Today is the last day of summer, and fairly soon a bunch of "Snowbirds" will start heading for their winter destinations, including Mexico.
I've posted a ton of information about using Mexican diesel since 2007, but I like to give an update at the start of every winter season.
For those with an interest, see the text pasted below regarding the effects of sulfur in Mexican diesel fuel on the DPF and SCR of our trucks.
SULFUR IN MEXICAN DIESEL FUEL – AN UPDATE
FOR OWNERS OF 2007.5 THROUGH 2014 PICKUP TRUCKS
This informational article summarizes the latest available data regarding the effects of sulfur in Mexican diesel fuel on pickup trucks from the 2007.5 model year through 2014. It is based partly on “real-world” experiences with Mexican diesel fuel, shared with the author by Snowbird pickup truck owners over a 6 year period, but also references the scientific knowledge base that has been built up through emissions system research, and laboratory testing by manufacturers of pickup trucks. Nothing contained herein is to be interpreted as an endorsement or encouragement by the author for owners of 2007.5 and later pickup trucks to drive them into Mexico. The article is written in the interests of information sharing. How you choose to use the information is your own responsibility.
For those who are not yet familiar with this topic, Mexican diesel fuel contains higher levels of sulfur than is mandated in the USA and Canada. The ultra low sulfur fuel in Canada and the USA contains no more than 15 parts per million of sulfur, while Mexican diesel can contain up to 500 ppm. As a result, there is a potential while driving in Mexico for “sulfur poisoning” of emissions system components to occur in pickup trucks which have diesel particulate filters (DPF) and selective catalytic reducers (SCR) included in their exhaust systems. DPFs were introduced in the 2007.5 timeframe, and SCRs were added in the 2011 model year.
THE GOOD NEWS
Despite the potential for emissions system problems, there is some good news, because, consistent with laboratory test results prior to 2007, all 2007.5 through 2010 model year diesels, whether Ford, GM, or Dodge, are continuing to tolerate well the higher sulfur Mexican diesel. While there are minor issues, like the occasional emission of blue smoke in the exhaust during a regeneration cycle, (i.e. When soot is being burned out of the DPF), these occurrences are temporary and rare. All of the testing prior to release of the DPF equipped pickups indicated that there would be no permanent degradation of the emissions system, as long as higher sulfur fuels were not used for more than 40,000 continuous miles. The real-world field evidence certainly appears to be supporting those predictions at this point in time.
For the 2011 and 2012 model years, some owners have been seeing Diesel Exhaust Fluid (DEF) warnings from time to time, but in all of the cases made known to me, the warning messages have cleared following a 15 minute high speed run, OR during subsequent heavy trailer towing, OR after the next regeneration. All three situations raise exhaust gas temperatures high enough (sometimes above 740 degrees C at the SCR) to purge sulfur compounds from the system.
The DEF warnings, if they occur, only seem to happen after a fifth wheel or other heavy trailer has been disconnected, and the truck has been driven around locally in Mexico for several weeks. The lower exhaust temperatures, when there is no heavy load to pull, permit the gradual build up of sulfur compounds until the efficiency of the emissions system is reduced and an error code is triggered. There is actually nothing wrong with the Diesel Exhaust Fluid, even though that is the message displayed. It is simply a case of the engine computer interpreting higher than specified NOX (oxides of nitrogen) in the exhaust as evidence that the DEF is not doing its job.
THE “NOT-SO-GOOD” NEWS
Unfortunately, the 2013 model year appears to have brought with it a bit of a complication, because, it seems, the Environmental Protection Agency made changes to the requirements for monitoring NOX (oxides of nitrogen) in the exhaust for 2013 and beyond. Monitoring has to be more frequent than was the case for earlier models, and NOX reduction must remain within a tighter tolerance level. In addition, regenerations are less frequent because less soot is being produced due to less exhaust gas recirculation in some of the 2013s. As a result of the delayed regenerations and tighter NOX monitoring, 2013 and later model year diesel pickups appear to be more likely to register fault codes while in Mexico, and the process required to clear the codes is more complex.
Also for 2013 and later model years, some owners have noticed that the distance which can be travelled after a DEF fault is triggered, and before “limp mode” (maximum speed 4mph) is initiated, gets accelerated with time. This means that the available non-limp-mode miles disappear more quickly than warranted by the distance travelled. This in turn can create a lot of stress, because it is a very upsetting experience to see a message on the dash that your truck will be in limp mode in a few hundred miles or less.
The key to clearing the fault situation for 2013s, and likely also for later model years, if the fault situation even occurs, is to get the truck to do a regeneration. This is because the regeneration process burns the sulfur from the SCR and returns the NOX processing part of the emissions system to normal operation. Once the emissions system is able to again properly reduce NOX levels, the engine computer stops thinking that there is a problem with the DEF.
FORCING A REGENERATION CYCLE
Unfortunately, there is no direct method an owner can use to force a regeneration, but feedback from owners in Mexico over the 2012/2013 winter season resulted in development of what appears to be a very practical indirect method. Apparently, EPA regulations require regenerations to occur more frequently, approximately twice as often, if there is a problem with the DPF pressure sensors which measure soot load in the DPF. In other words, disconnecting the DPF pressure sensors can force a regeneration, provided that more than half the normal distance between regenerations has already been travelled. I have personally seen this procedure used on more than one Duramax powered 2013, and it DOES work.
As mentioned in the previous paragraph, how soon the induced regeneration will be triggered depends on what distance has been travelled since the last regeneration. The theory is, if more than half the normal distance between regenerations has already been travelled, the driver will immediately see a message advising that a regeneration (filter cleaning) has started and to keep driving until it is finished, up to 30 minutes, at highway speed.
If half the normal distance between regenerations has not yet been travelled, it could be anything up to a couple of hundred miles before a regeneration is triggered. Odds are though, for excess sulfur buildup to have occurred in the SCR, and a fault condition to have been triggered, it is very likely that more than half the normal distance since the last regeneration has already been travelled.
Bottom line is, knowing how to unplug electrical power to the DPF pressure sensors on 2013 and later model years will usually allow an owner to trigger a regeneration, which in turn purges the SCR of sulfur compounds, and clears the DEF warning.
Hopefully, before too many more years have passed, Pemex will refit its refineries to produce ulsd diesel, and this annual complication for many Mexican snowbirds will be eliminated for good. ULSD is already available at most Mexican border towns and cities, and in some larger non-border cities, but the higher sulfur fuel is still widely distributed throughout Mexico.
While we wait for Pemex to make changes, anyone needing more specific information, or with a personal experience to share, can contact me directly at firstname.lastname@example.org. Please note that there is no information available yet for the latest model Dodge pickups, because the 2014 model year is the first year for Dodge using DEF (Diesel Exhaust Fluid). As a result, there is no real-world field experience to draw upon, and I would welcome input to help improve the knowledge base for all owners.
Irrespective of the manufacturer of your pickup, if it requires Diesel Exhaust Fluid, be sure to take LOTS with you into Mexico. I recommend at least 5 gallons, because the only confirmed source in Mexico at this time is Napa Auto Parts, which will special order DEF from the USA at around twice the normal price.
September 22, 2013
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