Fuel vacuum with clean flter? Tech Help requested?

[Jim Cobler]

Does anyone know the proper fuel vacuum with a clean filter and the vacuum level when a filter change is recommended? I have done some searches and have not apparently used the correct terms to get my question answered.

I intend to install an in cab fuel vacuum gauge that does not require a fuel line into the cab. In this manner, I hope to detect when my filters need changing.

Currently, I have a frame mounted Baldwin 1259 as a pre-filter. In addition, I have a Baldwin 1259 on my bed tank which has fuel pumped continuously from the bottom of my bed tank through it by an extra fuel pump and back into the bottom of the other end of the tank.

Thank you,

[OC_DMAX]

I can answer part of your question. Using my Kent-Moore gauge vacuum gauge, I measure about 2.50 inHg of vacuum on a new filter with the engine idling. This is a fact.

I have heard that when the vacuum level rises to 8 inHg at idle that it is time to change. I am less sure on this number. Additional info, there was a post by Racor (the forum member) a ways back where he indicated the vacuum number when the filter should be changed. Unfortunately, I do not remember the number he posted.

I currently have 4K miles on my OEM and Racor supplemental filter and am still reading 2.5 inHg at idle.

Lets see what others come up with.

[OC_DMAX]

I found the Racor post with regard to filter restriction:

http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=006553


To quote Racor "If you put a vacuum gauge at the outlet of the filter, you can read when the filter needs changeout. For a single filter system, note the starting vacuum at idle and change when vacuum raises 3 to 5 inches Hg over the start. If it is a two-filter system, you can take it to 6 to 10 inches Hg vacuum over start. Keeping to these guidlines increases the chance that your filter will remove most all the water when you need it to. "

[mdrag]

Here are my results (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=005344;p=2) using the Kent Moore gauge to measure the fuel filter restriction:


I measured the Dmax fuel filter restriction at normal factory idle/high idle (rev limiter) after the truck was up to operating temps. Results are inches Hg vacuum:

OEM Racor with 1.6K miles 3.0"/3.5"
OEM Racor NEW filter 2.5"/2.75"
OEM Racor/KD Megafilter(both NEW) 3.5"/3.75"Measuring the restriction with an empty fuel tank will add 0.5" to 1.0" to these numbers (as compared to a full tank). Also, the position (height) of the gauge will slightly affect the readings.

[jbplock]

Originally posted by Jim Cobler:
...I intend to install an in cab fuel vacuum gauge that does not require a fuel line into the cab...Jim, can you post some details on the gauge that you plan to use? Sounds nice! :cool: Does it use an elctrical vacuum sensor to drive the gauge? Who makes it? cost ? ect...

smile.gif

[Jim Cobler]

I am working with the local Kenworth service center and the service man has told me about the gauge but I don't have specifics yet. My question was ask so I could make sure the guage had the correct vacuum range. The service man told me the guage (2.5" diameter) would cost around $60 dollars and it does have some sort of electrical sending unit. As soon as I can make sure the range is correct, I will install and post the information here.

For information, the local GMC dealer either did not know or would not disclose the vacuum information. Makes me wonder whos side their on.

[OC_DMAX]

Jim,

After reading your post above, let me add a little bit to what I posted originally;

At idle, the figures that have been posted above are correct.

However, when the vehicle is under full load (max acceleration) other factors must be taken into account. Fuel demand goes way up plus the pump must overcome the vehicle acceleration to move the fuel from the tank to itself. This results in a much larger vacuum level.

I have measured up to 10 inHg of vacuum with the Kent-Moore gauge while accelerating at full throttle. My engine is stock (no juice, etc). I would imagine that others that have modified their vehicles (with power boxes) are probably pushing 15 inHg of vacuum (a guess - if anyone has additional info you need to post). Take that into consideration when estimating the correct range of your vacuum gauge. A point of reference, the Kent-Moore gauge goes to 30 inHg.

Alan

[Kennedy]

IMHO, there are tioo many variables involved to put any faith into a dynamic test. My suggestion is this.

FULL tank level ground, cap loose, eliminate any other variables that you can think of.

Measure at idle, and high idle (3200RPM no load) and establish a baseline, then check periodically in identical circumstances.

Fuel tank level is the big factor, as is incline/decline of the vehicle.

