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MEXICAN DIESEL FUEL – WILL IT HARM YOUR LATE MODEL PIC UP TRUCK, AND WHAT IS THE BEST TRUCK FOR MEXICO?

The Owners’ Manuals of Dodge, Ford, and GM diesel powered pickup trucks have been warning, ever since the latter half of 2007, that using Mexican diesel fuel, which is higher in sulfur content than the fuel in Canada and the USA, could cause serious damage to the emissions system, and that any such damage will not be covered by warranty. Despite these warnings, hundreds, if not thousands, of Snowbirds have driven their 2007.5 and later model diesel pickups into Mexico over the past 5 years.
So what has been the typical experience for owners of pickups using Mexican diesel fuel, and what exactly are the potential risks? This article sets out to clarify the issue, first by explaining how the emissions system works in 2007.5 and later diesel powered pickups, and secondly by identifying known “real world” issues and risks reported to the author by owners of 2007.5 and later model pickups. This article is not to be interpreted as an endorsement of the actions of owners who have ignored their Owners’ Manuals warnings. It is purely a sharing of information, in the interests of ensuring that affected owners are fully informed about their options and risks. Any decision to drive a 2007.5 or later diesel powered pickup truck into Mexico, and run it on Mexican fuel, is the sole responsibility of the owner.
If you don’t want to wade through a lengthy description of the emissions system
operation, but would like to read about symptoms which might occur when using Mexican diesel fuel, and which late model pickup trucks cope well with the sulfur levels in Mexican diesel fuel, skip to the section labeled “The Question Everyone Asks”. If you have personal experiences to share, good or bad, please provide your input and feedback, by emailing me at whitetmp@aol.com. I have been gathering as much data as possible, since late 2007, so that there is a knowledge base to draw upon when, or if, an owner contacts me with a fuel related problem. The database already in place has helped clear emissions system fault codes for a number of owners, and is getting more and more useful by the day.

DIESEL EMISSIONS 2007 THROUGH 2010
Beginning in the second half of 2007, diesel powered pickups started being fitted with a new type of emissions system designed to reduce the amount of oxides of nitrogen (NOX) leaving the tailpipe, and virtually eliminate emissions of black soot (carbon) in the exhaust.
Reductions in NOX at that time were achieved mainly by sending some exhaust gas back into the engine intake, (Exhaust Gas Recirculation, or EGR), a process which reduces the amount of oxygen available for combustion. This in turn causes oxygen to be stripped out of the recirculated NOX, so that less NOX, and more Nitrogen exits the exhaust pipe. Nitrogen is a harmless gas which makes up approximately 78% of the air we breathe, so converting NOX to plain old Nitrogen is very desirable.
The second, and biggest change, introduced in the latter half of 2007, was the
incorporation into the exhaust pipe of a diesel particulate filter (DPF) to trap soot from
combustion. We’ve all been behind black-smoke-belching diesel powered vehicles from time to time, so most of us are happy that post 2007 diesels emit no sooty exhaust. The carbon is captured, instead, by a special ceramic “honeycomb” in the DPF. The DPF though, gradually fills up with soot, so, typically around once for every tankful of fuel, the soot has to be burned out of the DPF. This is achieved by injecting fuel into the exhaust stream, either by the engine fuel injectors during the exhaust stroke, or by a separate fuel injector in the exhaust manifold. The injected fuel burns, using oxygen released by a special catalyst in the exhaust line, known as the Diesel Exhaust Catalyst (DOC). This raises exhaust gas temperatures high enough for the
soot in the DPF to “light off”, and combine with oxygen to form carbon dioxide (CO2), another gas found in our atmosphere, and one we all exhale with every breath. This process is called “regeneration”.
In order for all of the above emissions equipment to work properly and efficiently, a
change also had to be made to the diesel fuel available at the pump. This is because the sulfur content of standard diesel fuel in North America prior to 2007 was high enough to “poison” the DPF, by depositing in the DPF sulfur compounds formed during combustion. These compounds tend to clog the ceramic pores, gradually building up over time, until the efficiency of the DPF is reduced, causing more and more frequent regenerations. Eventually, the DPF becomes so “poisoned” that it no longer functions properly. The good news, however, is that extensive testing by the EPA and manufacturers, prior to the first DPFs being installed in vehicles, showed
that permanent damage only occurred if higher sulfur fuel was used continuously for more than 40,000 miles. In other words, the DPF normally recovers completely after occasional use of higher sulfur fuels. This is why Snowbirds, who have been bringing their 2007.5 through 2010 model pickups into Mexico, have not reported in the on-line diesel forums any negative experiences. As soon as the truck returns to burning ultra low sulfur diesel fuel in the United States and Canada, after a winter in Mexico, the ulfur compounds burn out of the DPF during soot burning regeneration cycles.
For most owners of 2007.5 through 2010 diesel pickups, there are usually no observable effects from burning Mexican diesel fuel, but sometimes regeneration cycles cause blue colored smoke in the exhaust for a few minutes as the sulfur compounds burn off with the soot. The blue smoke can be quite noticeable if regeneration is happening at slow speeds, such as in-town driving, and can easily be mistaken for an oil burning problem, such as worn rings, or failed turbocharger bearings. Embarrasing though it might be to have clouds of blue smoke billowing
out of the exhaust pipe of a recent model pickup, if the “problem” quickly disappears, it was probably just an indicator of a soot burning regeneration under way.

