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Computer to old school engine swap

2K views 7 replies 6 participants last post by  BogiesAnnex1 
#1 ·
60's hotrodder decided to swap 4.3 with my dream 350 sbc built to spec.
install completed now fumbling thru wiring. Question ? WANTED TO JUST HERE MY NEW MOTOR RUN, wired my s-10 extreme fuel pump direct and it completely flooded my df holley! HOLY CRAP almost a disaster... I did not have the fuel regulator on yet is that the reason? too much fuel pressure what do you think . Is a return line a must.
Already drained engine and back to the drawing board.
 
#2 ·
Yup.. Too much pressure and flow for the carb.. Sooo get a good regulator with the bypass return line and install that so you have proper pressure and flow to the carb and you are golden.. BTW I have found the good regulators to be a 100$ bill or so,,

Sam
 
#3 ·
just to clarify..


almost all FUEL injection systems that have a return line have fuel pumps without a bypass. they don't like to be dead headed... they will over work and burn out..

you have several options with fuel pumps also...

vortec fuel pumps put out like 90 PSI max..

TBI fuel pumps put out like 33 PSI max..

the few fuel pumps from the 85,86,87 model years where cars and trucks were equipped with either fuel injection of carb had fuel pumps that put out 4 or 5 psi.. airtex E3903 is one that will install.. in most gm fuel injection type tank hangers... with a proper strainer..

Airtex Electric In-Tank Fuel Pumps E3903 - Free Shipping on Orders Over $99 at Summit Racing

you might be better off with a TBI pump... and the return type fuel pressure regulator ..

a huge tip..

from 1984 thru 2002... gm trucks and most cars had a redundant fuel pump power supply system..

they have a fuel pump relay .. it has a orange wire with constant power.. the grey wire goes to the fuel pump.... the black wire is grounded and the green wire with the white stripe is switched positive from the PCM.. so when you turn the key on.. the computer turns on the pump for 2 seconds.. and then will turn it on again while cranking.. keeping it on in most but not all..


the oil pressure switches... some have 2 oil pressure switches a single wire for the gauge and a double wire version that is in parallel with the fuel pump relay.. orange wire hot and grey wire to the pump. . so when the oil pressure comes up this switch closes across the terminals and sends voltage to the fuel pump.

the 3 wire oil pressure switches used from the early 90s to 2002 or so.. have the orange power wire on one side.. the gauge wire in the middle and the grey wire to the fuel pump on the other..

the tip... install the oil pressure sending unit that came with the vehicle so the gauge works.. but also so the fuel pump gets powered with oil pressure.

but you can... with skill... attach the green and white stripe wire to the yellow or purple wire to the starter solenoid.. so the fuel pump relay comes on while cranking..

how to tell if your oil pressure switch fuel pump contacts are working.. with the engine running.. unplug the fuel pump relay.. if the engine dies.. then the oil pressure switch is not working.. this is a test i do on many TBI and Vortec motored cars.. it also works on TPI and PFI...

just a few thoughts.
 
#4 ·
Need the year of the Extreme for exact parts recommendation, but generally what you will need if you don't replace the factory in-tank pump with something that develops less pressure what you will need is a bypassing regulator because the fuel pressures used on EFI is way above what a carb will work with. TBI systems use 10-15 psi and port injection systems use 40-60 PSI where a carb uses 4 to 6 psi.

A by-passing regulator is needed because some of the earlier EFI's use continuous running pump designed around max flow requirements these bypass back to the tank the unused fuel portion when operating at less than full throttle. Newer versions of EFI use a speed or duty cycle regulation scheme from the computer to control the motor which then controls line pressure at a constant regardless of the volume being consumed. Since I'm assuming the computer is gone, you will have the pump running at full output all the time so a bypassing regulator will return unneeded fuel back to the tank. If your model doesn't use a return you'll have to plumb such a circuit from the regulator back to the tank. Without a by-pass the pump will overheat and fail if not start a fuel fire. These fuel circuits all use high pressure fuel injection rated hose the only exception to that would be from the regulated output to the carb.

Bogie
 
#5 ·
Thanks for the information, it's a 2000 extreme i've had since new and finally went for the gusto, I may have put in alittle more motor than I should have but its for as much show as anything, 350 putting out alittle over 400 hp just to hear it run today I put a holley fuel regulator w/ return line back to the tank. only thing is I am by passing fuse box for now as all computers are gone.... I wanted all old school
when I first toggled pump on I got 7 psi at the carb and rear bowl pushed out fuel, found that needle stuck
freed that and reinstalled and started pump again and no leaks or push back. pulled the trigger and holly crap what power... still have open headers so didn't want to upset the nabors so shut it down
do you think 7psi is too much for the 750 holley?
 
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