Remember when diesel vehicles were smelly, smoky, noisy units that needed minimal service work to run trouble-free? Well, the new diesel vehicles aren’t like that at all. New diesel vehicles with common rail fuel injection systems are quieter, more efficient and less polluting than ever before, and they’re becoming so popular that odds are good that they’ll be rolling through a bay near you if they haven’t already. And thanks to their unique service requirements, there’s money to be made servicing them if you’re prepared for the challenge.
The bigger fuel door is an indication that the diesel fluid is filled back here. The reality of work trucks is that dirt and debris build up by the filler necks and can easily work their way into the systems. Keeping the filler neck area clean and wiping up after spills is important even if it's seldom done.
Because new generation common rail diesel vehicles are similar in operation to the fuel injection systems most of us are familiar with, it’s not very difficult to get comfortable working on them. They’re controlled by a module which gets operating data from various sensors and controls fuel injector operation to meet demands while keeping emissions as low as possible. They warm up much more quickly than before, and they have sensors and emission-reducing technology to meet strict new requirements. And they set and store diagnostic trouble codes to help diagnosis. But even if you just perform maintenance services on these vehicles, it’s still important to get comfortable working on and around the systems.
Even though many systems are familiar to the systems you’ve known for years there are a few important differences to be aware of to keep repairs quick, safe and profitable and to keep the job safe.
Here’s what you need to know.
Fluids
Diesel exhaust fluid is one of the most discussed and mentioned systems found on new-generation diesel vehicles. Actually, some early versions of these diesel vehicles didn’t use it (and some still don’t) but it’s extremely common now so it’s important to understand when to top it up, what to top it up with and what goes wrong when you don’t (and of course, how to fix it).
Note the difference in the location of the dipsticks on these two Ford Power Stroke trucks. It's all the way at the back on the newer model.
In brief, exhaust fluid is the consumable fluid injected into the exhaust to help keep emissions low. Vehicles with high fuel consumption, such as ones that tow trailers or vehicles and drivers with aggressive driving habits, will use more of the fluid than their fuel-efficient friends.
The diesel exhaust fluid reservoir has a monitoring system to let the driver know when the fluid needs to be added, and it does this at various levels so that there’s plenty of warning before the system runs to empty. This warning system is needed because when the fluid runs out, the vehicle imposes a speed-limiting condition, which means that the vehicle cannot go above a certain speed until fluid is added. And if fluid still isn’t added at that stage, eventually an idle-only condition is imposed until the fluid level is corrected (the vehicle will only idle). The system doesn’t mess around.
This is important to keep in mind if you’re test-driving a vehicle that has the diesel emission fluid warning on. Be careful where you park or stop that vehicle – it might restart with a speed limiting condition or idle-only condition making it tough to get back to the shop. It’s best to top it up regularly, but human nature is what it is and it’s becoming common for vehicles to limp in to garages after they are run out of fluid.
The fill point usually is under the hood or next to the fuel fill point (a larger than normal fuel door is usually an indicator that the diesel emission fluid’s fill point is located there). If you’re intending to repair a speed-limiting condition, bear in mind that the system might not reset unless it’s filled right up – adding just a bit of fluid isn’t good enough. But on the other hand, be sure not to overfill the tank since this can damage the system (when it stops filling, it’s full so stop adding more). Once you’ve refilled the system it may take at least 30 seconds of idling or a few miles of driving to reset the system completely.
Quickly testing the battery or batteries during service can identify batteries that won't make it until next service so they can be replaced in your service bay.
If you’re in the colder parts of the country, keep in mind that the diesel exhaust fluid does freeze at about 12 degrees, and even though the lines and storage tank are heated to prevent freeze-up, if the vehicle is parked for a while with an over-filled tank serious damage could result.
If you’re attempting to fill up the diesel exhaust fluid from a nozzle and it just won’t fill up the vehicle, it could be a problem with the nozzle rather than with the vehicle. Some nozzles are known to be problematic with certain systems. Try filling from another nozzle or bottle instead. One important note about the fluid – don’t spill it. If you do spill some, wipe the area right away with a wet cloth so it doesn’t damage painted surfaces. And the fluid is poisonous, so wear gloves and be careful with the container.
Even partially restricted air filters can cause problems on these vehicles. A great habit to get into is wiping down the air filter housing before opening it so that debris and dirt don't get in to the system during service.
A final note about diesel exhaust fluid – there’s no point trying to top up with something else other that the correct fluid to try to fool the system, because the system monitors for contaminated fluid. If the system does become contaminated the vehicle’s speed will be limited and a warning message will be displayed and eventually an idle-only condition will be imposed until the system is repaired.
Filters
Replacing filters that are even only slightly restricted is critically important on new generation diesels to keep them running properly and trouble-free. The high operating pressures that new generation diesel engines operate at combined with the very small passages used in the engine management systems mean that these systems are very susceptible to restrictions like carbon and dirt particles and great care must be taken to keep debris from getting in and getting around the various systems.
The info button on the steering wheel resets the oil life monitor and shows how the other systems are doing.
When common rail diesel trucks first started coming in for service, one of my colleagues inspected a common-rail diesel vehicle’s air filter and decided not to replace it at that time because it wasn’t extremely dirty, thinking he was saving the customer money. Less than a month later, he was picking pieces of that air filter out of the cylinders of that engine. The diesel engine’s intake force was so strong that it actually sucked in that partially restricted air filter and caused serious engine problems. Since that incident, I’m fanatic about changing air filters and I explain why to customers: these things can eat their filters.
