Hello all:
I am having warm start problems. I believe it is caused by fuel draining back to tank. If I park with front of the truck down hill I do not have the problem. I have been reading the threads on this issue. What I would like to know is why (Bosh or DC puts a bypass hole around the overflow valve )" in the banjo bolt. to my way of thinking this promotes fuel drain back?
1999 dodge 2500 cummins, five speed.
ps
If I jog the starter so the primary pump runs longer it starts much quicker.
Help!
Don H

 

The bypass only opens up at 14 psi or above so it shouldn't cause drainage back to the tank when the truck is shut down. Sounds like air somewhere else....

 

the bypass hole I am talking about allows fuel to return even if the overflow valve is closed. I have looked at two valves and they both have a small bypass hole drilled in them. Also I can't get an answer as to what prevents fuel from returning to the tank by the supply line. there is no check in the filter body,there is no check in the "airtex pump" is it in the tank??
thanks for your reply.

 

My version of overflow valve functions. If you replace the filter or open the supply side from LP to VP, you get air in system. The (.050" or so) hole allows air to be easily purged. When air is purged fuel does not flow as easily through the orifice and presents a restriction. As pressure (and flow) builds to 14 psi the check ball provides pressure regulation at perhaps 14 psi. So unless your LP can provide more flow than the check ball can regulate down to 14 psi, you will not see more pressure. Additionally the orifice does provide backflow capibility when shut down. I also believe the VP44 will allow fuel to siphon backwards when shut down.
There is no check valve in supply side, however I believe there is a check valve in the return side of fuel module. In other words, leak at a connector O-ring or the "T fitting could allow fuel to siphon backwards through overflow valve, VP44, filter, LP and into bottom of fuel tank. Park the rear high and siphon cannot take place.
It certainlly behoves us to carefully inspect the supply side for air leaks first. The quick connect fitting at LP is certainlly a prime suspect. Along with filter cover, banjo bolt gaskets, ect on supply side.
On return side the T fitting and banjo bolt washers at rear of cyl head is highly suspect. The O rings on connector tubes fall into suspect also.
JMHO and good luck

 

dozer12216
Thanks for the detailed but concise answer to both my questions. Greatly appreciated.
Don H

 

The overflow has an air bleed in it. This is to allow for air to escape from filter changes, running out of fuel, ect.

There are no check valves on the return side of the fuel system. And depending on the year, there are none in the suction side either. The pump typically prevents fuel from draining back.

You can get hard starts from an overflow hanging open. As this does not allow for enough pressure on the other side of the VP. However, I know many guys not running a check valve at all.


Dave

 

It seems that backflow should be prevented, just like when you hold a straw at one end filled with water, it doesn't come out. Unless there's air in the system somewhere I believe that fuel should be prevented from flowing back into the tank....

 

dozer12216 is right on target with this in my opinion! Good explanation!