|
Fuel flow problem. Help!
I have a 383 fuel injected Mercury Scorpion) with electric fuel pump. Fuel goes through the filter, through the fuel pump, and then through the regulator on the way to the engine (fuel bladder is in the closed bow). After the regulator, there is a "Y" that returns fuel to just before the fuel filter. The filter and fuel pump sits horizontal on the stringer at about the same level. The regulator is a tad bit lower.
When I get up to about 4000 rpms, I start to get some "cutout". It is worse if I am in rough water where the attitude of the boat changes. It can also begin to cutout if I lift the trim too high, putting the nose just a bit higher in the air. At 3000 there is no "cutout" unless I hit some rough water, or raise the bow with trim. The fuel pressure remains at 37-38 pounds. When it happens, I get out of the throttle, come to a stop, and raise the hatch. I disconnect the fuel line (there is about 3 feet of braided line between the regulator and the intake) on top of the intake just before the pressure gauge, I put the line in a bucket and have Jr turn on the fuel pump. Just air comes out at first and then a steady stream of gas. Reconnect and good to go. Before taking the fitting loose, the fuel pump runs and makes pressure, but you can tell by the sound there is no gas moving, it is just compressing air. After I bleed the system, the fuel pump changes tone after just a couple of seconds telling me that fuel is in the line again. Where is the flaw in the fuel system? I was going to talk to my mechanic tomorrow, but some insight would be helpful. What could be happening in the plumbing to make this airlock? Should the regulator be higher than the pump? Should the filter, pump and regulator be in a straight line? I did try loosening the gas cap to see if I had a blocked vent, and it did not help. I checked the fuel filter a couple of times and it is fine. Thoughts? |
Originally Posted by 36Tango
(Post 3466021)
I have a 383 fuel injected Mercury Scorpion) with electric fuel pump. Fuel goes through the filter, through the fuel pump, and then through the regulator on the way to the engine (fuel bladder is in the closed bow). After the regulator, there is a "Y" that returns fuel to just before the fuel filter. The filter and fuel pump sits horizontal on the stringer at about the same level. The regulator is a tad bit lower.
When I get up to about 4000 rpms, I start to get some "cutout". It is worse if I am in rough water where the attitude of the boat changes. It can also begin to cutout if I lift the trim too high, putting the nose just a bit higher in the air. At 3000 there is no "cutout" unless I hit some rough water, or raise the bow with trim. The fuel pressure remains at 37-38 pounds. When it happens, I get out of the throttle, come to a stop, and raise the hatch. I disconnect the fuel line (there is about 3 feet of braided line between the regulator and the intake) on top of the intake just before the pressure gauge, I put the line in a bucket and have Jr turn on the fuel pump. Just air comes out at first and then a steady stream of gas. Reconnect and good to go. Before taking the fitting loose, the fuel pump runs and makes pressure, but you can tell by the sound there is no gas moving, it is just compressing air. After I bleed the system, the fuel pump changes tone after just a couple of seconds telling me that fuel is in the line again. Where is the flaw in the fuel system? I was going to talk to my mechanic tomorrow, but some insight would be helpful. What could be happening in the plumbing to make this airlock? Should the regulator be higher than the pump? Should the filter, pump and regulator be in a straight line? I did try loosening the gas cap to see if I had a blocked vent, and it did not help. I checked the fuel filter a couple of times and it is fine. Thoughts? well... the short answer is yes but the first question would be " has it ever worked correctly in this configuration before ?" never the less ,for me it sounds as if the fuel delivery to the the inlet of the pump is at capacity limit for any number of reasons... length of line, tank too far away, picking up air during low fuel/ agitation issue... who knows ... any number of things but the solution is easy in concept if not a bit of work in execution. you create a fuel accumulator in the engine bay anywhere above the pump. you make or buy a 1 or 2 quart "tank" ( ATL sells them) that you pump your primary tank into the top of with a conventional hi volume /low pressure electric pump like a carter... that " accumulator" gravity feeds the electric pump for the injection. the accumulator needs a return line to the tank so it doesn't pressurize and while you are at it , you run the return line from the injection into that return as well. so... fuel is pumped at hi vol/low press from the tank to the accumulator. that 2 quarts gravity feeds the hi press injection pump. the injection return line goes to the accumulator return line which goes back to the tank. what that does is that no matter what happens to the boat as far as g forces or anything else, the injection always has 2 quarts of relatively cool , non aereated fuel to draw on . this system solves the dreaded vapor lock issue on the mpi motors as well. |
check the fuel pickup tube in the tank
|
The boat has an ATL bladder mounted in the bow approximately 12 feet in front of the motor.
