Mercedes MBE 900 Parked Regen

Using Mercedes Software To Perform a Regen from John Whelan on Vimeo.

In 2007 everything changed for diesel engines. The newly integrated emission systems were now the most important cog in the wheel. They had to meet certain parameters according to the onboard computer programming and if they did not an engine code would appear and stare you in the face until the fault was repaired. At first it was frustrating since we had not worked extensively on these emission controlled MBE 900 models.

The Mercedes dealer become regular aquaintances and saw our buses many times over the 5 year warranty period. Engine codes appeared then went away and popped back up again a couple of days later and so on. Once warranty expired we knew it was time to get into these engines more than ever. The online resources called DDSCN was very helpful along with the Detroit Diesel engine software we had loaded up on our laptop.

There was a lot to absorb since everything was monitored by the MCM (motor control module). Turbo boost, EGR and diesel particulate filter cleanliness determined how well these engines were going to run. Once there was a restriction in the DPF a regular code 'dpf out of range high' would pop up until we did a parked regen or repaired a sensor or plugged up sensor air line. Without the diagnostic software we could not do a thing to get these engines back in shape.

The DPF section in the software allows you to watch all of the temperatures in the DPF and DOC. The differential pressure indicated if there was a restriction (3 psi max). The video goes into a parked regen where the temperatures go as high as 1,000 degrees cooking out the DPF. This half hour process does the job and most times it makes a huge difference in driveability.

Another option to troubleshooting was an over the road regeneration where you could monitor the regen process while on a road test and record the data. The Detroit Diesel software is very good for narrowing down a problem. Once there is a code the software can troubleshoot the code step by step which really made life easier for the techs.

The filter cartridge in the DPF is replaceable which we had to do a few times because the regen process was not working. It's similar to an air filter that you clean out and stick back in the cannister. Eventually it's not going to clean up properly over time due to the compounded accumulation of debris. Soot and ash are a never ending problem throughout an emission controlled diesel engine and the MBE had lots of that with sensors plugging up and EGR valves sticking.

They are definitely not the perfect engine when combined with emissions but working on them and gaining experience helped our shop know what steps to take whenever a fault occurred.

Diesel Engine Emissions and DPF Diesel Particulat Filter Codes

If you look at this DPF diesel particulate filter you'll notice  the clamps around the outside. Fortunately for all of us diesel techs this exhaust system is serviceable. The filter inside can be removed and serviced or if it's too far gone replaced. There are many shops now that have made the investment and have the equipment to clean the DPF filter properly.

 

The cost is about half compared to buying a pre-cleaned unit from the dealer. This is what I experience anyway... I'm not sure what the set up is at your location. The Detroit Diesel dealer has a cleaned DPF filter on the shelf for around $800.00 while the cleaning process is in two stages if it needs a 2 step melt down then the bill may run up to $500.00.

 

The good thing about this operation is it does not have to be done on a regular basis. Mercedes recommends every 125,000 km for a filter service. On the other hand if there is a over fueling or if the engine is using excessive amounts of oil due to a defect then the filter will plug up much faster.



 

 

 

The photo above shows both the MIL (malfunction indicator light) and the engine warning light illuminated. The MIL indicates there is a fault in the emissions system. This could be the DPF needs a regen or there is a lack of air flow in the intake system or numerous other problems. Most times we have found that the DPF regen is the most common service procedure.

 

With the laptop we do a forced regen and this cleans out the DPF filter using heat and diesel injection (Mercedes) or DEF (diesel exhaust fluid) for Cummins 2010 and newer engines. The DOC or diesel oxidation catalyst built into the DPF causes the chemical reaction to take place breaking down the soot and ash that builds up in the filter.

 

Cummins has taken it one step further with the SCR (selective catalytic reduction) process using DEF to reduce emissions even further. Low ash engine oil and low sulfur diesel fuel has also contributed to reducing emissions. If you have anything to add please do so below in the comments section. What do you think of the emissions in today's diesel engines?

Mercedes MBE 900 Diesel Engine Emissions and Engine Codes

EGR - Exhaust Gas Recirculation Maintenance

I want to share some observations and solutions with emissions and engine codes we have been experiencing with the Mercedes MBE 900 diesel engines in our bus fleet. We have a dozen of these engines 2007 - 2008 emission controlled and they are all off warranty so this has allowed us to learn by "doing" with the various emission and engine codes that normally occur. The time we have spent troubleshooting these various problems has taught us a lot and we have adapted to the typical problems that happen with this model engine.

