Fuel pressure testing is an important part of the troubleshooting process when you are trying to determine why an engine is running poorly or will not start at all. The instructions below do not apply to 1991 models. Consult the 1991 Reatta service manual for more information.
The fuel system is under pressure! . Extreme care should be taken to prevent fire or damage to painted surfaces!
The three tests below should be performed in the order listed. Read through each test completely before starting the testing procedure.1. Pressure Test
Pull the vacuum line off the fuel pressure regulator and see if gasoline is present in the line. If gasoline is present in the line the fuel pressure regulator is defective and should be replaced before continuing.
Below is a photo showing the items I use for testing the fuel system.
The Fuel Pressure Tester is all you will need to determine if fuel pressure is the reason your engine won't start. The jumper wire will be needed to do the Pump Load Test and the Pressure Leak Down Test.
Attach the tester to the fuel rail:
In the photo below the fuel pressure tester hose was bent and twisted to keep the photo more compact. Sharp bends in hose should be avoided when doing the fuel pressure tests.
- Remove the plastic cover from the intake manifold to expose the fuel rail.
- Remove the cap from the Schrader valve by unscrewing it. The cap shouldn't be extremely tight but you might need pliers to loosen it. The cap isn't what prevents the fuel from coming out. The Schrader valve underneath the cap does that.
- Screw the fuel pressure tester onto the Schrader valve. Once you have the tester's hose fitting started onto the threads of the valve, screw it on quickly until it is tightened securely to the valve. Doing so will keep the loss of fuel to a minimum.
Check for fuel leaked from the connection to the valve and clean up excess before proceeding with this test.
Test to see if the pump will build proper pressure under normal conditions:
- Have an assistant turn the ignition switch to the run position (do not start the engine) while you observe the reading on the fuel pressure tester. The fuel pump will only run for about 2 seconds each time you turn the ignition key to the run position.
Be alert for any fuel leaks and instruct your assistant to turn the key to the off position if any leaks are observed. Eliminate the leak and clean up any leaked fuel before repeating the test.
- Next, instruct your assistant to turn the key to the run position once more to verify the results of your first test. Each time the key is turned to run the results of the pressure test should be consistent.
Test results:
Norman reading for this test is 40-47 psi. If your car is within that range and you are having problems starting the engine, fuel pressure is not the problem.
If your reading is above 35-39 psi the pressure should be considered out of the normal range but the engine should start and run. If the pressure reading is much lower than 35 psi you may experience starting difficulties and poor engine operation. You should also perform the fuel pump Load Test below.
If your pressure is below 38 psi you should determine and correct the cause of the pressure being so low. You should also perform the fuel pump Load Test below.
If your tester reads 0 psi you should check the following:
Listen carefully for the sound of the fuel pump running at the rear of the car while an assistant turns the ignition key from off to run several times.
- If you can hear the pump run for two seconds when the key is turned run you should continue on to the fuel pump Load Test.
- If you do not hear the pump run use the instructions below to check for power going to the fuel pump
Connect a volt meter, (set to test for 12 volts DC), to the green fuel pump prime/test connector and the negative post of the battery. Each time your assistant turns the ignition key to run you should see a reading of 12 volts displayed for a period of about 2 seconds.
Without the engine running the fuel pump is not powered continuously.
If the green test connector is not getting 12 volts when the ignition key is turned to run you should do the following:- Check/Replace fuel pump fuse. Then check for power at the green connector again.
- Check/Replace the fuel pump relay. Then check for power at the green connector again. [Fuel pump relay location]
The wire going to the Green fuel pump test connector is connected directly to the electrical circuit that powers the fuel pump. Any problems that prevents the fuel pump from getting 12 volts at the green connector should be corrected before proceeding with other tests.
The fuel pump Load Test will bypass the fuses and relays that normally control the fuel pump in order to do a thorough test of the fuel pump for proper operation during continuous operation.
2. Load Test
Test to see if the pump will operate properly under load:
1. Make certain the ignition key is in the off position.
2. Use a length of wire, 14 gauge or larger, to connect the green fuel pump prime/test connector to the positive side of the battery to supply the fuel pump with 12 volts. The pump should begin to run.
NOTE: The wire I use to test the fuel pump has connectors on each end to make the job easier. Having the connectors on the length of wire is not necessary as long as you can connect a wire between the green connector and the positive terminal of the battery safely.
3. With the pump running, observe the fuel pressure tester for 15 to 30 seconds.
Test results:
The pressure should reach between 40 and 47 psi and hold that pressure continuously with no more fluctuation than 1 or 2 psi while the pump is running. If you are seeing a lot of fluctuation in the gauge reading it indicates you have a problem. The problem could be caused by:
- A failing fuel pump
- A defective fuel pressure regulator
- A restriction, such as a blocked in-line fuel filter or a dirty sock/filter at the bottom of the pump.
If the pump does not run you have a bad connection to the fuel pump or the fuel pump is defective.
Connecting the fuel pump directly to the battery in this test eliminates the possibility of a blown fuse or bad relay being a problem that is keeping the fuel pump from running.
3. Leak Down Test
Test to see if the fuel system will hold fuel pressure:
1. Make certain the ignition key is in the off position.
2. Use a length of wire, 14 gauge or larger, to connect the green fuel pump prime/test connector to the positive side of the battery to supply the fuel pump with 12 volts. The pump should begin to run.
3. Allow the pump to run and build maximum pressure for about 10 seconds to make sure the pump is operating at full pressure.
4. Disconnect the wire powering the pump from the battery and continue watching the fuel pressure tester for about 15 seconds and take note of any drop in the fuel pressure.
Test results:
Ideally the pressure should remain steady for a minimum of 10 seconds without dropping. If you see a rapid drop in pressure during that time period it indicates there is a problem with the fuel system that should be corrected. A rapid drop in pressure could indicate:
- A badly leaking fuel injector
- A leaking check valve in the fuel pump
- A faulty fuel pressure regulator
NOTE: On higher mileage cars you may observe the pressure dropping slightly during that time period. A drop of 5 psi or less might be considered acceptable for an aging fuel system with mostly original parts. I would not consider that as the cause of the engine not starting or running poorly although it could have an effect on gas mileage.
