Don’t make aftertreatment an afterthought

When an emissions aftertreatment issue rears its ugly head, one of the biggest mistakes a technician can make is to assume it’s an emissions aftertreatment problem.

Often, issues that present in the emissions system are in fact the symptoms of problems within the engine itself.

When an aftertreatment fault code appears, “the reality is a large percentage of time the real source of the problem is coming from the engine,” explains John Renno, manager of Isuzu’s Center of Excellence. He was presenting to technicians during a recent webinar as part of Isuzu Truck University.

If the engine isn’t performing properly, the diesel particulate filter (DPF) and selective catalytic reduction (SCR) systems can become overwhelmed with particulate matter and NOx, and are unable to function properly. Renno gives the example of a customer who visited the shop complaining of frequent DPF regenerations. But the DPF itself wasn’t the problem. Scored cylinder walls in the engine created higher crankcase pressures and were choking the DPF.

A proper DPF cleaning will remove ash from the filter, restoring it to like-new condition. (Photo: The DPF Company)

“A lot of times people are focusing on the aftertreatment system when in fact there was nothing wrong with this aftertreatment system. This truck needed a new engine – not a new aftertreatment system,” says Renno.

But Kevin Dejong, a technician with Rush Truck Centres of Canada, says early response to engine issues can prevent further downstream issues in the aftertreatment system.

“Usually if the root cause is repaired when it occurs, the aftertreatment will be okay,” he says. “If the truck is driven for an extensive period of time with an engine-related problem, then it will lead to aftertreatment damage. The most important thing is to get the vehicle serviced as soon as possible. Driving a vehicle with an engine lamp on for extended periods usually leads to extra problems and possible aftertreatment damage and a more costly repair.”

Another common misconception in the industry is that the DPF and SCR systems are one. Most OEMs have begun tidily packaging them into a single box, but they remain two separate systems with unique purposes. The DPF, explains Renno, “Is nothing more than an air filter” with ceramic interior to withstand the high temperatures produced during a regen. It captures leftover particulates that were not eliminated by the diesel oxidation catalyst (DOC), housed ahead of the DPF.

The SCR system, on the other hand, breaks down harmful NOx into harmless water and nitrogen. “It takes a bad gas and converts it to two good ones,” Renno explains. But high temperatures are required to facilitate this process, and the engine has a role to play in generating those temperatures as well as limiting NOx and particulates in the first place so the aftertreatment systems can do their jobs.

Common sources of aftertreatment system breakdowns not related to the engine, are corroded or chafed wiring, according to Dejong, and both are preventable.

“When installing a new harness or repairing a harness, it’s important to ensure that all wiring is tied securely in a manner that it will not vibrate and rub on another surface,” he explains. “The correct size of the wire loom is also important. If the loom is too big, the wires move inside and eventually the plastic loom will cut through the insulation on the wire, leaving it exposed.”

When it comes to SCR failures, Dejong says common mistakes include overfilling the DEF tank in the winter.

“Depending on the model, if the neck is in the top of the tank and the tank is full, then there is no room for the DEF to expand when it freezes,” he explains. “When it does freeze and expand, it will break delivery lines or even the pump itself. If the pump ruptures, then the DEF will travel into the wiring harness and cause more problems.”

Paul Deayton, national accounts manager for Winnipeg-based The DPF Company, says regular maintenance of the DPF is also essential to ensure proper performance.

“As an industry, we have tended to leave DPFs until they are plugged or failed before they are serviced,” he says. “We wouldn’t do this to our air filter or oil filter, so why our diesel particulate filter?”

Most OEMs now package the DPF and SCR into a single module, but the two systems operate completely differently. (Photo: Cummins)

Rush Truck Centre’s Dejong breaks down the need to maintain the DPF as such: “The DPF filter works on the same principle as a fire pit. You can fill the fire pit, then burn the contents into ash. Eventually the fire pit will fill with ashes. The filter will fill with soot, and when required, the soot is burned into ash through regeneration. In time, the filter will fill up with ash and require cleaning.”

When servicing the truck Dejong suggests examining the DPF. “A simple visual inspection can prevent a costly repair. I have seen simple problems such as a broken DPF clamp turn into repairs costing thousands of dollars and nearly catching a truck on fire. Aftertreatment temperatures can reach over 1,000 F and can quickly melt any surrounding parts when not contained.”

When it comes to cleaning, some fleets have invested in their own DPF cleaning machines, which clean the filter of leftover ash. Some other alternatives are DPF exchange programs, or using third-party service providers that provide a range of cleaning options. Pay attention to the pre- and post-flow numbers, advises Dejong.

“The numbers are very important. A faulty filter can be caught based on the flow results, preventing the extra labor costs associated,” he says. “A customer will assume just because they had their filter cleaned that it’s as good as new, but this is not the case. I’ve seen instances where a filter passes on the flow spec’ but still can’t do its job on the truck.”

For its part, The DPF Company offers three cleaning and restoration options. The bronze method is a widely used “blast and bake” method. “We have seen this only clean the filter to around 65-70% of its original condition due to some of the impacted ash residue not being able to be cleaned.”

The silver method employs a pneumatic flush system to clean the filter, restoring it to about 85% of its original condition. The gold level is a full restoration using ultrasonic technology along with the pneumatic flush. “This restoration process will bring the filter back to 98% of its original condition and we have seen filters restored to a better condition than many of the remanufactured options being offered on the market,” says Deayton.

“A reman is just somebody else’s filter that has been cleaned. You have no idea of its history.”

Paul Deayton, The DPF Company

He cautions against reman options.

“A reman is just somebody else’s filter that has been cleaned. You have no idea of its history,” he notes.

The cleaning frequency of the DPF is highly dependant on duty cycle. Highway tractors should have their DPF serviced every 300,000 to 400,000 kms, and city trucks every 75,000 to 100,00 kms, The DPF Company suggests. Isuzu recommends servicing the DPF every 100,000 miles or 3,000 hours. Check with OEM recommendations and air on the side of caution. Ensure any service providers clean the DOC as well as the DPF. But maintaining the emissions system begins with proper PM of the engine itself.

“There’s a common saying that anything wrong before the DPF, ends up in the DPF,” warns Deayton.

When servicing the DPF, Deayton urges technicians to handle with care. The ceramic-based filter substrate can crack if dropped. He also urges them to examine the DPF when mechanical failures such as blown turbos or coolant leaks are discovered. “It is highly likely the DPF has become compromised and should be serviced at the same time,” he adds.

Other mistakes technicians are susceptible to are incorrect wiring repairs, which leave the core of the wire exposed to the elements, subjecting it to premature failure.

“The other most common mistake is wiring that is not secured or routed correctly,” Dejong adds. “This allows the wires to rub through on surrounding surfaces, creating a break or a short in the wiring. Having a qualified and trained technician with the proper tools and software to diagnose the electrical circuits is essential. A technician needs to understand how the system works to be able to properly diagnose and repair it.”

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