Fuel Pump Woes and Questions

[Ricko1966]

I take the pump out. Hook up a remote start switch. Push in on the pump push rod with 1 finger and squeeze the remote start switch. No the scientific, but you can feel if the pushrods moving, or just barely moving, or not moving.I am braver than most you may want to remove the pump plate also . I don't but as said I'm stupider than most.

 

[Bextreme04]

Roger that, thanks for that Ricko!

Still, I think I'll tear into her this weekend, and get rid of the Mr. Gasket electric, install a new mechanical pump, blow out all the lines and maybe replace the fuel caps.

Speaking of which, is there a good way to see if a fuel cap is bad? I know that it ran better with the caps barely installed, but I was thinking that it was plugged vent lines. Thoughts?

Thanks again!

The caps are not why the tanks aren't venting, your vent lines on the sending units are likely clogged. My 1980 has three lines on the sending unit. Feed, return, and vent. The vent line just has a few inches of hose the is plugged by wobble check valves on mine since I am federal heavy duty emissions. Most lighter duty trucks will have the vent lines running to a carbon canister that is having vacuum pulled from a port on the carburetor. I would suggest dropping the tanks and inspecting the sending units. You might pull them out and find the tanks and socks full of garbage or you might find the senders are all rusted out and clogged. Its not a major job... I pulled both tanks, cleaned them out and installed new sending units in an afternoon with dual 20 gallon saddle tanks on a K20.

 

[Old60Driver]

'Mornin' folks!

Thought I'd give an update...

Dropped the LH tank Saturday morning with the main concern being a clogged pickup sock. That, my friends was a serious PIA. Should have lifted the bed, but I figured "how bad can it be???". Yeah, that was mistake number one. Not confirming that the tank was empty was mistake number two. Turns out the gauge is extremely inaccurate, and I found out later that she still had about 6 gallons of fuel in her.

Got the tank dropped, cleaned off the area around the fuel tank sending unit, and pulled it off. It looked perfect. Sock was immaculate, no corrosion in tank, nothing looked bad. Welp, I thought, I guess I'll just return the new sending unit back to the local parts store, and use the 60 bucks on something else I need! That was mistake number three. I should have just changed the sending unit, but at that point all I'm thinking about is why the engine was acting fuel starved. Drained the tank. Should have been step number one, but oh well. Put her back together, and started checking vent lines. Remember when I said that someone had put in an aftermarket fuel pump? Well, a hidden portion of the feed like from the tank selector valve had a small kink in it. Yup. A damned kinked line. smdh... I had extra fuel line, so I changed it out, put some fuel in the LH tank, and she fired right up. Drove to the gas station to fill her up, and she ran great, other than a possible locking hubs issue.

Here's the punchline. At at full twenty gallons, she only indicates a shade over 1/4 tank. I'm so mad at myself I could spit! Should have just replaced damned unit. Or at a minimum, confirmed operation of the gauge while I had her out. But like I said, I was really only looking at why she was acting fuel starved. Oh well, I'll just monitor mileage and change out the sending unit when I have proper lifting equipment AND another pair of hands to help.

On another note, I found a long 5/16" vacuum line coming off of a 3 way toward the rear of the intake that was wide open, and not connected to anything. I'm pretty good at remember how I took things apart, but I don't think I touched this line. It's about 2.5 feet long, and angled toward the passenger side. I searched for what it could possibly be, but no luck. Had other things to do, so I plugged it. LOL Man, that made a ton of difference! She settled right down! And isn't running rich anymore, plugs are looking like they should

I still have a problem with my fast idle cam (binding maybe?) on the QJet, but other than than she seems to be running loads better. I'll keep tinkering...

Thanks for reading y'all!

 

[75gmck25]

The vacuum line off the intake might be the one going to the vacuum canister for the HVAC. The connectors on the canister point straight down, so it’s not obvious when a line is off. The other line running in that direction would be to the transmission modulator.

 

[Bextreme04]

'Mornin' folks!

Thought I'd give an update...

Dropped the LH tank Saturday morning with the main concern being a clogged pickup sock. That, my friends was a serious PIA. Should have lifted the bed, but I figured "how bad can it be???". Yeah, that was mistake number one. Not confirming that the tank was empty was mistake number two. Turns out the gauge is extremely inaccurate, and I found out later that she still had about 6 gallons of fuel in her.

