The 5.9 Cummins fuel pressure specs can change while driving. But on average, the fuel pressure should be about 25-27 PSI at idle.
However, with no load, it should be about 17-22 PSI at 2500 RPM. On the other hand, you should get about 32-35 PSI at WOT.
If you’re not quite sure if you’re getting the correct fuel pressure, hook up one of those fuel pressure gauges to your car, and you should be good to go.
Need more info about the fuel pressure specs? Below, we’ll go over everything you need to know to ensure your engine runs at peak condition.
Contents
High Fuel Pressure And How It Can Affect Your Vehicle
High fuel pressure is not necessarily bad. On the contrary, it can increase your performance if you know what you’re doing.
Still, there are some things you need to know about it.
We’re Getting Higher Fuel Pressure Each Year
Every new year the trend seems to be higher fuel pressure.
Why is that? Manufacturers seem to have caught up because the higher fuel pressure leads to higher performance numbers, drivability, and emission controls.
In short, they can get around limitations to make your driving experience better.
You’re Going to Have Some Damage
Like we said, increasing your fuel pressure has many benefits. The problem: you’re going to have some damage if you don’t know what you’re doing.
For example, you could have a lot of hot fuel in the engine compartment. This could lead to many issues like the engine running too rich.
This just means that the engine is getting too much fuel and little to no air. When this happens, the vehicle will crank.
Furthermore, you could experience things like low gas mileage and slow acceleration.
4 Reasons Why You Should Check Your Fuel Pressure
We know it’s easy to ignore some of the problems you might encounter with your vehicle—especially when they do not affect your performance at first glance.
That being said, here are some reasons why you should check your fuel pressure:
The Fuel Pump May Break
If you drive with low fuel pressure, you will permanently damage your pump. Why is that? Well, the reason is that fuel in the tank is supposed to be cooling down the unit.
So, if the pump is running, it is going to be generating heat. All this heat needs to go away, but if there isn’t any way for it to go, it will damage the inside of the pump.
It Could Damage the Engine
Never drive with low fuel pressure since it could damage your engine. Now, there’s a high chance you won’t blow it up if it’s just a one-time thing.
But if you let this problem go by, it could quickly go out of control.
You Might Get Stranded
I don’t know about you, but we wouldn’t want to get stuck in the middle of nowhere with no signal. To avoid such a scary scenario, check your fuel pressure.
We know this sounds tedious, but you could get a fuel pressure gauge, set it up, and always view the fuel pressure as you’re going down the road.
For example, you could have issues with your throttle response, but you would immediately spot the problem if you have a fuel pressure gauge.
This is super helpful and helps drivers prevent problems from getting worse.
It Saves You a Lot of Money
Keeping track of your fuel pressure in real-time is one of those things you’d wish you had thought of earlier.
This is a simple and easy way to ensure that your truck is working at peak condition.
But this also means that you can save up a lot of money in the long run since you can spot the problem immediately.
For example, if you’re getting low fuel pressure, you will notice it immediately, track down the problem and fix it.
8 Reasons Why You Have Low Fuel Pressure On Your 5.9 Cummins
To know your actual 5.9 Cummins fuel pressure specs, you need to figure out why you’re getting low fuel pressure.
That said, here are the top 8 most common reasons why you have low fuel pressure:
Clogged Fuel Filter
A common symptom you might notice is throttle response. For example, your vehicle might be idling just fine, but as soon as the light turns green, your vehicle will stall.
Why is this happening? Well, it’s usually a clogged fuel filter, which is super easy to replace.
However, this problem could be related to your pump in other cases since it has low fuel pressure.
Check Engine Light
If you have an old car, there’s a high chance that the check engine light won’t come on, but on newer vehicles, the check engine light will pop up. This usually means that you have low fuel pressure.
Damaged Fuel Pressure Regulator
The fuel pressure regulator’s job is to make sure that you don’t have constant fuel pressure.
If you had constant fuel pressure, then you’d never get the correct fueling for the engine.
If there’s something wrong with this part, then you will get low fuel pressure.
It’s pretty rare for this part to stop working. However, it wouldn’t hurt to diagnose it and rule this out.
Damaged Fuel Pipe Line
This is not unheard of, but fuel pipelines can get damaged as you’re driving over bumpy roads. When this happens, your fuel pressure will drop.
To make sure that this is the problem, get underneath the vehicle and inspect the fuel pipeline.
Fuel Pressure Sensor
Your fuel pressure sensor has a simple job: sending data to the computer and then use this information to adjust the vehicle’s performance.
But when this unit stops working, it’ll read the wrong pressure, leading to low fuel pressure.
