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EFI fuel supply setup
- Thread starter sledge
- Start date
Airpacker
New member
Having just gone down this road, I can tell you exactly what I used and how.
I run a Holley "Black" pump off an ignition switched relay. The pump feeds an inline regulator set at 3psi. It draws from my tanks thru the seperating filter and feeds a 3 gallon pony tank mounted right beside my engine. It is fed from the top and gravity ( 3lbs pressure) feeds out the bottom to my inline SX high pressure pump via a fuel cooler that is a modified mercury power steering cooler with 1/2 npt bungs silver soldered in where the 3/8npt bungs used to be. The SX pump and cooler are mounted on a plate below the crank pulley. My raw water pump sends the water thru that cooler before the oil cooler.
After the cooler, my -10AN fuel line goes to the HP pump and out to a bronze 5 micron filter and then to a fuel block I fabricated where it splits to two -8AN lines to feed the fuel rails and injectors. The block also has a test port, pressure sender and the OE merc pulsater mounted on it. After the rails,two -8AN lines exit and meet at the pressure regulator and become one -6AN return line.
From the regulator, it heads back to the pony tank to start the trip all over again
The fuel is cooled right before it hits the high pressure pump no matter how long it stays in the loop.
I run a Holley "Black" pump off an ignition switched relay. The pump feeds an inline regulator set at 3psi. It draws from my tanks thru the seperating filter and feeds a 3 gallon pony tank mounted right beside my engine. It is fed from the top and gravity ( 3lbs pressure) feeds out the bottom to my inline SX high pressure pump via a fuel cooler that is a modified mercury power steering cooler with 1/2 npt bungs silver soldered in where the 3/8npt bungs used to be. The SX pump and cooler are mounted on a plate below the crank pulley. My raw water pump sends the water thru that cooler before the oil cooler.
After the cooler, my -10AN fuel line goes to the HP pump and out to a bronze 5 micron filter and then to a fuel block I fabricated where it splits to two -8AN lines to feed the fuel rails and injectors. The block also has a test port, pressure sender and the OE merc pulsater mounted on it. After the rails,two -8AN lines exit and meet at the pressure regulator and become one -6AN return line.
From the regulator, it heads back to the pony tank to start the trip all over again
The fuel is cooled right before it hits the high pressure pump no matter how long it stays in the loop.
Airpacker
New member
Chris, the way I figured it, the fuel travelling in the lines around the engine and in the injector rails beside my blower are exposed to the most heat soak so its the "recycled fuel" that concerns me for heat thusly I cool it right before I pump it to the injectors a couple feet away.
I didnt like the idea of having 45psi fuel in the cooler much either.
The pony tank serves several purposes. One, it assures an air free fuel supply to the HP pump without having the HP pump need to "pull" the stuff 5 feet from the main tanks. HP pumps tend to be good pushers and poor pullers.
Two, it gives me a place to return to ONE point instead of the two saddle tanks in my cat.
Three, it eliminates a ton of evaporative emissions and their associated volatile fumes that would occur if I returned warmed fuel to the tanks which of course are vented directly to the atmosphere.
Four, I had an extra 1/2 NPT bung welded into the top where I can add storage oil and stabilizer easily for the winterization run up.
It appears to all work well so far
I didnt like the idea of having 45psi fuel in the cooler much either.
The pony tank serves several purposes. One, it assures an air free fuel supply to the HP pump without having the HP pump need to "pull" the stuff 5 feet from the main tanks. HP pumps tend to be good pushers and poor pullers.
Two, it gives me a place to return to ONE point instead of the two saddle tanks in my cat.
Three, it eliminates a ton of evaporative emissions and their associated volatile fumes that would occur if I returned warmed fuel to the tanks which of course are vented directly to the atmosphere.
Four, I had an extra 1/2 NPT bung welded into the top where I can add storage oil and stabilizer easily for the winterization run up.
It appears to all work well so far
MOBILEMERCMAN
Founding Member / Competitor
The race outboards have had puke tanks for 20 years. Like Sean says it keeps the pressure loop short and void of air. The puke tanks still have a return line to the main tanks in many applications. As far as the cooler placement goes. It is my understanding the point is to cool the recirculating fuel. In the production merc engines the separater filter is where the fuel returns and acts in part as the puke tank. The early merc EFI engines didn't have coolers and had vapor lock issues as a result. Here is a quick example from '85
Airpacker, have any pics of your setup? Am I counting that right...3 different pumps? Low pressure to the sump tank, SX through the cooler, then HP to the distribution block/etc.
Man do I appreciate the simplicity of a mechanical fuel pump...
Does the Merc setup push through the cooler before or after the high pressure? I can appreciate not wanting to push HP through the cooler but I would think ~50psi wouldn't be overly risky for a trans/PS/oil cooler?
Man do I appreciate the simplicity of a mechanical fuel pump...
Does the Merc setup push through the cooler before or after the high pressure? I can appreciate not wanting to push HP through the cooler but I would think ~50psi wouldn't be overly risky for a trans/PS/oil cooler?
Airpacker
New member
No, two pumps. One LP holley to draw from the tanks through the seperating filter and feed the pony tank. One SX HP pump to feed the motor. The cooler is on the LP side after the pony tank and just before the SX HP pump. The return is from the HP regulator back to the pony tank.
I prefer to keep pressurized fuel in thick walled places. Power steering coolers are pretty thin walled copper tubing as they live on the return side of the PS system.
Jim, my LP pump is self regulating so if the pony tank gets over filled, the LP pump just stops pumping. That way I do not need to return to the tanks.
I prefer to keep pressurized fuel in thick walled places. Power steering coolers are pretty thin walled copper tubing as they live on the return side of the PS system.
Jim, my LP pump is self regulating so if the pony tank gets over filled, the LP pump just stops pumping. That way I do not need to return to the tanks.
MOBILEMERCMAN
Founding Member / Competitor
Here is a 525 flow chart
MOBILEMERCMAN
Founding Member / Competitor
The outboard pumps do not want pressure on the inlet side.
The 525 is a simple dependable set up. I prefer a lp pump set up. The down side to the 525 is if it gets air in it from a low level or transfer from multi tanks the motor has a hard time clearing the air.
The lp set up with a return to the tank is the most forgiving.
The 525 is a simple dependable set up. I prefer a lp pump set up. The down side to the 525 is if it gets air in it from a low level or transfer from multi tanks the motor has a hard time clearing the air.
The lp set up with a return to the tank is the most forgiving.
Airpacker
New member
so the 525 is a semi returnless deal? Never liked a dead end fuel rail. Any crap in the system is gonna end up in one injector.
MOBILEMERCMAN
Founding Member / Competitor
It is simple. It seems to be engineered to have one fuel line attachment to the motor. Return lines and the need to have puke tanks complicates coast guard approval and liability issues.
