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Fuel Density Compensator
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rustystud
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Basically the Fuel Density Compensator gives you the same power or pedal "feel" no matter what fuel your using. To do this it actually lowers the power level of Diesel so that a fuel like Gasoline will have the same pedal feel. I know it sounds silly at first, but if you look at it from the military's point of view it does make sense. Say you have a private 1st class who is used to driving a truck that is only run on diesel. Then in a combat situation he is forced to fuel up with gasoline. The truck would have a totally different engine power feel . He would make mistakes shifting and generally be frustrated with the engines performance. Which in a combat situation is not good. Now lets make all the fuels act the same. This same driver who is now forced to use gasoline will still drive the same as if it was diesel fuel in his truck. The FDC accomplishes this.
Now onto the problems the FDC has. First, it robs power from the engine if your just using Diesel or oil for fuel. Second, it has a shaft that is a closely machined piece that has no seals to keep the fuel from the engine oil. When this shaft or the housing wears it leaks fuel into the engine oil. I actually looked into installing a seal there, but it would not work due to the extra friction added to this shaft. Again it is a precision ground unit that moves according to fuel pressure differences. These are very small differences and anything acting against this shaft will effect them. So if your shaft is leaking then you only have two options. One, replace the FDC with a good one. Or two, eliminate the FDC totally from the fuel system.
gimpyrobb
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The fdchas nothing to do with the ability to run any fuel you want.
It ONLY serves to limit your available power.
It ONLY serves to limit your available power.
Captaincarrier
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There is a big difference in the density of fuel. We find the specific gravity per API as:
Diesel fuel poor quality in the low 30 degree range, high range in the upper 30 degree range
Gasoline in the low range of 59 degree range, high range of lower 60's degree range
Jet fuel and kerosene in between diesel and gasoline
Diesel fuel poor quality in the low 30 degree range, high range in the upper 30 degree range
Gasoline in the low range of 59 degree range, high range of lower 60's degree range
Jet fuel and kerosene in between diesel and gasoline
rustystud
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What was your point ? This thread is about the FDC and how it works.
dmetalmiki
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'Beg yer pudding'.."The fuel density compensator does not provide 'feel'..(though it MIGHT seem to between grades of fuel).
And is not for 'driver awareness'
Captain carriers point is perfectly valid (but not elaborated on), As different fuel values (The Cetane/Octain Ratings). Have 'differing' densities. And these values are used by the Fuel Density Compensator To METER the AMOUNT of fuel available. VIZ> Petrol has little 'bang. and diesel has more 'bang for the buck. And 'Mixes' range in between.
Thus, the F.D.C. Strives to deliver the SAME amount of power from the range of fuels available.
And yes briefly without going too deep into it, This 'System' IS therefore a "Jack of ALL trades", and "Master of None" Regards 'Power'.
Thinking about it realisticly, A young combat 'squadie' would not know the difference of feel, (If it 'bit him'!) As he is not Directly Controlling the 'Power'. Again without going to deep into it, The diesel engine injector pump governor (In conjunction with the F.D.C.( Or NOT)) Maintains R.P.M. (or tries to) Irregardless of LOAD or GRADE.
Sit with your foot anywhere on the 'go pedel' Or Set the Hand throttle for a speed range required, and Come a hill, The Engine (seems to) 'power up' , Come a downgrade, The engine Seems to "Shut off".
That's only a 'snippet of what's going on in a VERY tech and complicated sequence of events in the Hypercycle engine. All diesels are the same. With diesel cars the throttle is usually "Loaded with back pressure for driver 'feel'.(The Actual 'tech' runs to some 400 pages or more!). Just My 2 penne'th.
rustystud
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Sorry but your wrong here. Because there "is" a difference between fuels and how they perform, they added this FDC to make everything feel the same. Why in the world would we even need this device in the first place !?!?!? If according to you, you just use the throttle. That is why everyone and their dog eliminates the FDC . It is not needed. It performs no function what-so-ever "except" to make all the fuels "Feel" the same.
Please show me where in the TM's the FDC performs any other function "except" to make all the fuels act the same. I have rebuilt these pumps for years and believe me there is no other function for the FDC. In fact it is "Only" the military that uses them. Why is that ? To make all the fuels "Feel" the same.
The earliest pump models (G in particle) had no FDC. Then later the military had them added.
So please show me this 400 pages of "Tech" information. I truly would love to read it.
rustystud
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View attachment Scan0241.pdf Here is the TM's description of the FDC. Note where it says it must maintain a constant power output "regardless of the fuel used" . Well since anyone with common sense knows you cannot make a fuel have more power then it actually does (BTU's of energy) , then you must bring the higher BTU fuels down to the level of the lowest. In paragraph "D" it goes on to say "compensation is required" . Well if I'm compensating that means it is not the max I can do but I'm adjusting to a lower level. I'm compensating. That in a "nutshell" is the whole function of the FDC. It is "compensating" to bring all fuels to the same level. If you go and read the "calibrating the FDC" you will see how you must lower the diesel fuel RPM's to average against gasoline's lower RPM levels.
rustystud
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I'm sorry, I forgot to address your question. Yes eliminating the FDC will give your truck more power, "BUT" you must be careful or you could melt your pistons ! If you bypass your FDC then get an "Exhaust Gas Temperature Gauge" so you can monitor your temperature. Or turn down your fuel just like the FDC did.
Do you have a good source for the EGT gauge?
rustystud
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The gauge is actually called a "pyrometer" . I just called it a "exhaust temperature gauge" as that is it's function and some people would not know what I was talking about if I just said "pyrometer" . You can get them all over. "Summit Racing" sells a few good ones. There are quite a few good threads on people installing pyrometers. Look and see what others have bought and get their opinions. "Autometer" and "ISSPro" and "Stewart Warner" all make really goods ones.
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gimpyrobb
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18operator
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Hewitt Industries
P/N 010-306-1W-1 Pyro 2" dual 6-16F B/W 1 shipped
P/N 102-100-3W-1-24 Turbo boost 15psi B/R 1 shipped
P/N 015-001 TC "K" GRD 2-3" Turbo 1/4 2 shipped
P/N 035-004 Leadwire 7ft K 100^ only 2 shipped
This is what I used. Worked great and the customer service was spot on.
P/N 010-306-1W-1 Pyro 2" dual 6-16F B/W 1 shipped
P/N 102-100-3W-1-24 Turbo boost 15psi B/R 1 shipped
P/N 015-001 TC "K" GRD 2-3" Turbo 1/4 2 shipped
P/N 035-004 Leadwire 7ft K 100^ only 2 shipped
This is what I used. Worked great and the customer service was spot on.
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So how much effect would this have on a non-turbo over a turbo truck? Is a pyro necessary for me when I don't have the turbo?
Treating the bypass idea really as a preventative maintenance item, i am considering doing it on my 68 M46A2C because it seems like it would eventually cause an issue and i can avoid that.
Treating the bypass idea really as a preventative maintenance item, i am considering doing it on my 68 M46A2C because it seems like it would eventually cause an issue and i can avoid that.
rustystud
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That's pretty close to the model I used. Hewitt makes a great product.
rustystud
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It's not about the Turbo, but about the amount of fuel your pumping into the engine when you bypass the FDC. You need to know how much fuel is being injected.
gimpyrobb
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It is much more imoprtant on a turbo truck, but its still good to know whats going on in your motor with a non-turbo.