DIESEL EMISSIONS 2011 THROUGH 2013
For owners of 2011 through 2013 model year pickups, things are quite a bit different. Starting with the 2011 model year, Ford and GM introduced further changes to the emissions control system, using urea injected into the exhaust to drastically reduce NOX leaving the tailpipe. This new system allowed for a reduction in exhaust gas recirculation, leading in turn to



3. The DEF tank, which all 2011 and later Ford and GM pickups utilise, contains Diesel Exhaust Fluid (DEF). The urea (CO(NH2)2) in the fluid is injected into the hot exhaust just ahead of the SCR. As the urea enters the exhaust stream it turns into ammonia (NH3). This ammonia reacts with NOX in the SCR to form water vapour, CO2, and nitrogen. Reduction in NOX is typically in the range of 90% or more.

4. Finally comes the DPF, which captures the soot in the exhaust. Pressure sensing across the DPF is the main signal for a regeneration (soot burnoff) to begin, at which point the fuel injector in the exhaust manifold, or the engine injectors during exhaust strokes, begin injecting fuel into the exhaust. This fuel burns fiercely, raising exhaust gas temperatures high enough to oxidise the carbon in the DPF, and convert it to carbon dioxide. Regeneration can last as long as 30 minutes, depending on the individual manufacturer programming.

5. The end result of all of this exhaust treatment is extremely clean exhaust. Emissions are almost entirely composed of water vapour (H2O), carbon dioxide (CO2), and nitrogen (N), which are all naturally occurring components of the air we breathe.

THE QUESTION EVERYONE ASKS
So, the question everyone asks is, “Which late model diesel pickup best tolerates the higher sulfur Mexican diesel fuel?”
In general terms, Dodge Ram has the edge through the 2013 model year because there is no SCR, which is the most sulfur sensitive part of the system. This means, if the only thing you care about is minimal sensitivity to sulfur in the fuel, a Dodge Ram appears to be the best choice. As of the 2014 model year though, Dodge will be using DEF and an SCR, so the sulfur tolerance advantage will disappear.
For Ford and GM products, 2007.5 through 2010, the issues are minimal, typically only an occasional “blue smoke” regeneration, and most owners are unaware of any sulfur effects. If you prefer a Ford or GM truck, these model years do not seem to require any owner intervention to clear codes, and for all intents and purposes operate exactly as they would back in the USA or Canada, as long as they do not remain on Mexican fuel for more than 40,000 continuous miles.
Unfortunately, the SCR, found in 2011 and later model year Ford and GM pickups, is quite sensitive to sulfur in the fuel, and is easily poisoned, resulting in less than ideal NOX reduction. Eventually, for many owners, the decline in SCR efficiency results in a “Check Engine” light, or “Poor Quality DEF” light coming on. The problem, of course, is not due to bad DEF, but the vehicle computer interprets the out-of-spec NOX levels as being caused by the DEF not doing its job, so that’s the message it gives to the driver.
For 2010 through 2012 Ford and GM vehicles, a normal regeneration cycle, or raising exhaust gas temperatures by towing a heavy trailer for 30 minutes, or travelling at, say, 75 mph, for about fifteen minutes, will usually clean the SCR enough to return tailpipe NOX levels to normal. Following one of these activities, the NOX sensors will indicate to the onboard computer (ECM) that things have returned to normal. This does not mean that the warning lights will extinguish immediately though. Typically, it can take 20 miles (35 kms) or more, and 2 or 3 separate engine starts, before the warning lights go out. Many owners, it should be noted, based on reports I have collected since 2010, have never experienced this type of scenario, and have never seen any warning lights, while others have seen them every few weeks while in Mexico.
The 2013 model year appears to have brought with it a further complication, because the Environmental Protection Agency apparently made changes to the requirements for NOX monitoring for 2013 and beyond. Monitoring has to be more frequent, and NOX reduction must remain within a tighter tolerance level. As a result, initial feedback from Snowbirds who have contacted me indicates that 2013 diesel pickups are likely to register fault codes more frequently,
and the process required to clear the codes is more complex.
For 2013, the distance which can be travelled after a DEF fault is triggered, and before “limp mode” (maximum speed 4mph) is initiated, gets accelerated, which can create a lot of stress for an owner. There is no doubt that it would be 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, especially with the knowledge that it requires a regeneration to fully clear the SCR of sulfur compounds.
Unfortunately, there is no direct method an owner can use to force a regeneration, but feedback from an owner of a 2013 in Mexico this season has turned up what appears to be a very effective fix. The information provided indicates that EPA regulations require regenerations to occur more frequently, as much as twice as often, if there is a problem with the DPF pressure sensors, so disconnecting the power to the DPF sensors can force a regeneration.
How soon that regeneration happens depends on what distance has been travelled since the last regeneration. If more than half the normal distance between egenerations has already been travelled, the driver will immediately see a message advising that regeneration 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 hundred miles before the regeneration triggers. Odds are though that for a fault condition to have occurred, it is very likely that more than half the normal distance since the last regeneration has already been travelled. I have seen this procedure used, and it did work, but it would be helpful to receive feedback from other owners of 2013 model year diesel pickups in Mexico about any
problems they have experienced, and how they dealt with those problems.

REMOVE AND DELETE
Some owners of 2007.5 and later diesel pickups do promote the idea of removing all the emissions equipment and using a programmer to delete the DPF and SCR controls. This may have been a solution up until 2012, albeit a very expensive, and illegal, solution. As of the 2013 model year though, new regulations require that the vehicle ECM (on board computer) be locked . As a result, removal and deletion of the emissions equipment does not seem to be an option going forward.

THE LONG TERM SOLUTION
In the longer term, the best solution for all Snowbirds would be for Mexico to introduce ultra low sulfur diesel throughout the country, as it has been promising to do for many years. In the meantime, owners of 2013 and later diesel pickups, if they decide to ignore warranty warnings and drive into Mexico, might be well advised to carry a large amount of ulsd fuel with them, so as to delay or eliminate the need to use Mexican diesel.
Ted White
March 13, 2013    whitetmp@aol.com