I here some CTD owners say the have 25# of pressure at idle and 18# at WOT. Dosen't the Injector Pump have a setting that if the pressure gets to 14# it relieves back to the tank. If so won't this wear out the diaphram in the Injector Pump when relieving back to the tank. The reason I ask, I'm looking at trying to increase my pressure, because I have the in the tank pump and can drop the pressure to my IP to O# real easy.
Any help, Thanks

Idle @ 7#
Run @ 4-5#
WOT @ 0#

 

Even owners manual says that 7 psi is the minium, I'm pretty sure that your lift pump is allmost dead and so is your injector pump soon. Quick, buy new pump.

I bought this one http://www.glacierdieselpower.com/pr...?pf_id=3929852

I have pics in my gallery.

 

i'm going with the vulcan relocate kit, comes with bigger fuel lines plus I got the bigger line that goes from fuel filter to IP

 

I have 29psi at idle and 14 at WOT. I don't NEED 29psi at idle, stacking the Holly blue and stock pump just turned out that way, however I do need the 14psi at WOT so I'm not inclined at this point to mess with it. So far everything seems fine with the 29psi at idle. Daily driven 90km a day for 3 months and one 2000km trip 2 weeks ago.

 

That is the beauty of the Glacier setup with the 392 walbro pump and full flow return style regulator. You get a superior pump that is much more reliable and vastly out performs the others and you get constant adjustable fuel pressure regardless of the flow requirement of the engine at any given operating condition. 29 psi at idle will cause more problems than it solves and like you said, you want your 14 psi at WOT.....why not just do a full flow return regulator and just have 14 psi all the time instead of this dead head regulating method that uses the VP check valve to dead head the over-abundance of fuel which results in wild variations in pressure which everyone seems to claim they don't want?

 

25# of fuel pressure is good for giving you less fuel flow. Pressure is a measure of restriction.

 

25# does not mean less fuel flow... it means more pressure... the only time you'll see less fuel flow is if the injection pump has to suck fuel instead of having a nice pressurized supply waiting for it at the inlet

 

Pressure is the measure of resistance to flow.....however, if all the restrictions within the system remain constant, the only way for a pressure increase to take place is by a corresponding increase in flow.

 

Because I'm a cheap bugger and don't see why I should spend big money on a fuel pump thats way bigger than what I need just to have it bypass back to the tank. Not sure what you mean by dead heading? Any excess fuel is returned to the tank. So far I'm into this for $100 so untill it gives me a problem I cann't justify spending more time/money on it. If I do decide to play with it more I'll upgrade the lines.

 

The question that seems to be getting side tracked is whether running over 20 psi @ idle damages the VP-44. I have been running 24 psi @ idle and 15 psi @ WOT for about 3000 miles now with no sign of problems. I would like to know if anyone else has had problems with the higher pressure so I don't ruin my new VP-44.
Thanks

 

Some good reading here:
https://www.dieseltruckresource.com/...ad.php?t=82970

 

ive been pushing ~28 psi for well over a year now. No problems....

 

For the record, Walbro 392's are quite inexpensive.

Dead heading is where excess pressure is NOT relieved and bypassed to the tank and is allowed to build up....this is the entire reason for the wide fluctuation in fuel pressure. The pressure in a dead head system is entirely dependent on the flow requirement at any given moment....when the flow requirement goes up, the pressure goes down. The VP44 returns fuel to the tank with a 14 psi valve. When excess fuel from the outlet side of the VP is less than 14 psi, no fuel is returned. When return (OUTLET) fuel pressure hits 14 psi, the gate opens. Please note, this return pressure is not directly related to the inlet pressure on the VP....meaning, the VP44 return line is NOT and will NOT return excess lift pump pressure back to the tank - this is exactly why excess inlet flow will turn into VP inlet pressures beyond 14 psi. There is NO full flow regulation for the VP44 inlet that is within the VP44 itself...excess fuel flow from the inlet side of the VP will not be returned to the tank - only excess OUTLET flow is returned.

Full flow regulation changes all that.....a full flow regulator does not allow dead heading to occur and instead utilizes it's own return circuit back to the tank to exhaust excess flow when there is no demand for it. When the flow demand is high, return flow diminishes to fulfill the demand. So, regardless of the flow requirement to the VP44, pressure will remain constant. This allows for constant and even fuel pressure at all times regardless of of the flow requirement and typically also results in notably longer pump life. When you set the regulator to whatever pressure you desire, it will maintain that pressure no matter what the flow requirement is.....assuming, of course you are operating the regulator within it's intended parameters.

Excessive inlet fuel pressure to the VP44 has been proven to be detrimental to the integral vane pump that feeds VP.

 

How complicated this all is.
I will try to simplify for my own sake.
1. Fuel is delivered to the VP44 by the LP. VP44 has a spring loaded ball check valve (not a regulator, it is not calibrated). The purpose of it is to stop fuel from draining from the VP44 when the engine stops (per FSM).
2. The check valve has to open at 14 psi but not open at 10 psi (per FSM).
3. The VP44 is fairly restrictive. It will let like 40 gpm through at 12-14 psi.
4. When your high performance LP pumps more fuel than the 40 gpm the fuel system can pass at ~14 psi, the restriction will not allow fast enough flow, and the pressure on the input line of the VP44 will increase. This is how you get 26 psi etc.
5. To avoid high input pressure on the VP44, put a back pressure regulator upstream of the VP44. These have much higher flow capacity and will effectively dump any flow in excess of what the VP44 can pass, provided a separate, 3/8" or so return line is used.
6. Dumping high excess flow into the stock 5/16" return line can cause pressure backup in the line and exhaust port of the back pressure regulator, change of the set point of the back pressure regulator and increase in VP44 pressure.

-P

 

This question posted is the exact reason I "re-engineered" the bypass valve on my walbro 392 setup. I run 13-14 psi at idle, 10 WOT. This way I know there is no chance of over pressurizing the vp and 10 WOT seems to me to provide plenty of excess fuel for cooling and lubrication. I also have the bigline kit installed. My rational for laying out a few hundred for the "oversized" fuel pump was that I only wanted to do it once, and not have it be a constant wonder as to when it will fail. I run some long distances and don't want to be stuck in the middle of nowhere with a frankensteined system.