Replacing the Lotus Fuel Pump with a Walbro 255
As we make more and more power, the constraints of the stock fuel delivery system becomes evident.
The easiest step to add a little capacity to the stock fuel system is to simply "hot wire" it. This simply means to power the pump with battery voltage rather than reduced "system" voltage. The Stock fuel pump wiring travels a path of thin gauge wire through the immobilizer and the inertia switch before it every gets to the fuel pump. This path robs the pump of needed power. You can help boost its output by feeding a basic relay power from the battery or charging system. Cut the fuel pump hot wire and use it as your trigger wire for the relay. Your pump will remain wired for theft safety and inertia kill using this method. I placed my relay behind the drivers seat as the pic below indicates. This will give you about 1-2 psi more fuel pressure across the board and will "buy" you some wiggle room for mild SC'er applications
If you're going to add some big boosted power to your 2ZZ Lotus, you'll need a bigger fuel pump. The pump of choice is the Walbro 255. It's almost a drop in unit. However, Lotus did not make replacing the pump and easy task. There are two ways to gain access to the pump. Either through the access hole behind the driver's seat or to drop the tank. The easy part of the operation is getting the pump assembly, so it’s flip a coin on dropping the tank or using the access hole, as either of those methods is the “easy” part of this procedure. Lotus clearly spec'ed the hole for the pump assembly to fit into several thousandths too small and consequently the pump housing is very difficult to remove. Inching the housing out will be very tedious and frustrating. If you have the space, I recommend dropping the fuel tank for easier access to the pump assembly. However, should you choose to replace the pump from inside the car, I hope this tutorial helps guide the way.
Below you can see some data logs of the stock pump verses the Walbro 255. These are taken within a week of each other with the car making about the same power under very similar conditions. While both pumps lose some pressure as the dyno run goes on, the 255 is maintaining much higher pressure and flowing considerably more fuel than the stock pump.Here's the Stock Pump
Here's the Walbro 255 Pump
After you've located the access panel, your first should trace the area around the access panel so you know how much to trim later...
Then you'll want remove the access panel and make some room as you're going to need all the room you can get
Then remove the little orange clips that hold the sensor and fuel line in place. The Vent line on the left can be removed by pushing down on the retaining ring with a screw driver.
Next, you need make the access hole bigger, as the white fuel pump cartridge will come straight up and out of the tank. So trace an area that appears to clear the white cartridge and dremel the hole larger. Similar to the pics...
Examine the pump area to ensure that all fixing and retaining nuts have been removed. It should look like this.
Next you'll need to pry up on the pump housing a bit. The vent is very strong. I used a pair of channel locks as shown to help start the progression up. The pump is in the hole very tight--- too tight. It will eventually come out a bit as you work with it.
Once you get the pump up an 1/8" or so, you'll be able to fish the retaining rings out. Then you'll need a small pry bar, screw driver and that vent line and channel locks to inch the pump out little by little. This may take an hour or more, so be patient. It's a very tight fit.
The next steps assume that you have the pump out and it's time to take apart the pump housing... First split the housing in two
Then, disconnect the wires
Now remove the bottom of the housing. This secures the pump in place. Remove the rubber cushion as well
Next pull the pump out of the housing. It may help to push from the top side as well. Remove the fuel sock when complete
Compare the two pumps. The Walbro is a bit longer.
Install the fuel sock onto the Walbro. You must use a new retaining clip!
Trim the retaining cap as shown. A Uni-Bit works very well for this modification
Reinstall the pump and retaining cap. The rubber cushion will not be used.
Cut and solder the Walbro pigtail onto the stock wiring harness.
Reassemble the housing after connecting the wiring harness to the pump and housing. Pay special attention to be sure the pump wires are configured in such a way that they won't be rubbing on each other in the tank as shown in the picture...
Install the fuel level arm assembling and install the new setup in the car. It's much easier to put it all back in the car... Cycle the key and be sure everything is working correctly. If so, have a beer and give yourself a pat on the back!
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