Fuel Pump: 2 Line VS 3 Line.

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Jul 3, 2018
Annapolis, MD
Hey y'all, background info:
1972 Olds 350 being put into a 1987 El Camino. The El Camino has three fuel lines, and an in tank pump. On the new engine, I have installed a 2 line mechanical fuel pump.
My question:
What are the three line vs two line uses? Without having to buy and install a different pump, what modifications may I have to do to use the two line pump in the 3 line car? How would I remove the in tank pump and set up the tank for a mechanical two line system?


Nov 15, 2014
Des Moines, Iowa
3 lines. as said, vent, return, feed. not all had all 3.


Comic Book Super Hero
Supporting Member
Jan 4, 2009
Wellston, OK
Sounds like the Camino was injected, which is likely going to be more pressure than a mechanical pump can handle. Either use the in-tank pump and regulate the pressure down to 6 pounds, or pull the pump/sender and install an earlier sender without pump for a carburated application, using the mechanical pump on the Olds engine.


Aug 2, 2018
New Orleans, LA
Last edited:
Oct 14, 2008
I have used these in both 2 and this 3 line with good results. https://www.summitracing.com/int/parts/crt-m6109/make/oldsmobile You can use the inline tank and regulator or add a higher pressure pump for an aftermarket EFI. With a 454 TBI with factory Qjet intake adapter, 307 CCC distributor and even just a sbc 350 prom or whole computer, you can run TBI on your Olds 350, especially if you are running the stock cam. I can tell you, the timing needs advanced about 20 degrees over stock to run the sbc swirl port tune.


Feb 10, 2018
the original factory 3 line purpose is to help keep the fuel supply cooler,,

,less knocking ,less boiling of fuel in stop and go driving
and not pressure change related,,,however,, corvette and hi-po 350s pumps did have a slight pressure increase as in the old 2 line pumps,,
also,,the pumps exit -entry line direction vary ,per application , which would mean a new steel line to carb,, if you mis-order..
so better off going to napa-autozone, oriellys etc, for fast return,,turnaround,,visual inspection,, and if not in stock, you can look at their screen for pics of pump bottom to gauge outlet directions...
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