Why cant I use my stock fuel pump?
- Thread starter davelx
- Start date
jstang209
20+ Year Stangneter 
Vipersix
Founding Member
It will work fine. EFI regularly uses higher pressures than carbs which allows most any pump designed for EFI more than adequate for carbed applications.
jstang209
20+ Year Stangneter
I know it will have enough pressure but can i regulate it down without it screwing up? read what these guys said.
http://www.corral.net/forums/showthread.php?t=762946
http://www.corral.net/forums/showthread.php?t=762946
I think as long as you have a return line for the excess fuel then you should be able to regulate the pressure where you need it. Its not rocket science, its just a positive displacement pump. More pressure, less volume. Less pressure, more volume. If you dead head the pump, you will see all sorts of pressure spikes and whatnot. As long as you return the extra volume, then you should have no problem maintaining 7psi or whatever you need to run.
Vipersix
Founding Member
There is no need to run a return line with your setup. In fact, it would probably make you LOSE pressure. Just make sure you use an adjustable regulator that can handle the higher pressures of an EFI system and that the post regulator pressure is sufficiently low enough for your purposes.
Another repost of EFI to carb comments,,, Doesn't anyone use the search function?
A word of warning on EFI to carb swaps: don’t expect to pass emissions in any state that does comprehensive smog inspections, because it won’t happen. You won't get any more power from a carb than you will from EFI.
Doing the swap: You must know how to read electrical diagrams and wire circuits properly to do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.
If you do the hack job that is common among folks who don’t understand electricity or computers and are doing the conversion because it is easier than dealing with the EFI system, the result will look like and run like road kill. Wiring harnesses chopped up and spliced together with electrical tape, loose and dangling hoses, fuel lines spliced together with 3 types of fittings speak of ignorance and sloppy workmanship. If you can't do it right, don't do it at all. I wouldn’t wish a car with that kind of workmanship off on my worst enemy...
Now that the rant is over, here’s some practical advice…
Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. Either go full EFI or use a tank/fuel pump/fuel lines out of an 84 or earlier Stang. Fabricating your own setup is possible but there are some snags to overcome.
Do not attempt to leave the EFI in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.
If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.
You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump.
You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.
While you are at the electrical part, you'll need a Durspark or similar ignition system. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Durspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information.
A word of warning on EFI to carb swaps: don’t expect to pass emissions in any state that does comprehensive smog inspections, because it won’t happen. You won't get any more power from a carb than you will from EFI.
Doing the swap: You must know how to read electrical diagrams and wire circuits properly to do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.
If you do the hack job that is common among folks who don’t understand electricity or computers and are doing the conversion because it is easier than dealing with the EFI system, the result will look like and run like road kill. Wiring harnesses chopped up and spliced together with electrical tape, loose and dangling hoses, fuel lines spliced together with 3 types of fittings speak of ignorance and sloppy workmanship. If you can't do it right, don't do it at all. I wouldn’t wish a car with that kind of workmanship off on my worst enemy...
Now that the rant is over, here’s some practical advice…
Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. Either go full EFI or use a tank/fuel pump/fuel lines out of an 84 or earlier Stang. Fabricating your own setup is possible but there are some snags to overcome.
Do not attempt to leave the EFI in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.
If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.
You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump.
You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.
While you are at the electrical part, you'll need a Durspark or similar ignition system. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Durspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information.
jrichker said:
Converting to carb properly is more expensive/time consuming than it first appears.Convert your efi 2.3 to an efi 5.0. The driveability and efficiency will be vastly superior for the same power level. The stock 2.3 efi fuel pump would be adequate for a efi 5.0.
I am not all that convinced that swapping to carb would be cheaper than swapping to efi. I would like to see parts lists/costs if you have them. I am curious.
This is just my opinion (that efi is better than carb), but I wish you the very best of luck with the swap, no matter what you decide.
jason
Vipersix
Founding Member
I want to hash on something I failed to mention earlier. The fuel system is probably the most confusing and disrespected system in an engine yet it seems to be the least understood (not to mention nearly always under modified).
Carburetors utilize a greater volume of fuel at a lower pressure than their EFI counterparts (thus the lower fuel economy). Most applications work fine with 5 to 8 psi at the jet due, in part, to the lower manifold pressures while EFI normally runs around 35 to 40 psi rail pressure.
A fuel pump is rated (or should be rated) by a volume at a certain pressure. As the pressure increases the volume decreases; the opposite is also true. To put this in perspective, open a Summit catalog and simply browse through the various fuel pumps.
