I have an electric fuel pump question.

[Tanner_Shany24]

Hey guys, first post here for me. Proud to say I picked up a 1983 k20 with a 454 bbc and I’m excited to start working on it. So the guy I bought it from had just put a new electric fuel pump in it, it’s mounted to the frame on the passenger side close to the tank. I’m a little confused about it however because when I turn the key on, engine off, the fuel mount primes, and continues to prime, and doesn’t stop. When I start the motor, the pump doesn’t ever shut off. You can continuously hear it whining under the bed. It shuts off as soon as you turn the key off though. My question is, is that normal? Most of the time it seems they prime for 3-4 seconds then shut off, then the motor relies on vacuum or a mechanical pump or something to keep it going? Maybe this is normal but it just seems odd to me. Can anyone give me some info or opinions?

 

[Blue Ox]

On fuel injected engines they shut off when they reach a certain pressure. Once the engine starts and the pressure drops they'll start again to maintain pressure. Not sure about carbureted engines, lower pressure to start with and they may just self regulate. However, I'm sure someone here with more gasoline engine knowledge will jump in.

Welcome to the site.

 

[Charlie]

 

[1987 GMC Jimmy]

No, it’s not normal, and the previous owner was an idiot for half assing that at the possible expense of your life and/or your truck. They just wired the pump to a 12V ignition source and called it a day. What they should have done is used a plain ole Bussman relay to mediate power to the pump while also putting an oil pressure shut off switch in the circuit to allow the pump to only be able to cycle for a few seconds without oil pressure. This does two things. One, it prevents the flooding of your engine, which can easily happen since it’s carbureted, and there aren’t any injectors to to stay closed and send fuel back the way it came. A flooded engine will dilute your oil over time, foul plugs, wash the oil out of high friction spots leading to premature wear, etc. Two, if you’re in some kind of accident, particularly a rollover, the lack of oil pressure being read by a safety switch would normally kill your pump, but in this case it would just keep running, and potentially engulf you and your truck in flames.

What I would do if it was me is, unless the cam eccentric was wiped and could no longer engage the pump lever, go back to a mechanical pump. External electric pumps are not a long term solution compared to how long in-tank electrical pumps or mechanical pumps last. It seems to me that a lot of people do this because they don’t want to fiddle with the pushrod and trying to get it on top of the pump lever. It can definitely be annoying, but the alternative is just an exercise in laziness. It’s possible that something went wrong within the original mechanical pump circuit, but I think that’s a relatively rare occurrence, and even if it did, the job should have been done right to begin with.

Welcome to the site, and I hope you don’t find too many bugs going forward. Time and time again POs leave a mess to their successive owners, but it’s good that you came for help and want to do things the right way.

 

[Blue Ox]

And there you go.

 

[Tanner_Shany24]

No, it’s not normal, and the previous owner was an idiot for half assing that at the possible expense of your life and/or your truck. They just wired the pump to a 12V ignition source and called it a day. What they should have done is used a plain ole Bussman relay to mediate power to the pump while also putting an oil pressure shut off switch in the circuit to allow the pump to only be able to cycle for a few seconds without oil pressure. This does two things. One, it prevents the flooding of your engine, which can easily happen since it’s carbureted, and there aren’t any injectors to to stay closed and send fuel back the way it came. A flooded engine will dilute your oil over time, foul plugs, wash the oil out of high friction spots leading to premature wear, etc. Two, if you’re in some kind of accident, particularly a rollover, the lack of oil pressure being read by a safety switch would normally kill your pump, but in this case it would just keep running, and potentially engulf you and your truck in flames.

What I would do if it was me is, unless the cam eccentric was wiped and could no longer engage the pump lever, go back to a mechanical pump. External electric pumps are not a long term solution compared to how long in-tank electrical pumps or mechanical pumps last. It seems to me that a lot of people do this because they don’t want to fiddle with the pushrod and trying to get it on top of the pump lever. It can definitely be annoying, but the alternative is just an exercise in laziness. It’s possible that something went wrong within the original mechanical pump circuit, but I think that’s a relatively rare occurrence, and even if it did, the job should have been done right to begin with.

Welcome to the site, and I hope you don’t find too many bugs going forward. Time and time again POs leave a mess to their successive owners, but it’s good that you came for help and want to do things the right way.

Thanks for the wisdom. I assumed he just jumped it to a power line somewhere. I like he idea of the mechanical pump more honestly so I will probably go that route. My father has a 72 Chevy with a mechanical pump and it works awesome. I don’t have the money to do so now as I am have to pay for my last quarter of college for the year, but I definitely don’t plan on driving the truck around much, as it gets around 8 mpg and it’s just a project rig that I bought for fun. Once again thanks for the help guys. I will probably end up being back on the site asking more questions because, well let’s just say the entire truck has been treated like a mud tuck it’s entire life. When I saw it for sale I just wanted to save it, I got it for a steal, and from what I can tell the motor, tranny and frame are very solid. So I’m my mind that’s a plus, but the wiring however, is complete trash. Random wires are cut everywhere and stuff is hanging out of the dash. There are literally countless wire splices done just buy twisting the bare wires together rather than using connectors. I honestly don’t even know how it runs haha.

 

[1987 GMC Jimmy]

Thanks for the wisdom. I assumed he just jumped it to a power line somewhere. I like he idea of the mechanical pump more honestly so I will probably go that route. My father has a 72 Chevy with a mechanical pump and it works awesome. I don’t have the money to do so now as I am have to pay for my last quarter of college for the year, but I definitely don’t plan on driving the truck around much, as it gets around 8 mpg and it’s just a project rig that I bought for fun. Once again thanks for the help guys. I will probably end up being back on the site asking more questions because, well let’s just say the entire truck has been treated like a mud tuck it’s entire life. When I saw it for sale I just wanted to save it, I got it for a steal, and from what I can tell the motor, tranny and frame are very solid. So I’m my mind that’s a plus, but the wiring however, is complete trash. Random wires are cut everywhere and stuff is hanging out of the dash. There are literally countless wire splices done just buy twisting the bare wires together rather than using connectors. I honestly don’t even know how it runs haha.

Uh oh. Yeah, I was afraid of that. You’re not the first, and you won’t be the last, but you can overcome with patience. I’m talking about the Mickey Mouse wiring that somehow operates the truck. That PO was ****** to the truck, but it’s not your fault, and it’s sure not the truck’s fault. I hope you get some enjoyment out of it and see it through. Feel free to post pics when you can. Depending on how much the fuel lines have been jacked up, a new pump costs like seventeen dollars at the store. You should be able to get it for cheaper through an online retailer like Amazon. Please do come back with questions when you start tearing into it.