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Mega Filter FAQ

Please note that the word air is used loosely in this document to describe any free gasses. JK

Note: The following link Suction Side Fuel Filters sheds further light on this subject.

Do I have air in my factory system?

It is important to note that the Duramax engine runs WITHOUT a feed pump.

The engine mounted injection pump basically draws the fuel from the tank by creating reduced pressure in the feed line. It is my belief that there is naturally and/or unnaturally occurring air in all suction type Dmmax fuel systems. If you haven’t tested with a clear hose, you do not know that you have no air. The best way is described in the Helms Service manual, and is the same method that I use. A clear hose between the EDU/FICM and the OE filter head. My preference here is to force a 7/16″x1/8″ wall hose onto the nipples for a super snug fit. This will diagnose the entire pre OEM filter plumbing. It is tough to get all the air out when installing, but basically, once evacuated, you will want to make a high loop for the air to accumulate in.

Where is the air coming from?

Barring any suction side leaks, (ie quick disconnect fittings, fuel filter orings, primer pump etc) it is vaporizing in the lines. Diesel fuel as a fluid has a vapor point that will vary based on the quality of the fuel and the region. The vapor point of fuel is influenced by both heat and pressure, or lack thereof. As fuel approaches it’s vapor pressure, which is LESS than atmosphere, it begins to vaporize. This is similar to gasoline engine vapor lock condition, water boiling etc. Simply put, the reduced pressure of the suction side fuel lines combined with the heat of the engine and computer electronics that the fuel is cooling appears to be pushing the fuel to it’s vapor point. If trapped air in the Mega becomes a problem, we have a simple bleed orifice that can be installed in the suction nipple. This tiny orifice will allow the air to pass through the system just as it does in normal operation.

Why does the Mega Filter trap air when others apparently do not?

The deep drop of my suction nipple, and the internal post seal ensures that there is no channeling of fuel through the threads, and that none of the microscopic filings generated when engaging the filter threads are dropped into the clean fuel below. This also creates a large area for air to collect as the fuel enters the filter. The lazy flow allows this air to rise to the ceiling and collect, waiting to be bled. Other filter designs have less depth to the suction nipple, and apparently allow the air to pass through the system.

Is air bad for my fuel system?

Air is never a good thing in a hydraulic system. Since air compresses and liquid does not, any air present can dampen the hydraulic pressures, just like a spongy brake pedal. Air can also cause cavitation erosion to mechanical to components of the injection system. Now I’m not saying that it is GOING to do harm to your injection system. In reality, we have seen NO documented proof that there have been any air related failures in the Duramax fuel system. We just know that air is equally undesirable as is dirt contamination. Time may prove that the Bosch common rail pump is capable of processing large amounts of air, but I am not willing to wait until that time comes!

How, and how often should I remove air from my Mega filter?

Again, this will vary from truck to truck. Bleeding is quite simple. You just pump up the factory primer pump until resistance is felt, and open the Mega filter’s bleeder using a long screwdriver from above. As soon as fuel starts to spit, close the bleeder. Frequency will vary, but the simplest approach is to do this when refueling.

What do I do in the event of a stall or no-start situation?

I have not heard of any stalling issues except at start-up after standing for a significant amount of time. The range here is from a total no start to a start and then stall seconds later. Once underway, the pump seems to do fine. If a stall/no start occurs, simply bleeding the Mega filter will get you rolling again. If, for some reason, the operator lacks sufficient skills to open the bleeder, one can pump the primer until pressure is felt and the engine will generally start. Of course, opening the bleeder and evacuating the air present is the best solution. This is NOT a situation that will leave you stranded on the road. The ultimate solution in my opinion will be a lift pump.

How long will a Mega Filter element last?

Service life will vary depending on fuel quality, but I expect to see them run for 30,000 plus miles, or an annual servicing when installed as a secondary unit. The OE unit should be serviced at or BEFORE the GM recommended interval. I typically change my OE unit at every other oil change or 7-8k miles. I will soon have a filter restriction gauge kit available that attaches to the sampling port provided for the GM technicians to measure restriction for diagnosis of performance related issues. This will be a simple, compact unit and will be priced at about $100 which is about ½ of what the GM gauge setup runs. The user will need to baseline his truck to determine what a new filter setup reads, and then occasional checking to monitor trends will allow the user to diagnose a potentially plugging filter. Care must be taken to eliminate variables such as fuel tank level, and angle of vehicle as the positioning of the fuel tank can have a profound effect on the gauge reading.

How do I prevent the vaporization of fuel in my lines?

Adding a lift pump ensures that the fuel in the lines remains under constant pressure well above the vapor point. It is my opinion that this addition is a very good thing, as it will maintain your filters full of fluid allowing them to perform more effectively. While I personally have never experienced an air related no start condition, but had large amounts of accumulated air when bleeding. I have recently added a lift pump for experimentation purposes. With the fuel under constant pressure, I collect absolutely ZERO air in my filter! It has been a slow process, but I am working on what I will call a “universal” lift pump kit which will include a pump, fittings, and a relay setup which should be available in the not too distant future.

“It should be noted that in speaking with an engineer at Bosch, although they DO use a lift pump on the common rail 5.9 Cummins in the Dodge truck, Bosch does not feel that there is a need, nor do they recommend a lift pump for their common rail system on the Duramax. Right or wrong, I have a different opinion based on my field observations…” JK