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Ideal fuel pump location

anwat

anwat

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So, to mount my rear shock brackets, I'm going to need to drop the fuel tank on my K5. Seems like the time to take on the fuel pump question I've had for a while. I'm running a FiTech, so I need the higher fuel pressure that comes with the later throttle body style pumps. When I bought the truck, it had an external pump mounted inside the frame rail, which is working perfectly. I even have a spare pump for the trail.
Problem is, I've read countless places that the pump is supposed to be mounted lower than the pickup, usually recommended that it's lower than the tank. As you all know, that's pretty hard to do on a K5 with a stock fuel tank, unless the pump is in the tank. So I'm looking for a little advice from those of you who have had an external pump: Where did you mount it, and did it last? It's certainly easier to change out a bad pump on the frame rail than one in the tank, so maybe it's worth it to just leave it where it is. The pump is pretty close to the tank, but it's just above the rear axle, making it a good 10" higher than the bottom of the tank.
What is the best way to set this up? I know changing an in the tank pump on the trail with a half tank of fuel can be a problem...and it usually happens in the rain or when it's 115 degrees in the shade. How important is having the pump be lower than the tank?
 
It sounds like your pump is mounted correctly. I think the only thing you need to design is fuel pump regulators. This way you can guarantee you do not run the pump dry for even a second. If you run pumps dry for even a second over the course of a few hundred starts this will kill your pump eventually.
 
Don’t know if it would help, but is it possible to put a check valve in the tank so it doesn’t lose prime?
 
rampage said:
Don’t know if it would help, but is it possible to put a check valve in the tank so it doesn’t lose prime?
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That is what I did with my TBI Square body. I got a couple of Russel brand one way check valves. One is located between the TBI and the fuel tank selector valve, and the other on the left side saddle tank between the selector valve and the left side tank of my pick up.
 
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So the issue isn't really the height of the pump, it's the fuel running back down into the tank and leaving the pump dry at startup? And the way to solve this issue is to put a check valve in the line somewhere lower than the pump so the fuel can't run back into the tank? I hate to say this, but that sounds easy enough.
 
anwat said:
So the issue isn't really the height of the pump, it's the fuel running back down into the tank and leaving the pump dry at startup? And the way to solve this issue is to put a check valve in the line somewhere lower than the pump so the fuel can't run back into the tank? I hate to say this, but that sounds easy enough.
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Even though fuel pressure regulators would be more optimum, one way check valves will still do the trick. Fuel pressure regulators are just fancy one way check valves themselves anyway, just more optimum for the job.
 
I've got a regulator at the throttle body, and the pump pressure is controlled by PWM. It's set up like the GM TBI system, with the unused fuel going back to the tank in a return line. Are you saying another regulator between the pump and the tank?
 
Lower is better. My first install got me half way up a 10% grade. A truck towing a 5th wheel camp trailer lost a tire and was blocking road. I stopped to offer assistance. Later when we tried to get back going, my truck wouldn't start. acted like no fuel. I could hear the pump run. Inlet to pump was 1" below the middle seem on my 40 gl tank. The mounting bolts were vertical, I move the top pump bracket bolt to the lower chassis hole lowering the pump @ 1 1/2". The truck got fuel, and started. Finished the climb, and was good for rest of trip.
I eventually replaced that pump with a better Holley one, and mounted it even lower. The inlet is 1/2" from bottom of the tank. I have towed up that 10% grade 3 more times now no issue. The grade, you may know, is highway 18 from High Desert side to Big Bear.
 
anwat said:
I've got a regulator at the throttle body, and the pump pressure is controlled by PWM. It's set up like the GM TBI system, with the unused fuel going back to the tank in a return line. Are you saying another regulator between the pump and the tank?
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The TBI regulator will be fine.
 
I feel if you put a good Walbro pump in a TBI tank it will last longer than an inline pump. I put my Walbro in 12 years ago, still works like new. In fact I stock that exact pump now it works so well, for a stock engine all the way up just over 700 HP NA, and it's pretty quiet in the tank too. Many Walbro pumps have a check valve in the pump outlet. Not all.
 
