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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 425hp87chevy on November 26, 2009, 07:11:09 pm

Title: Fuel pump return ?
Post by: 425hp87chevy on November 26, 2009, 07:11:09 pm

I bought a truck and they had the return on the fuel pump blocked off and the return on the tank blocked off. Would there be any explanation for this, and what will it affect (fuel millage, performance, idle)?

Title: Re: Fuel pump return ?
Post by: campcrf on November 26, 2009, 08:14:36 pm

i dont have a return line on mine either. I blocked mine off aswell when I put the stroker in... it uses all the fuel it pumps, so therefore the return line is not needed.... (mechanical pumps are on demand if i am not mistaken)

  hope that helpes a little

Title: Re: Fuel pump return ?
Post by: 425hp87chevy on November 27, 2009, 05:01:23 pm

If my engine is not burning all the gas the pump is pumping would that make it flood or a least be hard on the pump?

Title: Re: Fuel pump return ?
Post by: campcrf on November 30, 2009, 10:18:28 am

hmmm?... I am not sure.. I'll get back to you later tonight.

Title: Re: Fuel pump return ?
Post by: SUX2BU99 on November 30, 2009, 10:34:15 am

Is your pump mechanical or electric? Your name indicates an 87, which would be electric fuel pump on the TBI system right? Most electric systems, or at least the older ones anyway, had return lines. Some newer systems are better at being 'on demand' and don't require on. I'm really not sure if or why a mechanical setup has or would have the return line since it's entirely RPM dependent.

Title: Re: Fuel pump return ?
Post by: Captkaos on November 30, 2009, 11:30:07 am

If it is an 87 and you are running EFI you have to have a return for the excess pressure to bleed back to the tank.

Title: Re: Fuel pump return ?
Post by: 425hp87chevy on December 02, 2009, 08:46:15 pm

yes its an 87 but it converted to carburated with a manual fuel but there is a return on the pump but it it blocked off

Title: Re: Fuel pump return ?
Post by: Layne on December 03, 2009, 04:59:54 pm

hmm. My 250 didn't have a return, and when I dropped my 305 in, the fuel pump had a return, but the guys at O'reillys said it wasn't really necessary. I bought a new pump for my 400  and I got one without the return. I think it's an evap thing or epa. hope this helps any.

Title: Re: Fuel pump return ?
Post by: Captkaos on December 03, 2009, 05:13:43 pm

If it is mechanical, it won't "hurt" anything.

Title: Re: Fuel pump return ?
Post by: Stewart G Griffin on December 03, 2009, 10:46:32 pm

Quote from: 425hp87chevy on November 27, 2009, 05:01:23 pm

If my engine is not burning all the gas the pump is pumping would that make it flood or a least be hard on the pump?

This is an excellent question, and i think Hauling it pretty much summed it up in another post;  Basically when the float in the carb "closes off" flow to the bowl, the pump basically "freewheels,"  and no fuel goes into the carb ASSuming everything is working right----the float is at the right level and the pump produces LESS lbs. of fuel pressure than what the float is producing in terms of resistance in lbs.   i think?

i used to worry about this too, but then i realized the power of buoyancy----have you ever tried to push a beachball or basketball underwater in a pool?  Not easy.  Well, i think the same thing is going on with the float in the carb.

Title: Re: Fuel pump return ?
Post by: 78 Chevyrado on December 04, 2009, 08:54:58 am

my 78 3/4 ton has a mechanical pump and never had a return line.