Air/Fuel Separator

[bsmith0404]

I have been looking at the Air/Fuel separators from FASS and Air Dog. They claim to help injector life, I can see/understand that as a possibility. Diesel owners all know how bad diesel can foam and there is the possibility that air can make it to the injectors,. That was the partial blame for some of the injector problems on the older duramax. They also claim that you get a better shot of fuel which increases horsepower and improves fuel mileage.

At $500-700 it is a big punch to the wallet and I am very skeptical of the benefit to cost ratio. Any thoughts?.

[bsmith0404]

Okay, I've modified my original post some. There has to be some people out there with opinions/thought/experience with these systems. I'm checking the diesel forums as well, but a lot of the people over there are into performance mods for the sake of performance not for longevity and towing.

[jtyphoid]

I'm skeptical about the need. Yes, diesel foams, but the foam floats and dissipates rather quickly and the fuel pickup is at the bottom of the tank. Unless there's a design flaw in the fuel system or some other unusual situation, I don't see the need.

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[Bob Landry]

If air makes it to the injectors, the engine shuts down and you have to bleed it from the high pressure pump. There is air in the tank because the tank is a vented system, but the pickup is on the bottom, so nothing but liquid fuel gets sucked up. I serviced small sailboat diesels for years and never had a fuel foaming problem, never herd of it. The only air problems I encountered was from cracked fuel hoses and faulty fittings sucking air between the tank and the lift pump. I'm going to have to call BS on that one.

[bsmith0404]

I first saw info on these systems in a diesel truck magazine where they brought up the concern of the injectors. The basic message was small (microscopic) amounts of air will cause the injector to slam shut vs. a smooth cushioned closing on fuel. The "diesel experts" stated this slamming action and the lack of lubrication from the low sulfur fuels is the major cause of injector failure.

I've looked at quite a few different post and reviews, for the most part it's been mixed. Some say they noticed immediate results with a smoother running and more responsive motor. Others said the results were minimal and the power/fuel mileage gains were not as much as expected for the cost. One guy made his own system based on a design from an engineering major in college and raved about how much better his power stroke performed. So it seems as though there are noticeable improvements/results, but the cost vs reward is questionable.

Sounds like $500 for a product that may or may not benefit the truck is money better spent somewhere else.

[GMcKenzie]

As an aside, not convinced this is the problem with the early Duramax injectors. After reading up and dealing with my own, there is just something wrong with them.

[jsmith948]

If you are concerned with the lower lubricity of ultra low-sulfur fuel, you could use an additive that increases lubricity such as 'Power Service Diesel Clean'.
Agree with previous posts - foaming is a non-issue. JMHO

On edit: When I started out driving over the road, diesel fuel was some pretty nasty stuff. It stunk (smelled like sulfur - go figure), it was dark in color and actually felt 'gritty'. I have read comments on here about the poor quality of today's diesel, but, I think the low sulfur fuels are better. Less corrosion, less water in the fuel vendors' tanks. I'm sure one can still find a load of 'bad' diesel out there. But I haven't had to stop 50 miles from the fuel stop to change fuel filters in a long, long time. The fuel I buy today feels clean and smooth, and, is a nice, clear to bluish color. Of course, it costs a bunch more! Just sayin'

[christopherglenn]

I put lift pumps on my trucks more for the extra water separation then the air separation. The returning fuel will leave small bubbles (as well as the sloshing within the tank) that will make it to the fuel pickup, but real world the mpg improvement is 0.0x %. You will see many times that with even the cheapest bottle of additive.

[bsmith0404]

Been reading more on these and the injector problems in the early dmax. I stand corrected, the info I found points more towards water than air in the fuel. Basically blaming poor filter design along with higher pressure systems allowing water to get through the filter. There is some info out there that contributes air as a problem as well. It basically states that older systems used to operate at roughly 3,000 psi, newer systems operate at 45,000 and higher. When a microscopic size air bubble makes it to the injector, it will close under pressure basically slamming just vs closing on a lubricated cushion of fuel. The low sulfur gets some blame as well as it does not lubricate the systems as well. I've found articles saying use additives, others saying don't. Articles saying the GM and Isuzu have fixed the problems with the injectors, other saying they haven't, some saying lift pumps & 2 micron filters are the way to go and of course, others saying not needed. I've only put 50,000 miles on my dmax engines, so I haven't experienced any problems. I can see how a better 2 micron filter can help, better is always better right? The question is just how much and is it worth the cost? I guess I'll put it on the wish list and add it when I have nothing better to do with all of the extra money I have just laying around

[DirtyOil]

"points more towards water than air in the fuel. Basically blaming poor filter design along with higher pressure systems allowing water to get through the filter"


From the refineries (at least here in Canada) water content right from the producer may contain up to 200ppm water in the diesel. This amount will be suspended in the fuel and will not affect the injectors. The water/fuel separators on modern diesel engines is more then sufficient. Its the maintenance of these filters or lack of, I should say, is what causes issues. Water destroys injector tips primarily. There isn't a filter on earth that will completely remove the water from diesel fuel. If you read enough you will also note these FASS and AirDog pumps/filters have issues as will, IMHO they're not worth the money.

If your fuel tank gets a build up of "free water" at the bottom of the tank, then a good aftermarket water/fuel separator may be required and this filter should be drained each time you fill up. As a preventative maintenance measure, I will drain some fuel off the filter on my truck at every third fill up. I drain it into a old mason jar to check for water or debris.

In a nut shell the amount of "microscopic" water in the fuel is really nothing to worry about, its the amount of "free water" that should be of concern.

[Desert185]

We've put almost 300,000 miles on a Cummins with no aftermarket air/fuel separator and no issues experienced. Original injection pump and injectors.

