Engine/Transmission (1998.5 - 2002) Vp44 return line MUST NOT work against pressure

[rweis]

I am installing an aux bed tank.



I have my VP44 return line plumbed into the OEM tank vent line up high almost to the bend where the vent line attaches to the OEM tank filler line.



I plumbed my aux bed tank to gravity feed the OEM tank through the alternate DrawStraw port (right to the top of where the cannister screws down to the tank body)



What I found:



When the aux had fully filled the OEM tank and the engine was at idle (only) the VP44 threw a 0602 code. Would not throw the 0602 if any above idle.



I stopped the aux feeding the OEM and burned down several gallons. Reset the 0602. No more 0602 codes at any rpm.



I returned the aux to feeding the OEM and let the OEM get fully full. VP44 threw 0602 at idle. Same scenario as above.



Stopped the aux feeding the OEM and burned down several gallons. Reset the 0602. No more 0602 codes at any rpm.



Got home took the VP44 return line from the tank vent line and plumbed it into the aux bed tank vent line. No codes. Yes you have to leave the aux tank filling the OEM because the VP44 is returning OEM fuel to the aux bed tank and it would overflow.



What I think happened:



At rpm's above idle the VP44 body bypass valve pressure could over come the pressure in the tank vent line. At idle the VP44 bypass valve pressure could not overcome the pressure (air pressure or fuel weight pressure) in the OEM tank vent line.



Side benefits of the VP44 return line into the aux bed tank.



The aux bed tank acts as a passive fuel cooler worth about 5* of fuel cooling.



You can literally see the VP44 return fuel flow by taking the aux tank fuel cap off and looking at it VP44 return fuel stream.



You can pump the OEM tank out to a reasonably low level (not dry) by stopping the aux tank flow from the aux tank to the OEM tank and letting the VP44 pump fuel from the OEM tank to the aux bed tank for you.



Just something I found out, thought it might help someone



Bob Weis

 

[Fishin Guide]

And to think some guys runa restrictor in the fuel return...



Dave

 

[NoSeeUm]

Is the fuel foamy coming from the return line?



Jim

 

[rweis]

No the fuel is really clear. I looked at it caefully to see if the VP44 was getting air in the fuel input line and passing the air out the VP44 return line.



At idle the fuel flow is barely a trickle, ie the cooling fuel flow is barely a trickle.



It is one of those things you really never get a chance to look at and you hope the heck it is working correctly (VP44 bypass valve). I think it just may be a good tool to "see" what the fuel aeration is, / or is not, like and if the fuel system is sucking air some where or not.



I think I may build a connector of clear hose, to attach in line from time to time, so I can run it up on the outside to the drivers mirror and keep a check on it visually at normal driving conditions. Could be interesting to do that.



Bob Weis

 

[paulb]

How much of the fuel that is being returned is coming from the injectors, and how much from the VP44? There is a t-fitting at the back of the head...



Paul

 

[rweis]

If you go back to the thread "Pump, lines, whatnot... . " they looked at the differences in the volume of fuel from the injectors and the volume from the VP44.



The injector fuel is for lubrication of the injector internals and only amounts to a very small quantity I think measured in ounces per hour. The VP44 supposedly returns 70% of the injested fuel back to the tank for cooling purposes. I think the VP44 is 45 gph and it did measure about 30 gph back to the tank in the above thread.



Interestingly enough, when I removed the OEM fuel return it was a nylon type tube from the T that became inserted into a 5/16 ID steel line on the frame. It appeared to me that the id of the nylon line was 2/16" - 3/16" maximum.



The fluid dynamics folks can calculate what it takes in psi to get 30 gph of fuel through a 2/16" id line and a 3/16" id line. Might be interesting information.



Mine is a AN-6 from the output of the T (which is still about 3" of the 3/16" id OEM hard line) then goes to 3/8" id of the AN-6 to the aux bed tank. .



I thought the nylon line that coupled to the metal line at the T output was a restriction point. The nylon flex line from the T output then went down and was swedged inside of the OEM steel fuel return line on the frame. Now remember ALL the cooling fuel goes through this path back to the OEM tank.



Bob Weis

 

[Boondocker]

When the aux had fully filled the OEM tank and the engine was at idle (only) the VP44 threw a 0602 code. Would not throw the 0602 if any above idle.

Are you sure about the fuel plumbing as the reason for the 0602 code? The Smarty is known to throw this code. Maybe you should load stock software and see if the code persists through your test cases. (Just try not to over-boost while stock ).



Neil

 

[rweis]

I can test that. It will be a while as we are going on a 3 week vacation the first 3 weeks of July and until July is getting the honey do list done.



Bob Weis

 

[NoSeeUm]

Are you sure about the fuel plumbing as the reason for the 0602 code? The Smarty is known to throw this code. Maybe you should load stock software and see if the code persists through your test cases. (Just try not to over-boost while stock ).



Neil

I thought the same thing... .



Jim

 

[rweis]

Well, I am finding the VP44 return can be more volume than an almost empty aux tank will gravity flow to the OEM tank, ie the aux tank starts to slowly fill to about 1/4 full.



My inline valve may not have suffcient ID inside the valve head and may be where the restriction is. Mine is 1/4" ID ends with a ball valve in the middle that has about a 1/8" orifice passage. NOT ENOUGH to stay ahead of the VP44 return fuel at cruise speed.



I am going to install the Northern Tool gravity feed valve tommorrow and see how that does, and reroute the VP44 return feed line back to the tank filler vent line.



EDIT- Hopefully the Northern gravity check valve will keep the OEM tank from over filling and not create a condition that the VP44 will throw a 0602 CEL code as the VP44 return line is positioned above the level that the check valve should stop the fuel into the OEM tank and the VP44 return line should see an air space rather than a fuel space as I had before.



Just some findings so far.



Bob Weis



Edit - Northern Tool gravity feed check valve installed. Easy install, fits well, easy to get valve horizontal, easy to orientate the valve verticle. There was some concern about valve inlet barb size being too small (about 1/8" ID). I think it should be ok because: The VP44 uses 45 gph max, returns 70% (31. 5 gpm to the tank NOT through this valve), this valve is responsible for 13. 5 gpm. So will a 1/8" ID line flow 13. 5 gpm? Probably when the aux bed tank is full and there is some verticle fuel weight. However when the aux tank gets low the flow through this valve is going to be slow, but you still have to burn the OEM tank while the aux tank is trickling the last bit of fuel in. Should be ok I think. However, I will report back fill data as I gather it.