Modified Fuel Pump
08-15-2018, 06:59 AM
#1
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Year: 1998
Engine: 4.0L 162,000
Modified Fuel Pump
Over the years the stock XJ Fuel Pump has served me well. Very reliable, rarely fail.
When I have replaced it, I've always used a Bosch part which has been equally reliable. Now they are not being made anymore.
Problem is the fuel flow of the stock pump. It is more than adequate for stock, stroker and even mild supercharger builds.
Notice the 50% Safety flow number. This is to account for clogged filter, low voltage, low pump output, increased wiring resistance, etc all which decrease actual pump performance.
Here is some data that I have found on different flowing fuel pumps.
FUEL PUMPS
-All at 12v, if old wire, poor battery or alternator, actual voltage and fuel pump output may be lower
-LPH = GPH x 3.785, 1 Gallon Gas = 6.5lbs
-?stock 110LPH = 29GPH at free flow, 23GPH at 50psi =150 lbs/hr
Max HP- N/A .50BSFC = 300HP, Boost .55BSFC = 275HP (50%safety-190HP)
-?stock 130LPH Walbro GCA733 = 27GPH at 50psi = 175 lbs/hr
Max HP- N/A .5SFC = 350HP, Boost 0.55BSFC = 315HP (50% safety-210HP)
-upgrade 190LPH = 50GPH at free flow, 42GPH at 43.5psi, 36-38GPH at 50psi = 234-247lbs/hr
Max HP- N/A .50BSFC = 475-500HP, Boost .55BSFC = 425-450HP (50% safety- 285HP)
-upgrade 255LPH Walbro = 67GPH at Free flow, 53GPH at 43.5psi, 47-55GPH at 50psi = 305-357lbs/hr
Max HP- N/A .50BSFC = 650-710HP, Boost .55BSFC = 590-650HP (50% safety- 400HP)
-stock in-tank fuel pressure regulator BWD 23079
-upgrade 300LPH Bosch 044 = 79GPH
Max HP- N/A .50BSFC = 1030HP, boost .55BSFC = 936HP
So I am looking to build a new fuel pump with a 255LPH and another with a 340LPH pump.
I am going to take a 'cheapo' Chinese pump assembly and take it all apart and figure out the weakness and failure areas and 'rebuild' it with better parts and of course better WALBRO fuel pumps.
I want to make it just a straight 'plug in' for the XJ and also for the ZJ fuel tank(it's bigger than the XJ and fits in the XJ stock location).
Why am I doing this? I think that we are near the limit of the stock Bosch fuel pump.
We are looking at the next rounds of modifications and More Boost is in the future and I want to make sure that there are no fueling issues.
__________________
When I have replaced it, I've always used a Bosch part which has been equally reliable. Now they are not being made anymore.
Problem is the fuel flow of the stock pump. It is more than adequate for stock, stroker and even mild supercharger builds.
Notice the 50% Safety flow number. This is to account for clogged filter, low voltage, low pump output, increased wiring resistance, etc all which decrease actual pump performance.
Here is some data that I have found on different flowing fuel pumps.
FUEL PUMPS
-All at 12v, if old wire, poor battery or alternator, actual voltage and fuel pump output may be lower
-LPH = GPH x 3.785, 1 Gallon Gas = 6.5lbs
-?stock 110LPH = 29GPH at free flow, 23GPH at 50psi =150 lbs/hr
Max HP- N/A .50BSFC = 300HP, Boost .55BSFC = 275HP (50%safety-190HP)
-?stock 130LPH Walbro GCA733 = 27GPH at 50psi = 175 lbs/hr
Max HP- N/A .5SFC = 350HP, Boost 0.55BSFC = 315HP (50% safety-210HP)
-upgrade 190LPH = 50GPH at free flow, 42GPH at 43.5psi, 36-38GPH at 50psi = 234-247lbs/hr
Max HP- N/A .50BSFC = 475-500HP, Boost .55BSFC = 425-450HP (50% safety- 285HP)
-upgrade 255LPH Walbro = 67GPH at Free flow, 53GPH at 43.5psi, 47-55GPH at 50psi = 305-357lbs/hr
Max HP- N/A .50BSFC = 650-710HP, Boost .55BSFC = 590-650HP (50% safety- 400HP)
-stock in-tank fuel pressure regulator BWD 23079
-upgrade 300LPH Bosch 044 = 79GPH
Max HP- N/A .50BSFC = 1030HP, boost .55BSFC = 936HP
So I am looking to build a new fuel pump with a 255LPH and another with a 340LPH pump.
I am going to take a 'cheapo' Chinese pump assembly and take it all apart and figure out the weakness and failure areas and 'rebuild' it with better parts and of course better WALBRO fuel pumps.
I want to make it just a straight 'plug in' for the XJ and also for the ZJ fuel tank(it's bigger than the XJ and fits in the XJ stock location).
