EFI with factory Fuel Tank??

[stevencvn72]

So this is my first post on the first forum I've ever found worth reading. I've already learned vast amounts and enjoy the "build" threads emencly. Here's my question. New project is a '67 step, 305 ('85 IROC Z I suspect) EFI with a 700R4. The previous owner routed pick up and return lines and tapped into the factory fuel tank along the bottom corners using JB weld and parts from the local hardware store. Is there a reason that the origional pick up line couldn't be used? Are these EFI pumps too weak to draw the fuel up the line? As unorthadox as it may be I like the tank behind the seat. I have since ripped out the old tank (due to leaks around the previously stated JB weld and hardware) and have a new one poised for the next move. Does anyone have any expirence with this matter? Forgive me if this is elementry or if I've posted this thing incorrectly. Forums are new to me...just like EFI.

[Gray Ghost]

I don't know of anyone running the stock tank and EFI. Not sure why you want it behind the seat, but the blazer tank lends itself well to EFI setup and it mounts under the bed out of the way [no fumes]!!

[stevencvn72]

I figured plenty of people would try to talk me into the K5 tank route. I dunno why, but I guess it's just the nostalgic feel (and smell) of the tank behind the seat. (my first truck was a '53). So....back to the origional question.

[Blue_71]

steven, youll be happy to know I too like my behind the seat tank and am running efi!! (throttle body from an 89 truck) i havent excactly perfected it yet though.. if i manage to get it running 100% correctly, i'll post my results and how i did it... i'd hate to give someone incorrect info on something as dangerous as fuel!!

[FuelCellGuy]

do you still have the stock fuel pump drive on the engine?

[PHAT TONY]

I think if you use a "self priming" in line pump on the frame you should be good; I hope 'cause that's what I'm doing with a tbi motor in my '67 with stock tank(I don't know why either!) If yours is tpi then you need WAY more pressure than me, but still doable.

[stevencvn72]

There is an electric pump mounted on the frame rail just below the driver door. I have heard these pumps are better at pushing fuel than sucking it in. I suppose that's why most EFI engines have the pump in the tank. My plan is to use the stock pick up and secure a return line in the dimple adjacent to the pick up in the sending unit. The origional set up (fyi) with a pick up on one side of the tank, and return on the other had issues when the tank was about 1/4 full due to sloshing around corners. A center pick up (physics would tell me) shouldn't have the same problem to such a degree.

[svgould]

I'm running an LT-1 EFI motor and am using the stock behind the seat tank. I did exactly what you describe........used the original pickup tube for the feed and then soldered a second tube into the sending unit for the return. My inline pump is mounted on the framerail. I have had no problems with this set-up. I read somewhere that the return line should extend down into the tank and be submersed in the fuel to eliminate static charges (if this is true or not, I do not know), but I did extend mine down to the same level as the pickup tube. By the way....Welcome to the forum!!

[TP from Cntl PA]

I have my 250 EFI running out of the stock tank........No issues. Welded a bung on the sending unit for a return and ran hose next to the feed up to the engine compartment.

[DirtyLarry]

’72 C20 TBI 5.7L running a frame mount electric pump and stock tank. No issues to speak of.

[LockDoc]

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I bought a book on TPI installations and the guy that wrote it recommends a 78-81 Nissan/Datsun 280ZX external pump. Advance Auto Parts online # is E8312. When I looked it was $107.98.

LockDoc

[leatherhead63]

I am using the tank behind the seat with a in line fuel pump (Summit brand) to run a 5.3L. Works great but the fuel pump is louder than the engine. Maybe someone else has a brand or model number that they could recommend. I have heard the in tank pump is quiet, but have not found any info on the set up yet. I do have problems if my tanks gets below a quarter tank. Working on a solution. Glad to see others are having success. Love the forum

[stevencvn72]

Thanks a ton for all the responses. I'm siked I took the plunge, swallowed my pride and posted a thread on this topic. Looks like running parallell lines through the sending unit will be my master plan. Good note BTW about the static discharge on the return line. Thanks Svgould! Leatherhead, my pump is pretty loud too. I'm guessing that's why someone caked silicone all around it. Not really sure if that's helping or not, however I have heard that OE pumps are quieter than aftermarket. Not really sure how true that is....anyone else? SVgould, what type of pump are you running? Are all EFI pumps self priming? What type of pressure are we talking about? The LT1 service manual calls for about 44-47 psi. Questions, questions, questions...I know.

[DirtyLarry]

Originally Posted by leatherhead63

I am using the tank behind the seat with a in line fuel pump (Summit brand) to run a 5.3L. Works great but the fuel pump is louder than the engine. Maybe someone else has a brand or model number that they could recommend.

I had that same problem on my ’78 with an 8.1L. Same Summit house brand pump too and the hotter it gets the louder it gets. Very annoying. I fixed it by removing it and going to an in tank pump.