All things considered, sounds like the best option for now is to stick with the setup I have, but install a check valve and see how it goes. Minimal work and money, I can rethink this if the pump goes out prematurely and run the spare while I figure it out.

I take it the check valve should be in the tank as close to the bottom as possible?
Wes Harden said:
Lower is better. My first install got me half way up a 10% grade. A truck towing a 5th wheel camp trailer lost a tire and was blocking road. I stopped to offer assistance. Later when we tried to get back going, my truck wouldn't start. acted like no fuel. I could hear the pump run. Inlet to pump was 1" below the middle seem on my 40 gl tank. The mounting bolts were vertical, I move the top pump bracket bolt to the lower chassis hole lowering the pump @ 1 1/2". The truck got fuel, and started. Finished the climb, and was good for rest of trip.
I eventually replaced that pump with a better Holley one, and mounted it even lower. The inlet is 1/2" from bottom of the tank. I have towed up that 10% grade 3 more times now no issue. The grade, you may know, is highway 18 from High Desert side to Big Bear.
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Where/how did you mount it? Mine currently sits at the top of the rear axle arch...is there a somewhat protected spot lower than that? Here's a couple of photos of where mine is now.

IMG_0323.JPG


IMG_0319.JPG
 
Left hose is inlet, right out let loops around and to factory line to front.

I have intentions of building a cover for it. That is t case drippings all over.

IMG_20220810_123306.jpg
 
@anwat Are those AN style fittings where the feed hose connects to the sender on top of the tank? If so, I'd get whatever fittings are needed to put it there. You'd end up with probably close to 2' of hose with fuel in it for the pump and the 4"-6" off added length from the fittings and valve can be used up in the curve above the tank instead of making an awkward loop/curl at the pump.
 
They are, and that's a good idea...doesn't make it any lower, but both ideas are better than where it is now. Putting it on top near the edge would get it away from the exhaust heat, something I would like to do. As long as it's not tucked up there too much, it would still be easy to access.
I like the height of @WesHarden, but I'm a little concerned about the pump and lines getting hit by gravel and whatever else I run into.

Correct me if I'm wrong here, but the fact that the pump has to pull the gas out of the top of the tank would negate the advantage of the pump being lower in the line, correct? Unless the pump is in the tank, it's still got to fight to pull the fluid up to the top to get it out, so there's really no difference if I mount it on top or in front. It's the fuel draining out of the line back into the tank that presents the problem, so a check valve low in the pickup line is the solution to that it would seem.

The top of the tank would be out of the heat, and a pretty safe place as far as getting struck by debris. Plus the draw line from the tank would be as short as possible, as long as the pump fits in the space, it sounds like a good idea.
 
To be clear, I was talking about putting the check valve on top of the tank not the pump.

I'd be putting the pump n top of the tank would make it loud because of it vibrating and echoing in the tank.
 
I think as long as you have the shortest distance possible between the pump and where it has to draw from you’ll be okay….unless you have a bottom feed fuel cell mounted in the rear and the pump below it on the frame it’s almost impossible to get the fuel higher than the pump inlet….just my .02

I think the trouble comes when people mount a pump below the drivers seat or somewhere there on the frame and it has to pull fuel half the length of the vehicle.
 
nvrenuf said:
To be clear, I was talking about putting the check valve on top of the tank not the pump.

I'd be putting the pump n top of the tank would make it loud because of it vibrating and echoing in the tank.
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Thanks, I did misunderstand, but it's all good. I'm thinking of mounting it to one of those little crossmembers that I have and using (like the one next to the rear end breather in the above photo.) I couldn't secure it to the tank since I can't drill into it.

Is there a reason you wouldn't put the valve in the tank other than it being a pain to get in there? I'm thinking is all fuel safe materials, it would seem submerging it wouldn't hurt it and would be the only way to ensure I don't get air in the fuel line.

Odd that @Wes Harden doesn't have those little crossmember things on his bed. I would think they would be even more important on a sub.
 
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