Replace IP or bypass FDC?

[andyindy]

I have the same problem at highway speeds. How big a job is it to bypass the compensator? Andy.

 

[avengeusa]

the fdc can be bypassed easily, mine was already done, there was a thread on it recently, just do a search for fdc bypass and see what comes up, i will take a couple snap shots of mine and post em so you can see, you are just removing a couple lines and plugging off the threaded holes, the lines are then moved to a different spot, i seen a pic of one here, it showed what needs to be done

 

[Westex]

Reviving an older thread here, I recently blew up the "baby" in Sanderson, Texas, and the fee to truck it to El Paso is $1,000.00 Not what I wanted to spend. Problem is that it was leaking like a sieve out of the bellhousing drain hole, and it was engine oil. Checked oil level and it seemed higher than when I filled it. So........anyone got any advice/diagrams, etc on bypassing the fuel density compensator?

 

[stumps]

Don't know if you can really pressure test it, you would have to hook it up to a set of injectors and turn the pump with a motor, all the while supplying it with lubricating oil. I run diesel mixed with some WMO, so I don't really need the FDC. I don't run gasoline, so no issue.
IP swaps are a pain. You really need a helper and pull the drivers fender and radiator out.

Pressure testing the FDC is actually much simpler than you might imagine. It is a totally separate assembly that bolts onto the IP. It is plumbed between the tank fuel pump and the IP, so all you have to do is unbolt it from the IP, and turn on the accessory switch. The tank fuel pump will pressurize the FDC, and if it is going to leak, fuel will come dribbling out the bottom of the FDC where it bolts up to the IP.

The sole and only thing the FDC does is provide a movable mechanical stop that determines how much flow the IP gives at full throttle. In other words, it decides how far you can depress the fuel pedal.

With light fuels, like gasoline, the FDC allows the greatest maximum fuel flow from the IP. With thick fuels like WMO, it allows the smallest maximum fuel flow from the IP.

[I hate all of those abbreviations FDC is Fuel Density Compensator, IP is Injector Pump, and WMO is Waste Motor Oil.]

-Chuck

 

[stumps]

I have the same problem at highway speeds. How big a job is it to bypass the compensator? Andy.

It is easy. The FDC is plumbed, with plastic hose, inline between the fuel pump and the Injector Pump. All you have to do is remove the fittings on the FDC, replace them with pipe plugs, and take the plastic hose that comes from the fuel tank and connect it to the Injector Pump inlet.

Because the FDC moves the pedal stop so that you get maximum pedal for light fuels, and minimum pedal for thick fuels, a disconnected FDC is going to think you are running gasoline as a fuel, and is going to allow you way too much pedal. You will have to crank down the FDC's stop plate adjusting nut 12 to 16 flats, and the IP's droop screw 1-2 turns clockwise. That should get your IP in range for diesel fuel.

-Chuck

[FDC = Fuel Density Compensator, IP = Injector Pump]

 

[Earth]

You also have to plug the line at the HH on the pressure valve, as it returns to the FDC. By passing takes all of a few minutes--easily done or un-done, so you can use bypassing for trouble shooting.

 

[Westex]

OK, so again, I have questions:
1. Does bypassing the FDC still allow you to run waste motor oil in hot climates:
2. Is it likely if sump oil comes up on the dipstick that bypassing the FDC will 'most likely' solve the problem?

 

[stumps]

OK, so again, I have questions:
1. Does bypassing the FDC still allow you to run waste motor oil in hot climates:
2. Is it likely if sump oil comes up on the dipstick that bypassing the FDC will 'most likely' solve the problem?

Your engine is still an MF engine even if you bypass the FDC. All the FDC does is prevent you from giving it too much fuel.... In other words, it sets the stop on the gas pedal.

The oil in your deuce is supposed to be 1-1/2 inches above FULL when the engine is cold, and has been sitting for several hours. It should be at FULL warm, and exactly 1 minute after shut down... So says the pretty elf in PS magazine.

The FDC is simple as can be. If you can get the parts, it couldn't take more than 30 minutes to rebuild... probably take you longer to find a clean spot on your workbench.

-Chuck

 

[Westex]

So, are you saying, leave the FDC in the loop?

 

[stumps]

So, are you saying, leave the FDC in the loop?

The FDC is a convenience. If it is working reliably, you will be able to toss just about anything in the fuel tank and go. You shouldn't notice any power difference between gasoline and heavy fuel oil. You will notice big differences in fuel consumption between the different fuels, though.

Like most conveniences, the FDC adds complexity, and with the increased complexity comes an increased likelihood of failure.

If you leave the FDC out of the loop, your deuce will be optimal for only one fuel (or any blend of fuels that approximates that fuel). If you run WMO, you will need to mix in gasoline to balance the high energy content of the WMO down to something more like diesel. A lot of guys do just that with their ordinary diesel engines.

I intend to refurbish my FDC back to new condition and plumb it back into the system. But then, I intend to burn WMO, stale gasoline, diesel, bat wings, and eye of newt.... and I don't want to have to remember that WMO might burn up my turbocharger if I put the pedal to the metal... but stale gasoline needs a lead foot.

-Chuck

 

[Earth]

To your second question: yes, it is likely the oil is compromised compliments of the FDC.