Tool Q&A: Diesel Service

Q: I heard that to work on diesels, I don’t need that many new tools. Is that true?

A: Yes, working on diesels does not require a great deal of different tooling. There are some tools that you probably don’t have and might need. One may be an EGR cooler element pressure tester, because your regular pressure tester will not fit on it. You might have to get one from the dealer.

Many diesel fuel injectors go bad and create misfires, especially on Fords, and oftentimes you will need specialty tools to service these vehicles (See Fig. 1). If Mode 6 cannot tell you what cylinder has the misfire, a fuel injector tester that can fit the fuel injectors or test them indirectly (such a Strategic Tools’ Diesel Injector Test Kit that measures unused diesel per injector by volume, as seen in Fig. 2) might help as well. You may also need a special set of fittings to do diesel compression testing.

You will need the right scan tools to work on these vehicles that are particularly strong in American trucks. (If you want suggestions on scan tools, read the blog post at VehicleServicePros.com/10816382.)

These scan tools need to be able to do certain bidirectionals (such as opening the EGR valve on new diesels) and read certain PIDs (Turbo Boost Sensor voltage, which is listed as a “MAP Sensor” on Dodge diesels) that some other aftermarket scan tools might not have because they focus on more common vehicles. When looking at PIDs, watch out! Odd diesel parts (i.e., NOx Sensor) might be listed as something else, such as a HO2S on GM diesels. Your scan tool will also need to be able to do relearns/adaptations. For example, new Ford 6.7L diesels need each new fuel injector coded to the PCM in order for the engine to run right. Cummins diesels are the same way.

If you don’t have a smoke machine, you will need one now. Air leaks are notorious for creating major driveability issues on diesels. For example, a 97 Chevy K3500 had a diesel fuel injection pump replaced because it had CMP codes, but it kept coming back with driveability problems. The root cause? An aftermarket fuel level sender unit that would quickly lose its seal. Whenever it was sent back to the parts store, the new one would quickly develop the same problem. Intake leaks can also cause their share of problems. The only way to catch this is with a smoke machine.

Many of the hand and shop tools used to repair diesels are exactly the same as the ones used on gasoline vehicles. Keep in mind the following: You might need a vacuum extractor in order to remove water from some diesels’ water separators, but most can be drained simply by turning a screw or knob. The primary and/or secondary fuel filters might come as filter elements instead of in a “can,” so you will need a torque wrench to properly tighten the fuel filter housing. Just remember to prime the fuel pump (either by turning the key or using a scan tool) in order to get air out of the system after installing a new fuel filter. Diesels often need the same maintenance services that regular vehicles need. These include coolant flushes, transmission fluid exchanges, etc.

If you are getting into passenger-car diesels, you will need to get acquainted with VWs. The way you would diagnose and service a VW diesel is not particularly special, but you will need a fluid extractor/installer to do a transmission service. Why? It has a single drain plug that acts also as a fill hole. As you can see in the picture, we made an adapter simply by drilling a hole through a matching drain plug and snaking the fluid extractor’s tube through it! (See Figs. 3, 4, 5 and 6 on details how to do this.)

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