When I first built the JYD (grey car seen in pics in my sig) I had to overcome the problem of the in tank pump. I have seen a few thirdgens cruising around sucking fuel through the old dead/disabled electric fuel pump in the tank. I didnt decide to make it EFI until later.

Most of them couldn't make enough power to exceed the amount of restriction the in tank pump was causing so it didnt matter. Once in a while you will see a car that does have the power for this to be a problem.

The more creative somlutions I have seen have involved using a nicer aftermarket return style fuel pressure regulator. Others have simply pulled the tank and removed the pump and or installed a better "pick up" line.

To utilize this setup the factory fuel pump relay must be wired like the fan relay was so that it comes on with the key.

this setup is very simple, the in tank pump is made to pump reasonable amounts of fuel at higher pressure to run an engine to some decent horse power levels. When it freeflows as it will in my diagram the volume it is pushing is greatly increased. It really isn't supplying the engine as much as supplying the mechanical fuel pump with a nearby and easily drawn supply of fuel.

since both lines are constantly full there is no way that the mechanical pump can out draw both the supply of fuel being pumped from the intank as well as draw the return line empty.

Even though this setup is to help those of you with regular mechanical pumps mounted on the side of the block as an experiment I tried to "out draw" a stock 2.8 MPI in tank pump with a brand new holley into gas can. even free flowing the holley blue it could never "out draw" the in tank pump.

 

what about it drawing air from the return line ??
could this happen at all if you say it can draw fuel from the feed and return if needed in high hp apps how about if it uses all the fuel supplied by the feed line at the time and draws off the return for a moment long enough to pull it dry but still get feed from the original line is this possible at all??

just curious...other than that it seems to be a good idea

but why not just get a pickup made for a carbed thirdgen and drop your tank and put it in and be done with it and then add an high flow pump on the block ...wouldnt that work just as good?

 

If you are running a holley blue now drawing through an old in tank that is dead you can just "shorten" up where this fuel "tee" is to the lines back by the tank get the in tank working and keep the holley blue pump near the tank as well still.

I do not recommend that you try to run a electric pump up in the engine compartment as I did when I ran the test. electric pumps are designed to push not pull.

 

"since both lines are constantly full there is no way that the mechanical pump can out draw both the supply of fuel being pumped from the intank as well as draw the return line empty.

Even though this setup is to help those of you with regular mechanical pumps mounted on the side of the block as an experiment I tried to "out draw" a stock 2.8 MPI in tank pump with a brand new holley into gas can. even free flowing the holley blue it could never "out draw" the in tank pump."

in other words not only did it not do this during the year I ran it this way, but it also couldn't during the test I ran which simulated greater than high horse power apps could.

I don't know, Why dont they? I rarely in person see a car converted from FI to carb that the owner even bothered to think about the pump in the tank let alone address it. Those that do simply just pull through the dead pump because of project time constraints or fear of not knowing how simple it would be to fix.

Otherwise I couldn't agree with you more, absolutely pickup modification is the most ideal way to do it other than sumping the tank. I must remind you that due to fuel injection baffling most years of tanks wont accept the carb style pickup.

But there is nothing to stop you from pulling the tank, pulling the pump off the pickup assembly and using a brass ferrule union to extend the pickup line to the same length previously occupied by the 5 or 6 inch ling fuel pump. heck you dont even need to put a sock on it if you run fuel filters.

this mod is to help those with engines to the 500 hp range anyways. The only reason I can say this is because the JYD made 435 RW HP any day on the dyno and it was drawing through the active stock in tank pump with fuel to spare.

I just wanted to offer another option for those of you out there trying to go fast and keep the bills paid.

 

Well you just met another one. I will say a few things. Its not hard to mod the pickup, and install a mechanical pump, and its realyl the "right" thing to do, IMO. No regulator to deal with, or leak for that matter. No mile of fuel lines across the engine either. As far as a problem pulling through the intank, some have problems some dont. I have seen stock engines that cant get enough fuel through the pump in tank when its dead. Seems to be hit and miss.

 

cool, that is basically why I though about this and figured I would pass along an easy, quick, and successful fix for this problem. It is for piece of mind for guys with dead pumps mainly

If a car works "ok" sucking through a dead pump, then it ought to work awsome through a working pump.

 

Consider using a (bypass type) TBI regulator,
then feeding a carb 'dead head' regulator
from the (tbi regulator) supply line.
What would go wrong?

