to avoid stripping the nuts. Take your time with this step, especially if the fuel filter has never been replaced before, as the lines may be rusty. Hold the fuel filter steady while loosening the nuts to avoid breaking the fuel lines.

After the nuts are loosened, carefully remove the old fuel filter. Be prepared for fuel to leak or gush out, as there may still be some pressure in the lines. Have your buckets and rags ready to catch the spilled fuel.

Now that the old fuel filter is removed, you can install a new one if desired. This process involves reversing the steps and ensuring that all connections are secure without being over-tightened.

Using a fuel pressure gauge

To check the fuel pressure on a 1988-1996 C/K1500 truck with a TBI throttle body intake, you can use a fuel pressure gauge. Here is a step-by-step guide on how to do it:

Step 1: Prepare the Vehicle

Park your vehicle on flat ground and turn off the engine. Engage the emergency brake for safety. Open the hood and locate the air cleaner. Stand on the driver's side of the truck and look at the back of the throttle body intake (TBI).

Step 2: Access the Fuel Line

Using an open-end wrench, remove the air cleaner and loosen the fuel line nut closest to you at the back of the TBI. You may have a braided steel line, as some trucks come with this from the factory.

Step 3: Connect the Fuel Pressure Gauge Adapter

Take the fuel line adapter from your fuel pressure testing kit and screw it into the TBI. Ensure that it is snug, but do not over-tighten as the adapter is made of brass and can strip. The Schrader valve on the adapter will swivel, so you don't need to worry about its orientation.

Step 4: Connect the Fuel Line and Fuel Pressure Gauge

Connect the fuel line to the adapter, again making sure it is snug without over-tightening. Connect your fuel pressure gauge to the setup before starting the truck. Be careful as this connection can leak fuel, which can be dangerous. Tuck the gauge under the hood and hold it by your door while you stand outside the truck.

Step 5: Start the Truck and Observe the Gauge

Start the truck and observe the fuel pressure gauge. Acceptable readings for a TBI system are between 9 and 13 PSI. Turn off the truck before disconnecting the fuel pressure gauge.

Additional Notes:

It is also possible to check the fuel pressure by connecting the fuel pressure gauge to the fuel filter, but this method requires more tools and can be messier. This method is also more difficult to access, requiring you to crawl under the hood or under the vehicle.

Checking the fuel pressure at idle

Method 1: Using an Actron Fuel Pressure Tester

• Purchase the Actron fuel pressure tester kit, which includes a fuel line adapter and a fuel pressure gauge. You can order this kit online or from an auto parts store.
• Open the hood of your C1500 and locate the throttle body (TB).
• Remove the air cleaner to access the TB.
• Stand on the driver's side of the truck and look at the back of the TB.
• Using a 3/4" open-end wrench, hold the TB's fuel line nut closest to you.
• Use a 3/8" or 7/16" line wrench to loosen the actual fuel line. Be careful not to overtighten the connection as the adapter is made of brass and can easily strip.
• Screw the fuel line adapter into the TB first. This will make it easier to connect the fuel line and fuel pressure gauge.
• Connect the fuel line to the adapter. Again, do not overtighten the connection. Just get them snugly tightened.
• Connect the fuel pressure gauge to the adapter before starting the truck.
• Start the truck and observe the fuel pressure gauge.
• Acceptable fuel pressure readings, according to General Motors, are between 9 and 13 PSI at idle.
• Turn off the truck before disconnecting the fuel pressure gauge and adapter.

Method 2: Using a Fuel Filter Adapter

• Purchase a fuel pressure adapter, such as the OTC 7665 fuel pressure adapter. You will also need a fuel pressure gauge, penetrating oil or lubricant, and a line wrench.
• Locate the fuel filter on your C1500. It is usually found on the frame rail just underneath the driver's seat.
• Place buckets and rags under the fuel filter to catch any spilled fuel.
• Hold the fuel filter with one hand and use the line wrench to loosen the fuel line nuts. Be careful not to strip the nuts.
• Remove the fuel filter and install the adapter in its place.
• Connect the fuel pressure gauge to the adapter. If your adapter has a quick-disconnect fitting, you can connect it with the truck running. Otherwise, connect it before starting the truck to avoid fuel leaks.
• Start the truck and observe the fuel pressure gauge.
• Turn off the truck and remove the adapter when you are done.

