A second FDC, why not

[cranetruck]

Another first from the Meadows of Dan skunk works.
A second FDC was installed to monitor leakage and to serve as a sending unit for a more sensitive Fuel Viscosity Meter.

The FDC on the IP is now bypassed. The second unit, which is the one originally mounted on the Injection Pump, sits on an aluminum box to collect any fuel that might leak from it. It is fully operational, just not affecting the governor.

Time will tell how badly it leaks.

 

[OPCOM]

That is interesting. I never considered it could be used off the engine!

 

[cranetruck]

Tapped the fuel collected from the leaking FDC today.
Got 60 ml, which has leaked after only about two hours of engine operation.
That's approx 1 qt/16 hours of engine time.

 

[gimpyrobb]

Is that from your original fdc, or another one in "suposedly" working order? If so, its time to take mine out of "the loop".

 

[cranetruck]

The FDC I'm testing is the one that was on the IP to begin with.
The latest oil analysis report indicated fuel in the oil so I removed the FDC and mounted it on a box as shown above. I put a drain valve in the box to be able to drain it at intervals and that's what you now see, fuel leaked from the original FDC (The fuel lines are hooked up to the FDC on the box so that it functions normally, just without affecting the IP).
An FDC from a parts engine was installed on the IP, but it's not in the fuel circuit, it's bypassed.

Past oil analysis reports have not shown any fuel, so this leak developed while I was on the cross country trip. The FDC has been hooked up and working without leaking for about ten years while I have owned the truck.

 

[rmgill]

Gaah! Look at all the plumbing! It's starting to look like it's got emissions control gunk for california!

 

[jimk]

The FDC has been hooked up and working without leaking for about ten years while I have owned the truck.

So the increased boost first realized after bypassing is caused because it ,when working properly, allows some addition fuel to the injectors (irregardless of the leaking to crankcase problem)?
Any thoughts on using valves to control the bypass [of one FDC]??
JimK

 

[cranetruck]

...
So the increased boost first realized after bypassing is caused because it ,when working properly, allows some addition fuel to the injectors (irregardless of the leaking to crankcase problem)?
Any thoughts on using valves to control the bypass [of one FDC]??
JimK

When the FDC is NOT operational (bypassed), the stop plate is fully extended permitting a maximum of fuel delivery.
When operational, the stop plate is moved up and reducing the maximum amount of fuel delivered. Even for gasoline it moves up a bit, so when it's bypassed the fuel delivery is as high as can be without turning the adjustment screw.

In has never really been "needed" on my truck, but until it started leaking fuel into the crankcase, I didn't care except I did hook up a potentiometer to monitor the movement, which translates into fuel viscosity.
Now, it's separated from the IP and can do no harm, I only use it to monitor fuel viscosity and the amount of leakage.

I have no intention to put it back on the IP with or without a valve to bypass it. A different, non functional FDC takes its place on the IP, since the stop plate is part of it and is needed by the IP.

Ryan, I agree that the plumbing is getting out of hand, but some is temporary and think of what has been learned from it (I do post my findings).

The image below shows the guts of an FDC, the piston, shaft and stop plate. This particular unit did not have any kind of seal for the shaft which has pressurized fuel on one side and the IP housing below. It's only a tight smooth fit, metal to metal....

 

[jwaller]

no seal. now thats scary no matter how tight the tolerances.

 

[SasquatchSanta]

I hate to admit it (show my ignorance) but afterr reading this several times I'm having a major dumb attack.

Help me out here if you will.

Are you saying if the FDC is bypassed the injectors will see appreciably more fuel and therefore to get back to something that resembles an original fuel setting (to the injectors) that the pump will require re-calibrating?

With the current price of fuel I wouldn't want to do anyting that would increase my fuel consumption.

I'm happy with the performance (scoot factor) of my truck with the current stock pump setting BUT I've heard a truck will run better with the FDC bypassed. I also worry about developing a leak in the FDC.

It seems like I remember reading that removing/bypassing the FDC could cause cold weather problems when it comes to running cold fuel and number 1 diesel fuel. Personally, I can't see why because civilian/commercial trucks handle cold (winter) fuel and # 1 without an FDC?

What's the downside of just bypassing the FDC?

 

[cranetruck]

Are you saying if the FDC is bypassed the injectors will see appreciably more fuel and therefore to get back to something that resembles an original fuel setting (to the injectors) that the pump will require re-calibrating?

With the current price of fuel I wouldn't want to do anyting that would increase my fuel consumption.

I'm happy with the performance (scoot factor) of my truck with the current stock pump setting BUT I've heard a truck will run better with the FDC bypassed. I also worry about developing a leak in the FDC.

It seems like I remember reading that removing/bypassing the FDC could cause cold weather problems when it comes to running cold fuel and number 1 diesel fuel. Personally, I can't see why because civilian/commercial trucks handle cold (winter) fuel and # 1 without an FDC?

What's the downside of just bypassing the FDC?

Your foot ("throttle") controls the fuel to the injectors. More available just means that you don't have to be so heavy on the pedal. Doesn't change the fuel economy at all.
The FDC has nothing to do with warming the fuel. The fuel in the tank will warm up on its own due to return flow. I happen to have a temperature sensor in the tank and have seen 125°F after an hour's drive with an ambient of 65 degrees.

There is no downside to bypassing the FDC, unless you run on gasoline, in which case you will have to step a little harder on the pedal for equivalent performance.
Really makes you wonder why the FDC was approved in the first place.

 

[rmgill]

Ernie, you just have to turn the fuel pump down to prevent delivering TOO much fuel.

 

[SasquatchSanta]

Bjorn Sez:

[/quote]The FDC has nothing to do with warming the fuel.

Thanks for the insight. My concern wasn't that the FDC heated the fuel but that it somehow compensated for changing viscosities when fuel gets cold in extreme winter weather "OR" to compensate for the thinner viscosity of number-one diesel.


Your explination makes sense as does Ryan Gill's

Ernie, you just have to turn the fuel pump down to prevent delivering TOO much fuel.

I guess I can always turn the fuel down if EGTs get hard to control OR fuel usage goes through the roof.

Thanks.

 

[m38inmaine]

I looked at my pump today and it looks like a "cover" where the FDC should be, does this mean it has been bypassed and covered. Here are a couple of pictures.

 

[cranetruck]

Interesting Mark, never seen one of them before. Must be a substitute for the "Stop Plate" in there somewhere.
Thanks for posting the image.

 

[sparkylisle]

I looked at my pump today and it looks like a "cover" where the FDC should be, does this mean it has been bypassed and covered. Here are a couple of pictures.

Is there a NSN # on the plate? Any chance of removing the plate and taking photo's of the inside? I'm really curious about it????

 

[OPCOM]

I think that model is in the TM on rebuilding the pump.

 

[cranetruck]

Found this. As usual, you have to know what you are looking for to find it, a variation of "not seeing the trees for the forest".

 

[wolfmangk]

I have a question... Via manually actuated valves, or electronically actuated ones-what about making some extra plumbing and having a bypass/non bypass situation at the flip of a switch or lever(s)? So you can have the performance and non leakage of a bypassed FDC, but the ability to run gasoline or keorsine without wrenching on the engine? Is the fuel delivery adjustment absolutely neccesary?

 

[FSBruva]

Wolfmangk-

Read and re-read the posts covering this. A multifuel with a bypassed FDC is still a multifuel.

Matt