not firing but have prime?

[Mopar1973Man]

I Still don't see it, I MEAN I'LL give you that Air "could" meaning its Possible be sucked into the return, BUT ITS in the return, SO WHAT. its going back to the tank so

as long as theres plenty of fuel to keep pick up tube/draw straw submerged it should not matter unless its capable of vacuum pulling fuel out of the injector line to head which i would think there is some kind of valve in VP to keep this from happening

 

     wHere am i wrong???

 

So people have found that the return line can draw air in but the air allows the prime on the VP44 to be lost. Now the weird part is the return line is not submerged in fuel but hanging at the top of the tank. So the return line should be dry technically. But if the VP44 is able to use the air leak for back draining the fuel to the tank then prime is lost. The overflow valve does have a unsealed hole.

 

[rburks]

So people have found that the return line can draw air in but the air allows the prime on the VP44 to be lost. Now the weird part is the return line is not submerged in fuel but hanging at the top of the tank. So the return line should be dry technically. But if the VP44 is able to use the air leak for back draining the fuel to the tank then prime is lost. The overflow valve does have a unsealed hole.

 

Thats what i said, as long as the truck/tank isn't low on fuel level and the PICK UP/DRAW STRAW TUBE IS SUBMERGED,

  I don't see it possible for return line to suck air int the VP when fuel in the return is exiting the VP... I mean like, i know Venturi suction type senerio is possible but the air would only get delivered to tank so if pick up tube is submerged i don't see it returning into the suction side of LIFT PUMP..

 

AS I SAID ABOVE  'UNLESS" it can pull fuel from injector line thru the VP pump,  Is this possible, i would have thought BOSH would have designed it with some sort of reverse flow protection on the HP INJECTION SIDE

[rburks]

And another thing might point out is wouldn't the air suction from the VOID in return have to be strong enough to override the 14psi overflow valve.???

[Mopar1973Man]

And another thing might point out is wouldn't the air suction from the VOID in return have to be strong enough to override the 14psi overflow valve.???

 

No. Just because of the bleed hole the air can bleed back through the bleed hole in the overflow valve. As for the return line its NOT submerged in fuel it terminated near the top of the tank where the suction line is terminated at the bottom of the tank. Let's say with the overflow removed the lift pump can barely pump fuel through the VP44 with 14-20 PSI its just a trickle. If the engine is cranking the flow is greatly improved.

[jigdog]

I recently had a drain back from the vp that was making it so I had to reprime each morning . I installed a check valve between the lift pump and the tank and it took care of the problem.

[Mopar1973Man]

I recently had a drain back from the vp that was making it so I had to reprime each morning . I installed a check valve between the lift pump and the tank and it took care of the problem.

 

Makes me ask th question what is still leaking? Being that our trucks don't have check valve you added a check valve to over come a loss of prime.

[jigdog]

That is a good question. I had leak issues that seemed to center around the fuel pressure gauge line or the oem filter seal cap never could find it

[Mopar1973Man]

Still worth keeping an eye on. The previous shop I worked for the owner was quick to use these check valves for prime issues on diesel instead of correcting the actual problem. I understand there is a lot of different parts and seals in all the different diesel manufactured but its always best to fix it than band-aid it. Eventually the band-aid will not cover the wound or in this cause the failure.

[rburks]

So people have found that the return line can draw air in but the air allows the prime on the VP44 to be lost. Now the weird part is the return line is not submerged in fuel but hanging at the top of the tank. So the return line should be dry technically. But if the VP44 is able to use the air leak for back draining the fuel to the tank then prime is lost. The overflow valve does have a unsealed hole.

 

 

 

I Still don't see it, I MEAN I'LL give you that Air "could" meaning its Possible be sucked into the return, BUT ITS in the return, SO WHAT. its going back to the tank so

as long as theres plenty of fuel to keep pick up tube/draw straw submerged it should not matter unless its capable of vacuum pulling fuel out of the injector line to head which i would think there is some kind of valve in VP to keep this from happening

 

     wHere am i wrong???

Michael,   I never said the return was submerged, I SAID IF THE DRAW STRAW/SUCTION TUBE WAS SUBMERGED. I'm quite aware that the suction tube comes in the top of tank and dumps "NO tube exerting through top of tank,,I got it

 

  THERE IS NO WAY THE RETURN LINE CAN SUCK AIR, ITS IMPOSSIBLE, Now there could be an issue  that could cause a BLEED OFF of Pressure  i suppose 

Fuel Pressure could bleed off thru the  BLEED HOLE as you've posted above but what would cause it , or what is keeping the VP from doing this under normal operation

 

If a return line or fitting is leaking off psi, a leak should be detected i would think

[rburks]

So would this be a bad overflow valve or something internal in the VP44

 

  Man, this is good stuff!!

