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Low Fuel Pressure Problems and How to Prevent Them

Posted by Scott Goldfarb on

Nearly every diesel engine on the road today uses fuel injection technology of some sort. That means the fuel injected into your combustion chamber must first undergo a process of pressurization before it's delivered to your injectors. Unfortunately, a lot can go wrong along the way to cause you to lose fuel pressure.

How Your Fuel System Works

First things first, though. Let's talk about how your fuel injection system operates. Since many high-performance diesels use a common rail design, we'll use this as our example. A common rail diesel (CRD) has three main segments:

  1. High Pressure - The fuel rail with injectors, a high-pressure fuel pump, a fuel pump regulator (FPR), and hoses
  2. Low Pressure - The fuel tank, lift pump, fuel filter(s), and hoses
  3. Return - The return hose that feeds back to the tank with any unused fuel

The lift pump pulls the low-pressure fuel out of the tank and through the hose to the filtration system. It's essential to verify how many fuel filters you have, as some engines have two, one by the engine and one by the fuel tank.

After filtration, the fuel travels through another hose to the high-pressure injection pump, where it's compressed and delivered to the injectors. The FPR is usually located somewhere nearby. It acts as a regulator to control the amount of fuel moving into the injection rail to maintain the appropriate air/fuel ratio for combustion.

You don't necessarily need to concern yourself with the return line other than to check it for leaks. It will not affect your fuel pressure from the tank to the injection rail.

How Do I Know My Fuel Pressure's Low?

Now that you know how your engine handles your fuel, you can narrow down the places to look when there's a problem. We have come across thousands of new and rebuilt diesel fuel pump parts over the years, so we listed below some of the more common indicators of low fuel pressure:

  • Check Engine/Low Fuel Pressure Light - Fuel pressure is one of the many things a modern electronic control unit (ECU) can show you immediately. The error code can also come up in a routine diagnostic check. If you're lucky enough to get this alert before noticing any other symptoms, pay attention and get your vehicle to a mechanic as soon as possible.
  • Engine - Your engine frequently stalls, misfires, backfires, or fails to start, even after you crank it several times.
  • Performance - Acceleration or deceleration is sluggish. Your truck doesn't have the power to make it up your driveway, much less the side of a steep mountain.
  • Exhaust - You see a lot of smoke (of any color) from your exhaust. While smoke can point to a number of different issues, it’s a big indicator of low fuel pressure.
  • Sights, Sounds, and Smells - A strong fuel odor lingers in and around your vehicle; your engine makes strange sounds or runs rough, or you see fuel puddles underneath your truck.
  • Fuel Efficiency - It seems like you're filling your fuel tank more often, but your driving habits have remained the same.

How Do I Keep My Fuel Pressure at the Right Level?

One of the best ways to stay on top of your fuel pressure is to test it about twice a year or install a pressure sensor. Testing can tell you if your fuel pump system is starting to fail long before you get the dreaded Check Engine light or experience other issues.

Most major automotive suppliers carry fuel pressure test kits with the appropriate diesel valve attachments for your vehicle. They cost anywhere from $50 to a few hundred dollars. You'll spend about the same in labor and parts to install a fuel pressure sensor. Be sure to consult your vehicle's manual to get familiar with your engine's exact fuel pressure specifications.

In addition, it's essential to change your oil and filters at the recommended intervals. Diesel fuel injection parts are incredibly precise, and the fuel that flows through them needs to be free of even the most minute contaminants and debris. Amazingly, most low-fuel pressure problems find their origin in dirty filters. Spending a few dollars on a new oil filter every 8,000-10,000 miles is infinitely cheaper than replacing your fuel pump.

Finally, it's a great idea to do a walk-around every few months to inspect your vehicle. Look at the fuel delivery hoses for kinks, cracks, and leaks, and watch the ground for oil or fuel leaks. Using high-quality diesel fuel will help, too.

Long-Term Benefits of Maintaining Good Fuel Pressure

Making sure your truck has consistent and adequate fuel pressure will pay dividends in the long run and not only in terms of the money you won’t have to spend on extra fuel, a new pump or other injection parts.

When your engine continues to operate at low pressure, it wastes energy and makes the rest of your injection system work that much harder to function. That wear and tear will eventually take its toll on other vital parts of your vehicle and could create much bigger (and more expensive) problems.

Maintaining the proper fuel pressure can save you the hassle of buying engine parts and supplies sooner than you expected.

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