Here is an iteresting article. When mine failed for the 3rd time, a diesel shop finally alerted me to this. Myabe I cna save soembody else here. The stems you need are FASS or Airdog or similar.
"The Black, White and Greys of the Duramax Fuel Filter"
Grandpa used to lecture me about the importance of draining the water separator on his farmโs diesel tractor. This man, who wouldnโt hesitate to fix things with haywire or binder twine was, however, a purist when it came to maintenance. Experience had taught him that draining the water separator could mean the difference between a well performing engine and one with problems โ or one that didnโt run at all.
The investment required to properly maintain the fuel system meant avoiding the corrosion and scoring caused by water when it runs amok in the fine-tolerance components of a diesel engine. Duramax engines are significantly more sophisticated than Grandpaโs tractor. One might think that these more sophisticated engines can look after themselves a little better. In a sense that is true: today, we have more feedback than ever coming from our engines. But to think that these engines can handle not being maintained as well as their less sophisticated forerunners is far from the truth. In fact, just the opposite: todayโs fuel injectors and other components require much higher tolerances. Consider that a typical conventional diesel fuel system prior to the Duramax operated at fuel pressures of 1,200 to 1,500 PSI. Then compare those numbers to the original LB7 fuel injector that operated in the range of 4,500 to 23,200 PSI!
Whatโs more, the Duramax injector has to seal tight at these pressures unlike the injectors of conventional, distributor injection pump systems. Additionally, the LB7 injector was easily 10 times faster than its conventional counterparts โ the response time from when the injection control module energized the injector to when it began delivering fuel was an incredible 150 millionths of a second and it was capable of two injection events per cycle. The newer Duramax injectors are even faster and operate at higher pressures. They are capable of up to five injection events per cycle and run up to 26,500 PSI. Really, the performance requirements of the new common-rail diesel injectors absolutely blow away any conventional distributor injection pump diesel fuel systems. The result of much higher precision, operating pressures and speeds is that modern fuel systems are much more intolerant to the fuel contaminants โ including water โ that we will discuss in this article. These engines must be properly maintained or they suffer the consequences. Knowing this, GM engineered a filtering system up to the task, right? Heavy equipment and highway tractors typically feature multi-stage water separators and fuel filters. The Duramax, with its super-fine tolerance injectors โ and smaller internal components than a common-rail injector on a highway tractor โ would possess a similar design, right?. Actually, and as you probably already know, the Duramax engine includes only one relatively small filter that pulls double duty as the systemโs water separator. This combination, sophisticated equipment and a single-stage fuel filter, was a formula for potential problems. Mix in Murphyโs Law and potential problems become real life bring-it-into-the-shop problems. The good news is that we now understand the source of the problems and GM has made significant improvements to the Duramax fuel filter.
Too Many Failed Injectors
For a while, the diesel techs at the dealership were changing Duramax injectors on a daily basis. We would see five or so trucks lined up waiting for those precious injectors. It didnโt take long to start researching why they were failing so often. We discovered quite early on that if one injector was failing, the other seven were right behind it. Either Bosch, who had been mass producing common-rail injectors since 1997, was consistently turning out junk or something was killing these injectors.
I thought the latter possibility made more sense. Other manufacturers, Mercedes Benz for instance, had been using the injectors for a few years by that point without such pervasive issues. Surely Bosch had it figured out? The hypothesis that something was prematurely killing perfectly good injectors seemed more likely: time to experiment. By this time, there were already a couple of manufacturers in the Duramax pre-filter business. Their sales pitch? They claimed that the fuel filter on the Duramax was nowhere near adequate enough to keep typical contamination from damaging the injectors. We had a supplier send us a kit.
Letโs Blame Fuel Quality
Nearly coincidental to our experiment, an internal preliminary information document gave us some key, though slightly misleading information: if you are experiencing a multiple-injector failure and you suspect fuel quality, install a pre-filter (GM had already set up a Parker-Racor kit). The misleading part about this document was that it tried to set the focus of the injector failure issue on the always nebulous area of fuel quality rather than on the Duramax fuel filter inadequacy itself. Theoretically, you could use perfectly refined diesel fuel and not have a problem; but refineries never perfectly separate the various fractions of crude oil from each other. The reality was that I could not find any obvious fuel quality or contamination issues with most of the trucks that I was replacing injectors on.