Also for reference, and consistent with Mdrag's findings, the Kent Moore gauge head isn't much to write home about. The movement is not smooth, AND it will vary readings depending on position and elevation. Hoking from hood latch will yield one number, laying on core support another, and on the ground yet another... :rolleyes:

As a result of this, I've been testing with liquid filled, temperature compensating gauges. I have also been working with a 15"hg x 7.5 psi scale to spread the dial a bit allowing more precise readings. Shown below is a rigid mount (quick coupled) which eliminates the potential for variables of placement. I haven't tested with a hose yet, but expect similar stable results.


http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest.gif


If one were to stick with a strictly suction system, you could take this further by going to a vacuum only gauge.

[OC_DMAX]

IMHO, there are tioo many variables involved to put any faith into a dynamic test

Actually, you missed the point, so let me take another approach here. My last post (dynamic effects) had more to do with sizing the range of the vacuum sensor than anything else. I did not want Jim taking away from this post that the total swing in vacuum pressure was just a few inHg. He goes off and buys a 0 - 10 inHG gauge. With his in cab installation he will read the entire range the fuel system sees. Suddenly he sees 15 inHG and blows the gauge. I have noted swings from 10 inHg to a (positive) 2 psi (on decelleration). Simple as that.

With respect to taking measurements on filter restriction, he also needs to be careful with his in-bed tank. He now has a system that can read almost 0 inHg if in bed tank is full.

[Jim Cobler]

Gentlemen, I am a rank amateur at this but let me expand on my idea a little. Once I obtain the proper guage, I intend to watch the guage carefully as I drive and observe the vacuum under all conditions. In this manner, I can tell when the filter restriction in increasing.

It is NOT my intention to squeeze every last mile from the filter but to avoid a failure on the road. I don't know whether you have changed a filter on a 100+ degree day along an interstate road with a hot engine but it is not my idea of a good time and believe me your wife will not be smiling either. This has happened to me with as few as 3400 miles on the filter and I do buy fuel from truck stops only.

[OC_DMAX]

Jim,

To measure filter restriction or the need to replace it, the method I use is what Kennedy describes above. I place the gauge in the same spot, check vacuum at idle and then with vehicle in Park, run the engine to max rpm. I do this after filling the fuel tank up. Usually every couple of thousand miles.

Your real-time always on monitor would alert you to filter restrictions because of a bad load of fuel or gelling due to cold weather. However, what you will find is that there is not one constant vacuum level. The gauge will be swinging from 0 to 10 inHG depending on how the vehicle is moving. Even slightly touching the accelerator will cause the gauge to move 1 inHg.

[Kennedy]

Originally posted by OC_DMAX:
Jim,

To measure filter restriction or the need to replace it, the method I use is what Kennedy describes above. I place the gauge in the same spot, check vacuum at idle and then with vehicle in Park, run the engine to max rpm. I do this after filling the fuel tank up. Usually every couple of thousand miles.

Your real-time always on monitor would alert you to filter restrictions because of a bad load of fuel or gelling due to cold weather. However, what you will find is that there is not one constant vacuum level. The gauge will be swinging from 0 to 10 inHG depending on how the vehicle is moving. Even slightly touching the accelerator will cause the gauge to move 1 inHg. That's kinda what I was getting at. May not have come across clearly, but basically running down the road will not provide repeatable results.

As for the changing on the side of the road, been there, done that, AND I leaned on the AC line atop the compressor letting out my refrigerant. I was paranoid after feeling fishbite (EARLY Edge Juice) enroute to the BC Rendezvous. I broke this in MN on the way out... :eek:

[ 01-14-2004, 06:05 AM: Message edited by: kennedy ]

[a bear]

I also established a baseline reading with new filters, full tank and a fixed elevation of the gauge. Then I just repeat under the same conditions. Need a better gauge though. The one John has pictured above is nicer than any I have been able to find. I still like Jim's idea about installing a in cab gauge. You could then check restriction at a glance during each fill up, at a red light or whatever. It would even give the ability to constantly monitor my lift pump operation. :D

[Turbine Doc]

Racor sells a vacuum switch set at 7" I have it mounted in a tee at filter outlet of my pre filt now soon on my fact filt outlet also, I have it wired to a 12v LED on my pilar post pod to tell me when it's time to change the filt. Racor also sells a gage kit I've not seen it though. This is on a 6.5 not sure of room to do it on the DMAX or ease of fitting a tee fitting on DMAX maybe it can be done with hose and barb fittings

[ 01-15-2004, 11:24 AM: Message edited by: tbogemirep ]

[Jim Cobler]

Do you have a part number and price on the Racor guage?

Thanks,

[mdrag]

tbogemirep,

Great idea with the Racor vacuum switch/LED set-up! Add another mod to consider...