I talked to my mechanic this morning and he questions whether we have enough fuel pump on it. He says that since the pump is so far away from the tank, it needs to be well oversized in order to draw the fuel that far. He tell me that once the pump cavitates just a bit, it will be airlocked. He suggested replacing the current pump with one of those big $$$ Aeromotive pumps. Any thoughts? |
I agree with Redcheckmate, check the pick up, see how close it is to the bottom of the tank. Pump size won't matter if it's picking up air.
|
Originally Posted by 36Tango
(Post 3466217)
The boat has an ATL bladder mounted in the bow approximately 12 feet in front of the motor.
I talked to my mechanic this morning and he questions whether we have enough fuel pump on it. He says that since the pump is so far away from the tank, it needs to be well oversized in order to draw the fuel that far. He tell me that once the pump cavitates just a bit, it will be airlocked. He suggested replacing the current pump with one of those big $$$ Aeromotive pumps. Any thoughts? i don't know... seems to me a pretty clear cut problem... you need to not make the efi pump do the work of lifting the fuel and pulling it forward... how you do that is just a matter of how much work you want to do. and the efi return line really needs to go back to the cell... don't put hot aereated fuel right back in the inlet ... i know merc does it but thats a mistake. the guys talking about the pickup have a point but i used ATL bladders by the hundreds... great stuff... and the chances of the pick up falling off or being misplaced are zero... but having said that, i did have a number of times, fuel contamination with water that would form a slime and coat that fine fine little screen they use at the bottom of the pick up and cause starvation. i presume that it has a 16 bolt access panel in the top... just unbolt that and pull the assy out and see what in there. should be pretty easy assuming you can get to it. and while we are on that subject... you could always just put a submersable pump in that cell to act as your lift pump... that hardware is off the shelf for those cells. every efi race car on the planet has at least two of them in there... often 4 |
Originally Posted by stevesxm
(Post 3466240)
you could always just put a submersable pump in that cell to act as your lift pump... that hardware is off the shelf for those cells. every efi race car on the planet has at least two of them in there... often 4
|
Originally Posted by 36Tango
(Post 3466251)
Can you give me a link to this pump? Does it get wired together with the fuel pump in the bilge to come on at the same time?
this is what they look like... http://www.jegs.com/i/JEGS-Performan...ductId=1167182 this one is 125 bucks and it probably isn't anything special... but this is what it and all others like it look like. i would wire it directly to a separate switch on the dash but thats just me and i don't know what the CG says about that. i certainly don't know what your installation looks like but , i suppose you could just use the in tank pump to replace your standard pump... i mean once you confirm the volume /pressure numbers then the rest is plumbing... gm uses a pump just like this to run the 400 plus hp corvettes... so capacity and location ought not be an issue... |
Originally Posted by stevesxm
(Post 3466256)
no link. they are generic . the ones i used to use were for all manner of gm cars but napa has a billion different types... i might give ATL a call. they certainly didn't have anything dedicated when i was working with them but that was 15 years ago and they might now. stand by and let me run a search
Thanks! |
3 Attachment(s)
Here are a few pics.
One is of the pump and the regulator. Both are mounted on the stringer with the regulator being slightly lower. The return line is on the bottom side of the regulator. We have it set at 37-38 pounds. Another pic shows the Y where the return comes back in, the filter, and the pump. The incoming fuel line comes on from above. Last pic shows the boat. The bladder is in the front, so it takes climbing over the dash to get to it. This is why I need to have some skinny friends! |
Originally Posted by 36Tango
(Post 3466273)
Here are a few pics.
