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After kicking around many ideas I decided to go with an external surge tank and external pumps to feed the fuel rail of my rb25det in my 240z.  I tried an intank fuel pump previously.   The intank pump is the way to go for sure as long as you have adequate baffling and good general design.  My problem stemmed from a poor design and using a rusty tank a buddy gave me.  I started a thread on that.  




I will update that thread with some lessons learned soon.  


Luckily I still had the original tank I pulled out of the car at the start of my project. It had a little rust, the local radiator shop was able to clean it out using acid and hot tanked it ($89).  


The key to my project is that there are no modifications to the stock tank.  I chose to use the bcbroncos product, Accumulator Tank, ( http://www.bcbroncos.com/fuelefi.html ) scroll to the bottom the page.  The tank is a converted remote oil filter.  The guys at bcbroncos use this tank for their EFI conversions (if the customer does not want to spring for  the intank solution).  Fuel goes in the top, pass through the filter, there is a pickup tube that extends to the bottom of the filter where the fuel is picked up by the HP pump.  bcbroncos added a third fitting (5/16ths) to the top of the modified oil filter to manage the return system (see tee fitting in website image).  You plumb the return from the engine to one side of the tee and the return to the tank to the other side. 


I am feeding the surge tank with a low pressure Airtex 8016S pump.  On the engine side of the surge tank is a high pressure Walbro GSL392 pump.  




The obvious problems with this kind of are the following:

1) Mounting everything (there aint much room) while staying away from the exhaust and the suspension and anything else that moves (rips).

2) Return Pressure Part A - there must be free flow from the fuel pressure regulator (FPR) to the tank.  If the system lacks enough return capacity (adequate fuel line inside diameter), pressure can build up in the surge tank.  In this case that is not an option because the tank is nothing more than a thread on filter.  People have reported problems with their bcbroncos accumulator tanks leaking.  I suspect that is because they did not have adequate return capacity to the tank and pressure built up inside the surge tank.

3) Return Pressure Part B* - if there is not free flow after the FPR then the HP pump has to work under load and will get HOT!  = BAD for pump and WIRE!  If the HP pump is working hard and getting hot then the WIRE feeding it juice is getting HOT.

4) Noise of external pumps (live with it)

* - source Tony D.


1) After looking around the back of the car for a while I found a cluster of three threaded holes.  I made a plate (1/8-inch) and threaded M6 hardware into the holes.  I use the plate as a base to weld an extension out of some small box tubing.  This was needed to move everything away from the Mustache Bar.  I welded another plate to the box tubing, drilled to accept the surge tank and pump mounting plate (16-gage sheet metal).  






2)  After exchanging emails with Tony D, I was convinced that I needed to increase my return capacity to the tank.  I already replaced the little pinner 3/16ths return line with 5/16ths when the drivetrain was out.  But the stock tank has that 3/16ths return above the 5/16ths pickup.  I decided to swap my usage of the 3/16ths return line with the smaller top of tank vent line (@ 5/16ths or a little bigger.  At this point you simply need to make a 3 to 5/16ths adapter to plump the stock return to the vent tank.  


3) After doing some research on the amp draw of the pumps and exchanging emails with Yury at Wiringspecialties.com we decided that I would be OK running both pumps over the stock 10-guage wire that runs from the back of the car near the tank (Nissan ran it back there to allow for an optional electric fuel pump on the carburated cars) to the front (Green wire).  


I am monitoring the wire (grabbing it to see if it gets hot) as I've running the cat over the last few weeks and have felt to heat at all.  The Walbro has never gotten hot at all.  The LP pump gets warmish, but not hot.


4) The Airtex pump makes a lot of noise (grumble) at idle.  Can't hear it when you are underway.  It doesn't bother me.  








Priming the system, I disconnected the power and ground to the Walbro and cycled the car in the ON position running the LP pump.  I waited until I heard gas falling from the vent fitting back into the tank. I connected the HP pump back up and went for it.  Damn thing started right up.  Crazy.  


The Bad/weird part.  When I shut the car off the LP pump continues to run for a second or two.  I have a an inline fuel pressure gage in the engine bay.  After I turn the car off it reads @ 25 psi pre-rail.  After 20 minutes or so the pressure bleeds off.  I am concerned this may not be good for the FPR.  BUT the remnant pressure is great for one thing, starting the car back up.  When I had my intank setup.  I had to prime the system in the ON position everytime I started the car.  Now, no need, the fires right up on the the first crank everytime.


Thanks for reading.





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  • 1 month later...

READ THIS! I found that you CANNOT use the upper tank vent line as a return and the tank return for vent. If you fill the tank air builds in the tank and forces fuel up the filler neck and vent hoses, which is bad. I returned the system to stock, which means I am using the stock return (3/16ths). So far no leakage from the surge tank. I will keep you all posted.