 

the TBI regulator and the deadhead style regulators together could be too much of a restriction.

As I stated earlier unless your engine can consume more fuel than a holley blue can pump at 0.1 to 0.5 psi (huge huge volume no load) you will be fine.

 

B4C...
I don't understand how a bypass-type regulator could
be a restriction,... if you're concerned,
you could simply 'tee off' ahead of the BP regulator,
with any diameter fuel line.(goes to second reg)
Keep in mind what a bp regulator does,
when inlet fuel pressure drops below 12 psi (or whatever),
it stops flowing.

 

sure that would not be restrictive and certainly is more ideal than what I stated in a theoretical sense, but it deviates from the whole simple "tee" idea of this thread

 

Granted, adding a bypass regulator (tbi or whatever)
to the return line is adding complexity, but, it would
seem to me that tbi regulators would be available
from junkyards for next to nothing, I'm surprised
it isn't done more often.

 

a TBI regulator is built into the tower that holds the injectors on the TBI throttle body.

 

Sure, there is going to be some unneeded stuff,
unless you're very skilled with a hacksaw.
.
But an advantage is..., the tbi regulator can be located
anywhere, even near the tank. Its main purpose
is to allow flow, even at times of low engine fuel demand.
The entire supply line is reduced in pressure to about 12 psi.
The supply to the carb regulator can be 'tee offed'
anywhere upstream of the tbi regulator.
A carb 'dead head' regulator is inexpensive.

 

can you show me sume examples of these externalized TBI regulators?

 

Sorry, don't know about any standalone tbi regulators.
.
A bit of caution, if you try the junkyard tbi regulator,
watch out for fuel leaks from the other bs attached to the regulator. An 'off' tbi injector can leak.

 

if you dont know of any then what TBI regulator are you talking about?

 

The tbi you circled, or one like it from a JY.
The regulation, and more importantly, the constant flow,
would be in the use of the 'whole tbi thing', for only
its (bypass)regulation function.
Other bypass regulators could be used here, but i don't know
of any cheap enough to make this worthwhile.

Note, in a 'return' style regulating system, the whole supply line,
from the pump, to the regulator, is pressurized at 12 psi.

 

let me make this easy for you, you cant use a TBI regulator, so unless you are ready to pay for an expensive return style regulator you may as well use the T-fitting suggestion I gave already. In this case the in tank pump which was designed for higher pressures will be free flowing back to the tank, supplying your engine and engine mounted fuel pump more fuel than you could ever dream of using.

 

Note, a 4 psi deadhead, for 20 bucks, would (additionally)
be needed. Using the tbi regulator, instead of (return)
line restriction, enables the full flow of the fuel pump to be available to the carb, if needed.

 

yep too bad you cant use the TBI regulator

 

This is what I'm about to do with my holley regulator, and edelbrocl 750, and walbro 255 pump.

If your gonna do this make sure the relief you use can flow enough to get rid off the extra pressure your pump makes (ie: hook up a cap to your supply line instead of your regulator). I'm using an adjustible relief from swagelok.

 

Pic

 

just pull fuel from the return line. It goes all the way to the bottom of the tank. Actually a little lower than the electric fuel pump. The line that dumps off at the top of the tank is the vent.

 

thats good in thought but what about the line size and restriction you would have ????

 

wow two regulators? you have REALLY over complicated this

Thats right! That must be why it works so well. Based on that little jewel of info here is the new diagram.

 

info confirmed

 

it's the same size line. GM's too cheap to use different stuff

 

returning fuel to the tank via the vent tube will cause vapors to build up in the tank resulting in a really nice fire and possibly explosion

 

Not on my car it wasnt. I did the v6>v8 swap this past winter, and I can say 100% that the return line was definately a different size than the feed line. No doubt about that at all. I still have pieces of the return line in THEGENERAL's garage.

 

That may very well be. I'm just going on the 2 that I've looked at recently. 1 out of a 91 RS V6 and 1 out of a 82 crossfire car.

 

hmm the 91 rs i had also had 2 different sized lines on it ????

so does my gmc we just got done swapping engines in and going from injection to carb....

 

agreed all post 85 efi cars TBI, tpi, V6 all have a 3/8" feed and 5/16" return

 

Interesting read. My 86 was originally a TPI car and has been pulling fuel through the smaller return line for about 4 years now. The only fuel pump I have is the mech pump on the engine. I keep figuring everytime I get some more power out of it that I will start to starve for fuel, but so far so good. I can't pull fuel through the in tank pump at all so it probably needs to come out. This is definately going on the to do list.

