Fuel pump and other wiring issues

[RoryH19]

To add, I have to ask since this may be new to you, is the rod that actually moves the lever of the mech fuel pump installed? The cam will not be ale to work the pump if not there.
Also, many SBC's have the ability to use a bolt to hold the rod up while a pump is changed.
May be worth a look.

 

[80BrownK10]

I'm working on a 84 k1500, and I have a 350 in it. At the end of the swap, but I'm struggling on the wiring side. There's a few different issues I'm having.

1 - My junction block wiring. I can't find a diagram I can make sense of for this junction block. The drivers side post has a couple wires on it, but currently I don't have anything hooked up to the other side. What goes there?

2 - I'm pretty sure I have some issue with the tank fuel pump wiring, since I don't have any fuel getting to the mechanical pump on the engine. Where would I find the wiring (in the engine bay?) for the pump?

3 - I have one constant hot wire coming off the bulkhead wiring, but I don't know where it goes, any suggestions?

Thanks for the help!

Power wires to mechanical fuel pump?

 

[80BrownK10]

Ok, thanks for the clarification, I wasn't thinking I had a pump in the tank, and then someone told me I did so that's what I went with. When I pulled the other engine (305) the pump worked. I can get a new one for pretty cheap, but I'm curious what the lobe is. I cranked for a long while, with no fuel coming through. I'll test the pump and see if it needs replaced.

The hot wire is coming from the bulkhead wiring, I just didn't know of anything that needed power constantly.

Hood light that you don't have...has an inline switch maybe?

 

[80BrownK10]

To add, I have to ask since this may be new to you, is the rod that actually moves the lever of the mech fuel pump installed? The cam will not be ale to work the pump if not there.
Also, many SBC's have the ability to use a bolt to hold the rod up while a pump is changed.
May be worth a look.

Good call. If someone just bolted the pump there not knowing?? But unless the fuel pump was stripped off old motor and rod fell out or someone just bolted it in place without a rid , I don't think that would be the case.

 

[leviwatson]

If the new engine uses a carburated fuel system - with a mechanical fuel pump - the wiring required to make it run is really simple. But before you get into the wiring, you need to confirm an adequate fuel supply into and out of the carburetor along with a proper spark. Do it like this:

1. Release the supply line from the pump at the carb inlet and separate

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2. Attach a rubber hose to the end of the steel tubing

3. Lead the other end of the hose to a container (12 oz. beer bottle is fine)

4. Disable the ignition system by disconnecting the power to the coil primary. This will prevent a fire.

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5. While you hold the rubber hose in the container, have an assistant crank the engine.

Fuel pump should supply 1/2 pint (8 oz.) or more in 15 seconds.



If fuel supply to the carburetor proves sufficient, reconnect the power to the coil primary.

The next check is that the carb is supplying fuel to the cylinders.

1. Get a can of ether (starting fluid).

2. Then while your assistant cranks the motor over, shoot a few short blasts of starting fluid directly down the carburetor throat.

3. If the engine fires up, and then quickly dies out, it would suggest that the carb is not supplying gas to the cylinders.

4. If it doesn't even kick over, that would point to a problem with the ignition system (i.e. a lack of spark)

Ok thanks for that great info! I'm at the point of not getting fuel to the carb. I replaced the fuel pump today, thinking that could be the problem, but there's still no fuel reaching the carb. Any ideas on why this would be? There should be sufficient fuel in the tanks. When I sucked on the 5/8" line, no fuel came out, and there was no vacuum created, I'm not sure if there should have been one? It just kinda gurgled on the other end of the line. Thanks for the help!

 

[Frankenchevy]

Do you have a return and supply line into the engine bay? My sender has a 3/8” fuel supply, 5/16” return and 1/4” vent. Did you possibly hook the return line to the supply feed on the pump?

