Lift pump and air in system

[Oilburner]

I am having a heck of time pulling fuel out of the tank on my 4D34T Fuso powered Land-Cruiser conversion. I have the original water separator plumbed in before the lift pump and the original lift pump, main fuel filter and lines are used. The fuel system is essentially unchanged from how it was in the Fuso, except for the fuel tank, which has a standard draw tube setup (I removed the original petrol fuel pump and put in a piece of line to the bottom of the tank)

It will not pull fuel from the tank unless I "prime" the lift pump. I took the pump apart and cleaned all the valve seats and the filters, and did not notice anything abnormal. I also did the siphon test on the feed line to check for blockages etc and got a mouthful of fuel without too much difficultly, so the feed line does not appear to be clogged. I even bypassed the water separator in an effort to find the issue and still have problems. I also checked all the connections and don't see any obvious air leaks.

If I manually fill the fuel filter on the engine, fuel trickles down into the lift pump and then it seems to start working, almost like the viscosity of the fuel is required in order to make the pump work. When it is dry, it doesn't seem to want to pump anything, or I have an air leak somewhere.

I suspect the check valve plungers are probably getting worn and the pump cannot seal well enough to pull a vacuum but will work when fuel is present due to the viscosity, but I wanted to see if anyone had experience with these pumps and what I should expect. In all my other diesels priming is easy, but from what I have seen online these look to be a pain to prime. I even started the engine by filling the filter and pump and it ran well for a few minutes and finally died as no fuel was pulled from the tank.

Ideas?

Thanks!

 

[kerry]

Put a piece of clear tubing in the system just before the lift pump and see if there are bubbles in it. If so, you're sucking air somewhere.

 

[FusoFG]

I removed the original petrol fuel pump and put in a piece of line to the bottom of the tank

what did you use for the line to the bottom of the tank? where does the return line go?

but from what I have seen online these look to be a pain to prime.

Isn't it just as easy as opening the bleed screen on the fuel filter and manually operating the Fuso lift pump with the built in plunger?

 

[1Engine]

Try these
1- Without opening the bleed screw, pump the hand primer pump 2 or 3 times before starting

2-If you have been running the unit for a while, open the fuel filler cap & see if there is any vacuum in the tank. Even to the extent of leaving the fuel cap off over night & see if it will start in the morning without priming.
In automotive setups the fuel tanks normally run in a vacuum so to prevent hydrocarbons going into the atmosphere. Trucks tanks don't run in a vacuum.

You may need to modify the fuel tank breather arrangement:coffeedrink:

I had this type of problem once with a Cat D11 Dozer & all the specialists wanted to rebuild the engines fuel system & it was a blocked breather

 

[Oilburner]

Fixed!

Bad sealing washer at the banjo bolt on the lift pump. They looked fine but as soon as I swapped them out, it started pumping like mad and I had it bled in a minute. Runs great now!

Thanks for the assistance!

 

[gait]

thanks for that oilburner. You are not alone, I think the system is very sensitive to small leaks.

I have two tanks with a Pollak 6 port changeover switch. One tank has fuel lift problem, other tank ok. I'm steadily working my way through all connections between the tank and the switch. Struggling for new flexible pipe in Laos but I'll get there. I have some the wrong size (bother!).

I do have some suitable transparent plastic pipe to play with though - nice idea thanks Kerry. I can try one section at a time to help isolate the leak.

 

[gait]

found some new flexible pipe in the last major town.

Yet to confirm by driving tomorrow but looks like the problem is a small crack in the bowl of the water separator. It was almost dark before shining a torch on it showed a stream of small bubbles from halfway up the bowl. The stream of bubbles was very obvious in transparent pipe.

Rescue tape didn't work for fixing the bowl. I've bypassed the water separator for now. Hopefully our guide in China will help us find something.

 

[kerry]

Epoxy on the outside of the separator?

 

[Tony LEE]

I hope that guide you have lined up does better for you than a couple of students we took on trips to help us manage. Couldn't find themselves in a dark room.

 

[gait]

a couple of days ago I checked that the translation of "diesel" was understood Tony. As long as we can find diesel, water, somewhere to stop, and somewhere to empty the loo cassette, the rest will all work out. ATMs seem to find themselves. I'm also hopeful that "turn left here" will be uttered before the junction rather than after.

I must have more than one fuel problem. Inserting clear tube between the separator and the changeover switch was reluctant to prime and showed me bubbles from the separator. Inserting clear tube between tank and the steel pipe that crosses the chassis (just bypass separator) refused to suck fuel.

Today I'll try clear tube from tank to changeover switch. Bypass everything. I hope the changeover switch doesn't have a problem.

I'll have a look around town (small town in Eastern Lao) today. Would you believe I don't carry epoxy and have no cleaning solvent.

 

[gait]

so far so good. I now have a transparent pipe from tank to changeover switch - and its full of diesel, and not running back into the tank when the engine is stopped. I'll be more confident after the next 30km drive. Probably tomorrow. Hopefully I now have a known working condition.

Interesting trying to prime the pipe from the tank when the rest of the system is full of fuel! The manual pump got me nowhere, just a sore hand. Opening the bleed screw on the filter at the engine simply got diesel everywhere. Running the engine took many minutes.

I have a 5 year old model Canter with the manual pump at the engine. It would be nice to have a priming pump on the water separator. Like the newer models!

Just to mess with my brain ... I did a major service before starting the trip. One item was open the water separator. Another was replace the priming pump as there was a small leak around the screw in push thingo. The new pump "feels" different to the old one.

 

[1Engine]

I replaced the primary fuel filter with a Racor 230R on my 2002 NPS300
http://www.westmarine.com/webapp/wc...toreNum=10106&subdeptNum=10407&classNum=10410
I use the 2 micron element & replace every 25000kms
I have also put a water sensor & it wires directly to the dash light
Not cheap but I have used them on boats & on bulldozers with great success

 

[Tony LEE]

Would you believe I don't carry epoxy and have no cleaning solvent.

Sigh!!!! S'pose no duct tape and fencing wire either.



Good that you found the general area of the problem

 

[gait]

got the duct tape and the wire (last used to hold a fuel tank on when straps snapped on last trip), and a few other varieties of tape ... Feeling silly about the epoxy. Must have left in a hurry!

Good news. Transparent pipe from tank to changeover switch stayed full overnight and did 270km today with no problems. Interesting observation is engine seems to have more power / torque pulling up hills at 40 km/hr in 4th gear around 1100 rpm. Of course it may be my imagination ...

Maybe the air that was getting in hung around the engine filter long enough to effect the good tank.

No luck finding anything like a separator / filter yesterday.

Of course now I've got the water separator / filter off the chassis I can't find the leak. I can block one end and suck air out of the other. No loss of suction, no obvious leak.