73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: lilkiduno on August 13, 2016, 07:18:22 pm
-
Okay, hopefully this is in the right section. My father and I purchased a crate engine (The L31-R) and swapped this into h is 1986 Suburban with a Holley 750 Carb. When we purchased this crate motor we didn't see that we couldn't use a mechanical fuel pump so we have been using universal electric fuel pumps mounted on the frame. The first one ran for a year without problems. Because electric fuel pumps are meant to push and we have it pulling from the tank trough the factory sending unit and put the universal 12 volt pump on the frame rail were the hard lines were already running. Once the first pump went out we have had nothing but issues since. We tried a carter inline canister style and that lasted a few weeks before it wouldn't push enough pressure. then the second universal (holley red knock off) pump wouldn't supply enough pressure out of the box. it would initially pump 5.5 lbs of pressure and as it ran the pressure would drop down to 2 lbs in a few minutes. The third universal pump was pushing way too much pressure. the pressure gauge is a 0-15 psi readout and it pushed all the way past 15 and was pegging on the back side of the 0 psi peg. we shut it off really quick, bought a fuel regulator and sat it to 5.5 psi. however not the pump gets too hot and then loses pressure.
So after doing some looking around it would appear there are guys that run a 87-91 r10 pump and sending unit assembly and upgrade the pump when doing ls swaps. Can we use the factory pump sending unit for a submerged fuel pump. can I either hack off the threaded portions of the feel line and attached the rubber lines to the feed line and regulate the pressure to 5.5 lbs. Also the wiring is different so I am kind of confused about he pump power vs the sending unit fuel level wire. I don't mind chopping the weatherpak connector and crimping the sending unit wire and the pump power wire but I do not know which would be which.
https://www.amazon.com/Spectra-Premium-SP12L1H-Assembly-Sending/dp/B000VB0ZQ2
Here is the pump/sending unit I am thinking about
-
1) i don't trust spectra quality, so why not just use a GM pump?
But if you're going to drop the tank anyways, then it's easy to mount an external pump below tank level.
2) If you are going to use an in-tank pump then i'm concerned that regulating it down to 5lbs or so for a carb, would this strain the pump? i don't know? Would a return line help?
i ran into the same problem as i found out my new engine also does not have anywhere to mount a mechanical pump.
But there ARE electric pumps that can self-prime. See this thread:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=33205.0
Granted it's only been on the truck for about 2 weeks, but it seems to work well.
-
Do you still have the old engine wiring in the burb? On my 91 crew cab i put a Cummins in it and kept the stock oem fuel pumps from the tanks. I just used the gm oil pressure switch and kept it wired in. Once the oil psi reached 3 psi it will kick on the fuel pump. Keep your regulator in place and either run the oil pressure switch or hot wire the fuel pump while the key is "on" (but you have to worry about accidents and the fuel pump not shutting off) or you can buy aftermarket fuel pump switches that will prime the engine for 3 sec then as long as the distributor is receiving 12v it will give the pump power
-
As Stewie says there are self priming fuel pumps that can be mounted on the frame.
You can use a bypass regulator with TBI in-tank pumps that feeds excess fuel back to the tank through the return line. The good quality Delphi Sender and Fuel pump assembly is roughly $200-$220.
If you use in-tank pumps get the 87-91 RV series TBI tank with the baffles. The 87-91 TBI senders will fit the earlier tanks but they could pump air occasionally without the baffles.
-
Sorry guys for the no reply. I ended up putting a bypass regulator before the carb which got the pressure down to 10 psi. Need to get it down below 7 psi. Idk if the return line is too small. 3/8 feed bypassing into a 1/4 return line. Going to red neck it and see what the pressure is with the non-bypass regulator after the bypass regulator to knock down the extra 3ish psi. If it runs dependable for a while like this I'll run it until that pump kicks crap then either go with a Holley red/blue or get one of the self priming pumps that was posted in the other thread. If running the in tank pump means replacing the tank for the baffled tank I really would like to void that since the tank in it is only a year old.
-
So what tank and pump do you have now?
-
3/8" or at least 5/16" return would be more like it.