The EGR Cooler above had to be replaced due to a leakage problem. With a coolant leak they will eventually plug up with a sludge build up if it does not get attended to. If the EGR cooler is not leaking and has a soot build up it will require removal and a hot tank cleaning at your local radiator repair shop.

They are not cheap to replace however if they leak you'll experience coolant loss and engine code problems because of the soot wet mess that will develop inside the cooler exhaust core. This will cause poor exhaust gas flow and reduce engine power. The EGR cooler exhaust gases flow to the EGR valve which mixes the cooled gases with the charge air intake reducing NOx (oxides of nitrogen) creating reduced emissions out of the tail pipe.

Charge Air Cooler Failure Mercedes Code 2631

The charge air cooler to the left split open right at the core on the engine side. This problem was hard to detect because of the noise going on when the engine is running.

The reason we found it was because of a pressure check on the cooler itself. There was a 2631 Mercedes engine code which is a "turbo boost performance" issue.

Mercedes has a procedure for troubleshooting this code and it's quite involved. You have to check the boost pressure sensor for soot build up then using the software check the EGR operation along with the intake throttle valve etc. Any part of the engine that isn't allowing full flow including the air intake and boost side will produce the 2631 code.

In this case we have blown charge air cooler causing a big drop in boost pressure. The good part is we found a problem the down side is it's located 10 days away in Memphis. This bus is down until then. NOTE: We used a regulator to pressure test this cooler at 30 psi and made plugs that can be clamped at both ends.

Mercedes Diesel Engine "low doser fuel pressure" Code

The doser code activated because the fuel pressure supply in the system was too low and this caused the regeneration process to fail.

The "doser" system shoots a mist of diesel fuel down stream to cause the regeneration operation to activate at the DPF (diesel particulate filter).

No regen operation meant the DPF was going to build up soot and ash to the point where the engine would eventually shut down. This is serious since the engine control unit is programmed to protect the engine and will not allow it to run when the emission parameters are out of the ball park.

The Mercedes power service literature is very good for troubleshooting information. This test shows how to measure the return fuel going back to the tank. At idle the lines are hooked directly to the secondary fuel filter return and a tee fitting is hooked into the overflow valve.

There are 2 fuel regulators one for the doser fuel side and one for the high pressure injection side (unit pumps). If there is too much fuel returning back to the tank the fuel pressure reading drops.

The fuel pump is a positive flow gear pump that is engine driven. Fuel pressure must get up to at least 65 psi to supply the doser system (does the exhaust regen operation) and the unit pumps which provides the high pressure fuel to the injectors.

Once we changed the 2 valves in the fuel return lines "overflow valve" and "doser fuel pressure regulator valve" the exhaust regen started working again and the engine power improved drastically. So it was a win - win in this case.

If you're interested in viewing more blog posts photos and videos check out mechanicshub.com and look for "blogs". I'm posting under the name "schoolbusmechanic"

Mechanic Tips-School Bus Fleet Preventive Maintenance

Every Fleet Mechanic will have there own ideas on how to set up the best PM program for their equipment which will vary for different locations. With different climates, road conditions and power trains the procedures will never be exactly the same. Our shop likes to condense the annual PM since the regular checks are carried out every 5000 Kilometers (3000 Miles). Oil changes are done every 15,000 Km with an oil sample to be analyzed. Fuel filters are replaced at every oil change.

The Allison 2000 and 3000 Transmissions  are all running on TES-295 Synthetic oil which has drastically cut down on repairs. Right now we change the oil every 3 years, the newer buses have prognostics which tells us with a dash light indicator when the filter and oil needs to be changed. Air filters are replaced every year regardless of the mileage. Steering Filters are serviced along with changing the oil every 2 years. Valve Sets are carried out according to the Manufacturer i.e Cummins every 5000 Hours or 240,000 Km (Electronic Models). With the introduction to emission controls in 2007 we now have to perform manual regens if required and replace the DPF (diesel particulate filter) every 150,000 Km (90,000 Miles)

Air Dryers every 2 years with a new unloader kit and dessicant filter. Dirt is a factor on school buses so we service interior heater filters and the entire lighting system (Non-LED lights). We check the starting and charging systems including the battery pack. If necessary we will run tests on the batteries and alternator. years ago alternators and starters were removed for rebuild but the time and parts did not add up as an economic strategy so we decided to give these components a 5 year life span before determining if they would need replacement. The cost has come down so much on electrical reman units, it's feasible to go this route with the added bonus of a warranty period.
 
