okay guys, i got a problem here. i bought an 86 k5. it came from the factory with a 305 4bbl. wheni bought it, it didnt have an engine cuz it was blown up. it took a 350 out of a 77 k10 pickup, and threw it into the blazer. now here is where things get interesting. the blazer has a fuel pump at the tank, that puts out around 60 psi (that number could be wrong. my father is the one who looked at the fuel pump at the tank). the engine has a pump on it, too, that puts out 14 psi. we aren't sure what to do. the blazer looks like it was set up to have fuel injection (whichi dont understand, because the vin and everything says it came with a carb). do we have to take the pump out of the tank, or can we just remove the fuse, or can we use the pump in the tank AND the pump on the engine with the addition of a pressure reducer valve (if they even make one). we are stuck, we don't know what do. can somebody please throw us a bone.

 

You only want about 7.5lbs fuel pressure to the carb.
You have a number of options. I would probably bolt on an aftermarket electric fuel pump on the frame rail, connect to the fuel line on the outlet side of the tank pump, remove the fuse for the in tank pump and bypass the engine fuel pump.

 

we thought about taking thefuse out, but we werent sure if it would still pump the fuel through that pump. why wouldnt the pump on the engine work? its a rebuilt engine with an aftermarket carb.

 

I don't actually know if the fuel would still come through the in-tank pump if you removed the fuse, but you could test it by removing the fuse and just running the pump on the engine to see if you get fuel.
My concern about using the fuel pump on the engine is that you said it puts out 14 psi. I believe that at 14 psi you would have to much pressure into the carb and it would push up on the float, lift the needle off the seat and flood the engine. You could use the 14 psi pump if you installed a pressure regulator between the pump and the carb.

 

Terry,

First of all congrats for making home from worlds largest litter box.[sm=americanasmiley.gif]
If memory serves me correct the first year for factory fuel injection on a K5 blazer was 87.(TBI)
Reading your post I am just a little confused (ok, a little more than normal[sm=smiley36.gif]) In the begining you stated you have a fuel pump (at the tank), but later you ask if you can pull the pump (out of the tank). If the pump is in the tank I would suspect that you have a VERY late production Blazer for the 86 model year. I personally have never heard of an 86 with factory installed fuel injection, but lots of things can happen at the end of a production run (esp when a change is forthcoming,......carb tofuel injection for example.) I have to assume one of the following,without knowing what pump you currently have. (in tank or external electric, stock or after market)
(1) The previous owner installed the pump to try and overcome a pump volume or pressure issue.(maybe the stock pump itself failed)Fuel pumps are better at pushing fuel (withthe pump mounted close to the fuel tank) than pulling it (with the pump mounted to the engine block)
(2) The previous owner istalled an aftermarket fuel injection system, (Holley,Edelbrock,etc)
(3) It truely is a factory installed system (unlikely but possible).

So let's look at some options.
(1) Assuming that the pump at( orin) the tank is functioning correctly, then you could just add a block off plate to the the engine block where the mechanical pump would bolt up. Then add a fuel pressure regulator as close to the carb as possible, set the pressure to 6.5-7 psi and you're done.
(2) You could remove the electric pump, and go back to the old style mechanical pump( with associated fuel lines) and you're done.
(3) You could leave the electric pump in place, connect the fuel line to the mechanical pump, and add a pressure regulator before the carb.
Any of the above will work, but you have to ask yourself how am I going to drive it, what do I want to spend, and how much work do I want to do.
Be advised that with the electric pump, if it doesn't have an internal bypass, (built in) or you don't run a seperate return line, then the pump will "dead head" against the pressure regulator, and over time (and it won't be long) the pump will overheat and wear itself out.
If you decide to leave the electric pump in place but not operational (unpluged, fuse pulled, etc.) and just add a mechanical pump, then you are going to work the mechanical pump harder due toincreased restriction thru the electric pump. (think wear and possible vapor lock issues)

Hope this helps, if you have any questions just ask.

Good Luck,

Gator

 

thanks for all of the advice guys. i think what we are going to do is just go with the pump on the engine. before we pulled it, the engine ran great its whole life, so i think we will stick with it for now. we are going to just pull the fuse for now and then get rid of the pump at the tank here pretty soon. me and my father too are confused as hell about the fuel injection. im getting the car history for it, so i can talk to all of the previous owners about it.



okay, another problem with the old 86. i mentioned in another post that there is an electric fuel pump at the tank. well, it wont shut off. its not all the time though. it has happened twice now. the pump keeps pumping when the truck is off, and kills the battery. there is a small leak in the fuel line, evidenlty, too. it wont leak when the truck is running, oranything. but the two times i shut off the truck and pump has stayed on, it hasforced it through the tiny *** hole. any ideas as to why it's not shutting off all the time? you can read about my other problems in my other posts, if you have any questions.


To avoid confusion and keep the information all in one thread, moving post to dueling fuel pumps.

< Message edited by Chevy Lover -- 12/7/2007

 

okay, another problem with the old 86. i mentioned in another post that there is an electric fuel pump at the tank. well, it wont shut off. its not all the time though. it has happened twice now. the pump keeps pumping when the truck is off, and kills the battery. there is a small leak in the fuel line, evidenlty, too. it wont leak when the truck is running, oranything. but the two times i shut off the truck and pump has stayed on, it hasforced it through the tiny *** hole. any ideas as to why it's not shutting off all the time? you can read about my other problems in my other posts, if you have any questions.


To avoid confusion and keep the information all in one thread, moving post to dueling fuel pumps.

< Message edited by Chevy Lover -- 12/7/2007 2:31:29 PM >

 

So what is powering the in tank pump and why can't you remove the power to it?

 

we thoughtit would be a fuse, but, we cant finda fuse to it. so i guess we'll just have to trace the power. honestly i dont want to pull the power to it, cuz im afraid it will burn up the pump in the engine. but i guess ill have to, since we cant figure out why it wont shut off when the truck is turned off.

 

Are you using the engine oil pressure switch from the '86 or the '77?
The wiring for the '86 may have a feed wire to the fuel pump that feeds the pump after the engine is running. ( this is designed so that if the engine loses oil pressure the fuel pump sill shut off)