Fuel Density Compensator by-pass

[cranetruck]

When bypassing the FDC, you pretty much just hook the line from the final fuel filter directly to the hydraulic head inlet, correct? (and then plug up the holes left in the FDC).

I ask because the hose in my deuce is not long enough.

Yes, you'll find this explained a few times in the old threads.
Also, remember to turn down the fuel when doing so, or you'll have some very high EGTs and boost pressures (also explained in the old threads).

The IP without the FDC is an early model and not a rebuilt one.

 

[Etnomaiab]

Cranetruck,

Thanks for the reply.

I asked because I thought it was possible to bypass the FDC with stock parts, and since my hose isn't long enough I wanted to make sure I was not doing anything stupid.

I have been reading through all of the threads that come up when searching for "FDC" but just wanted to double check.

Also, does anyone know what size hose/fittings are used since I need a longer one? My truck is on the other side of town and will not have time to get over there for a while (school and work are keeping me very busy). I'd like to order something online. What about pipe plugs? (1/4 and 1/8 NPT, correct?)

 

[cranetruck]

Here you go.

 

[kaiser2help]

I was told that the FDC piston assembly could possibly bypass diesel fuel into the crankcase oil and cause a dillution problem for you engine oil. Thus removing vital lubrication properties from the oil. Please elaborate a little for me Bjorn.

 

[cranetruck]

The plunger within the FDC is lapped to fit and micron size hard particles (rust) may score the surfaces and cause a leak of fuel, which will drain into the crankcase along with the lube oil from the IP.
This is a problem when the rust from the half century old fuel tank gets by the filters. The final fuel filter is rated at 5 to 6 microns and the lapped surfaces may trap a 2 micron particle. This goes for the fuel plunger in the IP hydraulic head also.
The real solution is to clean, replace or recoat the inside of the fuel tank.

Edit: Added image.

 

[kaiser2help]

Bjorn. Is there a NSN# for a rebuild kit for the FDC? And what must be done if I were to remove it entirely?

 

[cranetruck]

No rebuild kit available to my knowledge. Replace it with a good unit or by pass it as shown above. The unit without an FDC is a different early model IP and you can't just remove the FDC and install a cover plate in its place. The "stop block" and fuel delivery adj is different for that one...all below the cover plate.....

Edit: It is not a bad idea to have the oil analyzed on a regular basis if you put a lot of miles on your truck.

 

[kaiser2help]

Sounds good. Thanks. I wonder if there are specs available so that I could mic up the plunger and boar to see if infact it is worn out?

 

[cranetruck]

Just check for fuel in the crankcase oil.
When it happened to me after many years of good service, the leak amounted to about a quart/1,000 highway miles. Much less will show up on your analysis report.
Micing the plunger probably won't tell the story, a scratch is hard to measure, but it is visible under a magnifying glass.

 

[Etnomaiab]

Does anyone know where I can get a longer hose to go from the final fuel filter to the hydraulic head? I assume I need 1/4" NPT male fittings on each end. Any idea on length?

 

[cranetruck]

Go to your local NAPA and ask for air brake tubing, I believe you'll need the 3/8 O.D. It is black with nylon lining and perfect for this. Also get the brass inserts and ferrules and reuse the fittings already on you truck.

 

[Ford Mechanic]

So what do you do with the FDC return line port on the other side of the HH?

 

[phil2968]

Plug it.

 

[doghead]

So what do you do with the FDC return line port on the other side of the HH?

Picture #3, Post # 6. That is how the Military did(plugged) it when bypassing the FDC.

 

[Ford Mechanic]

Picture #3, Post # 6. That is how the Military did(plugged) it when bypassing the FDC.

Thanks guys. I just couldn't tell from the pic what they actually did to it, the valve elbow denotation I was unclear on.

 

[Ford Mechanic]

Here you go.

So how many turns or flats out do you think that would be? it's kind of a tight spot, I don't know if I can get a micrometer there to measure it correctly.

 

[Katahdin]

Just adding some info to a pertinent thread. The deuce's first multifuel engine, the LDS-427, did not come equipped with a FDC. The FDC is a feature that was introduced with the LDx-465 model.

Here is some horsepower and torque data using multiple fuels with the LDS-427. Theoretically the power output would be similar on a bypassed LD-465.

View attachment 407346

 

[dodgedougak]

My FDC was bypassed when I got the truck and still is bypassed. I do burn a mix of diesel and used lube oil (at times) but I have installed a pyrometer so I can be sure that my exh temps don't get too high. The FDC regulated the fuel delivered based on density and most fuels that are more dense have more BTU's. More BTU's = more heat. For example "winter diesel" (#1 or a blend) is less dense and has less BTU heat value than #2 diesel which has less heat value than other heavier oils. I stay under 1100 degrees exh temp on a hard uphill pull and have had no problems.

 

[Rusty nuts]

I got a question about the FDC. Picked up my truck today and am blowing oil out the vent tube and a lot of white smoke not steam coming out. Pulled the dipstick and oil was above full, dark and smelled of diesel. I am going to do the FDC bypass to see if this helps, but my motor is a non turbo. The fuel adjustment screw is still wire tied so being a non turbo, do I need to adjust this like is mentioned with the turbo motors? First 40 miles felt sluggish but stopped for fuel and added Lucas to the fuel and 2 hours later the truck really woke up and running strong....except for the oil blobby which I think is because of fuel getting in the oil and blowing out excess.

 

[gimpyrobb]

It is more critical for the turbo motors to know the EGTs. Its still a good idea for non-turbo motors to know whats going on. Basically, the fdc cuts the amount of fuel sent to the injectors in an attempt to keep the motor at a constant HP rating over a range of fuels. The FDC cuts diesel a lot more than gas, so when you by-pass the FDC, the motor sees more fuel. With that more fuel, you run the risk of high EGTs. If it blows black(or dark) smoke at idle, you will need to turn the fuel down. Some smoke during acceleration is good, but a lot can and will melt parts that should not be melted.