[Mopar1973Man]

Here is the guts of the VP44...

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/437-bosch-vp44-injection-pump-exploded-view

 

The only thing I can think of is the control valve in this pic #135. But never been reported as a problem.

 

[rburks]

Here is the guts of the VP44...

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/437-bosch-vp44-injection-pump-exploded-view

 

The only thing I can think of is the control valve in this pic #135. But never been reported as a problem.

 

I wonder how many people that have this issue chalk it up to bad VP and just lat down 1000+ for new VP Pump????  i agree that looks like it could be the culprit . and could be replaced on truck if I'm looking at it correctly

Edited August 2, 2015 by rburks

[Mopar1973Man]

I wonder how many people that have this issue chalk it up to bad VP and just lat down 1000+ for new VP Pump????  i agree that looks like it could be the culprit . and could be replaced on truck if I'm looking at it correctly

 

Sound great and all but you can't buy that valve. You have to get a reman'ed VP44.

[dripley]

I Still don't see it, I MEAN I'LL give you that Air "could" meaning its Possible be sucked into the return, BUT ITS in the return, SO WHAT. its going back to the tank so

as long as theres plenty of fuel to keep pick up tube/draw straw submerged it should not matter unless its capable of vacuum pulling fuel out of the injector line to head which i would think there is some kind of valve in VP to keep this from happening

 

     wHere am i wrong???

The way I saw when I had the leaky tee and fitting was like this. After engine shutdown the leaky parts were allowing air into the return lines and letting the fuel drain back into the tank thru the return line. When the return line emptied it was allowing fuel from the high pressure side of the VP to leak back thru the return by gravity. It would not make any difference with the supply being submerged or not. All the air coming in and fuel draining back was coming from the return.

[rburks]

THE REFERENCE TO fuel supply tube "BEING SUBMERGED" was to merely point out that if there is no "VOID, LEAK or CRACKED FITTING ISSUES,etc ON THE SUCTION SIDE OF SYSTEM....THATS THE ONLY WAY AIR WOULD GET IN IS IF FUEL TANK WAS RUN LOW ENOUGH TO PULL AIR IN.... thats it..

 

SO, dripley, it sounds like what your saying is confirmation that if there is a leak on the return side even beyond the overflow valve that it will allow the fuel pressure to drain off from the HP side of VP.     

 

  HERE IS the Only way i see this "AIR LEAKING IN THE RETURN SENERO possible, "IF the copper washers were compromised or"BAD" in at least one or two injectors

then if a leak developed {which could have caused the leak in the first place}  then Air would be forced into the return galley in the head and out into the "T' and into the return line to tank    Now this still doesn't deliver any "AIR" into the VP or cause prim issue IMHO...."BUT" What if the Compressed air from cylinder or cylinders was "GREAT" enough to create Venturi Vacuum  on the OVERFLOW VALVE THAT WOULD PULL IT OPEN AND COMPLETELY SUCK THE VP DRY>>> HUH  

[Mopar1973Man]

That's why I such a problem with prime loss issues. Lot of people claim the cross over tubes cause loss of prime. I struggle to understand how. Being the crossover tube is the return side of the system and the return side can and will drain back to the tank. The overflow valve is not a air tight valve being it has that air purge hole. Being the prime problem has to be on supply side to be effective. In other words there is air in the high pressure lines, injectors, or in the injection pump. Maybe even in the low pressure side feeding the high pressure side. Return is after the fact...

[rburks]

THANK YOU , Michael, thats what I've been saying, Air would have to be in the supply side to be induced int the pressure side of VP and cause problems, .Air getting into a Line that has already left the VP and is flowing the opposite direction "causing issues with sucking air" don't make sense.

 

   SO, do you think its possible for the overflow valve to be pulled open by vacuum instead of pushed open by pressure???  Could that much vacuum be pulled on that dia. line to equal the 14psi open pressure for the overflow???

[Mopar1973Man]

Overflow valve can't be pulled open on a vacuum but it can't bleed through the hole.

[rburks]

Overflow valve can't be pulled open on a vacuum but it can't bleed through the hole.

So are saying it can or can't  pull through the bleed hole??

[dripley]

I am assuming the Mike means that it can bleed thru the hole. It is the only way my explanation makes any sense. I know in my case when i replaced the o rings and sealing washer the hard start issue stopped. So there has to be a way for the fuel to drain from the HP side thru the return. My problem was definitely not as bad as what Hex is experiencing. 

 

Hex, any progress with your problem?

Edited August 4, 2015 by dripley