Why am I doing this? I think that we are near the limit of the stock Bosch fuel pump.
We are looking at the next rounds of modifications and More Boost is in the future and I want to make sure that there are no fueling issues.
08-15-2018, 08:33 AM
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The ZJ fuel tank is on my to-do list (including raising the breather tube, ~24 gal capacity)
I am curious to see what you come up with as I was planning on replacing my fuel pump at the same time!
The Walbro GCA733 is pretty reasonably priced at $100 and I ran their 225lph "improved" Ford GT supercar pumps in my mustang up to about 650hp where they were maxed out on a dual KB BAP controller. Always reliable, never leaned out on me
I am curious to see what you come up with as I was planning on replacing my fuel pump at the same time!
The Walbro GCA733 is pretty reasonably priced at $100 and I ran their 225lph "improved" Ford GT supercar pumps in my mustang up to about 650hp where they were maxed out on a dual KB BAP controller. Always reliable, never leaned out on me
08-17-2018, 07:50 AM
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Interesting.....
08-17-2018, 08:21 AM
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So the stock fuel pump assembly, FPA, is constructed very interestingly.
There is a spring and side clips that allow for it to slide and vary the height of the assembly.
I am sure that this is so that the bottom sits flat on the inside bottom of the fuel tank.
I think that it is also because the stock tank is plastic and flexible and will deform. If it takes a hit or jack etc it will deform and shorten the tank height.
If the FPA has a fixed height, the blow could break some FPA parts.
A potential flaw in this design is the 'slip' connections of the fuel line from the fuel pump and the top hat of the FPA to allow for the varying height. These are just O ring sliding connections. I can see over time this leaking or failing and loosing pressure.
The obvious fix is a fuel tank skid plate.
In fact, on our 'beater' jeep when wheeling in the big rocks without a fuel tank skid plate when we came down hard on a rock on the gas tank, the FPA popped out of the tank. There was a hole cut in the floor of the XJ and this was fairly easily screwed back into place on the trail. It did pop out a few more times while wheeling that weekend. The no cost solution was to put the gas tank inside and ratchet it in place. Not a good solution but for the 'no buck' 'Beater' it worked.
There is a spring and side clips that allow for it to slide and vary the height of the assembly.
I am sure that this is so that the bottom sits flat on the inside bottom of the fuel tank.
I think that it is also because the stock tank is plastic and flexible and will deform. If it takes a hit or jack etc it will deform and shorten the tank height.
If the FPA has a fixed height, the blow could break some FPA parts.
A potential flaw in this design is the 'slip' connections of the fuel line from the fuel pump and the top hat of the FPA to allow for the varying height. These are just O ring sliding connections. I can see over time this leaking or failing and loosing pressure.
The obvious fix is a fuel tank skid plate.
In fact, on our 'beater' jeep when wheeling in the big rocks without a fuel tank skid plate when we came down hard on a rock on the gas tank, the FPA popped out of the tank. There was a hole cut in the floor of the XJ and this was fairly easily screwed back into place on the trail. It did pop out a few more times while wheeling that weekend. The no cost solution was to put the gas tank inside and ratchet it in place. Not a good solution but for the 'no buck' 'Beater' it worked.
08-17-2018, 08:25 AM
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I measured the new stock FPA while sitting on the table.
Fully extended in the 'resting' state, from the bottom to the underside of the flange that sits on the gas tank threaded flange, measures 11.625"
When fully compressed, it measures 10.125".
So there is 1.5" of travel in the FPA.
I need the installed height of the FPA in a good condition gas tank so I can build my 'fixed' length FPA.
Fully extended in the 'resting' state, from the bottom to the underside of the flange that sits on the gas tank threaded flange, measures 11.625"
When fully compressed, it measures 10.125".
So there is 1.5" of travel in the FPA.
I need the installed height of the FPA in a good condition gas tank so I can build my 'fixed' length FPA.
08-17-2018, 08:29 AM
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Could you use it at the top of it's travel and install some kind of flexible pickup at the bottom?
08-17-2018, 05:11 PM
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I'm going to use a Holley HydraMat. It attaches right to the bottom of the fuel pump. It needs to sit right on the bottom of the gas tank.
The upgraded fuel pump is slightly longer than the stock fuel pump.
It will be tight.
I tried to measure one of my tanks but the bottom was caved in and measured like 8.125" which I know is wrong.
I'm going to have to pull a good tank from one of my parts jeeps and measure it. Probably will just cut it in half so I can see exactly what is going on.
The upgraded fuel pump is slightly longer than the stock fuel pump.
It will be tight.
I tried to measure one of my tanks but the bottom was caved in and measured like 8.125" which I know is wrong.
I'm going to have to pull a good tank from one of my parts jeeps and measure it. Probably will just cut it in half so I can see exactly what is going on.
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