Pressurized fuel routing

blamkin86

blamkin86

Well-known member
Folks,

By show of hands, which way do you guys plumb your fuel lines?

1) Pump -> Regulator - > split to fuel rail -> all pressured fuel goes into injectors

2) Pump --> fuel rail -> Regulator -> return to cell

Option 1 has the advantage of simplicity (no return line from the rail) but if any trash gets past the filter, that trash has to go through the injectors

Option 2 has the advantage that trash could make it back to the tank, but the fuel is constantly heated in the rail, and could cause a lean condition after a while (due to the hot fuel).

I'm asking because I switched from Option 2 to try and fix a lean condition, and almost immediately clogged my injectors (totally my own fault as the lines were not clean).
 
Option 2 means that now your injectors are the pressure regulator and usually see higher pressure than you see at the regulator. Go back to the regulator after the rails and get a higher volume pump or find what part is failing. No reason to have lean condition if you are running 70% or less duty cycle and have adequate volume.
 
How about option #3 which is the stock set up...

Pump -> Filter -> Fuel rail -> Regulator -> Return to Tank

If anything, I would think the stock setup would help keep the fuel rail cooler since you are constantly pumping the same volume of fuel thru the rail.
 
Greg Gauper":2ltymslb said:
How about option #3 which is the stock set up...

Pump -> Filter -> Fuel rail -> Regulator -> Return to Tank
Click to expand...

Mine is a slight variation of that ...

Tank --> Filter 100micron --> Pump -> Filter10 micron --> Fuel Rail --> Regulator --> Tank
 
I too have the stock screen in front of my pump...didn't include that in my response.
Don't know the size but would guess it is around 100 micron.
I wouldn't go any smaller than that for an inlet filter.
 
Sorry forgot to mention the filter, just trying for a little clarity on the setup.

Current setup is: In-tank Walbro pump, which has a sock/screen on the suction side. After that comes the regulator - which splits and goes back to the tank on one side - the metered side of the regulator goes into a nice Canton fuel filter.

After the filter, one line goes to the engine bay, where it hits a "y" fitting, then to both sides of the single rail.

The filter wasn't the problem - honestly - I did a very poor job of cleaning things out before I put it all together.
 
Steve Eckerich":3t11kb7s said:
Option 2 means that now your injectors are the pressure regulator and usually see higher pressure than you see at the regulator. Go back to the regulator after the rails and get a higher volume pump or find what part is failing. No reason to have lean condition if you are running 70% or less duty cycle and have adequate volume.
Click to expand...

Steve - sorry I'm not quite following you. Are you saying, that you like Option 1 better but I need to fix something?
 
...and finally...

The car started and ran fine for about 10 laps, then started going lean. Never a problem running hot on the dyno with the lean condition.

Also, the stock 99 miata has no fuel return line.
 
Not familiar with the Miata set up, but if your Canton filter is after the regulator, then your fuel pressure at the rail could drop as the filter gets dirty.

Another thing to watch out for...
Make sure the return line after the regulator is not too close to the suction line. The fuel coming out the return side of the regulator can sometimes become aerated and if it is too close to the suction line it will suck in aerated fuel.
Been there...fought that. If you have a couple of inches of separation between the suction and return lines, then I doubt this a problem. In my case I had an open top surge tank inside the cell and just had the return flow dumping into the surge tank. Problem went away when I place a scrap of fuel cell foam on top of the surge tank to provide a few inches of separation and to help break up the air bubbles.

Can you monitor the fuel pressure at the rail by moving your gauge/sensor?
Bottom line that is what you need to watch when you are on track.
 
Greg Gauper":2v891sxt said:
In my case I had an open top surge tank inside the cell and just had the return flow dumping into the surge tank.
Click to expand...

That is exactly how I had mine set up! Thanks for the tip.

Greg Gauper":2v891sxt said:
Can you monitor the fuel pressure at the rail by moving your gauge/sensor?
Bottom line that is what you need to watch when you are on track.
Click to expand...

Yeah, I added a sensor to my DA and dash before the last event last year - I was fighting other issues so I didn't get to stare at it on track...
...but on review the pressure was oddly swinging 5-8 lbs back and forth.

Which sounds an awful lot like air bubbles to me.

I've also replaced the regulator, just in case.
 
Let me throw this in
Smokey Yunick experimented with heated fuel in his quest for more power and found that the better atomization of warm fuel did increase power. Theory was smaller fuel particles burn better and more completely. You should be able to Google it - I read it in Circle Track some time ago.
 
blamkin86":1wdaostn said:
but on review the pressure was oddly swinging 5-8 lbs back and forth.

.
Click to expand...

Have a pressure gauge in my data system and I have the same thing, so that's not your issue.
 
blamkin86":n3h5v2v4 said:
...and finally...

The car started and ran fine for about 10 laps, then started going lean. Never a problem running hot on the dyno with the lean condition.
Click to expand...

Greg's coments about aeration is important. Also, you may already have cheked but you should verify your vent is clear and only flows air into the tank. I have seen these get clogged, sometimes by bugs/spiders where you would not know unless you blow through them.
 
mine runs as follows:
1. in tank walbro with sock
2. fram filter
3. fuel rail
4. regulator
5. return back to tank into black box

no issues down to 1 gallon in the cell.
 
Bobby, that's pretty much what I had before the big change.

Tom - where does your vent route? Does it go outside the car, or just to atmosphere near the cell?
 
EPrill":v36m2r7k said:
blamkin86":v36m2r7k said:
but on review the pressure was oddly swinging 5-8 lbs back and forth.

.
Click to expand...

Have a pressure gauge in my data system and I have the same thing, so that's not your issue.
Click to expand...

The pressure should be rock solid when under WOT. I would expect a slight drop when up-shifting or when the throttle is closed.
 
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