In fact, one of our fleet customers replaces their trucks’ fuel filters at every oil change. The trucks are driven through remote job sites and spend plenty of time in the bush where the fuel quality can’t be guaranteed, so they would rather change vehicle filters frequently than have a truck stranded or down. Frequent filter service is really important on these new generation diesel vehicles.
Oil Life Monitors
Oil life monitors on new generation diesel vehicles monitor weigh more than just vehicle mileage. Oil change intervals are determined by monitoring (among other things) driving habits, operating temperatures, time spent idling and engine speed and load to determine when the oil needs to be changed, using the manufacturer’s recommended oil. And these service intervals can be really long – in some cases up to a year between oil changes.
In addition to remembering to reset the oil life monitor – and the other monitors – when you change the oil, it’s also important to remember that if you’re putting an oil change reminder sticker in your customer’s vehicle the vehicle’s oil life monitor may not call for an oil change at the same time as your sticker. Just something to keep in mind to keep customers happy and confident in your work.
Not only will have to climb up to reach the dipsticks on some newer diesel vehicles, the dipstick itself may be frayed which can be really painful if you're not careful.
Intake and Injectors
Diesel injectors on new-generation vehicles operate under extremely high pressures. The pressure at the high-side of the fuel system can reach 23,000 psi. In comparison, port injected gasoline fuel injection systems typically operate at 60 psi, the same pressure used in a space-saving spare tire. Quite a difference indeed!
Also, the fuel injectors used in this high-pressure system can open more than once each ignition cycle and have been known to crack or leak resulting in hard start conditions and various drivability complaints.
One of the easiest ways to check for symptoms of this problem is by smelling the engine oil dipstick – a strong fuel smell may indicate problems, especially if the engine oil level seems to be overfilled (it actually might be fuel dripping down to the crankcase when the engine is shut off). I’ve encountered more than one vehicle with injectors that leaked so badly the crankcase filled right up with fuel.
Something to be cautious while checking the engine oil is that, in addition to often being way the heck at the back of the vehicle so it’s really tough to get at, the wire portion of the cable-type dipstick used in many newer diesel engines have been known to fray and separate, turning into little spikes that poke into sensitive fingers and sometimes actually breaking off inside the dipstick tube!
If there is an indication of fuel in the oil, continue your diagnosis by using the proper diagnostic tools so that you’re not injured or worse by these systems. Lack of pressure on the high-pressure side of the fuel system is not uncommon, but tapping a Schrader valve core to see if fuel is present is incredibly dangerous and should never be attempted, for any reason, ever. Using the proper tools is critical on these vehicles to keep you and the vehicle safe.
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Aluminum Components
Many new-generation diesel engines (in fact, every one that I’ve encountered) use aluminum engine components that become challenging to service when they become high-mileage units. Glow plugs that are threaded into aluminum cylinder heads can seize or break in much the same way spark plugs do on their gasoline-powered counterparts. This is something to be mindful of when diagnosing or repairing a hard-start condition. I wish I knew a foolproof way to remove components that are threaded into high-mileage aluminum heads but I don’t. Extreme caution and care are required and a bit of luck helps.
Another note, because of the smaller passages and higher pressures used on the units, vehicles that spend their lives idling along in traffic may develop carbon buildup that affects performance after a short amount of time. One tech I know was repairing poor idling on a car that was a few years old but had high mileage. He told me the carbon buildup on the intake manifold was so bad he was tempted to just chisel it off.
Emissions, EGRs and Coolers
No doubt the most noticeable differences in new generation diesels are the emission systems. In addition to the exhaust fluid that needs to be maintained, the exhaust system itself has changed considerably – for one thing, it’s more than just a pipe and a muffler. There’s a system that catches, collects and burns up diesel particulate when the filter gets full so that the vehicle’s emissions are minimized. This incineration of particulate matter is a “regeneration cycle” that occurs when certain operating conditions are met (in the same way certain conditions must be met before certain tests and monitors can be run).
The incineration process happens at extremely high temperatures, so the process happens during prolonged high-speed vehicle operation. An indicator will alert the driver when the cycle is taking place, and if it’s not done when required the particulate filter in the exhaust system plugs up and must be replaced – and it’s not cheap. This is important to note if you service vehicles that only operate at low speeds and never go on the highway, and there are quite a few of them out there.
And remember, they're indicators, not absolutes. Visually inspecting the element is the best way to be sure of its condition.
Also, many new diesel engines use an EGR system and often an EGR cooler which something to keep in mind if you’re diagnosing a coolant leak or drivability concern (people have been known to try to eliminate the EGR system with varying results).
Conclusion
While some of the basic principles of diesel operation remain the same, such as compression ignition rather than spark plugs and fuel that does not mix well with water, and batteries that need to be checked to make sure they’ll make it to the next service without stranding the customer, there are a few things to understand and a few common problems to know about the new generation of diesel vehicles to keep service work safe, problem-free and profitable. Some of the service techniques are familiar and some will take some getting used to but the end result is that you’ll be ready to tackle the new generation of diesel engines safely and very profitably indeed.
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