Bleeding those Cummins.

[Mikey]

In last week's posts several of you alluded to bleeding those 6BTA's. Since I have a service manual I assumed (you now where that goes) that it would give me the info necessary. Nah. It gives bleeding instructions for the individual components but not an entire system. Again, logic says start at the feed end of the fuel tank and work to the return. More easily said than done. I have electric fuel pumps which should help, no sore thumb from hand priming, but where do I go from here. If someone (Bruce, Vic Etc) could document the proceedure I'm sure this could be an archive item for the site. It sure would be a blessing to me.

[CaptPatrick]

Mikey,

Before anything else, make sure that all fittings are properly sealed and tight from the tank to the Racor. DO NOT USE any teflon tape on the fittings. Teflon is fine, but the others fillers in the tape WILL BE DESOLVED by the fuel. Spelled: LEAK... Flare fittings do not need any sealant at all if they are in good shape & properly installed. Pipe fittings need a fuel proof paste type sealant.

Fill the Racor 3/4 full of fuel & slowly put the filter element back in, add more fuel to top it off. Re-nstall the top plate. Attach your portable pump to the output side of the Racor, (or output side of AlgaeX if you have one), and start pumping, returning the fuel to the tank. Watch the bowl for signs of low capacity in the Racor. Add more fuel if necessary.

It isn't necessary to tap into your return lines, just use a clean 5 gallon bucket, pump into that, use a funnel & pour the accumulated fuel back through your deck fill.

Once you have a constant flow, without air in the bowl, you're primed to that point.

Remove the bowl of the secondary filter, (on the engine), fill 3/4 full & slowly put the filter element back in. Top it off & re-install to the engine.

Now, all that is necessary is to prime the fuel pump & injector lines.

Loosen the injectors so that air can escape as the fuel gets pumped up through the system. Start pumping the fuel prime pump until you see fuel starting to come through an injector line. Tighten that injector, and continue on untill all lines have gotten fuel to the injectors.

Re-check all your fittings for tightness, clean up any spilled fuel, & crank her up.

There will probably still be some residual air in the system. Watch the racor bowl & add fuel if necessary. When the engine starts it will have a tendancy to stall as any left over air works it way through. Be ready to tickle the throttle linkage until you get past the hesitation phase.

Br,

Patrick

[algillen]

I might add that once you have the filters filled up, you can crack the relief valve on the fuel injection pump (on my 6Bs, on the front half of the inboard side of the pump), then you should be able to work the manual pump lever (on the side of the motor sorta in front of, but also somewhat under the aftercooler - look for a rubber covered knob to push).

You can pump that until you get bubble free fuel coming out of the relief fitting. Once you are done with that, then you are ready to crack the injector nuts... however, it's unlikely the injection lines are dry unless you had them off, and if not, you may be able to go directly to starting the motors up. Remember to only give it 30 seconds of cranking at a shot, then give your starters lots of time to cool off unless you would like to buy new ones.

ag

[Mikey]

First of the week I will try all of this. One more question at this point. Since I have added electric fuel pumps can I sub them for all the manual pumping?
More questions after I read all of this in the a.m.
Bless you both.

[algillen]

Not clear where your electric pumps are, presumably you are using them as a lift pump to get the fuel from the tank to the on-motor pump. I doubt that you can just turn them on and expect them to push air out of the fuel injection pumps.

For that matter, not sure they will even push the fuel past the on-engine fuel pumps.... best thing I can suggest is to crack open the injector pump relief valve, and see what happens.

In general, there are no shortcuts here, and this process is something you must understand and know how to perform, since if you were to accidentally pull air into your motor from something as simple as a fuel filter change, that motor won't start until you re-prime the system. There are not very many at-sea repairs you can hope to do on a diesel, but re-priming is one of them.

ag

[IRGuy]

Al Gillen...

I agree with your comments about bleeding the fuel system with the relief valve plug behind the injector pump, at least with my 6Bs that have the Nippon Denso injector pumps (This is the technique my diesel guy explained to me).. but I would caution that the other injector pump manufacturers might not have their relief valve fittings in the same place as ND. As I recall there are possibly 3 different injector pumps Cummins has used on the 6Bs.

