Engine loss of prime

[Jamesc83]

I have a 03 cx613 with AC 350 and it will have a loss of prime intermittently when shut off for the night or week. It doesn’t do it constantly any ideas or feedback would be appreciated.

thanks

[mrsmackpaul]

You have a leak in your return to  the tank fuel lines

 

Pressurize the tank a little to find the leak

Use a old piece of inner tube and a hose clamp over filler neck 

Wind the air pressure regulator right down on the work shop compressor and pressurize the system and the  search for the leak

Good luck

Paul

[MACKS]

Wow so many people with this problem,you can also

do a search on here,lots of info on this,good luck and don’t forget to tell us your fix..

[Joey Mack]

do you have a DAVCO filter on it?  If so replace the $7.00 check ball in it... 15 minutes,,,,  MACKS is right,  lots of postings on this issue, and please post the fix,,,

[AZB755V8]

1 hour ago, Joey Mack said:

do you have a DAVCO filter on it?  If so replace the $7.00 check ball in it... 15 minutes,,,,  MACKS is right,  lots of postings on this issue, and please post the fix,,,

I don't know about check valves in filters but from personal experience. To start the only way to loos the prime is for fuel to drain out of the fuel galley in the injector pump. The only way that happens is that air is getting in to the galley. Stop the leak to maintain the prime. There are a few ways this happens and a few more than that if the first few don't Geter-Dunn. I work on older engines so some of this may not apply to the newer stuff. 

Goes without saying, Check and tighten all fuel line connections.

First, to check if equipped the manual hand primer. The o-rings in them leak after time. Just replace it, real Bosch replacements are under $35. 

Second, the charge, lift or little pump the primer is attached to, what ever you want to call it will leak internally. There are 2 little plastic disc check valves in it that wear and leak fuel back to the fuel tank. The disc can be removed and sanded flat again with 600 grit wet sandpaper. Finish be rubbing them on a matchbox cover to polish them with a little rubbing compound.

Third, The fuel return valve on the side of the injection pump is not sealing when the engine is shut down. This is were the fuel return line from the pump is attached. There are several different styles ranging from $15-$250 to replace. There maybe several other lines connected to it from the fuel injectors drains. It is not repairable and would need replaced.

Last if fuel lines are old they can have micro cracks in them and leak air in when not under pressure. Replace the supply and return fuel lines. 

These are the EZ fixes I have done. If one of them don't work then onto a second round of fixes...

 

[Onyx610]

MackPauls trick works real well. Also Joey Mack is right about the Davco those check balls get stuck every once in a while with grime and dirt. He also seems to know these engines pretty damn well. Interested to see what you find. 

[Jamesc83]

Update: I replaced check valve, and checked for leaks could not find any so far. See where this thing goes thanks for all the feedback!

[mrsmackpaul]

16 hours ago, AZB755V8 said:

I don't know about check valves in filters but from personal experience. To start the only way to loos the prime is for fuel to drain out of the fuel galley in the injector pump. The only way that happens is that air is getting in to the galley. Stop the leak to maintain the prime. There are a few ways this happens and a few more than that if the first few don't Geter-Dunn. I work on older engines so some of this may not apply to the newer stuff. 

Goes without saying, Check and tighten all fuel line connections.

First, to check if equipped the manual hand primer. The o-rings in them leak after time. Just replace it, real Bosch replacements are under $35. 

Second, the charge, lift or little pump the primer is attached to, what ever you want to call it will leak internally. There are 2 little plastic disc check valves in it that wear and leak fuel back to the fuel tank. The disc can be removed and sanded flat again with 600 grit wet sandpaper. Finish be rubbing them on a matchbox cover to polish them with a little rubbing compound.

Third, The fuel return valve on the side of the injection pump is not sealing when the engine is shut down. This is were the fuel return line from the pump is attached. There are several different styles ranging from $15-$250 to replace. There maybe several other lines connected to it from the fuel injectors drains. It is not repairable and would need replaced.

Last if fuel lines are old they can have micro cracks in them and leak air in when not under pressure. Replace the supply and return fuel lines. 

These are the EZ fixes I have done. If one of them don't work then onto a second round of fixes...

 

People including me dont understand fully how the fuel system works 

If any of the valves etc are leaking mentioned here are leaking it is only a issue if you have a leak in the return line 

If any of these valves leak and lets fuel return to the tank the return line when sealed air tight and fully functional will siphon fuel from the tank thru the injector pump until there is a balance of vacuum between the supply and the return 

What this does is maintains the prime under any conditions

People change valves, add check valves and do this and do that and it appears to solve the problem 

Then one day maybe a month, maybe a year maybe 5 years time for no apparent reason it has lost prime when sitting

Might be a microscopic piece of dirt under a valve, a spring has lost a poofteenth of tension and the valve never shut correctly 

However the misconception we are under is that bloody vavle has failed again

It hasn't, diesels are desgined for this to happen and when they do the return side of the fuel system is meant to siphon fuel up from the tank to maintain prime

This is the part people do not understand and some just plain refuse to accept 

I wont be drawn into a long drawn out conversation about it, I will explain the facts and leave you to 

Not been rude here and not trying to be a smart ass, just trying to explain whats what and how it works

 

Paul

 

 

[Joey Mack]

check valves are a common issue with this complaint. The 03 engine probably has 2 spin-on filters at the top left corner, but I have had some with davco 382 filters and replaced the little check valve in the inlet of the filter housing. no pics of the engine so I can only guess what is on it. the hand primer at the right front corner on the fuel pump is another part that can allow air to enter, or fuel to leak out, in some rare cases the fuel pump leaks into the engine,  usually a high level of thin engine oil will occur. dry rotted fuel lines can cause this if fuel is 'bleeding' through the lines... lots of good info is posted here,   jojo