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How to test VP44 overflow valve


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Just found  a  pic of  overflow valve..

 

I always  figured  when  pressure was below  14 psi,  there  was  NO   return to tank...     Not  true!    there is  a  second  unregulated  port (free flow)  that always  allows   at least  a little  flow  

Probably there for  2  reasons...  to  help  allow  air out... and  to ensure  some  cooling  no matter  how  pathetic  the lift pump is..

 

post-980-0-96354500-1409747730_thumb.jpg

 

 

are you wanted to  test it  for   'amount of  return' ??    Or  to see if it's  stuck open ?

Edited by rancherman
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I thought there was a procedure on here but I can't find it. Can someone point me in the right direction?

 

All right here...

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/88-bosch-vp44-injection-pump-overflow-valve

 

overflow-valve3.JPG

 

The bottom hole is only for air bleed it too small for cooling. Even Bosch states 70% of the fuel should be return for proper cooling and there is no way you can get proper cooling in that tiny hole.

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Just found  a  pic of  overflow valve..

 

I always  figured  when  pressure was below  14 psi,  there  was  NO   return to tank...     Not  true!    there is  a  second  unregulated  port (free flow)  that always  allows   at least  a little  flow  

Probably there for  2  reasons...  to  help  allow  air out... and  to ensure  some  cooling  no matter  how  pathetic  the lift pump is..

 

attachicon.gifpressure-valve.jpg

 

 

are you wanted to  test it  for   'amount of  return' ??    Or  to see if it's  stuck open ?

See if it's stuck open. My hard start cold condition is back and so bad that I need to bleed fuel system every morning if I want to use it. Someone else changed O.F. valve and fixed problem.

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All right here...

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/88-bosch-vp44-injection-pump-overflow-valve

 

overflow-valve3.JPG

 

The bottom hole is only for air bleed it too small for cooling. Even Bosch states 70% of the fuel should be return for proper cooling and there is no way you can get proper cooling in that tiny hole.

THANK YOU!!

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yah,  I figured  too the  hole  was too small for   cooling...   I just  pasted  the  pic and  some text  from  another   forum...

 

heres    a   post  that  caught my eye,  this was posted  in 2002,  in a reply to  the exact  same question  as  OP  here ^^^^^

 

KYLE--- Your electric lift pump has little or nothing to do with fuel return,except to bleed air out of the system after filter change etc. The lift pump can then force fuel and air thru the small orifce under the overflow valve and back to the tank. The VP pump has a 5 blade vane type positive displacement pump that pressurizes the high press. plungers,provides pressure to operate the hydraulic advance system,and provides a internal housing pressure in the VP assembly. The over flow valve maintains the housing pressure at 14 psig. This return aids the cooling and lubrication of the internal components and also vents out any air bubbles that get in the pump. The vane pump pressure is a function of pump/engine speed,and the pressure is regulated by the internal pressure control valve. It is a spring loaded slide/piston valve that is adjustable during calibration. It simply returns excess pressure to the inlet side of the vane pump. The vane pump pressure is approx. 150 psig . Estimate, as I am not priveledged to test specifications.

 

^^^^  if  this  is correct,  then  this  answers my question  on  fuel flow through the  body..        1.  vane pump  supplies  high pressure to head and  the advance system.  2.  internal pressure regulator  maintains   this  pressure   3.   overflow from  THAT   goes  back  into pump body.... then  back to tank via   overflow

 

edit:   I  can  agree with  everything  said  except for the opening  sentence....'nothing to do with overflow"....   ummmm,    pretty sure  'volume' must  be there  (at the inlet side)....   and  of  course  one way of  measuring volume is   psi  (which  most  are monitoring these days)   so  a weak  pump  that  can't  supply enough  fuel,  will have poor psi,    and  may or may not  'fill'  the vane pump  efficiently.  (starve).       which then    limits  severly the amount  available for  downstream  cooling

Edited by rancherman
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Yeah, but if it is stuck open and there is a slight air leak in the fuel can it will create a siphon effect and suck air in the feed line or at least that's what I am hoping. Disabling my LP at startup helped for a little while. Now after sitting overnight I pretty much need to do a total priming to get it to start. I'm going over the system looking for leaks and have found none but white smoke and foaming fuel mean air is in there. The other day I took off both my FP gauges and plugged the ports on the fuel can to rule that out. So the fuel can was open ( just the 2 test ports) for a max of 5 min. The truck started and ran for a sec w/ the fuel in the VP and then shut off w/ a white puff of smoke. I see no way for air to siphon down in to the feed line so quickly unless overflow is open . And the air was not up at the injectors cause the truck ran briefly. I'm pulling my hair out with this thing so I'll take any suggestions.