Edelbrock makes a Quiet-Flo electric fuel pump in various flavors for both carbureted and EFI applications at a substantial price difference. Comparing the basic models, the carb version has a rated 120 gph free flow output while the EFI version is rated at 80 gph @ 45 psi. How much would you be willing to bet that these two pumps are identical? The only cosmetic differences are the inlet and outlet fittings.
If you are able to track down the manufacturer’s rating schematics, they normally test the pump outputs at various pressure ratings and organize them in a table. The following would be my best guess as to our example pump:
120 gph @ 0 psi
110 gph @ 10 psi
100 gph @ 20 psi
90 gph @ 30 psi
80 gph @ 40 psi
70 gph @ 50 psi
And so forth…
This is the problem normally associated with people who add some sort of power adder to their engine and disregard the increase in pressures. The entire fuel system must be able to supply the appropriate number of gallons at the necessary fuel pressure. This means that if you need 40 psi at the injectors and are running 20 psi of boost, the system needs to deliver the correct amount of fuel at 60 psi. This is where you see the air-fuel mixture leaning out and causing detonation which leads to real money in damages.
When in doubt, get a larger system!
Carburetors utilize a greater volume of fuel at a lower pressure than their EFI counterparts (thus the lower fuel economy). Most applications work fine with 5 to 8 psi at the jet due, in part, to the lower manifold pressures while EFI normally runs around 35 to 40 psi rail pressure.
A fuel pump is rated (or should be rated) by a volume at a certain pressure. As the pressure increases the volume decreases; the opposite is also true. To put this in perspective, open a Summit catalog and simply browse through the various fuel pumps.
Edelbrock makes a Quiet-Flo electric fuel pump in various flavors for both carbureted and EFI applications at a substantial price difference. Comparing the basic models, the carb version has a rated 120 gph free flow output while the EFI version is rated at 80 gph @ 45 psi. How much would you be willing to bet that these two pumps are identical? The only cosmetic differences are the inlet and outlet fittings.
If you are able to track down the manufacturer’s rating schematics, they normally test the pump outputs at various pressure ratings and organize them in a table. The following would be my best guess as to our example pump:
120 gph @ 0 psi
110 gph @ 10 psi
100 gph @ 20 psi
90 gph @ 30 psi
80 gph @ 40 psi
70 gph @ 50 psi
And so forth…
This is the problem normally associated with people who add some sort of power adder to their engine and disregard the increase in pressures. The entire fuel system must be able to supply the appropriate number of gallons at the necessary fuel pressure. This means that if you need 40 psi at the injectors and are running 20 psi of boost, the system needs to deliver the correct amount of fuel at 60 psi. This is where you see the air-fuel mixture leaning out and causing detonation which leads to real money in damages.
When in doubt, get a larger system!
The EFI pumps are typically a gear type, like the oil pump for the engine. Carb pumps are centrifugal pumps, like a supercharger. When you stop to think about a gear pump making high pressure at low volume and a centrifugal pump making low pressure at high volume, it makes sense.
MrKwik
Founding Member
I personally think its easier to use an electric pump. You will need to change the pickup and lines either way. The electrical is easy as installing a relay in the kickpanel and then you can wire the electric pump to the factory wires and retain the inertia switch. I also like to wire in an oil pressure safety switch.davelx said:I guess I have decided to use all the stuff from a 84 or so carbed fox. I already have all the motor stuff(carb,intake,and so on.) I will just need the fuel tank, fuel lines, and a new mechanical pump. anything else? The motor is NOT a late 80's roller so the timing cover is one for a mechanical pump already. This will save me the headache thast i have recieved asking and wondering wbout this for so dang long. I really didnt want the drag of the mchanical pump, but its the easiest thing to do.
As far as the sump problem goes, there a few low buck options. On one car, I used a fuel cell bulkhead fitting and installit in the bottom of the tank inside the baffled area where the stock pump sits. I then removed the stock pump and cut off and sealed the tubes and reinstalled the pickup in the tank. I have also used an earlier pickup tube (I believe an 85) in the stock tank. It had the level sensor on it as well where as the later ones had it in the other side of he tank. I removed that part of it and just used the pickup tube portion of it. Both times I used a Holly red pump and -6 line. I imagine sumpung the tank or using one of those aftermarket pickups would be the best way to go but it wasnt in my budget.
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