I'd put the money in something else that rings my bell.

[Sulphur1]

Originally Posted by bsmith0404

Been reading more on these and the injector problems in the early dmax. I stand corrected, the info I found points more towards water than air in the fuel. Basically blaming poor filter design along with higher pressure systems allowing water to get through the filter. There is some info out there that contributes air as a problem as well. It basically states that older systems used to operate at roughly 3,000 psi, newer systems operate at 45,000 and higher. When a microscopic size air bubble makes it to the injector, it will close under pressure basically slamming just vs closing on a lubricated cushion of fuel. The low sulfur gets some blame as well as it does not lubricate the systems as well. I've found articles saying use additives, others saying don't. Articles saying the GM and Isuzu have fixed the problems with the injectors, other saying they haven't, some saying lift pumps & 2 micron filters are the way to go and of course, others saying not needed. I've only put 50,000 miles on my dmax engines, so I haven't experienced any problems. I can see how a better 2 micron filter can help, better is always better right? The question is just how much and is it worth the cost? I guess I'll put it on the wish list and add it when I have nothing better to do with all of the extra money I have just laying around

Have a look at Summit Racing Brent
PureFlow AirDog A4SPBC085 - Pureflow AirDog Fuel Air Separation Systems

Fuel Pump, Adjustable, 8 psi, 100 gph, Fuel Filter, Fuel Pressure Regulator, Chevy, 6.6L Duramax Diesel, Kit
$585

I intend to fit one as 'insurance' - Those CP3 injector pumps and systems can be big$ to repair. Have read Isuzu originally intended for a finer filter to be used but unsure of authenticity.
Cheers
Jon

[bsmith0404]

All good information. Thanks for your inputs. With as many diesel owners on this forum I was surprised we didn't have more opinions/discussion on this. It took a while, but finally starting to get some good input and interesting points being made.

[mguay]

FWIW Brent, I am in the same boat as you and thinking about bullet proofing the system.

While GM has cleaned up the injector issue...the problem child is the new CP3. On other forums there are many posts of CP3 failures while still under warranty...

GM has had issues with fuel filter adapters letting air into the system and supposedly cleaned it up in the LBZ generation...but I'm not convinced. My LBZ would only make half a turn before it fired and if it went more I new I didn't get all the air out during my filter change. Open the bleeder screw and a few pumps on the primer till it was hard and problem solved. On my LML it has always made a turn or two before it fires. When changing the oil and checking the air filter I always find a mushy primer and air in the top of the fuel filter adapter.

I think the problem with the newer trucks is the higher fuel pressure. While driving the pressure up the fuel gets hotter and then when it is not needed and returned to the tank water droplets are formed from the hot to cold action. Although it is a very small amount of water...wherever there is water, there is air. IMO the tank vent does not remove all this air/water and "some" is sucked back to the engine.

I am on the fence as well about throwing the $500+ at it!

[Hoojs12840]

Originally Posted by Desert185

We've put almost 300,000 miles on a Cummins with no aftermarket air/fuel separator and no issues experienced. Original injection pump and injectors.



I'd put the money in something else that rings my bell.

I agree. If any of these add ons really did good without harming reliability, they would be standard.


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[LittleJoe]

Better fuel filtration is the best thing you can do to increase injector life.

Runing a lift pump on the early DMax helps but they were designed to run without it. Keeping a positive suction pressure is all thats needed so going overboard is not necessary. IF you run a water separator and 2-3 micron filtration your injectors will last MUCH longer than factory 10micron filtration

[DiverB]

I run the FASS 95 and have so on previous diesels, but again I'm running a twin CP3 and larger injectors, so the stock lift pump simply wont supply the fuel at the higher rate my engine requires.

I also like the FASS system for ease of changing my fuel filters and being able to filter down to a smaller micron. I run bio-diesel that I make at home, so I do change fuel filters more often then what a completely stock truck would need to.

If your going to keep your truck stock, then I'm sure you don't need a higher volume lift pump and dual filters, but I like the FASS system. Just my two cents

[bsmith0404]

Originally Posted by DiverB

I run the FASS 95 and have so on previous diesels, but again I'm running a twin CP3 and larger injectors, so the stock lift pump simply wont supply the fuel at the higher rate my engine requires.

I also like the FASS system for ease of changing my fuel filters and being able to filter down to a smaller micron. I run bio-diesel that I make at home, so I do change fuel filters more often then what a completely stock truck would need to.

If your going to keep your truck stock, then I'm sure you don't need a higher volume lift pump and dual filters, but I like the FASS system. Just my two cents

Have you noticed any power/fuel mileage gains that they claim?

[DiverB]

I can say the throttle response is a little crisper since the rail is getting pure fuel and not fuel/air. The only mileage gain was maybe 1/2 mile better per gallon. I am pretty anal on keeping track of my fuel mileage and fine tuning my tuner to get the best fuel mileage while towing. My truck is set up for towing and efficiency, not speed.

What I did was on an identical trip (same location, road, distance) I hand calculated my fuel consumption with certain settings on my tuner and then made the same trip to compare. I usually see 11.5-12mpg while towing. The one time I drove my truck with no trailer to my parents house (340 mile round trip) I was getting 22.4mpg.

I only use my truck for towing, other than that it sits in the garage until the next time its needed.

You wont hurt your truck by adding the FASS system, but it all honestly you wont see a huge jump in fuel mileage to justify the $635 price tag. I have to have it since my twin CP3 needs the higher volume lift pump, but a stock engine gets by just fine on the factory pump/ fuel filter.

Also you don't need to run "FASS Filters". I run Fleetguard filters that I purchase on line in bulk, much cheaper.

[bsmith0404]

Good feedback, thanks for the info.