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Have you checked the return line going to the back of the head? It is a pain to get to but there are a couple of sealing washers on a banjo fitting back there that are very common to fail. Even on the return system, if there is a leak it will cause problems starting. Also, I have seen the drain valve on the stock filter canister not sealing all the way and causing a small leak down over time. Geno's garage has a replacement drain valve that works very nicely.

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all I can  suggest right now is  to look for  ANY  signs of  dampness  at the fittings and lines..  might as well  start at the tank!     Although   a  bleed back won't be too easy  if  the leak is near the tank.    Your problem  almost has to be after the lift pump

 

I know  after bleeding,   everything is   soaked and wet.. and it's hard to  see  any 'new'   dampness..   wash it up as  good as you can,  and   check again.

 

I swear,   sometimes I find  the  dangest  things...     a  fitting that  may seal up fine on pressure,  but as soon as  a  vacuum hits...  poof.     ilikeoldfords  has  a  good idea with the drain valve.

 

BTW,  when you get this  fixed,  could you snap some pics of how you got your  flat bed  attached?  :)

Edited by rancherman
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Have you checked the return line going to the back of the head? It is a pain to get to but there are a couple of sealing washers on a banjo fitting back there that are very common to fail. Even on the return system, if there is a leak it will cause problems starting. Also, I have seen the drain valve on the stock filter canister not sealing all the way and causing a small leak down over time. Geno's garage has a replacement drain valve that works very nicely.

I have checked and tightened them a little. None where even damp but I'm gonna order new washers and grommets and a new Overflow and start there. Anyone have any shortcuts to rebuilding that T in the return line? Looks like it would be easier to pull the dang motor to get to it.

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all I can  suggest right now is  to look for  ANY  signs of  dampness  at the fittings and lines..  might as well  start at the tank!     Although   a  bleed back won't be too easy  if  the leak is near the tank.    Your problem  almost has to be after the lift pump

 

I know  after bleeding,   everything is   soaked and wet.. and it's hard to  see  any 'new'   dampness..   wash it up as  good as you can,  and   check again.

 

I swear,   sometimes I find  the  dangest  things...     a  fitting that  may seal up fine on pressure,  but as soon as  a  vacuum hits...  poof.     ilikeoldfords  has  a  good idea with the drain valve.

 

BTW,  when you get this  fixed,  could you snap some pics of how you got your  flat bed  attached?  :)

No problem, I'll get you some pics of the bed mounts. Hopefully I'll get this fixed soon. Hunting season's coming and I need this truck to start in the morning.

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Get the new grommets from Cummins, do the lower first, then do the horizontal, then pull the upper & back of head banjo & lay across the valve cover. Stick the tube in the T, with the nut & grommet on it, then tighten the banjo. Then, tighten the T fitting. Hold the T in place when tightening any of the grommet nuts.

To make it easier & less bloody, remove the bracket with the 2 electrical connectors on the cowl, pull the bolt that holds the dipstick & swing it out of the way. Pull the stock fuel pump if it is still there.

Be sure the kids aren't around, because you will be swearing like a drunk sailor that got mugged by a transvestitie prostitute.

 

Ed

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Jeese...I had no troubles with the banjo fittings and grommets on mine. Was just in there putting on a new IP and injectors.

Smartest thing I did was building a platform like a big set of steps right in front of the truck.

Lots of room for tools and parts. It helps that I am not a very big lad and can just about lay down on the valve cover LOL. 

Regards Chris

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Be sure the kids aren't around, because you will be swearing like a drunk sailor that got mugged by a transvestitie prostitute.

 

Ed

They're already used to that. Remember I probably bled the thing 5 times in the last week :lmao2: Seriously though, thanks for the tip. I'll try it.

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