Got the tank dropped, cleaned off the area around the fuel tank sending unit, and pulled it off. It looked perfect. Sock was immaculate, no corrosion in tank, nothing looked bad. Welp, I thought, I guess I'll just return the new sending unit back to the local parts store, and use the 60 bucks on something else I need! That was mistake number three. I should have just changed the sending unit, but at that point all I'm thinking about is why the engine was acting fuel starved. Drained the tank. Should have been step number one, but oh well. Put her back together, and started checking vent lines. Remember when I said that someone had put in an aftermarket fuel pump? Well, a hidden portion of the feed like from the tank selector valve had a small kink in it. Yup. A damned kinked line. smdh... I had extra fuel line, so I changed it out, put some fuel in the LH tank, and she fired right up. Drove to the gas station to fill her up, and she ran great, other than a possible locking hubs issue.

Here's the punchline. At at full twenty gallons, she only indicates a shade over 1/4 tank. I'm so mad at myself I could spit! Should have just replaced damned unit. Or at a minimum, confirmed operation of the gauge while I had her out. But like I said, I was really only looking at why she was acting fuel starved. Oh well, I'll just monitor mileage and change out the sending unit when I have proper lifting equipment AND another pair of hands to help.

On another note, I found a long 5/16" vacuum line coming off of a 3 way toward the rear of the intake that was wide open, and not connected to anything. I'm pretty good at remember how I took things apart, but I don't think I touched this line. It's about 2.5 feet long, and angled toward the passenger side. I searched for what it could possibly be, but no luck. Had other things to do, so I plugged it. LOL Man, that made a ton of difference! She settled right down! And isn't running rich anymore, plugs are looking like they should

I still have a problem with my fast idle cam (binding maybe?) on the QJet, but other than than she seems to be running loads better. I'll keep tinkering...

Thanks for reading y'all!

Yep, if you have AC it most likely runs to the accumulator for the AC. Its usually a round ball bolted to the firewall right above the blower fan in the engine bay. You'll have a soft line off the intake that runs to a nipple on the bottom towards the front and a hard line that comes off the bottom towards the back and goes through the firewall to the AC door actuators in the cab.

 

[Old60Driver]

If memory serves (the truck is still in KS), the AC accumulator was hooked up. And it used a pretty small vacuum line. Maybe 1/8" ID? This line was large. Like maybe 1/4" ID. As I said, she ran a ton better when I plugged it. I'll double check it again when I get up there, just to be sure.

Looking into the transmission modulator possibility now.

 

[Bextreme04]

If memory serves (the truck is still in KS), the AC accumulator was hooked up. And it used a pretty small vacuum line. Maybe 1/8" ID? This line was large. Like maybe 1/4" ID. As I said, she ran a ton better when I plugged it. I'll double check it again when I get up there, just to be sure.

Looking into the transmission modulator possibility now.

The trans modulator should not be a long hose. It should be a short hose to a hard line that runs all the way back to the modulator and then switches back to a short run of hose. The only large hose I know of from back there would be for cruise control.

 

[Old60Driver]

Okay, so I figured it out. I'm an idiot. Looking at too many things at once, and inadvertently put blinders on.

The accumulator has TWO ports. One going to the inside of the truck, and one being fed by vacuum from the intake manifold. Yep, the larger diameter vacuum line was for the accumulator.

Now to figure out how to get the AC compressor switched over to 134. The list grows....

Thanks again y'all, I appreciate it!

 

[DoubleDingo]

To answer your question why someone would add an electric pump when a mechanical is feeding the carburetor, it could be a backup. My Pop has this setup on his truck. The mechanical pump can fail, and if it does you could be stranded. But with an electrical backup pump, you flip the switch and off you go. This actually happened, but to some friends of his that borrowed his truck. They were up in the mountains, and the mechanical pump failed. They walked 25 miles to town to use a pay phone to call him to come get them. He asked them why they walked to town when they could have driven the truck. They reiterated that the fuel pump went out. He told them he heard them the first time, but why didn't they use the electric pump. They felt as small as a mouse, because they even helped him install the electric pump.

 

[Raider L]

@Old60Driver,

How long have you had this truck?? Is this your daily driver, but only when you're home? How long does it sit up and not started? You might ask your wife to start it up once a week and let it run for a bit. Is it under cover? Is it inside a garage?

 

[Raider L]

@Old60Driver,

I'll guarantee you if your modulator valve wasn't hooked up to vacuum you'd know it!