Fuel System Modification: Thoughts?

R u serious. You better tell cummins. Detroit .cat and fleetguard they have been advising people for decades to prefill fuel and oil filters.

 

I would suggest the op finds a way to clean or replace his tanks. All this talk of altering the fuel system is just a bandaid. He needs to fix the cause of the problems. There is always a way.

 

two separate issues.
1. to allow the engine to "self bleed" small amounts of air it would be better to take the leak off line from the last injector back to the fuel tank rather than going back to the filter housing as it currently does. however as this is dealing only with nozzle leakage it wont help much.
2. for filling the filters and priming through, another pump (additional to the lift pump) is a good idea, this can be electric, can be a squeeze pump like for an outboard, in either case it should be on a bypass line with isolation when not in use. I prefer the racor housings with a priming pump built in. much simpler solution allowing the empty filter to be fitted then filled correctly and pump through to the lift pump.

 

What's been done for "decades" isn't acceptable by manufacturers any longer in many cases.

On lots of the newer diesel equipment we have in the rental fleet, pre-filling filters is not recommended. One manufacturer has even taken the step to shut the engine down when the fuel drops to a certain level. The operator can restart it immediately...after which it will run for about ten seconds before shutting down again. This is done specifically to discourage what's common practice on jobsites, i.e. running everything around until it runs out of fuel. Running out of fuel leads to all sorts of haphazard "bleeding" techniques....one of which is filling filters and filter housings out of whatever *possibly* contaminated fuel container is at hand. Even with clean fuel and fuel containers, filling a filter means you're sending unfiltered fuel straight to components that aren't supposed to see unfiltered fuel.

This is one of those situations where listening to the advice of random individuals on the internet can be costly.

There are no "secrets" to properly bleeding a fuel system. You don't need to add any devices to accomplish it. Follow what's in the manual, if that doesn't work...find out what's going on. Usually it's a line or connection somewhere sucking air in.

Someone has already mentioned why the fuel pump ought to be wired to a keyswitch with a bypass circuit that allows for starting. In addition to that, I'd add that on some applications where diesels run unattended, (some of our generators for example), they've made the fuel pump circuit too simple. You turn the key to start, and the pump runs. When the key is in the run position the pump runs. If the engine dies for any reason, the pump runs....until the key is shut off or the battery goes dead. We've replaced quite a few electric fuel pumps that have chattered themselves to death when the fuel tanks runs empty and there's nobody around to notice for hours. I wire the pump to a relay that's closed as long as there's oil pressure...if the engine dies for any reason, the relay drops out and the pump stops running. If you want to power up the pump for bleeding/testing/whatever, temporarily jumper out the relay.

Adding a relay might seem contradictory because I already said to listen to the manufacturer's recommendations....and they're the ones that didn't install a relay in the first place. However, with a variety of people "responsible" for one piece of equipment, often times it ends up being a, "I thought so and so was going to top off the tank" situation rather than a single operator being the only one involved.

 

I am serious, and would not be saying this if I were not well acquainted with problems that arise as the result of contaminated fuel.
There have been recent changes in diesel fuel itself, as well as in injection systems that make it advisable to do everything one can to insure that your injection system drinks only clean fuel.
It is a simple matter, and cheap insurance, to pump fuel through the filters rather than prefill.