 

[leviwatson]

Accidentally double posted and can't find delete ha

 

[leviwatson]

To add, I have to ask since this may be new to you, is the rod that actually moves the lever of the mech fuel pump installed? The cam will not be ale to work the pump if not there.
Also, many SBC's have the ability to use a bolt to hold the rod up while a pump is changed.
May be worth a look.

Yes, the rod is installed, and I pushed it up prior to installing the pump. Thanks!

 

[leviwatson]

Do you have a return and supply line into the engine bay? My sender has a 3/8” fuel supply, 5/16” return and 1/4” vent. Did you possibly hook the return line to the supply feed on the pump?

I have two solid gas lines coming along the frame to the pump. One is 5/8", one is 1/4". They fit onto the 2 nipples on the pump, and there is a threaded fitting that runs to the carb intake. Fairly positive I can't run it any other way.

 

[leviwatson]

Power wires to mechanical fuel pump?

I thought I may have a pump in the tank that sent fuel to the mechanical pump... my first time working with a mech pump.

 

[leviwatson]

Hood light that you don't have...has an inline switch maybe?

Hmmm I'll have to look at that. Thanks! I plan on doing a more in depth post on the wiring when I have daylight to take photos with everything. Chasing the fuel for now ha.

 

[chengny]

Ok thanks for that great info! I'm at the point of not getting fuel to the carb. I replaced the fuel pump today, thinking that could be the problem, but there's still no fuel reaching the carb. Any ideas on why this would be? There should be sufficient fuel in the tanks. When I sucked on the 5/8" line, no fuel came out, and there was no vacuum created, I'm not sure if there should have been one? It just kinda gurgled on the other end of the line. Thanks for the help!

There should be sufficient fuel in the tanks.

Ah, you failed to mention that the truck is equipped with dual gas tanks. Not that it matters at this stage, but that is the type of info you should share when asking for help.


When I sucked on the 5/8" line, no fuel came out, and there was no vacuum created, I'm not sure if there should have been one? It just kinda gurgled on the other end of the line.

I think you mean when you sucked on the 3/8" line - you got no fuel or vacuum. That is the supply line to the pump.

What do you mean when you state that "it just kinda gurgled on the other end of the line"? In the tank? Are the lines all connected? Or are they open to atmosphere?

Does your tank transfer valve appear to be shifting from the left to right tanks? If the tanks have significantly different levels, a good way to confirm the valve is shifting is if the gas gauge shows a discernible change when the L/R control switch on the dash is toggled. To achieve a full shift, the switch must be held over for at least 2 seconds.

Take a close look at the plumbing that connects to the Pollak valve. There should be two (2) 3/8" lines that run from each tank to the valve and one 3/8" line that runs forward to the fuel pump. Also one (5/16") return line coming back from the fuel pump and two (2) 5/16" lines that run back to the tanks.

There's something wrong here. You should have got a mouthful of gas and/or been able to develop a vacuum in the supply line to the pump.

 

[Snoots]

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Yes, the rod is installed, and I pushed it up prior to installing the pump. Thanks!

That rod will drop if you don't have it held in place. There is a bolt in the front of the block that is there to keep oil from coming out. IIRC it's a 3/8-16 x 3/4". Temporarily replace it with a longer (1-1/4") bolt while you are holding the rod up. Install the pump and then swap the bolt. If you don't have that short bolt in there you will have a delightful oil leak.

 

[80BrownK10]

I thought I may have a pump in the tank that sent fuel to the mechanical pump... my first time working with a mech pump.

You do have a wire that goes back to the tank, but it's for the sending unit... probably adding to you confusion?

 

[80BrownK10]

Let's simpleize this thing so you can narrow down components or systems. Do you have an old lawn mower tank or boat tank that you can gravity feed this thing from or lay on ground to see if pump is working? If you gravity feed the carb you can run it and prove if your engine is good. If you lay the tank beside the truck and hook it up this will show you that everything from pump forward is working of that runs.

I think you may be sucking air somewhere in your fuel lines and so you can't overcome that leak to get fuel to the pump.