Have you noticed if the LED lights under hard acceleration? I've heard that 7" of vacuum (and higher) can occur with hard acceleration - especially if using a power adder. The LED might come on more than expected. But if cruising down the highway and it comes on, time to look more closely...

[Bellrule]

My Kenworth has fuel vacuum gauge setup as a fuel filter-minder. I have never looked to see how it is plumbed though. Last year after I bought the truck the gauge slowly rose from 0 to about 8 over several trips. I changed the primary filter and it DEFINATELY needed it. The gauge reads red at 10. It does not vary under different loads like a pressure guage, it behaves more like the air filter-minder. One other note the fuel pressure guage will read from about 50 psi at idle to 25 psi under full load.

[20050528|8|000731|000000|205.188.117.71]

Just browsing thru the Auto Meter catalogue and I checked the Ultra-Lite section for vacuum gauges. In the 2 1/16 size I see a 30 In Hg mechanical gauge, but it does not have an isolator for mounting inside the cab. Diesel fuel in the cab is not a big threat like gas, but an isolator is the best way with a mechanical set up. There is an electric vacuum 30 In Hg gauge, but it is the larger 2 5/8 size. Also, there is a 2 5/8 liquid filled mechanical vacuum 30 In Hg gauge. I did not check the other styles since the Ultra-Lite is one of the most popular and has the best variety of products.

Isspro in the enhanced visibility line shows a mechanical 0-30 In Hg in the 2 1/16

[mdrag]

Originally posted by Bellrule:
My Kenworth has fuel vacuum gauge setup as a fuel filter-minder. I have never looked to see how it is plumbed though. Last year after I bought the truck the gauge slowly rose from 0 to about 8 over several trips. I changed the primary filter and it DEFINATELY needed it. The gauge reads red at 10. It does not vary under different loads like a pressure guage, it behaves more like the air filter-minder. One other note the fuel pressure guage will read from about 50 psi at idle to 25 psi under full load. I was also surprised to find out that the vacuum reading could increase this much under hard acceleration - I'm talking, pedal to the floor 0-60 or 1/4 runs. The vacuum gauge reading differs from a semi pulling a heavy load due to .....

The answer will be obvious once you read it (the concept was already discussed in this topic).

[mdrag]

Bellrule,

On reflection, the answer may not have as obvious as I thought... It has to do with the fuel and how it reacts.

Physics 101 was too long ago, but I'll try to explain. One of the HP versus Torque types or recent repatriates could better explain I'm sure.....

During acceleration, the fuel will slosh to the rear of the tank. One of the differences in the loaded semi truck versus Dmax truck has to do with the rate of acceleration. As the Dmax truck rapidly accelerates forward, the fuel wants to remain stationary until acted upon by an outside force (the fuel tank) - thus exerting force in the opposite direction. For a given level of fuel, this opposing force is transmitted through the column of liquid (diesel fuel) and will make the fuel 'harder' to pull through the fuel system and filter, quantified by a transient increase in the measured 'vacuum' readings.

These same forces will occur in a loaded semi truck to a smaller degree, since the rate of acceleration is less . Don

[Kennedy]

What OC and myself have experienced is wild swings in readings under variuous conditions. Eliminating variables of fuel level, vehicle angle, engine/pump rpm, and inertial loads is IMHO the only practical way of doing this.

I have been running my SPA digital (no need for isolator) on the test port for some time, but the readings swing wildly as soon as you start to accelerate hard, or start braking.

[Jim Cobler]

I talked to the technical people at Racor and they said their gauage (RK 20163) is preset to 7" HG and probably should not be used on my Duramax because the normal vacuum on a truck with two filters should be around 5.5 to 6 and a person needs to be able to read at least 10 HG over the normal for a clean filter. Therefore, the gauge should be able to read at least 15 to 16 Hg and theirs will not.

I need help guys because I have spent a lot of time on the phone trying to locate a gauage with no luck. I have called truck service centers, part houses, and several gauge makers. I thought the Kenworth center had one but it would not work. Also, I have e-mailed Stewart Warner but no response thus far.

If you know of a gauage that I can read from inside the cab without running a fuel line into the cab, please let me know with all the specifics about the gauage you have.

Thanks,

[Idle_Chatter]

mdrag, I don't think acceleration will have much effect on the process (not really big enough to quantify, anyway). As long as the fuel pickup suction is not uncovered by the "slosh," that is. My reason is that we're dealing with a suction system, so the process is actually dependent on the difference in pressure between the fuel pump inlet and the tank, which is basically atmospheric all the time. The depth of the changing diesel fuel level in the tank is so small (10" to 12"?) between full and empty that it produces very little variation in the "atmospheric" pressure in the tank. The fuel will slosh, but the pump, lines and tank are all accelerating and decelerating together, so the major force at work throughout is the "suck" (or delta pressure) exerted by the fuel pump. Fuel line inleakage will have much more effect than acceleration/deceleration.

