losing prime to injectors.

[dieseldude]

Good afternoon everyone.

I had my little kubota (Z482) out for a maintence run today and it seems to have developed an issue. Since the last starting last week, I now have to bleed air out of the injection lines if it sits more than a few hours. I rebuilt this engine last spring and it has been running well with no big issues until now. It seems to have developed this since moving it from one side of the shop to the other.

As far as I can tell, fuel is not draining back to the tank and the return line still has fuel in it. To verify this I replaced my original tubing with translucent tygon tubing to look for air, all that is seen is a colomb of fuel with the same results as before.

I first thought the IP was leaking back, but no wet fuel anywhere and oil level is not rising. Has anyone else had this happen? any Ideas?

Thanks.

 

[Stubbyie]

You mention rebuilding the engine.

Did you replace all the hoses at that time?

Perhaps a longshot, but it's possible a hose has developed a crack or split such that it doesn't show a 'leak' but does allow air to be sucked in when the engine is turning over.

Perhaps a bleeder valve/screw/port not sealing when closed? O-ring?

Please post back your continuing experiences so we may all learn.

 

[dieseldude]

Yes I did replace all the rubber hoses when I rebuilt the engine. I used new fuel hose from the local auto store.

Your mention of a longshot brings something to mind, between the lift pump and the injection pump I put in a fuel filter. I know its not the right place for one. The way the hoses are attaced has some tension pulling sideways on the hose barbs. Maybe one of those has developed a small crack. Now that I think about it, in the past there has been little fuel showing in that filter and recently since these problems started it's starting to fill up. I had a similar setup on another engine a while back and when it developed a leak, the fuel filter would fill. Thanks for the idea.

As far as a bleeder screw, I only know of 1 and its tight.

I definately plan on reporting back. The good people here have helped me alot with this rebuild, hopefully someone else can make use of this expierence. Next time I'm in the shop, I will try these ideas.

Thanks

 

[Stubbyie]

We each do things our own way and follow whatever works in our given situation...but unless you have a specific problem event I'd suggest removing the filter between the two pumps.

I've always had a concern about hoses and deterioration over time--especially feeding into something sensitive as an injection pump.

Habit formed over time is (because we keep excellent maintenance logs on our eqpt) is to change out hoses every couple years regardless of apparent need. New hoses are swabbed repeatedly with cloth plugs saturated with plain old alcohol and allowed to dry a few minutes then installed.

Consider replacing line(s) and creating some slack to remove tension. Even the better quality fuel-type hoses (I've seen windshield washer squirter hose used) will rapidly fail in tension: just not made for it.

Your observation that a filter is now showing fuel when it didn't previously causes me to think you've got an elusive air leak in a line not holding.

Another consideration involving filters: The larger the better. I've seen those little flat red disk-type (about size of a quarter) lawnmower filters stuck in lines. Gaaahhh!

I use those clear plastic (two-hose-size barbs stacked each end) about the size of golfball and change them at every oil change or if there's even the slightest bobble or trash. Cheap online if you buy a box at once. And cheap insurance.

Thanks in advance for your continuing to post your experiences.

 

[dieseldude]

I put the filter between the 2 pump as a precaution only. After this it'll probably come out. Air leaking around that filter is starting to sound more and more likely.

maintenance log for this engine are impossible. I picked it up at a swap meet where it supposedly came from a refridgerated truck that a tree crushed. So as far as its history, hours, or anything for that matter I'm starting form scratch assuming the worse case scenario. Just that fact it runs amazes me after how much was missing when I brought it home.


I do plan on hose replacement hopefully this week if all goes right. Will be going back to my favorite diesel fuel line, tygon.

On the subject of filters, I have a hard time calling those little red things filters. They are more of a strainer and in my opinion not worht the plastic they're made of. I, like you, use only the clear plastic ones. An engine show I go to every years has a great deal on them. Last time I picked up 15 for $5.


Hopefully I'll get out to the shop this weekend and try some of these Ideas. Thanks for the info and feedback. I'll keep everyone posted.

 

[dieseldude]

Update:

The new fuel tubing did not come in so I moved on to another idea to find a leak. I removed the fuel return line off the last injector and attached a hand vacuum pump with a catch cup. while pulling a slight vacuum I noticed a small sting of fine bubbles appearing at the edge of the the filter inlet hose barb. It appears as if my one hose may have a very small stress crack. Small enough to keep fuel from leaking out but big enough to let air in. The good new is I saw no other leaks. when the new tubing gets here I'll replace that entire section and repeat the test and see what happens.

Thanks.

 

[dieseldude]

Update:

It's fixed. Replacing the tubing between the lift pump and the injection pump made all the difference. I suppose either the tubing or filter had a very small hole, but big enough to draw in air.

thanks for the feedback and ideas.

thanks again.