Spring brake chambers are replaced every 5 years regardless of mileage and condition. The Mercedes MBE 900 requires a coolant and thermostat change every 2 years, the other diesel engines in our fleet do not have a time or mileage limit but we're working on that to prevent antifreeze deterioration and thermostat failures. Our tires tread depth is measured every Summer and pressures checked during each service.

Common sense plays a role with any preventive maintenance program and we found the best way to set one up is to sit all the Mechanics down in one room and go through the fleet  figuring out the best program to cover all the bases. Breakdowns will quickly eat up your labor time and parts budget like wildfire so keeping on top of maintenance with a feasible program will pay you back 10 times over.                                                                     

International DT Engines Overview

DT Engine Design & The Wet Sleeve

International DT Engines have a wet sleeve meaning the cylinder wall is a seperate machined part that presses into the engine block. The sleeve is in contact with engine coolant which is why it comes by it's description "Wet Sleeve"

International runs the wet sleeve design because it increases the durability and the cylinder wall thickness has a much better heat transfer which allows the cylinders to stay round when going through thermal expansion. Also, the cylinder sleeve is much harder than the cast block cylinder making the DT design much more wear resistant.

Rebuilding the DT Diesel Engine is very convenient since the block stays in the frame, hence the term "In-Frame". The sleeves being removeable saves the block from damage since the sleeves are replaced during the inframe process, saving time and extra costs.

With standard cast engine blocks the cylinder bores have to be machined. If there is major damage, in some cases the block might not be salvaged. Standard block cylinders become out of round during thermal expansion and wear much faster than the stronger DT steel cylinder sleeves.

DT Engine Fuel Injection 

DT engines used a Bosch pump-line-nozzle (PLN) mechanical direct fuel injection system  from 1984 until late 1995.  DTs used a Bosch MW style pump 1984 through 1992, while the  Bosch P style pump came into force between 1993-1995 where the New Generation Diesel engine design began, which is still the same basic block design.

Up to 1997 mechanical injection was used but in rare occasions. Emissions tightening started in 1994 and the injection systems were redesigned using electronically-controlled unit direct fuel injection.

HEUI (Hydraulically-actuated Electronically-controlled Unit Injection) injectors, co-developed by Navistar and Caterpillar were unleashed from 1994 to 2004. From 2004 the engines use Electro-Hydraulic Generation 2 Unit Injectors nicknamed "G2 injectors".


Recommended

Diesel & Gasoline Working Together?

The Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine pictured has a thermal efficiency of 50% (the best in the world). There is new research going on in the University of Wisconsin, Madison that got 53% thermal efficiency out of a Cat Diesel Engine.

I just read the article about this new technology mixing gasoline and diesel into a diesel engine. This system increases the thermal efficiency by 20% but reduces the temperature in the combustion chamber by 40% creating less unburned fuel out the tail pipe.

The mix would be computer controlled and since there would be less energy loss through heat transfer, improved combustion would cause an increase in power with less emissions.

The computer age has allowed scientists and researchers to stretch the resources we have right now to the limit in a very efficient way. Without computer programming, monitoring, and adjusting operating parameters this new technical solution for decreasing vehicle emissions would not be possible.
I hope you found this Mechanic Information interesting...

California Cleaning Up School Bus Emissions on Diesel Engines

California school districts in the southcoast area are doing a major clean up on diesel engine buses in 13 school districts at the cost of 43 million dollars. They are going to start runniing them on compressed natural gas and propane.

This measure was implemented by the Air Quality Management District. Approxamately 176 newer buses will get particulate trapping devices as well at a cost of 3 million dollars. I'm impressed with the seriousness of the California Gov't to clean up the air but the expense is unbelievable.

Read the full article HERE

Our fleet of 75 school buses come with diesel emission controlled engines that the factories have spent millions of dollars on already. The buses are equipped with particulate filters from factory and they do an excellent job. It will take a long time to change over to Propane and natural gas due to the expense.

New Study Heavy Duty Diesel Emissions Reduced Drastically-New York Times

I'm Guessing The Next Study Will Be Lowering Emissions On Super Duty Diesels like the one ABOVE!