 

B4Ctom.... Think i've posted something like this allready once. Only its on my 87 lg4. In 87 carbed cars had both electric in tank pumps and mechanical fuel pumps. There are 3 lines on the mechanical pump. Input, output and return. If you cut apart the pump you'll find the input and return are basically connected(a T). So the intank pump shoves fuel up to the mechanical pump through the 3/8s feed line then is returned to the tank via the 5/16s return line. The mechanical pump then pulls this fuel from the moving stream and pressurizes it to the carb. The difference in fuel line sizes causes a slight positive pressure at the mechanical pumps inlet as well.

The post I made quite awhile ago explained how to install a 2 line performance pump in place of the 3 line when you had an intank supply pump as well. All thats needed is to add the external T just as you have. On my car I screwed the T right into the carter pump and ran lines to the supply and return. I've had no problems for a couple of years now. (except with the braided earls lines I installed recently! )

The only thing I can see that could happen with a tpi or even tbi pump is that their self limiting pressures are much higher then the stock carb supply pump. If a restriction in the return line ever occurs you take the chance of overflowing your carb and filling the motor with fuel. The original carb electric intank pump I beleive is limited to 1psi or something very low like that. No pressure all volume.

 

that is basically where my idea came from, it is not in fact really "my idea". after working on some very late LG4 cars (I think the monte ss did this as well) I saw how the factory did it. It never created a problem for them except when a pump dies and even then because there are two lines under the surface of the fuel to pull through:

1 dead pump on feed line
2 return line

even a restriction of the dead pump affects are so low as to be un-noticed by most owners.

The restriction of the return line never/rarely happens, other wise it would plague EFI owners too.

 

Never say never! Havent seen it in a gm product. But i've had several fords come in with stuck fuel pressure regulators.. 2 in fact actually had raw gas running out of the tailpipe while they ran! Was expecting an explosion the next time I started those.

 

I have seen stuck regulators on fords and pierced/leaky regulator diaphrams on both makes. That lets the fuel get sucked into the vacuum referrence. If your car runs like *** and you have or smell fuel in your Vacuum referrence you know hat it is ripped punctured.

 

Ok this is kind of related, on my buddys 87 IROC, we are going to use the stock fuel line, remove the intank, extend the line, hook up an inline electric fuel pump to the motor.. Use the return line as a second fuel line with a second inline fuel pump to run his nitrous off of.. Any comments or will this theoretically work?

 

I don't see any problems there

 

IMO that is the best way to do it.

 

next question, being that that is a good idea to hook up the fuel system.. his 355 is a pump gas motor pushing about 425-450hp at the crank, adding nitrous (150hp) he should be running a little higher octane than 93, like 100 or C12 perhaps.. yes or no? anybody else in the same catagory? With thought in mind i'm thinking about doing a separate fuel system like i have on my car, 2 gallon fuel cell with C12 for nitrous only..

 

That is how I am running mine on my 86 Iroc. With a holley black I still have a pressure drop from 8psi to below 5psi going down the track.

 

Ok I'm pretty sure I understand all this. I'm swapping TBI to carb. I have the in tank EFI high pressure pump and it still works. And i dont really wanna cut my welded exhaust AND drop my tank to replace the pickup. I have a holly 2 port mechanical on block fuel pump that I can put on. Now all I hafta do is run a T fitting on the mechanical pump and put the return line and the supply line onto the T fitting? Im pretty sure thats what you guys mean. But my question is, Am I supposed to have the in tank EFI pump run with this setup? Or will fuel actually run through the EFI pump with it off? BTW I know the return line is now also feeding the mechanical pump.

 

your factory pump is low pressure

TBI is low pressure

you can run it to the mechanical fuel pmp like Monte SS's did

low pressure in tank pump, to mechanical pump, to regulator, to carb.

Monte's didnt have the benefit of a nice regulator.

You will have to make sure the fan and fuel pump relays are grounded on the sensing lead (you will need a wiring diagram for this) and they will both come on anytime the ignition is switched on.

 

So I don't need to use a T fitting and use the return line for the supply? Also what should I use for a FPR?

 

if you dont want to run a FPR you can do the T fitting thing.

Im not sure if your mechanical pump will operate properly even with the low pressure TBI pump dead headed against it anyways.

 

Why not?

 

What I am saying is use the "T"