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Cummins 5.9 l fuel injectors repair - common issues and solutions

Cummins 5.9 l fuel injectors repair - common issues and solutions

It’s a real let-down when our trusted diesel engines fail us. Still, it does happen. And when it does, you had better have a solid, knowledgeable mechanic to help you. San Diego County can rely on PCE for any and all diesel engine troubles, including Cummins 5.9L fuel injectors repair, as well as a variety of other mechanical services.

Thanks to modern technologies, diagnosing a problem in a diesel engine has become a lot simpler; simply hook up your engine to engine scan software and all the data is given. However, to determine what the real problem is, you still need a good mechanic to analyze the said data. We have mentioned previously how the big fuel pump systems can go wrong. However, the problem can be more difficult to pinpoint.

Case in point, fuel injectors do not necessarily need to break down outright, they can simply malfunction slightly. This, in turn, can cause you performance issues, rather than a straightforward breakage. That is why there is a chance of fuel injector repair, rather than replacement. In order to understand this better, let’s delve into the inner workings of the fuel injector.

The fuel injectors in Cummins 5.9 l engines are electronic. This should facilitate the diagnosis of any problems. However, this may not always be the case. If the mechanical components of the injector malfunction, the best you can get form an electronic problem scanning is the cylinder which is causing the problem. The rest is up to the mechanic.

Physical damage

If the casing of the injector gets physically damaged, the only sign you may get is the longer crank time, with the engine performing just fine otherwise. This makes identifying the problem early on a bit difficult. The other sign of a cracked fuel injector is the fuel dilution in the oil which can be identified on the dipstick.

Increased crank time

Crank time is the amount of time it takes the pump to build up the fuel pressure sufficient for actuation. Cummins engines do not allow you to start the engine until the threshold pressure is attained. If the injector is cracked, it will take longer for the pressure to build up, up to three times longer. If you notice this, you can be fairly sure the injector is busted. Identifying it can vary greatly in difficulty, depending on the crack itself. The easiest way is to start the engine and visually inspect the injectors. If you are lucky, the crack may be identified by the thin smoke coming out of the injector. That is actually the vaporized fuel, so you should be able to smell diesel as well.

If that doesn’t help, each cylinder will have to be isolated to identify which one is causing the problem. The line between the injector and the fuel supply needs to be removed. The injector is then capped. The cap is a specialized tool produced by Cummins. It is vital not to use anything else, since it is extremely dangerous and high pressures created may cause physical injury or even death. Once you have capped the first injector, test if the crank time has reduced; if not, proceed to the next one, until you have found the culprit.

Check your oil

The Cummins 5.9 l engine uses hydraulics to generate the high pressures needed to inject fuel. The hydraulic oil used in the car may very well determine the lifespan of the injector. If the oil contains excess air, this air will cause misfires in the engine. To circumvent this problem, use the oil recommended by the engine manufacturer- they know what their engines need.


The ultimate reason why you could need Cummins 5.9L fuel injector repair is quite simply mistreatment. If you aren’t following the manufacturer instructions about servicing, you can count on a significantly shorter lifespan of your components. Debris and impurities will take their toll on the components over time. However, you can ensure that they serve you long and well by performing all the necessary maintenance as per manufacturer instructions.
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