Here's an interesting article on a 5 year study by several Environmental Groups including the Health Effects Institute, Coordinating Research Council, Energy Dept., EPA, Engine Manufacturers Association and the American Petroleum Institute.

Read The Full Article HERE

Researchers have found particulate matter called soot has been reduced by 99% from levels allowed in 2004. Emissions are also 90% lower than 2007 standard requirements. Good news for us and the air that keeps us alive!

Right now the new DPF (diesel particulate filter) mufflers are collecting soot and burning it off into the atmosphere automatically by way of computer technology. The DPF has sensors that tell the computer the temperature is getting excessive on one end and needs to start a regeneration.

Regeneration is computer activated which injects atomized diesel into the exhaust system burning off accumulated soot. If the soot buildup gets too much to handle, a manual regeneration is required using laptop software.

This manual regeneration takes about 45 minutes and the temperatures get at high as 1200 degrees. This is a very efficient way to burn off particulates/soot. Every Mechanic involved with today's diesel engines will be repairing and maintaining these emission controlled systems for many years to come.

Diesel Engine Oil - Switching to CJ-4 For 2007

To meet 2007 EPA standards low emission engines must use CJ-4 engine oil formulated especially for diesel engines using exhaust aftertreatment systems. New EPA standards are a 50% reduction in oxides of Nitrogen and 90% reduction in particulate matter. CJ-4 is a low ash diesel engine oil that can be used in older engines but comes at a higher price. The warranty becomes invalid if regular CL-4 oil is used in '07 diesel engines but the 10 to 30% increase in price is significant when it comes to a fleet operation.

You could stock both oils but there is a risk of operators who normally add oil to there assigned unit could inadvertently grab the wrong oil and mix the two. Mind you one litre of the wrong oil would not be detrimental to the life of the 2007 diesel engines but over time it would make a difference. The possibility of an engine oil test after a failure could happen.


Our fleet operation only stocks the CJ-4 so there is no confusion and zero risk to jeopardizing the integrity of the DPF [Diesel Particulate Filter]. The DPF has a regenerating cycle when a difference in input and output exhaust gases in the DPF [muffler] are picked up by the engine ECM [electronic control module]. The DPF literally cooks out the carbon build up and it gets kicked out the exhaust pipe which creates extremely high temperatures.


EPA standards are here to stay, with vehicle emission standards being on top of the heap when it comes to environmental concerns. Our School Bus Fleet will be receiving a Hybrid International School Bus next September. This will be an interesting technology to experience and another brand new learning curve to grasp.

Advantages of LPG and CNG in Diesel Engines

The vast majority of diesel engines in service today use solid injection and the information below relates to that system. In the diesel engine, only air is introduced into the combustion chamber.

The air is then compressed to about 600 pounds per square inch (psi), compared to about 200 psi in the gasoline engine. This high compression heats the air to about 1000 degrees Fahrenheit. At this moment, fuel is injected directly into the compressed air.

The fuel is ignited by the heat, causing a rapid expansion of gases that drive the piston downward, supplying power to the crankshaft. In Diesel's manuals, he described the supply of compressed gas into the cylinder to promote the final burn. It is now possible to fumigate the air intake with a small quantity of LPG/CNG.

The now air-gas mixture is compressed as above, and when the diesel ignites, the small quantity of gas ignites as well, causing a more rapid and more complete burn of the diesel. Most diesel engines waste between 30 and 15% of the diesel fuel, so by burning the near total amount of diesel consumed on each stroke, the mechanical effect is to improve the torque curve by as much as 28%.

The net outcome of applying gas into diesel is improved fuel economy via better torque at the driving wheels resulting in fewer gear changes, and greatly reduced exhaust emissions.

Advantages of the diesel engine are numerous. It burns considerably less fuel than a gasoline engine performing the same work. It has no ignition system to attend to. It can deliver much more of its rated horsepower on a continuous basis than can a gasoline engine. The life of a diesel engine is generally longer than a gasoline engine. Although diesel fuel will burn in open air, it will not explode unless compressed.

Some disadvantages to diesel engines are that they are very heavy for the horsepower they produce due to the required heavy design, and their initial cost is much higher than a comparable gasoline engine.