By following these steps, you can accurately check the fuel pressure at idle on your 1989 C1500 and identify any potential issues with your fuel system.

Checking the fuel pressure under load

To check the fuel pressure under load of a 1989 C1500, you will need to test the fuel pump. There are two methods to do this, depending on whether your vehicle has a TBI or MFI fuel system.

TBI Fuel System

If your vehicle has a TBI fuel system, you can tie into the fuel supply line. If your vehicle is high enough off the ground, it may be easier to get under the vehicle, remove the fuel filter, and tie in there. Ensure there is no pressure before removing the filter.

You will need to create or purchase a TBI fuel pressure gauge. You can do this by using a gauge from an air tank, screwing the gauge into the proper size pipe tee, and using the correct hose fittings and hose clamps.

The pressure for a TBI system is around 9-12 psi.

MFI Fuel System

If your vehicle has an MFI fuel system, there should be a Schrader valve on the fuel rail. You can use a fuel pressure gauge with a fitting that will screw onto the Schrader valve.

Actron Tester Method

You can also use an Actron tester, which comes with a gauge that makes reading low pressure easy. It also makes cleaning your injectors easy with a professional cleaning machine, and you don't need to work underneath the truck to mess with the fuel lines and filter.

To use the Actron tester, follow these steps:

• Remove your air cleaner and stand on the driver's side of the truck.
• Look at the back of the TB and put an open-end wrench on the TB's fuel line nut closest to you, and the other on the actual fuel line.
• Take the fuel line adapter from Actron and screw it into the TB first.
• Do not over-tighten the adapter, as it is made of brass and will easily strip inside the steel threads.
• Connect your fuel line, ensuring you do not over-tighten it.
• Connect your fuel gauge before you start the truck. This fitting is used on old R12 air conditioning systems and leaks quite a bit while connecting the gauge. Leaking gasoline on top of your engine can be dangerous, so tuck the gauge under the hood and hold it by your door while you stand outside the truck and crank it.
• Watch the truck prime, and check the pressure after it is running.
• Acceptable readings, as per General Motors, are between 9 and 13 PSI. A little higher than 13 PSI will not hurt, but anything lower than 9 will definitely impact performance.
• Turn off the truck before disconnecting the fuel pressure gauge.

Generic Fuel Filter Adapter Method

Another method is to use a generic fuel filter adapter, such as the OTC 7665 fuel pressure adapter. You will need a fuel pressure gauge, penetrating oil/lubricant, a line wrench, and possibly an assortment of other wrenches to hold the fuel filter. It is recommended to also buy a new fuel filter, as you will have your old one off already.

• Have buckets and lots of rags or paper towels handy, as your fuel lines will be gushing fuel while you work on the filter.
• The filter is located on your frame rail, just underneath where the driver seat is.
• Hold the fuel filter while you try to loosen the line nuts with your line wrench. Do not use any other kind of wrench on these nuts, as line wrenches grab all sides of the nuts and pose a much smaller chance of stripping them.
• Take your time, as your fuel filter may be rusty if it has never been replaced.
• Your goal is to remove the fuel filter and install the adapter in its place. If you break your fuel line trying to get the filter out, it will need to be repaired before you can test your fuel pressure.
• With the truck running, connect the adapter. If your adapter leaks fuel easily, connect it with the truck off. There is hot exhaust right in the path of the fuel stream, so be careful.
• The Actron adapter can be left in place, but the filter-style adapter needs to be removed when you are done.

It is important to note that gasoline is highly flammable, and the fumes are dangerous. If you are uneasy about doing this kind of work, it is best to take it to a professional.

Frequently asked questions