Should I test my vehicle's fuel pressure?
An engine requires four basic elements to allow it to operate properly â€“ fuel, air, compression and an ignition source. If one among these is missing or is not fully operational, the engine will run improperly or maybe not at all. Since we are discussing the importance of fuel pressure, we will consider the part that fuel plays in the operation of the vehicle.
Fuel, although it is required to run the vehicle, must be delivered into the engine at the correct pressure and volume, failing which, the vehicle might 'starve', causing possible engine damage and consequently poor performance. To make sure this does not happen, you need to test if the fuel is being delivered to the engine at the right pressure.
When Should The Fuel Pressure Be Checked?
Any regular tune-up performed on the vehicle must be followed up with a fuel pressure test. If the fuel pressure is too low or too high, the vehicle may need further diagnosis or repair to correct the problem. Unfortunately, many ignore the testing and non-optimum fuel pressure ultimately stalls the vehicle on the highway. Here are some indicators that a vehicle has non-optimum fuel pressure:
â€¢ No power or reduced power when going uphill or when pulling a load
â€¢ The intake backfires when accelerating
â€¢ Fuel economy is poor
â€¢ High fuel mileage that is too good to be true
Indicators as above, though insignificant, may lead to major problems if left unchecked.
How Is Fuel Pressure Checked?
There are several ways to test fuel pressure, but primarily the type of tester to be used depends on whether the vehicle is carbureted or fuel-injected. A warning here is necessary â€“ do not perform any of these steps when the engine is hot or if open flames, sparks or smoke is present nearby.
Carbureted Vehicles: A Vacuum Gauge/Fuel Pressure Tester of the type Mityvac Part No. 05511 may be a suitable choice. The instrument tests the suction/vacuum side as well as the pressure/output side of the mechanical pump associated with this type of system. Some users refit the fuel system on their vehicles with an aftermarket electric fuel pump. The tester will still work, provided the pressure is below 10 psig. Make sure of a proper diagnosis by testing on both sides of the mechanical pump.
Mechanical fuel pumps normally work in the range of 4-6psig. The tester will have different type of adapters that will allow you to tap into the fuel line for monitoring running pressure. With a straight fitting, you can clamp onto the fuel pump directly and check the suction/input or the pressure/output side. For some mechanical pumps, there may be problem that the tester works on the suction side but not on the output side. This is usually because the internal diaphragm of the fuel pump has a pinhole in it or it has stretched from wear. The mechanical pump will have to be replaced in such as case.
Fuel-Injected Vehicles: You need a Fuel Injection Pressure Test Kit of the type Mityvac Part No. 05515. Most domestic vehicles, including some of the foreign automobiles have a test port, usually located on the steel line of the fuel system on top of the engine near the center. For the exact location, you may have to refer to the manufacturer's literature.
In case your vehicle does not possess a test port, you will need an assortment of adapter fittings to make the tester work. However, such fittings are readily available at the local hardware store or from a nearby mobile tool vendor.
With the fuel injection pressure test kit, you will be able to test pressure ranging from 0-100psig. The exact pressure may depend on the manufacturer of the vehicle and you may have to refer to the listings for specific data about your vehicle.
After connecting the tester to the vehicle, turn the ignition key on, without running the engine. Monitor the tester's gauge reading, which should come up to the proper reading of pressure range. This indicates that your vehicle has passed the fuel test. However, if it did not show a proper reading, there may be a few things you need to check:
Make sure the tester is not leaking and that you have hooked it up correctly. Sometimes you need to tighten the O-rings on the inside of the pressure hose to allow the pushpin to depress the Schrader valve located on the vehicle's fittings.
Listen closely if the pump has been activated when you turn the key to the on position. For some vehicles you may need a helper for listening at the fuel filler door (you may need to remove the cap) for the buzzing or whirring sound made by the pump when it operates, which on most vehicles, will occur only for about 10 seconds. If the pump fails to activate, check all the fuses and relays related to the fuel system. Check the owner's manual or the repair guide of the vehicle for information on this.
If there is low or no pressure even after the pump has activated, then you must check for:
â€¢ Damaged or restricted fuel line
â€¢ Clogged fuel filter
â€¢ Damaged fuel line near the pump connection
â€¢ Defective fuel pump
â€¢ Bad fuel pressure regulator
Once repairs are done as necessary, test for fuel pressure again to make sure that repairs are effective and the readings are now correct. Also, check for any loose fittings or leaks that may cause problems down the road.