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mechanical fuel pump


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frickenbored's Avatar
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April 10th, 2011, 11:26 AM   #1  
mechanical fuel pump

So I think my mechanical fuel pump on my chevy small block is going bad. I don't know too much about these things. I have a small fuel pressure gauge in line between the fuel pump and carb, at idle it reads 4psi and when I hit the gas it'll will rise to about 5.5psi. I thought the psi was supposed to be constant at all rpms and I'm pretty sure the psi should be between 7 and 9.

Heres the thing when I swaped my tbi 305 out I didn't even attempt to remove the electric fuel pump from the tank because the tank straps are rust welded to the body and the tank, I didn't even want to attempt anything back there. So my mechanical fuel pump is just pulling the fuel through the electric one.

My question is is there really going to be enough drag through the electric fuel pump to cause 4psi or is my mechanical fuel pump going bad since the psi is moving up and down. Plus after I park the truck overnight the fuel line from the pump to the carb is dry and it takes about 4 cranks of the engine to fill it back up.

Now I also know I can just go ahead and use that electric fuel pump with a regulator. I can wire the pump to a toggle switch, then I believe the line from the tank goes into the regulator then a return line (which is think i left in the truck from the tbi system) goes back to the tank and the regulated fuel goes to the carb. But eventually that fuel pump is going to go bad and I have no idea how old it is so I'm leaning more towards keeping the mechanical fuel pump.

 
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April 10th, 2011, 11:36 AM   #2  
acutally I just took a look at my mechanical pump and I have the return line hooked up to it so I don't even have to run one back there. I'm just worried about that electric pump going bad and then i'm screwed.

 
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April 10th, 2011, 12:08 PM   #3  
I would try to use the electric one and bypass the other. For the older chevy's there only about 60 to 70 bucks,if they go bad. No more air in line. Quicker start ups in cold weather. Just wire it to a hot on ingintion wire. Also you can check out the fuel level sencer. Get it over with and you probabley wont ever mess with it again. Hopefully.

 
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April 10th, 2011, 1:28 PM   #4  
I think what I might do is cut a hole in the floor right over the fuel pump and then put in a door or something, that way I wont have to drop the tank, plus I'm prob gonna run a new wire from the pump to a toggle switch (I'd rather go to a toggle switch than an ignition hot, just a personal preference.) I have no idea where the old wire is anymore since the fuel pump relay is gone and all the old wiring is mostly gone.

If I can easily get to the fuel pump from a hole in the floor then I'll just replace the pump and run the wire. I think i still have the block off plate from my old 305 for the mechanical pump.

So is it really as easy as running a switch for the electric pump, then hooking up the feed, return, and carb fuel lines?

 
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April 11th, 2011, 7:55 PM   #5  
Well I don't think it's that easy. I hope it is. A good electric pump can go 8 to 10 years. If its a good one so don't try to get a bargin. Get a Delphi if you can. Talk to a mechanic. Last time I did that was more than 10 years ago. What I had trouble with was I had more lines out of the tank than I new what to do with.

 
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April 12th, 2011, 8:38 PM   #6  
Posted By: lowred1 Well I don't think it's that easy. I hope it is. A good electric pump can go 8 to 10 years. If its a good one so don't try to get a bargin. Get a Delphi if you can. Talk to a mechanic. Last time I did that was more than 10 years ago. What I had trouble with was I had more lines out of the tank than I new what to do with.
I'm not worried about that, this truck was fuel injected a little under a year ago. The TBI had a fuel feed line and a fuel return line. When I switched over to a carburator I just bolted on a mechanical fuel pump and took that same fuel feed line and same fuel return line and hooked them up to the mechanical pump (the return line isn't needed but it was there so why not, and I guess it helps cool the gas or something like that. So I don't have to mess with anything at the tank plumbing wise. All I have to do at the tank is find the hot wire so I can bring it up to the dash.

So the point is...GM already did all the plumbing for me in 1988 lol. All I gotta do is hook up the lines to a regulator and run a line from the regulator to the carb.

heres the simplified picture from the holley instructions:

 
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April 15th, 2011, 8:48 AM   #7  
Sorry took so long, having trouble with email. You should end up at tank with 3 wires. Gnd, Level sencer, and of course pump. Hook it up to hot with ingnition. DON'T USE A TOGGLE. If something goes wrong with regulator or anything like that in the fuel line, it's safer if you just shut if of when you turn the key. You could have like 60 PSI coming out of the line all over the place. Not good if you have a fire. No point in trying to put it out if the pump is running. Anyway good luck.

 
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April 18th, 2011, 11:28 PM   #8  
thanks man, I gotta get that regulator ordered. Ill think about wiring it to an ignition hot, I'll have to find one in the sea of wires behind the dash, my fuse box is all taken up.

 
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