Increase Fuel Pump Pressure

LeafPile · 12-16-2017, 11:33 AM

My 1993 YJ has a 20 gallon tank factory (with the "mod" of course). It doesn't fit well in between the frame rail, and I don't need that much fuel. So, I'm getting a 15 gallon tank meant for the 87-90 YJs.

Since these Jeeps run on either 4-5 psi (4.2L carb) or 15 psi (2.5L TBI), it's not even close to my 31-40 psi. My pump puts out 40 psi and is vacuum regulated down to 31 psi. I have three options (let me know if you have a fourth):
1. Find a pump (probably aftermarket) that fits into the new bolt pattern on the tank.
2. Put in a new regulator on the rail that ramps 15 psi up to 31 psi at full vacuum and 40 psi at zero vacuum.
3. Put in a regulator somewhere on the system (probably near the filter on the framerail) that ramps 15 psi up to 40 psi, and keep the factory regulator.

First off, I don't really like the idea of upping the pump pressure. I'm not sure this is even safely possible...

WrenchMonkey · 12-17-2017, 12:39 AM

A regulator can't create pressure. The pump has to do that, and the regulator chokes it back to where you need it.

Is there maybe an inline pump that will put out what you need?

Edit: Option Five, cobble your fuel pump together with the earlier tank's mounting flange?

93 Krawler · 12-17-2017, 10:01 PM

When I did the 4.3 swap on our 89 Wrangler, I used an inline pump just above the pressure I needed. The OE regulator handled the extra pressure it had. Same way my rig is done with the fuel cell. Make sure its a walbro.
http://walbrofuelpumps.com/walbro-gsl393-fuel-pump.html

blazerbrad · 12-18-2017, 08:21 AM

As mentioned above a regulator can not increase pressure. My first choice will always be a factory in-tank pump if there is anything out there with the correct pressure and will bolt into the tank. These just seem to be by far the most reliable, but also don't know right off hand what options there may be for this application.

An inline pump will definitely work, but a couple suggetions:
-Buy a good one.......cheap ones are junk and don't seem to last long.
-Be very careful where you mount it....they often don't like heat (exhaust) or being covered in mud and water.
-Mount it were you can get to it relatively easy and replace it, including the wiring....and carry a spare. Just can't count the number of times I've seen somebody have issues on the trail with an inline fuel pump.

LeafPile · 12-18-2017, 06:28 PM

Looks like I'm putting in a Walbro pump. Probably in the engine bay, unless it needs to be closer to the tank. I already have a regulator to use (cheapie, just to try it first then replace and chuck in the bag as a trail spare).

Would this pump alone be enough? Or would I need the factory pump?

I'm thinking about drawing up an aluminum plate on SolidWorks (to send to a machine shop), with a pickup sock on the bottom, return line, and make a sending unit out of a potentiometer and floater. That'll save $300 of the sending unit assembly garbage.

LeafPile · 12-18-2017, 08:54 PM

https://www.summitracing.com/parts/tnk-tan-gml

Forget that potentiometer idea, the resistance nearly matches what the factory specs are (0 to 90, as opposed to 1 to 88 ohms).

WrenchMonkey · 12-18-2017, 08:58 PM

I would think that the pump would be happier as low and as close to the tank as you can put it.

It might work in the engine bay, if you have the stock pump feeding it, AND the stock pump's flow rate is enough to keep it happy. I bet it's not.

But if you're willing and able to fab up a mounting plate, just make one that'll reuse your stock pump and be done.

93 Krawler · 12-18-2017, 10:29 PM

The fuel pump should be mounted on the frame rail somewhere as close as you can to the tank. I would not use a cheap pressure regulator. I thought you said it had a factory regulator built in? On my 4.3 conversion I utilized the factory pressure regulator at the TBI setup. You should be able to do the same.

Sent from my SM-G930V using Tapatalk

LeafPile · 12-19-2017, 08:20 PM

I need 40 psi of fuel pressure. The factory regulator brings it down to 31 psi.

It's vacuum regulated, so as the throttle opens, the fuel pressure increases. I don't want it to increase it beyond 40 psi.

The cheap regulator is just to test it out. I already had it to mess around with. If I get everything working, I'll get a good regulator that won't get eaten up by the fuel.

WrenchMonkey · 12-19-2017, 10:49 PM

I'm sure the stock regulator will drop whatever your pump pressure is, down to the 31-40 you need, depending on vacuum...

93 Krawler · 12-20-2017, 09:07 AM

If it had a carb, an aftermarket regulator is needed. Since yours is efi and has it's oem built in regulator, just add the pump i linked to and all should be good. Try not to over think this.

Sent from my SM-G930V using Tapatalk

LeafPile · 12-22-2017, 02:38 AM

Say the pump puts out 50 psi and the regulator brings it down to 31 psi at idle (like normal). At wide open throttle, with no vacuum, the fuel pressure will be 50 psi, when it should be 40 psi. That's why I plan on adding a regulator.

93 Krawler · 12-22-2017, 08:56 AM

Quote:

Originally Posted by LeafPile

Say the pump puts out 50 psi and the regulator brings it down to 31 psi at idle (like normal). At wide open throttle, with no vacuum, the fuel pressure will be 50 psi, when it should be 40 psi. That's why I plan on adding a regulator.

No, it will never get higher than the regulator was designed. I don't think the vacuum would reach zero at wot.

