Fuel Compensator & Tuning Questions

[SixSpeed]

Hey Guys,

I've spent the last few days researching turning up the fuel, and topics about the FDC (Fuel Density Compensator). If anything, this has left me with more questions than before. I will try to keep this organized, I have many thoughts running through my head.

1.) I have read (with a grain of salt) that the FDC isn't optimal for performance. I like the idea of the FDC compensating for various fuels if you were to find yourself in a situation which presented no diesel. My friends Deuce w/ the FDC still in use, runs WAY stronger (One of the best running I've seen in fact) than mine with the compensator bypassed, so I am not sure if the claim of FDC not being optimal for performance holds its weight. Anyone have any opinions?

2.) I came across this post HERE and I think the link in the post has what I need, which is a higher resolution picture of the attached diagram of the fuel pump with and without the compensator bypassed. Unfortunately the link is no good. Anyone know where to find the file?

3a.) Before I realized my truck had the FDC bypassed, I went and turned up the fuel via the FDC (I turned the nut a full turn). There was a noticeable increase in performance. After I went to lock down the settings, it was then apparent my truck had been bypassed. Now from what I have read, tuning a bypassed FDC should have no affect on performance. Can anyone confirm or deny? (If confirmed, I must be going crazy).

3b.) If turning the screw on the top of the IP on the FDC will not affect performance, what is the way to adjust fuel delivery with the FDC bypassed?


I think that should do it for now...

THANKS!!

 

[cranetruck]

Bypassing the FDC will not effect the ability to make adjustments, the stop plate is still in the "circuit"...
IMHO, the only reason to bypass the FDC is to prevent the leaking of fuel into the crankcase, which may occur if the rod within it gets scratched from contaminated fuel (rust particles etc).

 

[stumps]

The FDC does one thing, and one thing only: It moves the throttle stop to compensate for the heating value of the fuel being burned. It does this by running the fuel through an orifice that is mechanically linked to the throttle stop. Thin fuels (gasoline) allow maximum throttle, thick fuels much less throttle.

You can achieve the same result as an FDC by not stomping on the pedal as hard when you are running thick fuels.... This is dangerous without a pyro, and continuous vigilance, and could easily result in a burned up motor.

When your FDC is bypassed, no fuel goes to the density measuring orifice, and the FDC adjusts itself for the thinnest, lowest heating value, fuel. The result is your IP will be just right for gasoline, and way over-fueled for diesel (or WMO).... unless you turn down the fuel adjustment to compensate.

-Chuck

 

[cranetruck]

Chuck has it correct. Keep in mind that the FDC only works for the fuels listed in the TM and as long as the viscosity is directly proportional to the heating value of the fuel. Veggie oil and biodiesel, for example cause the FDC to react in the "wrong" direction...

 

[pjpiche1]

If you are going to turn up the fuel , It would be my suggestion to install a pyro. There is no need for a FDC if you install a pyro. The stud with the two jam nuts on the bottom of the FDC that you moved DOES change the timing on the plunger. I have actually added 8 -10 flats to most of the trucks that I have turned up. I am running at temps of 850 on the flat and 1150 on hills. Do not exceed 1200 degrees. Bully dog makes a very nice mechanical pyrometer. Install the thermocouple in the turbo.


Philip

 

[gimpyrobb]

Yup, what they said.

 

[SixSpeed]

Hey Guys,

Thanks for clearing that up. I can now sleep peacefully.

I am in the market for a good Pyro now. I turned mine up 6 turns, which from what I've read should be pretty safe. The truck is still nowhere near as fast as my friends Deuce, or others I have ridden in. At least now I don't have to drive around with my foot welded to the floor. I drive it conservatively, plus its not like there are many hills I need to power up in Florida.

 

[baxter]

Chuck if I may, what i think you are saying is that the fdc has nothing to do with the ability of the motor to burn various fuels it just regulates how much of a specific fuel is alowed to be burned at a time. I hope this makes sense.

Vaughn

 

[stumps]

Hi Vaughn,

Quite literally, all the FDC does is move the stop that decides how far you can push the pedal.

-Chuck

 

[baxter]

Great info thanks Chuck.

Vaughn