In the past checking your fuel pressure was a relatively hard task to do and required quite a bit of knowledge and a fuel pressure gauge to get the right results. But with all the modern vehicles that are now on the market, the process became a lot simpler and does not require a mechanic degree to complete it.
As a car owner, I know how crucial is to understand the importance of maintaining the right fuel pressure in your vehicle. It’s like the heartbeat of your car’s fuel system, ensuring that your engine runs smoothly and efficiently.
Nowadays it’s super important to know how to check the fuel pressure with an OBD2 scan tool. It not only saves time, but it’s also a lot safer than disconnecting fuel pipes and hoses which can cause engine damage.
For reference, a modern diesel engine can reach up to 2,000 Bar which is around 30,000 PSI at the injectors, surely not a safe job without a scan tool.
That’s why today I am gonna provide you with a step-by-step process on how to measure your fuel pressure and make sure that everything is safe and easy.
Let’s get started.
Table of Contents
Understanding Fuel Pressure
Before we dive into the process of diagnosing your fuel pressure, let’s first explain how it works.
What Fuel Pressure Is?
Simply said, the fuel pressure is what makes your car start. In other words, it’s the force that pushes gasoline/diesel from your fuel tank to the engine, You can pretty much take it like the blood pressure in a human’s body, but instead of pushing blood through the veins, it’s pushing fuel through the fuel system of your car.
How Does Fuel Pressure Work In Modern Vehicles?
Most modern vehicles are equipped with high-pressure fuel pumps (HPFP). The HPFP pushes fuel through the fuel lines and goes straight into the fuel injectors, and after that, they spray an exact amount of fuel into the engine. The fuel pressure needs to be just right, not too high or too low, otherwise, it will cause problems.
Of course, this is just a basic explanation of how this system works and if you want to learn more, you can check this article.
Symptoms Of Bad Fuel Pressure
If the pressure is too high, too much fuel will reach the engine, causing it to run rich (too much fuel in comparison to air). This can lead to poor fuel economy, reduced power, and increased emissions.
On the other hand, with low fuel pressure, not enough fuel will reach the engine. This can cause the engine to run lean (too much air in comparison to fuel), leading to poor performance, hesitation, or even engine damage in severe cases.
Now let’s dive into the process of checking your pressure.
How To Check Fuel Pressure With OBD2 Scanner (4-Step Process)
We’ll explore the process just in a second, let’s first share the main components that exist in a fuel system, so you can have a clear understanding of the process.
Here are the 5 main components of a fuel system:
- Fuel Tank – Where your fuel is stored.
- Fuel Pump – This is what pushes fuel into your system.
- Fuel Injectors – Each injector sprays an exact amount of fuel for its cylinder.
- Fuel Filter – Filters your fuel for any junk.
- Fuel Pressure Regulator – Regulates the amount of fuel that needs to be sprayed.
These are just the main components of a fuel system and you can check each one of them explained in more detail here.
Step 1: Attempt to start the car (If it starts)
If there’s not a severe problem that prevents your car from starting, that’s the first thing you need to do. The goal of this is to warm up the engine so it can give better and more accurate results on your reading. Measuring the pressure on a cold engine can alter the results and in many cases can misguide you to chase a not existing problem.
In many cases, a failed fuel rail pressure sensor can cause a no start at all. And if that’s your case, this is surely one of the possible reasons.
Step 2: Connect an OBD2 Scanner Or A Bidirectional Scan Tool
The next step is to actually connect your OBD2 scanner and process the fuel pressure reading. There are many tools on the market and it’s hard to give exact instructions for each one of them.
You can diagnose a fuel pressure problem with pretty much any tool on the market, but I would suggest getting a bidirectional scan tool because it gives you the possibility to diagnose the problem on a deeper level, which on the other hand will help you to diagnose properly.
The OBD port on most modern vehicles is located right under the dashboard, which makes it easy to connect no matter if you use a wired scan tool or a wireless one.
Step 3: Check For OBD2 Trouble Codes (DTCs)
The third step in the process is to read if there are any stored fault codes in your vehicle’s computer (ECM). This way you can check if there’s already a problem detected problem by your ECM which can save you time to diagnose further down the line.
Let’s see some of the most common OBD2 trouble codes that you can encounter:
- P0087/P0088 – Rail Pressure Too Low/High: – These two codes indicate that the fuel pressure in the fuel rail or fuel system is lower or higher than the specifications set by the manufacturer. It could be due to a faulty fuel pump, a clogged fuel filter, or a problem with the fuel pressure regulator.
- P0171 – System Too Lean: This code means that there’s too much air and not enough fuel in your engine’s air-fuel mixture. It could be due to a fuel pressure problem, a vacuum leak, or a problem with the oxygen sensors.
- P0172 – System Too Rich: The opposite of P0171, this code indicates that there’s too much fuel and not enough air in the air-fuel mixture. This could be due to high fuel pressure, a problem with the fuel injectors, or a faulty oxygen sensor.
- P0190 – Fuel Rail Pressure Sensor Circuit Malfunction: This code indicates a problem with the circuit for the fuel rail pressure sensor, which could be due to a faulty sensor, wiring issues, or problems with the fuel pressure.
- P0230 – Fuel Pump Primary Circuit Malfunction: This code indicates that there’s a problem with the primary circuit of the fuel pump. This could be due to a faulty fuel pump relay, wiring issues, or a problem with the fuel pump itself.
Remember that these are the most common codes that can appear, however, if you find yourself with an unfamiliar code make sure to do a quick check to get familiar with it before continuing further.
Step 4: Live Data Reading
This is the last and the most complex step which may require a little bit of know-how, but you can get familiar with it pretty fast.
So, if you didn’t find any luck with Step 3 and there are no obvious problems, you will need to continue with live data reading. The process of doing is pretty straightforward.
Navigate to your ECM control mode and scan it again, after that go to the “Live Data” menu and click on your “Fuel System”. Once you are there, you will have many different options which will help you to monitor different parts, like your fuel pump, injection readings for each cylinder, fuel pressure sensor, rail pressure and etc.
No matter which option you choose there will be the “specified” value from your manufacturer and your “actual” value which is your current reading. If both of these values are equal that means that there is no problem in the chosen area. To do a more accurate test you can rev the engine to 2000 RPM after that to 3000 RPM and watch the values in the meantime to see if they mismatch somewhere.
Another thing to try is if your car starts and runs, you can take your vehicle for a quick 10-15-minute ride and record your live data. Once you finish the ride, you can see the recordings of your live data and monitor if a problem occurs between the different RPMS.
Here’s a quick video that covers the basics.
Remember that not every tool has live data reading and recording, so it’s important to buy a scanner that supports these functions.
Common Questions
What is the correct fuel pressure of an engine?
The pressure on most vehicles can vary between 5PSI to 10PSI, but you should always check your car’s manufacturer specifications.
How do I check my fuel pressure without a gauge?
The best way to measure your pressure without a gauge is to use an OBD2 scanner. It’s the easiest and most safe way to do it.
Will a scanner tell me if my fuel pump is bad?
Certainly. An OBD2 scanner becomes a crucial tool in today’s world no matter if you are just an enthusiast or a mechanic and is surely the best way to check a failing pump.
