In our previous article, we have discussed the common problems after changing a fuel pump. One of the common issues is a hard start, possibly due to having low to no fuel pressure. To diagnose this, you need to measure the fuel pressure by using a gauge.
But what if you don’t have a gauge and you can only check how hard the fuel pump is working? In this article, we will try to answer this question.
How to Check Fuel Pressure Without Gauge
A fuel pressure gauge is an essential tool for diagnosing low fuel pressure. A weak pump that isn’t delivering adequate pressure can cause an engine to run lean, misfire, and hesitate when accelerating. However, what if you don’t have one and want to check the pressure?
There are two options how to check fuel pressure without a gauge. You can actually check fuel pressure with OBD 2 scanner, which will give you readings from the fuel pressure sensor. If you don’t have a scanner, you can listen to a buzzing sound when you try starting your car, which indicates that the fuel pump puts pressure on the system.
Using a diagnostic code reader
As mentioned above, if you don’t have a fuel pressure test kit, you can use an OBD-II diagnostic code reader to check the fuel pressure.
However, it only applies to newer cars with fuel pressure sensors that continuously monitor the fuel pressure across the fuel injectors.
If a vehicle was manufactured in or after 1996, it is OBD 2 compatible. However, the number of parameters will depend on the specific OBD 2 protocol of your car.
Some gasoline engine fuel injection systems have pressure sensors that can be observed via a diagnostic scan tool.
Although it cannot give you the actual fuel pressure readings, Diagnostic Trouble Codes can help you diagnose if the hard start is due to low or high fuel pressure.
What you’ll need:
An OBD II Scanner preferably with live data capability. We highly recommend the INNOVA 6100P OBD2 Scanner. The Innova 6100P shows fault codes with DTC Severity and quickly reveals the cause of “Check Engine” light warnings (MIL). It has a one-press hotkey to turn off the check engine light after vehicle maintenance. It also features live data displays which can show plenty of vehicle data present, such as engine coolant temperature, fuel injector pulse width(fuel trim), RPM, spark timing, etc.
Step by Step Instructions:
Step 1. Start your engine and let it idle for several minutes.
You can also take your vehicle for a short 10-minute drive to warm up the engine. This will avoid any problem with fuel pressure readings that usually arise from cold engines.
Step 2. Connect the scanner to your OBD 2 port
To find the port refer to your owner’s manual. It is usually located under the steering wheel and above the pedals.
If you are using a generic code reader or scanner, you can use the OBD 2 pin found in your vehicle’s engine bay.
Step 3. Pull-out Stored OBD-II Error Codes
If there is a problem with fuel delivery, the diagnostic scanner will display one or more stored OBD-II trouble codes in the “P” series.
Here are some common OBD 2 error codes you’ll see:
1. P0087 – “Fuel Rail/System Pressure – Too Low”
P0087 is a general code that indicates a problem in the fuel delivery system. It is triggered once the ECM has detected low fuel pressure at the fuel pressure sensor.
It is similar to P0088 which tells us there is high fuel pressure found in the fuel system.
2. P018C – “Fuel pressure sensor “B” Circuit Low”
There are a few things that can cause this code like a bad sensor, or high or low fuel pressure.
3. P0191 – “Fuel Rail Pressure Sensor Circuit “A”
It indicates a potential abnormality in the fuel rail pressure readings. Several mechanical and electrical issues can trigger the P0191 code including low or high fuel pressure.
Step 4. Check The Live Fuel Pressure Data
If the error codes don’t indicate a problem with fuel pressure, you can monitor the live fuel pressure data on your scanner. However, not all OBD 2 scanners have this capability.
That’s why you need to check the compatibility before buying one.
If your diagnostic reader supports real-time data, then connect and enter the engine DME diagnostic mode with a reading of the current parameter. After the reading is complete, choose the fuel delivery system option.
This option will show you the fuel rail pressure setpoint, which is the optimum fuel pressure on the fuel rail when the engine is running. You can use it to compare with the live fuel pressure value.
If the value remains the same even after revving, then there is no problem with the fuel pressure.
However, if there is a difference between the two values or you encounter any issue while revving, you need to check your fuel pressure and see why it is fluctuating.
You can use an OBD II scan tool to read out live data and monitor the fuel rail pressure in real-time. If the value remains the same while revving at 1500rpm up to 3000rpm, then the fuel pressure is fine.
However, if the readings change at a certain RPM range, then most likely there is a problem with fuel pressure.
2. Testing for fuel pump buzz
So here’s the scenario, you don’t have either the gauge and diagnostic tools to watch the pressure, neither you have access to it.
What can you do? You still need to know if your fuel pump is working correctly.
Well, there is still a way how to check fuel pressure without a gauge or an OBD II scanner.
What you’ll need:
- A sharp ear
Step by Step Instructions
Step 1. Turn your key from OFF to ON for the fuel pump to turn on.
Step 2. Listen for a buzzing sound as you turn the keys ON.
If you hear a buzzing sound, then this means your fuel pump is working fine. That’s your fuel pump priming.
To ensure a strong charge of fuel is pushed through, the fuel pump pressurizes the fuel in the lines leading to the injectors.
Step 3. If you don’t hear a buzzing sound, it’s a signal that there is something wrong with your fuel pump.
It could be a relay switch that is not working, a blown fuse, or a corroded or disconnected wire, or worst the fuel pump needs replacement.
Can you check fuel pressure with a tire gauge?
Do not use a tire pressure gauge. There has been a conflicting view on this but in most cases, the Schraeder valve in the test port is too deep to be depressed by a tire pressure gauge.
Moreover, there would be inaccuracies because a tire gauge is meant to measure air pressure and not liquid pressure.
To complicate matters, there might not be a place for the vacuum to escape and get trapped in the gauge.
Fuel gauges have a bleeder valve that gets rid of any air inside, but they also have long lines for air to settle. Finally, the gasoline will probably ruin the tire gauge.
How to check fuel pressure without a Schraeder valve?
In this video from Phillips Vision you will see how to check fuel pressure on a vehicle that DOES NOT have a Schrader valve. This showed this on a 2005 Dodge Neon SXT 2.0L using a Fuel Pressure kit purchased at Harbor Freight Tools.
What should be the fuel pressure of a car?
The fuel pressure of a car can vary depending on its model and make. A regular car should have a pressure of between 40-80 psi.
There are two ways to check the fuel pressure on your vehicle without a gauge.
You can use a diagnostic code reader or OBD II scanner, which will provide live data of fuel pressure. Alternatively, if you hear buzzing as you turn the keys ON but don’t see any other symptoms this means that your pump is working fine.
The more reliable (and accurate) way to measure fuel pressure is with a good quality fuel pressure gauge tool like the BETOOLL Pro Fuel Injection Pressure Tester Kit Gauge.
The adapters, hoses & fittings in this kit are compatible with the fuel injection systems of most cars & trucks worldwide, including Ford, GM, Jeep, Fiat/Chrysler, BMW, Toyota, Nissan, and more.