Recommended: Diesel Engine Repair Manuals

Diesel School Bus in UK Running on Rape Seed Oil

Here's an interesting video about a company called Regenatec that have developed a bio-fuel from rape seed oil. This is very impressive since it reduces emissions by 80%

B20 Biodiesel Approved for use by Cummins

{This is a from a recent article released by Cummins}
B20 Biodiesel
One reason for biodiesel’s popularity is its capability to reduce emissions. Biodiesel may also help to reduce reliance on imported oil, using renewable “homegrown” energy sources. Cummins has completed the necessary testing and evaluations to ensure that customers can reliably operate their equipment with confidence using any biodiesel blend from B2 to B20 biodiesel fuel.

The popularity and use of biodiesel fuel continues to climb. Recent studies predict that, by 2008, 1.2 billion gallons of B100 biodiesel will be produced in the United States. One reason for biodiesel’s popularity is its capability to reduce emissions. Biodiesel may also help to reduce reliance on imported oil, using renewable “homegrown” energy sources.

Pure 100% biodiesel contains no petroleum and is commonly referred to as B100. While it works in diesel engines, most manufacturers, including Cummins, recommend a blend with petroleum-based diesel fuel. B5 is a blend of 5% biodiesel and 95% petroleum-based diesel fuel and is the most readily available biodiesel today. Other blends that are also available include B2, B10 and B20.

All of these biodiesel blends up to B20 are now approved for use in Cummins diesel engines, including those in transit operations.

Cummins has upgraded its previous position on the use of biodiesel fuel for three key reasons: First, the American Society of Testing Materials specification ASTM D6751 now includes an important stability specification for B100 biodiesel; second, the availability of quality fuels from BQ-9000 Certified Marketers and Accredited Producers is growing rapidly; and third, Cummins has completed the necessary testing and evaluations to ensure that customers can reliably operate their equipment with confidence using B20 fuel.

“We have completed exhaustive analysis and test evaluations which enable Cummins to provide the necessary guidance and information to our customers for the proper and successful use of this fuel in our engine,” said Edward Lyford-Pike, Chief Engineer – Advanced Alternative Fuel Programs. “This will enable our urban transit fleets to have a choice that includes fuel made, in part, from renewable resources”. For more information, see the Cummins biodiesel FAQ.

Bio-Diesel...A Natural Alternative

In 2002, 15 million gallons of biodiesel was consumed in the United States (The American Soybean Association)

The National Biodiesel Board, a trade association for biodiesel producers, is a good source of additional information

The primary advantages of biodiesel are:

1) It has natural lubricating properties and thus eliminates the need for synthetic lubricating additives in ultra low sulfur diesel fuels

2) It is essentially sulfur free and has a very high cetane number (a measure of diesel fuel quality).

The other process for producing biodiesel is through a conventional petroleum refining process known as hydroprocessing. In Europe, the largest producer and user of biodiesel, the fuel is usually made from rapeseed (canola) oil.

Recent environmental and economic concerns (Kyoto Protocol) have prompted resurgence in the use of biodiesel throughout the world. In 1991, the European Community, (EC) Proposed a 90% tax reduction for the use of biofuels, including biodiesel.

There have been reports that a diesel-biodiesel mix results in lower emissions than either can achieve alone. Biodiesel can be obtained from vegetable oil (vegidiesel / vegifuel), or animal fats (bio-lipids, using transesterification).

Biodiesel has a higher gel point than petrodiesel, but is comparable to diesel and is made by transforming animal fat or vegetable oil with alcohol and can be directly substituted for diesel either as neat fuel (B100) or as an oxygenate additive (typically 20%-B20).

Biodiesel produced by this method is sulfur free and has a high cetane number but it lacks the lubricating properties of FAME.

*What Is FAME?

(Fatty-Acid Methyl Ester). Fatty-acid alkyl esters are actually long chains of carbon molecules (12 to 22 carbons long) with an alcohol molecule attached to one end of the chain. In a process called transesterification, organically derived oils (vegetable oils, animal fats and recycled restaurant greases) are combined with alcohol (usually methanol) and chemically altered to form fatty esters such as methyl ester. The biomass-derived esters can be blended with conventional diesel fuel or used as a neat fuel (100% biodiesel).*

Biodiesel is the best greenhouse gas mitigation strategy for today’s medium and heavyduty vehicles, is completely renewable and burns much cleaner than petroleum diesel (plus the exhaust smells like french fries).