Worn Spark Plugs
Spark plugs don’t get a lot of credit. We’d say that they are heroes working in the shadows.
Why are they so important? They keep your engine working, and your ignition system needs them to work correctly.
Many things can go wrong when there’s a problem with the spark plugs. It just takes a single spark plug to throw off the vehicle.
For example, one of the many problems you will face is low fuel pressure. How so?
An absurd amount of air is mixing with the fuel inside the combustion chamber, which causes the spark plugs to run incredibly hot.
This could be the reason why you’re spending so much money on spark plugs. So, we suggest grabbing a fuel pressure gauge to check your fuel pressure.
If you’re getting low fuel pressure, then that’s your culprit.
Bad Fuel Pump Relay
As you’ve seen by now, there are many culprits as to why your fuel pressure is low. That said, another culprit you could have is a bad fuel pump relay.
If this unit quits working, it won’t send any power to the pump, which causes the engine to act up.
Luckily, this is a cheap and straightforward fix. You can find a replacement for roughly $20, which is pretty inexpensive compared to some of the previous culprits we covered above.
Fuel Smell Coming From the Exhaust
Noticed that when you start the vehicle, you smell a strong gas smell? This means that your fuel pressure regulator is about to die.
In fact, you could pop the hood of your car right now, and there’s a good chance you will notice gas on the rim of your fuel pressure regulator.
You could also remove the hose going into the fuel pressure regulator and keep an eye on it.
If gas comes out of it when the engine is running, it stops working and needs to be replaced.
5.9 Cummins Rail Fuel Pressure Specs
Here are the 5.9 Cummins common rail fuel pressure specs:
Fuel Pressure At Idle
The average rail pressure at idle should be about 5,600-6,500 PSI.
Fuel Pressure to Start the Vehicle
You need at least 5,000 PSI to start up the engine.
DIY Guide: How to Check Your Fuel Pressure
Now that we’re all on the same page, here’s how you can check your fuel pressure on the 5.9 Cummins:
What You Will Need
Checking your fuel pressure is super easy, and anybody can do it. To check the fuel pressure, you need a fuel pressure gauge.
If you don’t have one, you could go on Amazon and get one. Fuel pressure gauges are relatively cheap, and you can find one for roughly $30.
Furthermore, they usually come with different fittings, so you can use your fuel pressure gauge for many other applications.
1. Find the Fuel Pressure Port
First, pop the hood of the truck and then find the fuel filter assembly.
On the back, you should see the port to check the fuel pressure. Now remove the plug from the port to check the fuel pressure.
2. Hook Up Your Fuel Pressure Gauge
Grab your fuel pressure gauge and hook it up to the fuel pressure port.
3. Check Your Cummins Fuel Pressure Specs
Get on the vehicle, and turn the key to get the fuel pressure rating at stationary.
With the car not running, you should get close to 20 PSI, and then it will back down when you turn it off.
Now start the truck and see what you get at idle. You should get close to 20 PSI.
When the vehicle is under load, you should get about 17 to 20 PSI.
4. Write It Down
This step is optional. However, we suggest keeping track of your fuel pressure history.
This way, you can keep a good eye on the fuel pressure and prevent issues in the future.
For more information about these steps, watch this video:
Frequently Asked Questions (FAQs)
Got any more questions about 5.9 Cummins fuel rail pressure specs? For more info about it, here’s some interesting information:
What happens if fuel pressure is low?
If you’re getting low fuel pressure, you won’t be able to start up your truck. But if you somehow manage to start it up, it will shut off as you’re driving down the road.
Can a weak battery cause low fuel pressure?
Yes! If your multimeter reads low voltage when testing the battery, it could be the reason why you’re getting low fuel pressure.
When there’s a problem with the battery, it can stop the injectors from working, which leads to low fuel pressure.
Should rpm increase fuel pressure?
Revving up the engine is not a great way to find if you’re getting low fuel pressure.
It goes up instantly when you hold the throttle open. After that, it will go down as your vacuum stabilizes.
However, testing your fuel pressure when the car is under a load will uncover any fuel delivery problems you could have.
What causes high fuel pressure in common rail?
If you’re getting high pressure, there’s a good chance that you have a damaged fuel regulator or clogged return line.
Conclusion
To recap, your 5.9 Cummins fuel pressure specs should be about 25-27 PSI at idle. If the vehicle is not under any load, you should get about 17-22 PSI and 32-35 at WOT.
As always get, get a fuel pressure gauge and write down all your logs. This can get you out of so much trouble in the future.
Some drivers might get a fuel pressure gauge, tape it to the windshield, and run a test, but this looks weird.
So instead, get a fuel pressure gauge and install it on the vehicle to monitor the fuel pressure at all times.