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I have run the right rear corner vent line as a return since 1985. I don't know if hat is the top of the tank or not, but it may be.

There were two tank top vents, only one needs to work o perform proper EVAP & Venting functions...


The very purpose of the large diameter vent hoses is in fact to allow for expansion of fuel into them to prevent an issue of belch-out through the filler neck.


If you have good vent hoses (the 15mm ones) then the smaller 8mm are redundant, and vice-versa.


I routinely re plumb these large, expensive 15mm hoses with commonly available 3/8"~10mm fuel line which seems to rout easier, it lighter, and has ABSOLUTELY corking the EVAP system tight enough to give a 5psi 24 hour leak down check.


If you eliminate the CRANKCASE ACCUMULATION feature of your 240Z, I have previously documented my setup so you don't push fuel out:


As I said, there are TWO points on the top of the tank. One is used as a return, the other goes up to the area of the vapor canister, makes a double loop, then exits the right rear near the filler neck hose on the tank. I use a small K&N filter on it as a breather filter.


Normally makeup air fur tank suck down or venting from expansion was directed to the air cleaner or crankcase, depending on running status of the engine.


In normal operation, the fuel WILL EXPAND up the 15mm hoses and even the filler neck...but ONLY SO FAR due o the pressure break action of the flow diverter valve. If you dont have that break on it (which you could install on the use I mention above...and run TWO small K&N filters for "makeup and vent") and don't vent the tank as I have repeatedly suggested whenever this comes up, one f two things will happen:

1) pressure builds and you find out how good your big vent lines are, or how good your tank cap gasket is (if they are good, like meme which hold 5psig) then you start sinking the floats on your webers while sitting in the hot sun and think you're percolating... Or some such high-pressure issue (leaks at tank filler hose, etc... Usually you find your leaking vent hoses...

2) under way, you don't notice a thing, unless like me you have tight good hoses everywhere on your EVAP system and don't have any air makeup... In which case, going batshit crazy banzai running down I15, you start running mysteriously lean, and eventually end up dead at the roadside. Then you can't restart even though you show 3/4 full of fuel. It sent until someone notices your tank filler neck SUCKED FLAT AS A PANCAKE that you realize you sucked your tank down, and without makeup air, you made a vacuum...which the pump can not overcome.


Then you remove the cap on the flow diverter valve in the engine bay and hear it whistle like mad ... Or you open your tank and hear a giant sucking WOOOOSH! After which you drive away.


Contrary to shade tree lore, things were not put on the car that don't need to be there, and that goes for "th' 'missuns crap" also!


You CAN use the EVAP return line for your fuel return. You just have to properly vent the tank (the line's original function) to maintain proper fuel NPSH to the pump.


You can do a simple single loop to filter as I did (straight vent) or incorporate the OEM Flow-control valve and two filters at the rear of the car to maintain residual pressure in the tank when expanding, and OEM vacuum break function whilst driving r cooling off at the end of the day.


You CAN use that fitting / fittings... I've done it without your issue going on close to 30 years now. No, you don't just cap it or delete it without knowing and replacing it's function. Since 1994 I personally have never said to do that--on the contrary in fact!


It's the easiest way to return fuel in a conversion, and he 3/16 line works great as a supplemental surge tank bleed. The top two 1/4" lines on the tank are employed as return for fuel, and vent for tank, and everything works just fine!

Edited by Tony D
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  • 2 weeks later...



After reading Tony D's post and giving it another go, I think I sourced my initial problem, inadequate venting. The setup I tried, using the smaller stock vent line on top of the tank for my return is ok. The problem appeared to be with the larger, top of tank vent line. It was kinked, which would account for air building up inside the tank and causing the boil over at the filler. I have been driving the car with this setup for several days without issue, including a fill up with gas.


I also tried running the return from the surge tank through the 3/16ths return, that did I not work. The return fittings leaked. The stock return fitting on the tank is just too small for fuel injection return, but we knew that already.


All in all, the system appears to work, but care is required when eliminating one of the redundant components of the vent system.



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  • 4 years later...
  • 2 weeks later...

It's the easiest way to return fuel in a conversion, and the 3/16 line works great as a supplemental surge tank bleed. The top two 1/4" lines on the tank are employed as return for fuel, and vent for tank, and everything works just fine!

Hey Tony, so the 3/16 can only be used as a supplemental? I'm going to be running a 4x4x7 box surge tank and was hoping to use the 3/16 as the main return to the tank.


I already had to cut about 3' of my return off in the engine bay back as the line was severally clogged. Then I was going to mount my surge tank right to the firewall by the battery.


I know wrcbonk had issues, but he was using the Bronco filter as his tank vs mine being a sealed aluminum box.

Edited by JSM
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