A bad diesel fuel injector is likely to cause a variety of symptoms that should help you narrow it down. Some of the main symptoms include poor fuel economy, rough idling, difficulty starting, and excessive exhaust smoke. A modern vehicle should also display a warning light, which might be just a check engine light.
Some of these symptoms can also intersect with other problems, so narrowing them down to indicate a bad diesel fuel injector involves carefully investigating several issues, including exhaust smells, engine sounds, and overall performance. A diagnostic tool can help give you a firm conclusion as well.
Symptoms of a Failing Injector
To figure out whether you have a bad injector or another problem, it’s important to look at all the symptoms together. Let’s take a look at the various symptoms by category. The more that match up with your problem, the more likely it is to be a bad fuel injector. A bad injector causes uneven fuel delivery, which results in some or all of the symptoms discussed below.
Performance and Starting Problems
Many of the symptoms of a failing injector or injectors come in the form of performance and starting problems. One of the most common is a rough idle or misfires. When this happens, the engine seems to shake or stumble, running unevenly at rest due to inconsistent fuel delivery. If you have a tachometer, you might notice the needle moving a lot and dipping down below normal.
Another issue is hard starting. In this case, you’ll experience longer cranking, or the engine might fail to start at all. This is especially noticeable when it’s cold. When the vehicle is in motion, you might notice loss of power, such as sluggish acceleration, bogging down on hills, or stumbling. The engine might also cut out unexpectedly.
Exhaust Look and Smell
Another area to look at when you’re trying to diagnose a bad fuel injector is the exhaust. You’re likely to notice excessive smoke, and it might be different colors from the usual gray. Black smoke indicates too much fuel, while white indicates unburned fuel passing through. Blue smoke can indicate burning oil, but it might be linked to bad injectors if they’re washing oil off the cylinder walls. A strong fuel smell is also common.
Sounds and Warning Lights
There are also sounds and warning lights associated with failing fuel injectors. Engine knocking or pinging is a common sound that is caused by bulk delivery of fuel instead of the usual fine mist. In most cases, failing injectors will also trigger a check engine light to let you know that something has gone wrong. Once you’ve confirmed multiple symptoms and there’s a CEL present, it’s time to diagnose the problem and find out if one or more bad injectors are the culprit.
How To Diagnose the Problem
The easiest way to diagnose a bad diesel fuel injector is to use an OBD-II scanner for light-duty trucks made from 1997 on. Specialized diagnostic equipment, such as the J1939 protocol, for medium-duty and heavy-duty trucks and equipment. Both look for diagnostic trouble codes, but scanners won’t tell you exactly what’s wrong; you can use the codes they give to narrow down the possibilities. Another method is to inspect the engine for leaks. Look for wet spots and a diesel smell near the injectors. Modern diesel systems can show injector balance/return rates through diagnostic tools.
Tools For Diagnosing a Bad Injector
Let’s take a closer look at the tools for diagnosing a bad diesel fuel injector. As mentioned above, the easiest way is to use a code scanning tool (OBD-II or J1939 Protocol scanners). You can also use a digital multimeter to measure injector electrical resistance and a mechanic’s stethoscope to listen for injector clicking. To measure fuel delivery and pressure, you’ll need a fuel pressure gauge and a fuel return line kit. A compression test can help you rule out other mechanical engine issues that cause the symptoms we’ve discussed.
Fuel Injector Diagnostic Steps
Step 1 – In the initial check, use the stethoscope to listen for a steady click. No click or an unusual sound suggests failure. Look for fuel leaks, wet spots, or clean streaks around the injectors.
Step 2 – Use the proper scanning tool for your diesel engine to reveal diagnostic trouble codes for misfires or fuel pressure. You can also do a cylinder isolation test. With the engine idling, disable one injector at a time. If the injector is good, it will cause the RPM to drop. If the RPM doesn’t change significantly, then the injector is likely bad.
Step 3 – Use the multimeter to check injector resistance against manufacturer specs. If you get a reading that’s way off, it indicates an electrical fault. You can also use a scan tool to check if each cylinder is producing equal power and balanced fuel delivery. A large deviation likely means a bad injector.
Step 4 – The most accurate method used by professional shops is a bench test with specialized equipment to simulate real-world conditions and check spray patterns, pressure, and flow.
Where To Get the Best Replacement Diesel Injectors
Does your diesel engine have the above signs? Don’t wait until it gets worse. At Highway and Heavy Parts, we have an expansive range of high-quality diesel engine parts for various makes and models. Our diesel experts are standing by to help you diagnose any issues you might have with bad diesel fuel injectors. Contact us today for assistance and find the best replacement injectors in our catalog. Highway and Heavy Parts is here to ensure that you have the parts and knowledge to keep your diesel engine running.
