1995 3000GT VR-4: MKIV Toyota Supra Fuel Pump Upgrade

• Why Do I Want To Do This?

  • After installing a differential fuel pressure gauge, I realized that my fuel pressure dropped by up to 12psi under high fuel flow conditions. I rewired the fuel pump with the RDR fuel pump rewire, and this helped, but did not eliminate the fuel pressure loss. I still observed up to a 10 psi loss of fuel pressure at high-load and/or high-RPM conditions. To address this loss of fuel pressure, the common solutions are: 1) run less boost, 2) further increase the voltage supplied to the fuel pump, and 3) upgrade to a fuel pump with a higher flow capability. I chose door #3, and this page shows the installation process.




• How Long Will It Take Me To Do This?

  • If your fuel fittings aren't excessively stubborn and you take your time to be careful not to spill/drip fuel everywhere, it should take you 1-2 hours.




• Anything I Should Do Prior To Attempting This Procedure?

  • Make sure you have a clean, well-ventillated workspace that has no sources of open flames or sparks. Remember, you'll be working with gasoline that is very flamable. Treat it with respect, even if you see this task as an easy one.




• What Mitsubishi Parts Will I Need?

  • None




• What Other Parts Will I Need?

  • Toyota Supra (MKIV) Fuel Pump
  • Penetrating Oil (Aerokroil, PB Blaster, or similar)




• Where Can I Get the Stuff To Do This?

  	Part	Company/Contact	Part Number
  	Toyota Supra (MKIV) Fuel Pump	Toyota Dealer	Denso: 195130-1020 Toyota: 23221-46110





• What Tools May/Will I Need?

  • #2 Phillips Screwdriver
  • 14mm Line (a.k.a. Flare Nut) Wrench
  • 19mm Open-end Wrench
  • 8mm Open-end Wrench
  • 7mm Open-end Wrench
  • Socket Wrench
  • 6" Extension for Socket Wrench
  • 8mm Socket
  • Rubber Gloves
  • Bucket
  • Small Flat-Blade Screwdriver
  • Impact Driver with #2 Phillips Bit (optional)
  • Rubber Mallet or Hammer (optional)




• Erik's Review

  • This is one of the best, and probably most needed, upgrades I've done with my VR-4. The high-RPM range is SOOO much smoother than it was before. I didn't have a datalogger before I installed the Supra pump, so I have no idea if I was getting knock in the top end. I suspect I probably was. I also see NO loss of fuel pressure in as load and/or RPM increase. It just sits there, rock-solid at 3.2kg/cm^2 (45psi).
  • One note, however, is that the Supra pump's increased flow and voltage sensitivity cause mild fluctuations in fuel pressure in the low-load range and around the voltage transition point. With the RDR Fuel Pump Rewire, I observed the following. At idle and low load, fuel pressure stays at 3.2kg. As load increases, fuel pressure will drop to 3.1kg as load approaches the pump voltage transition. If load increases enough to cause the ECU to run the pump at full voltage and the load stays very close to that point, fuel pressure will increase to 3.4kg. As load increases further beyond the pump voltage transition point, fuel pressure gradually falls back down to the target of 3.2kg. Pressure then stays at 3.2kg for all loads above this point. I have not definitively determined if this pressure fluctuation causes problems, but I suspect that it does. I noticed frequent low-mid level knock around throttle transitions at light to moderate loads. My suspicion is that this fuel pressure fluctuation interferes with the ECU's ability to properly set the low- and mid- fuel trims.
  • My current course of action (December, 2004) is to rewire the Supra pump to receive full voltage all the time and install a new fuel pressure regulator that can handle the increased flow at low loads. So far, with just the "hotwire" wiring change (i.e. running the pump at 13V all the time), knock levels at light loads and throttle transitions seems to be greatly reduced, but not eliminated. I suspect that the limitations of the ECU's 3 discreet fuel trim ranges prevent it from correctly accounting for the extra fuel pressure at low loads due to the full-voltage Supra pump and OEM fuel pressure regulator. Once I install the new fuel pressure regulator, that will validate or disprove my theory.