Time passed. The trucks on which we installed pre-filters ran fine. If one of them did experience an injector failure, there was a very obvious and atypical fuel contamination issue to blame. Armed with this empirical evidence, we concluded that fuel contaminants that should be caught by the systemโs filter were the cause of the Duramaxโs high-tech injectorsโ demise.
Double Teamed!
More bulletins followed which, again, again promoted the availability of the pre-filter kit and emphasizing the importance of adhering to fuel filter maintenance intervals. It wasnโt until I attended a course on the Duramax, however, that I learned what was actually happening internally in the fuel system to cause the injectors to fail. Sure enough, the fuel filter stood at the center of the storm.
Two things that I mentioned earlier now come into play. The first is that water is not the only contaminant found in the fuel you and I buy at the pump โ even if it is the primary culprit when it comes to actually damaging the injectors. Fuel also contains asphalt residual, called asphaltenes, that the refining process (the second thing) fails to completely remove when crude oil is broken down to its component parts or โfractionsโ as they are called. Asphalt is a heavy fraction that we all know and love as the substance used to hold aggregate together on roads and such. However, some asphaltenes are always undesirably present in diesel fuel.
Back to the fuel filter. During normal operation, the pores in the media of the Duramax fuel filter become clogged with the omnipresent asphaltenes. As more pores become clogged, the fuel has less and usable media through which to flow. Restricted flow increases fuel flow velocity. Now remember that the Duramax fuel filter doubles as the water separator. Normally, the tiny particles of dissolved water present in the fuel are too large to pass through the filter. They coalesce on the surface of the filter and run down to the bottom of the can where the water-in-fuel sensor resides. However, if the asphaltenes have plugged enough of the pores in the filter, resulting in a higher fuel flow velocity across the filter, those same water particles can stick to the filter media. If they stay there long enough, the filter media swell creating, one by one, larger pores that will now allow the water particles โ we could call them injector assassins now โ to pass through. What happens next? You guessed it: fuel injector homicide!
Importance of Maintenance
Looking at the photos below of the fuel filters that have reached or exceeded the maintenance interval, it should be obvious why replacing the fuel filter consistently before too much asphaltene restriction occurs is imperative. Accordingly, GM stipulated a replacement interval of every 15,000 miles / 24,000 kilometers. If the OEM fuel filter had been doing everything it should have been doing prior to being neutralized by the asphaltenes โ something that should not occur if a fresh filter has been installed at the proper service interval โ this would have been the end of the story
Unfortunately, it is not the end of the story. The original design, single stage fuel filter was rated for five microns. (To give you an idea of the size of five-micron particle, it takes 5,080 such particles lined up end-to-end to equal one inch). The filter, however, allowed too-high a percentage of particles larger than five microns to pass. This anomaly occurred because manufacturing filter media, like refining oil, is not a perfect process: it is not feasible to manufacture a filter where every pore is exactly five microns. So there will always be a percentage of larger particles that make it through the filter. These particles include dissolved water as well as the asphaltenes themselves. They can certainly be a contributing factor to injector failures. Research reported by sources such as Heavy Duty Trucking in an article entitled โFiner Filtration: Is it the Answerโ (October 2003, page 86) and todaystrucking.com โYour Engineโs Tiny Problemโ (October 2003) indicate that particles larger than seven microns can cause excessive wear in a high pressure fuel system such as the one in the Duramax. Both of these sources reference SAE Paper 980869 and Detroit Diesel Engine Requirements Manual 7SE70 0209. I will note here that the use of fuel additives that contain water emulsifiers increase the likelihood that dissolved water will succeed in getting through the filter โ be cautious about using them.
That leads us to the reason the pre-filter solved the problem. Suddenly the main filter had a much more manageable task: all it had to do was catch the small fraction of larger particles that made it through the pre-filter. The percentage of water and other contaminants making it through to the injectors dropped dramatically. The presence of a good pre-filter along with proper maintenance in keeping with the main filter service intervals generally allowed the early Duramax injectors to run quite happily.