One is of the pump and the regulator. Both are mounted on the stringer with the regulator being slightly lower. The return line is on the bottom side of the regulator. We have it set at 37-38 pounds. Another pic shows the Y where the return comes back in, the filter, and the pump. The incoming fuel line comes on from above. Last pic shows the boat. The bladder is in the front, so it takes climbing over the dash to get to it. This is why I need to have some skinny friends! i would like to give you some sht and point out something that i often complain about here... i see all this zoomy braided line and fittings into fittings into fittings into adapters into more fittings... and at the end of it is some piece of old gas line with a couple 10 cent hose clamps on it.. if you are going to use aeroquip, don't do it because it looks neat. use it intellegently and learn to do it properly so that it actually does what it is meant to do. which is NOT just to look neat and impress your friends. |
Looks like this might be the hot setup, as it comes with everything I will add the return line back to the tank at the same time.
http://www.atlinc.com/2010_Race_Catalog/page18.html Thanks for the education. |
Originally Posted by 36Tango
(Post 3466303)
Looks like this might be the hot setup, as it comes with everything I will add the return line back to the tank at the same time.
http://www.atlinc.com/2010_Race_Catalog/page18.html Thanks for the education. |
Originally Posted by stevesxm
(Post 3466307)
exactly what you need. i loved ATL stuff. you could call them on monday and talk to louis diamico , fax him a drawing and on thursday have what you needed. perfect every single time. great company.
When I took the pics of the current setup, the same thoughts went through my head about it being a bit cobbled. I am not a mechanic by trade and bought this boat last year with no engine, no drive, and it was red and white. It has been a helluva learning process. Forums like this, and people like you, have been alot of help. |
Either a pump in the tank or one very close to the tank is the answer. As mentioned, efi pumps are terrible at pulling fuel. They are designed to push the fuel. You could probably just mount your existing pump near the tank and not have to purchase a new one, assuming it has a large enough capacity. You also need to be sure to mount it at least at or below the top of the tank.
The other common mistake is putting the regulator just after the pump. Put it after the fuel rail so that you are sending a full volume of fuel to the rail. Right now with the regulator before the rail, you are dimishing the amount of volume going to the rail. By plumbing it after the rail, it allows the rail to get an unimpeded and unaerated volume of fuel. The regulator will then return anything over the set pressure. This is the only way to plumb it IMO. Also, as mentioned, you MUST return the fuel to the tank, especially if you get a larger pump. Since electric pumps are not rpm dependant like mechanical pumps, they pump the same amount of fuel at all times. At idle, you are returning 99% of the fuel that the pump is pumping. You will heat that fuel up really quickly. On the flip side, at higher rpms, you are not returning that much fuel.....certainly not enough to fill the return hose. So, you are introducing air into the fuel system. This air is going right into the suction side of the pump. This is why you are having problems with it losing it's prime at higher rpms. Merc returns the fuel to the filter head in an effort to keep the engine self contained. It works (for the most part) on the smaller engines with smaller pumps. However, they still vapor lock from excessive heat buildup. They are also a ***** to prime when changing the filter since they don't pull much fuel because it is comstantly running in a loop. Hope this helps. Give me a shout if I can help. Eddie |
Originally Posted by Young Performance
(Post 3466632)
The other common mistake is putting the regulator just after the pump. Put it after the fuel rail so that you are sending a full volume of fuel to the rail. This is the only way to plumb it IMO.