[mdrag]

Idle_Chatter,

My explanation may or may not be the correct one, but it makes sense to me.

How about another comaprison. Think of a 175 lb man that borrows Tomac's truck since it is capable of traveling 1/4 mile in 11.95 sec @ 111.46 MPH with a talented driver http://forum.thedieselpage.com/ubb/icons/icon14.gif http://forum.thedieselpage.com/ubb/icons/icon14.gif WOW!

We decide to measure 0 - 100 - 0 MPH times and distances to obtain baseline numbers. After the first run, the testor removes the seat back and seat belt. We discover that it takes the testor much longer (time and distance)to complete this test - both acceleration and braking take much longer. The driver has to overcome his inertial forces in order to maintain control of the truck - otherwise he will tumble backwards during acceleration and move forward into the steering wheel/dashboard during aggressive braking.

The driver in the truck behaves in a like fashion to the fuel in the fuel tank. 25 gal of diesel weighs pert near 175 lbs...

[OC_DMAX]

The fuel will slosh, but the pump, lines and tank are all accelerating and decelerating together, so the major force at work throughout is the "suck" (or delta pressure) exerted by the fuel pump

I disagree. I have accelerated and decelerated my truck while watching the vacuum gauge. There are major changes in vacuum as measured at the test port. As a matter of fact, with no throttle applied and coasting at 50 mph, if you brake stongly you can get a positive pressure at the test port.

[Idle_Chatter]

Well, actual evidence beats "cogitation" any day! If the vacuum is fluctuating there must be something going on, and sloshing must be a factor! Maybe there's something to do with the rate of fuel recirculation and that the fuel cap only vents inward - causing tank internal pressure to fluctuate too?

Mittie, how about this? If the Testor has consumed two-thirds of a 12 pack and there's 10 cubic centimeters of "head" on the beer in his belly at an inclination of three degrees above a line drawn tangential to the median elevation taken from a USGS topographical map (circa 1992) while executing a one and a half minute turn to the right at 157 meters/sec and producing a lateral net acceleration of 1.78 g: How wet will the resulting burp be in milligrams of beer per cubic milliter of air at standard temperature and pressure? :D

[mdrag]

Originally posted by Idle_Chatter:
...My reason is that we're dealing with a suction system, so the process is actually dependent on the difference in pressure between the fuel pump inlet and the tank... And IMHO, the pressure difference you describe is affected by inertial forces during accel/braking, accounting for the variation described by OC-DMAX and Kennedy.

mdrag.

[mdrag]

Idle_Chatter,

As a driver/pilot of the vehicle/plane in question, I would have to look to my passenger(s) for that answer since I would never drink and drive. I'd imagine it would be at least a 'wet' tasteful experience. At most - complete stomach emptying if inverted... :D

[Bellrule]

MDRAG,
I was not wondering about the drop in PSI when under load as I am pretty sure it has much more to do with fuel usage than sloshing in the accelleration forces, although I am sure that plays a part to some degree. I was merely pointing out another exple of how much variance you can get in a regular pressure\vacuum gauge. smile.gif

Jim,
What I was trying to get at is the gauge in the semi does not flucuate while driving. It simply increases over time and many miles as the filter becomes more and more plugged. You said Kenworth told you that their system would not work. I would assume this is because of a pressure system instead of a vacuum system. However, you might be able to fool it into working by "zeroing" the guage at the Dmax's starting point of 5-6 HG (or whatever it is determined to be).

[Kennedy]

Originally posted by Idle_Chatter:

Mittie, how about this? If the Testor has consumed two-thirds of a 12 pack and there's 10 cubic centimeters of "head" on the beer in his belly at an inclination of three degrees above a line drawn tangential to the median elevation taken from a USGS topographical map (circa 1992) while executing a one and a half minute turn to the right at 157 meters/sec and producing a lateral net acceleration of 1.78 g: How wet will the resulting burp be in milligrams of beer per cubic milliter of air at standard temperature and pressure? :D At that rate (depending on time frame) he should not be driving! :eek:

If we did saddle him up in a safe environment, I'd expect him to pee his pants or regurgitate after putting a load like that on his gut... :D


Reality is, a removeable, underhood gauge is the best solution. If restriction is such a concern, check at each fuel stop...