Wednesday, January 20, 2016
Mercedes MBE 900 Parked Regen
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.