Fuel Pump Woes and Questions

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
3,945
Reaction score
5,695
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
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

Full Access Member
Joined
May 13, 2019
Posts
4,135
Reaction score
4,984
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
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

1983 K20 Silverado
Joined
May 17, 2020
Posts
209
Reaction score
221
Location
Houston
First Name
Michael
Truck Year
1983
Truck Model
K20 Silverado
Engine Size
350
'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

Full Access Member
Joined
Oct 13, 2016
Posts
2,018
Reaction score
1,811
Location
Northern Virginia
First Name
Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
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

Full Access Member
Joined
May 13, 2019
Posts
4,135
Reaction score
4,984
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
'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

1983 K20 Silverado
Joined
May 17, 2020
Posts
209
Reaction score
221
Location
Houston
First Name
Michael
Truck Year
1983
Truck Model
K20 Silverado
Engine Size
350
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

Full Access Member
Joined
May 13, 2019
Posts
4,135
Reaction score
4,984
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
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

1983 K20 Silverado
Joined
May 17, 2020
Posts
209
Reaction score
221
Location
Houston
First Name
Michael
Truck Year
1983
Truck Model
K20 Silverado
Engine Size
350
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

Full Access Member
Joined
Jul 3, 2012
Posts
10,019
Reaction score
14,164
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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

Full Access Member
Joined
Sep 1, 2020
Posts
1,892
Reaction score
994
Location
Shreveport, LA
First Name
William
Truck Year
1974
Truck Model
C10
Engine Size
355
@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?
 
Last edited:

Raider L

Full Access Member
Joined
Sep 1, 2020
Posts
1,892
Reaction score
994
Location
Shreveport, LA
First Name
William
Truck Year
1974
Truck Model
C10
Engine Size
355
@Old60Driver,

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

Latest posts

Forum statistics

Threads
41,856
Posts
903,621
Members
33,370
Latest member
mitchell1128
Top