Eddie It makes perfect sense to have the regulator after the rails, but I do not see any taps that are after the injectors. Unless there is something that I am missing, I will just attempt to get the regulator as close as I can. The fuel cell, as you can imagine, is in front of the first bulkhead and it is very, very tight. I will remove the front windshields to make it easier, BUT, I am still concerned about the fumes up there. Could I pump all of the gas out and then fill it with water? The foam inside the fuel cell needs to removed anyway to make room for the black box, so I will be able to dry it out when it is out of the tank. the fumes thing just kind of freaks me out a bit. I do very much appreciate the insight that both of you have. |
Originally Posted by 36Tango
(Post 3470750)
I attempted just to run a return all of the way to the tank, and it may have helped some, but niot entirely. I just ordered the ATL Black box, so that should cure all that ails me.
It makes perfect sense to have the regulator after the rails, but I do not see any taps that are after the injectors. Unless there is something that I am missing, I will just attempt to get the regulator as close as I can. The fuel cell, as you can imagine, is in front of the first bulkhead and it is very, very tight. I will remove the front windshields to make it easier, BUT, I am still concerned about the fumes up there. Could I pump all of the gas out and then fill it with water? The foam inside the fuel cell needs to removed anyway to make room for the black box, so I will be able to dry it out when it is out of the tank. the fumes thing just kind of freaks me out a bit. I do very much appreciate the insight that both of you have. |
Can you post pictures of the fuel rails ? the fuel return could be tapped into the fuel fill hose. Is there a check valve in your pick up ?
|
It does appear that it will fit with no problem. After I completely drain it of fuel (using the fuel pump before I remove it), we will try to pull out the cell. It is pretty flexible, so I think that it will come out of the access hole. I hope that can happen, as it is a very confined space and the fumes do concern me alot. Even just a little static could be a very bad thing.
I'll take some pics and share as I tear into it. There is no doubt that this will cure my problem. Now my only challenege is to have it completed and any kinks worked out before the Lake of the Ozarks Shootout at the end of the month! Thanks again |
Good Luck !
|
1 Attachment(s)
Eddie- Here is a diagram of the intake manifold and the fuel rails on the 377 Scorpion. Off of which one of these taps would a guy connect the regulator and return line?
|
Out of the pump to a 10 micron filter, then Y block , then one end of both rails, out the other end to the regulator, return to tank.
|
Originally Posted by GPM
(Post 3470890)
Out of the pump to a 10 micron filter, then Y block , then one end of both rails, out the other end to the regulator, return to tank.
|
So I get to work last night on at least preparing for the installation of the black box. To gain access, I first had to remove a couple of the windshield panels which was a real treat. I got up in the bulkhead and I noticed a pretty strong odor of gas. Did some research to find that these bladders have a life of 5 years and it is about 10 years old (I always thought that I could smell a slight odor). Evidently, the bladders are also "permiable", so slight vapors can get through the material, even when new.
Anyway, I am still going to use the ATL black box that I ordered, but I am going to have a new aluminum tank fabbed this week. It will also make it easier to install a fuel gauge. Kind of sucks, but it really needs to be done. |
Originally Posted by 36Tango
(Post 3471326)
So I get to work last night on at least preparing for the installation of the black box. To gain access, I first had to remove a couple of the windshield panels which was a real treat. I got up in the bulkhead and I noticed a pretty strong odor of gas. Did some research to find that these bladders have a life of 5 years and it is about 10 years old (I always thought that I could smell a slight odor). Evidently, the bladders are also "permiable", so slight vapors can get through the material, even when new.
Anyway, I am still going to use the ATL black box that I ordered, but I am going to have a new aluminum tank fabbed this week. It will also make it easier to install a fuel gauge. Kind of sucks, but it really needs to be done. and your fabbed al box won't be nearly as good nor any less expensive than buying a new cell if you are compelled to go that route. your fumes are from dumping fuel everywhere for the last week... |
Originally Posted by stevesxm
(Post 3471344)
no... thats wrong. the date code you see stamped on it is an FIA requirement and has nothing at all to do with service life. in race cars the fia requires the cells and seat belts and a bunch of other safety related items to be date coded. they're french... what do you expect... and they are not porous under any circumstances. take it out, fill it with something and look at the seam areas... if the seams don't leak... and that happens from wear and abrasion... properly installed, the container always has some sort of tape or cardboard chafe barrier... then its fine.