Sent from my SM-G930V using Tapatalk

12-16-2017, 11:33 AM	#1
LeafPile Join Date: Nov 2017 Posts: 5	Increase Fuel Pump Pressure My 1993 YJ has a 20 gallon tank factory (with the "mod" of course). It doesn't fit well in between the frame rail, and I don't need that much fuel. So, I'm getting a 15 gallon tank meant for the 87-90 YJs. Since these Jeeps run on either 4-5 psi (4.2L carb) or 15 psi (2.5L TBI), it's not even close to my 31-40 psi. My pump puts out 40 psi and is vacuum regulated down to 31 psi. I have three options (let me know if you have a fourth): 1. Find a pump (probably aftermarket) that fits into the new bolt pattern on the tank. 2. Put in a new regulator on the rail that ramps 15 psi up to 31 psi at full vacuum and 40 psi at zero vacuum. 3. Put in a regulator somewhere on the system (probably near the filter on the framerail) that ramps 15 psi up to 40 psi, and keep the factory regulator. First off, I don't really like the idea of upping the pump pressure. I'm not sure this is even safely possible...

12-17-2017, 12:39 AM	#2
WrenchMonkey Mechanical Animal - CORE Member - - Moderator - Join Date: Feb 2008 Location: Beechmont Posts: 1,883	A regulator can't create pressure. The pump has to do that, and the regulator chokes it back to where you need it. Is there maybe an inline pump that will put out what you need? Edit: Option Five, cobble your fuel pump together with the earlier tank's mounting flange? __________________ DIRTY DEEDS, DONE DIRT CHEAP Whatever doesn't kill you makes you stranger

12-18-2017, 08:58 PM	#7
WrenchMonkey Mechanical Animal - CORE Member - - Moderator - Join Date: Feb 2008 Location: Beechmont Posts: 1,883	I would think that the pump would be happier as low and as close to the tank as you can put it. It might work in the engine bay, if you have the stock pump feeding it, AND the stock pump's flow rate is enough to keep it happy. I bet it's not. But if you're willing and able to fab up a mounting plate, just make one that'll reuse your stock pump and be done. __________________ DIRTY DEEDS, DONE DIRT CHEAP Whatever doesn't kill you makes you stranger

12-19-2017, 10:49 PM	#10
WrenchMonkey Mechanical Animal - CORE Member - - Moderator - Join Date: Feb 2008 Location: Beechmont Posts: 1,883	I'm sure the stock regulator will drop whatever your pump pressure is, down to the 31-40 you need, depending on vacuum... __________________ DIRTY DEEDS, DONE DIRT CHEAP Whatever doesn't kill you makes you stranger

12-17-2017, 10:01 PM	#3
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	When I did the 4.3 swap on our 89 Wrangler, I used an inline pump just above the pressure I needed. The OE regulator handled the extra pressure it had. Same way my rig is done with the fuel cell. Make sure its a walbro. http://walbrofuelpumps.com/walbro-gsl393-fuel-pump.html

12-18-2017, 08:21 AM	#4
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831 Images: 6	As mentioned above a regulator can not increase pressure. My first choice will always be a factory in-tank pump if there is anything out there with the correct pressure and will bolt into the tank. These just seem to be by far the most reliable, but also don't know right off hand what options there may be for this application. An inline pump will definitely work, but a couple suggetions: -Buy a good one.......cheap ones are junk and don't seem to last long. -Be very careful where you mount it....they often don't like heat (exhaust) or being covered in mud and water. -Mount it were you can get to it relatively easy and replace it, including the wiring....and carry a spare. Just can't count the number of times I've seen somebody have issues on the trail with an inline fuel pump.

12-18-2017, 06:28 PM	#5
LeafPile Join Date: Nov 2017 Posts: 5	Looks like I'm putting in a Walbro pump. Probably in the engine bay, unless it needs to be closer to the tank. I already have a regulator to use (cheapie, just to try it first then replace and chuck in the bag as a trail spare). Would this pump alone be enough? Or would I need the factory pump? I'm thinking about drawing up an aluminum plate on SolidWorks (to send to a machine shop), with a pickup sock on the bottom, return line, and make a sending unit out of a potentiometer and floater. That'll save $300 of the sending unit assembly garbage.

12-18-2017, 08:54 PM	#6
LeafPile Join Date: Nov 2017 Posts: 5	https://www.summitracing.com/parts/tnk-tan-gml Forget that potentiometer idea, the resistance nearly matches what the factory specs are (0 to 90, as opposed to 1 to 88 ohms).

12-18-2017, 10:29 PM	#8
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	The fuel pump should be mounted on the frame rail somewhere as close as you can to the tank. I would not use a cheap pressure regulator. I thought you said it had a factory regulator built in? On my 4.3 conversion I utilized the factory pressure regulator at the TBI setup. You should be able to do the same. Sent from my SM-G930V using Tapatalk

12-19-2017, 08:20 PM	#9
LeafPile Join Date: Nov 2017 Posts: 5	I need 40 psi of fuel pressure. The factory regulator brings it down to 31 psi. It's vacuum regulated, so as the throttle opens, the fuel pressure increases. I don't want it to increase it beyond 40 psi. The cheap regulator is just to test it out. I already had it to mess around with. If I get everything working, I'll get a good regulator that won't get eaten up by the fuel.

12-20-2017, 09:07 AM	#11
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	If it had a carb, an aftermarket regulator is needed. Since yours is efi and has it's oem built in regulator, just add the pump i linked to and all should be good. Try not to over think this. Sent from my SM-G930V using Tapatalk

12-22-2017, 02:38 AM	#12
LeafPile Join Date: Nov 2017 Posts: 5	Say the pump puts out 50 psi and the regulator brings it down to 31 psi at idle (like normal). At wide open throttle, with no vacuum, the fuel pressure will be 50 psi, when it should be 40 psi. That's why I plan on adding a regulator.