[Capt. Mike Holmes]

I have Bosch injector pumps on my 6B's, and large electric boost pumps between the Racors and the mechanical lift pumps. The electric pumps will push fuel past the mechanical pumps, so can be used for bleeding up to at least the relief screw on top of the secondary filers. After that, however, I have always cracked injector nuts - one at a time - and cranked over the engine to finish bleeding through the injector pump.

[Mikey]

I have the Nip injector pumps and like Capt Mike (actually followed his lead) my electric pumps are between the racors and the lift pump.

[Capt. Mike Holmes]

I would have put the pumps in front of the Racors, to use them to refill the unit after changing filter cartridges, but the pump manufacturer was pretty adamant about wanting a filter in front of the pumps.

[algillen]

Just curious, why do you guys insert an electric fuel pump into the system at all? Far as I know, the 6Bs don't require it. (And I, too, have the Nippondenso pumps, realize Bosch pumps will likely be different.)

[Capt. Mike Holmes]

Al, since I built my engines up from scratch from Dodge truck engines, I was looking for any edge I could to give me a little more "oomp". A mechanic friend told me Cummins admitted to him that in some applications - usually with 300 hp or more on 6BT's - they had to add a boost pump to get enough fuel to the engines. I also found out that Dodge pickups with the 24 valve Cummins engine were having problems, and after market boost pump kits were being sold because the electric lift pumps on these engines were only designed to pull proper suction from about 2.5 feet, and the fuel tank was further back than that. At first, I was having problems getting the performance I should have been, and a Cummins rep told me I needed more fuel. I rerouted all fuel lines to eliminate unnessary runs, moved the Racors behind the engines, instead of at the front, added the electric boost pumps, and eventually switched from 500 series Racors to 900 series. All of this seemed to help, but the problem turned out to be exhaust restriction. I did not know enough about diesels then to realize if the exhaust pressure is too high, it can't suck in enough fuel/air mixture, no matter what you do. A goes-inta, goes-outa thing. I'm keeping the boost pumps, like them. They "free-wheel" when the engines are running, and are flow through, so if they go out it won't shut me down. They are high volume pumps, rather than high pressure. Also have an electric pump in line for the genset, as recommended by Uncle Vic. The little mechanical pumps on most generators struggle to get fuel any distance, since pumps push better than they pull. It probably would have been better to locate the boost pumps at the tank outlet for this reason, but, again, the pump builders warned I needed a filter in front of the pump, and I felt I already had redundant filtration - or at least, enough.

[Mikey]

Al
What Mike Said.
Taking all the words posted along with my manual and giving it a shot.
Also building the supports for the hard top. That thing is going to be so cool you gonna smack yo mama.
Labor on today and contemplate the reason for the holiday.

[scot]

Good Luck Mikey.

Now, for all you guys that like to poke fun at my affection for dump truck motors, i.e, Detroits (you know who you are!)

....here's the correct procedure for priming a Detroit:

1) Connect fuel line to engine.
2) Start engine.

[In Memory of Vicroy]

Then stop engine, add oil. Add more oil. Put oil diapers in bilge. Buy new set of ear plugs.

yo Fren'

UV

[Capt. Mike Holmes]

Scot, the dealer who sold me the electric pumps assured me they were the same ones he uses on big Detroits.

[scot]

I knew you guy's were a bad influence on me....now I'm a "thread hi-jacker"

lol

[Bruce]

....here's the correct procedure for priming a Detroit:

1) Connect fuel line to engine.
2) Start engine.

While you do not need to bleed injector lines on a Detroit, there are requirements to makes sure the fuel is to your engine at least. Other wise you will burn out a starter trying to prime.

Thats where an electric pump is handy in the fuel system.

I'm a big believer in having a fuel priming pump set up to where it can be used as a backup for the primary pump.
I've seen every manufacturer have a primary pump failure and those who have installed them are able to run the egines and get it back home.

The wear and tear on a starter will pay for it over time in trying to prime.

For diesel, the walbro is a great pump.
For gas anything but those 20.00 auto parts store pumps will do. I prefer the carter rotary vane pumps.

[Capt. Mike Holmes]

I've been using the Walbros for a few years, and they are very good pumps.