However, my ’72 is running a Walbro frame mounted pump that I bought from a board member and it is surprisingly quiet. You can hardly even hear it prime when you first cycle the key.

Stevencvn,

Oh, yeah…the original ’72 sending unit already had a return line into it whereas, I think some of the older sending units do not.

[jorgensensc]

When I stuffed an LT1 in a '91 S10 I bought an in tank fuel pump of a 4.3 fuel injected s10 blazer. It were super easy since all I did was cut off the pick up tube and use the provided rubber hose to connect the Fuel Pump. Super easy!! I just made sure the bottom of the sock for the fuel pump was at the bottom of the tank. It seems the sending unit opening will be big enough t get the pump through. THen just route the wires through the sender and add your return fuel line to the top. You could probably use a '72 sender with the smog extra return line, maybe. Check on that. Hope this helps a little!
Shawn

[svgould]

Originally Posted by stevencvn72

SVgould, what type of pump are you running? Are all EFI pumps self priming? .

I'm running a Walbro, but don't remember the part number of it. The whine is a little loud, but nothing my headers and Flowmaster 40 series can't cover up

[clay68c10]

I've got the Holley TBI pump and the only time I hear it is when it primes. I mounted it to the rear floor brace of my cab. It looks like a wallbro in a Holley box.
My 68 sender doesn't have the return so I made one thru the sender. I ran it to the bottom and pointed it away from the pickup. I figure it won't make a waterfall noise when the level is low and it won't do any kind of 'swirly' vortex thing and introduce bubbles to the suction side when the tank is low.
That said, since there isn't any kind of sump in these tanks, I don't let the level go below 1/8.
So far, it's been about 2 years and I've had zero problems.

[lofly'a]

and i've read for years in lots of forums and mag. articles that these setups would'nt work. go figure.

[stevencvn72]

I like the idea that the '72 sending units have two lines into the tank. Is there anybody out there that has a '72 that can confirm this? I have to get a new sending unit anyways.

[Lugnut64052]

Originally Posted by stevencvn72

I like the idea that the '72 sending units have two lines into the tank. Is there anybody out there that has a '72 that can confirm this? I have to get a new sending unit anyways.

Yes, the '72 unit has two lines. I've been mentally working on the idea of putting a stock pump in the bottom of the tank myself but haven't done any actual work on it yet.

One problem is that the return tube on the '72 unit is pretty small. Looks too small to me. I'm planning to de-solder the stock return tube, drill the hole out a little, then solder in a bigger tube for the pressure side, then use the original supply tube for the return.

Problem #2 is getting the wiring harness into the tank somehow. The metal "lid" at the top of the unit is pretty small - much smaller than later injected vehicles, which doesn't leave much room to install a pass-through wiring bulkhead. I thought of a workaround, but like Blue_71, I'm going to sit on the idea until I see if it actually works or not.

I like the behind-the-seat tanks too, and other than those two issues, I don't see much of a problem with setting one up.

[DirtyLarry]

Originally Posted by stevencvn72

I like the idea that the '72 sending units have two lines into the tank. Is there anybody out there that has a '72 that can confirm this? I have to get a new sending unit anyways.

Here is my ’72 C20 with a TBI 350 sending unit with a factory return line. With the low fuel pressure TBI runs I haven’t had any issues running the return fuel through the little 5/16 line.

However, I wouldn’t recommend the little 5/16 return line on a higher pressure TPI system that runs in the 40 psi range or the later LS engines run up as high as 62 psi. The 8.1L in my ’78 K10 did not like the small 5/16 return line through the original fuel tank switch valve as it was way too restrictive causing the fuel pressure to run extremely high….like a 100 psi at idle! I ended up having to completely redesign the fuel system on that truck to create a larger return line and still have dual fuel tanks.

Again, this will work for low pressure TBI but not for higher pressure multiport.

[Lugnut64052]

Originally Posted by DirtyLarry

With the low fuel pressure TBI runs I haven’t had any issues running the return fuel through the little 5/16 line.

Again, this will work for low pressure TBI but not for higher pressure multiport.

Hey, thanks for the tip! I'll try it as is.

[sick69]

For those of you with loud electric pumps,,,,,Are they mounted with any form of rubber bushing between the frame and pump or are they in direct contact with the frame? I would think some form of insulation between the frame and pump would help quiet it down.

Great info in this thread! I have been collecting parts for a multi port injection install this summer so any info on it is much appreciated!


So the blazer tank is an easier set up to use with efi? I was alreeady planning on using the blazer tank and have noticed two extra ports. Haven't really looked at the outlet though.


Frank

[leatherhead63]

My loud pump is mounted with rubber pads and is loud. i pulled it away from the frame and let it just hang for a test and it is still loud. Works good just loud. Maybe its the summit brand. I may just try a different brand but more likely modify the sending unit for a in tank pump

[sick69]

Well it was a thought,,,,


Frank