and your fabbed al box won't be nearly as good nor any less expensive than buying a new cell if you are compelled to go that route. your fumes are from dumping fuel everywhere for the last week... http://www.offshoreonly.com/forums/g...k-leaking.html ATL does say that they are permiable and must be used in a well ventilated area (this is not the best ventilated). I will pull it out this weekend and take a look at it. What method would a guy use to pressure test it? I would imagine ony a few pound of air would do. I will pull it out this weekend and figure out at least what I think that I need to do. Thanks a ton for all of the advise. |
Originally Posted by 36Tango
(Post 3471365)
This thread got me thinking (and maybe over thinking);
http://www.offshoreonly.com/forums/g...k-leaking.html ATL does say that they are permiable and must be used in a well ventilated area (this is not the best ventilated). I will pull it out this weekend and take a look at it. What method would a guy use to pressure test it? I would imagine ony a few pound of air would do. I will pull it out this weekend and figure out at least what I think that I need to do. Thanks a ton for all of the advise. F1 cars ? and i wouldn't inflate it to test it. a cell is meant to be in a container. the seams aren't designed for significant tensile tensile or shear load. .. altho they will tolerate it. stop trying to reinvent the wheel... if the cell had leaked previously then you would have smelled it... if you need to test it, put it outside, support the sides and fill it with whatever you want. its not going to leak ... and then just button the thing up and get finished. |
I pumped out all of the gas, filled the tank with water (pretty confined space did not want to deal with fumes), removed all of the hoses and the top of tank, and then removed all of the foam. I pulled the bladder (it was custom built to seat inbetween the stringers), and then made a wood mock up in the shop to support it. I filled it with water and let it sit for several hours. No leaks. Once I get the ATL black box in, I will start to reassemble. I am also adding the Livorsi fuel tube type sending unit and gauge.
From another suggestion, i looked at the hoses. All looked good, except there is a bit of a kink closer to the tank where it turns a tight corner. Since this was a suction line, it could have been restricting flow. I will remove and inspect all lines before putting it back together. Thanks for the insights! |
Originally Posted by 36Tango
(Post 3472593)
I pumped out all of the gas, filled the tank with water (pretty confined space did not want to deal with fumes), removed all of the hoses and the top of tank, and then removed all of the foam. I pulled the bladder (it was custom built to seat inbetween the stringers), and then made a wood mock up in the shop to support it. I filled it with water and let it sit for several hours. No leaks. Once I get the ATL black box in, I will start to reassemble. I am also adding the Livorsi fuel tube type sending unit and gauge.
From another suggestion, i looked at the hoses. All looked good, except there is a bit of a kink closer to the tank where it turns a tight corner. Since this was a suction line, it could have been restricting flow. I will remove and inspect all lines before putting it back together. Thanks for the insights! |
Originally Posted by 36Tango
(Post 3470883)
Eddie- Here is a diagram of the intake manifold and the fuel rails on the 377 Scorpion. Off of which one of these taps would a guy connect the regulator and return line?
Sorry I missed this post previously. As mentioned, just come out of the pump with a -10 line into a Y block. You should mount the pump very near the tank. You can run (1) -10 hose back to the engine compartment. There, split it into (2) -8 hoses, one each that goes to each fuel rail. Then mount an Aeromotive regulator and have one line come out of each rail and into the regulator. The return will come out of the bottom of the regulator. This will return back to the tank. Give me a shout if you have any quesitons. Here are some examples of the parts. Y-block: http://www.jegs.com/i/JEGS-Performan...oductId=758483 or http://www.jegs.com/i/Aeromotive/027/15620/10002/-1 regulator: http://www.jegs.com/p/Aeromotive/Aer...50081/10002/-1 Hope this helps. Good luck. Eddie |
Originally Posted by Young Performance
(Post 3473457)
Hope this helps. Good luck. Eddie |
| All times are GMT -5. The time now is 06:27 PM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.