The Procedure

	Remove RHS Cargo Tray and Spare Tire
	The cargo tray is held in by 3 Phillips Screws; remove it and the spare tire.
	Remove Fuel Pump Access Panel
	The panel is held in by 4 screws - if they're stuck, try using the impact driver to loosen them.
	Disconnect Fuel Pump Wiring Harness and Relieve Fuel Pressure
	Unplug the black wiring harness to the right rear of the fuel pump access hole. Now go try to start the car. Once it dies (or if it never starts), you have releived the presure from the fuel system. Keep in mind that there is still fuel in the lines, and it will drip out when you disconnect stuff. This step only serves to prevent fuel from spraying out when you disconnect stuff. Use appropriate caution when working with fuel!
	Lubricate Fuel Line Fitting
	Technically, you'll need to loosen the lower fitting before you can completely disconnect this fitting. However, I've usually found this one to be the harder one to loosen. Just in case you can't get this one loose and have to drive the car somewhere to get some help, there's no point in loosening the lower one until you're sure you can get this one loose. Once you've soaked the fitting with penetrating oil, lightly tap it with a wrench to allow vibration to help the oil get into the threads of the joint. Let it sit for 5 minutes or so.
	Loosen Upper Fuel Hose Fitting
	Put your 14mm flare nut wrench on the rearward side of the fitting and then put your 19mm open-ended wrench on the foreward facing side of the fitting. Keep in mind, that it's the hose-side of the fitting that will move, not the pump-side. If you position the wrenches as shown in the picture, you can simply wrap both of your hands around the wrenches and squeeze them together. Assuming you break the connection free, move on to the next step. If not, keep trying, or enlist the help of your muscle-bound neighbor. This is likely to be the hardest part of the whole process. You can do it. Also, you may want to stuff some paper towels under the fitting to catch any fuel that drips out.
	Remove Lower Fuel Hose Fitting
	This connection is accessed from under the car. If you're a contortionist and know where the fitting is, you may be able to do this with the car on the ground. If you're a normal person, then you'll probably need to have the car up on a lift or jack stands at this point. Follow the same basic procedure as the upper fitting: soak it with penetrating oil, position the wrenches, and squeeze until it breaks loose. Completely disconnect this fitting once you get it loose. Be careful not to let the fuel from the line go everywhere, especially all over you.
	Disconnect Upper Fuel Hose Connection and Remove Hose
	At this point, the hose is free to rotate, so you can go back to the upper connection and fully disconnect it. This completely disconnects the hose from the car, so remove it and put it in a safe place.
	Unbolt Fuel Pump Housing
	There are a bunch of 8mm nuts around the perimeter of the fuel pump housing; remove them all.
	Remove Fuel Pump Assembly From Car
	At this point, the fuel pump assembly is no longer connected to the car. You'll need to lift it straight up for about 1/2" to clear the mounting studs, and then you can rotate, tilt, and raise it to get the assembly out. It probably seems like it won't come out, but it will. You may need to move the fuel vapor return line out of the way - there's no need to disconnect it unless you really want to.
	Examine and Drain Fuel Pump Assembly
	After you pull the assembly out of the car, it will probably drip for a while, so it'd be good to have a bucket handy to catch the fuel. Make sure nothing looks damaged or like it needs to be replaced. The yellow thing with the mesh on the bottom of the assembly is an intake filter for the pump; make sure it's not clogged or torn.
	Remove Lower Fuel Pump Bracket
	There is a bracket on the bottom of the assembly that supports the fuel pump. It's held in place by a Phillips screw, which is frequently really stuck on there. I went straight for the impact driver to get this one loose, but you can try a normal screwdriver if you like. Don't strip the head of this screw or you will hate life.
	Remove Pump Inlet Filter
	The fuel pump inlet filter is held in place by a little clip that can be removed by inserting a small flat-blade screwdriver under the edge and prying it off. Work around the edge like you would the lid on a paint can.
	Disconnect Fuel Pump Wiring
	Remove the nuts on the studs coming out of the fuel pump and disconnect the wires. Remember which wire is which! If you don't take note, then remember that the negative (-) terminal of the pump gets connected to the wire that attaches to the metal part of the assembly, which is grounded to the chassis. The positive connection uses a 7mm nut and the negative connection uses an 8mm nut.
	Remove Fuel Pump From Assembly
	Carefully wiggle and/or rotate the fuel pump so that you can remove it from the assembly. The only thing holding the pump in place at this point is the rubber O-ring that provides the output seal. Be careful not to tear this O-ring if you plan to reuse it.
	Remove Cap, O-Ring, and O-Ring Support
	Remove the two plastic pieces and the O-ring from the output of the pump. You'll need to reuse these on your new pump.
	Compare Old and New Pump
	Make sure they're the same size and have the same connections.
	Replace Cap, O-Ring, and O-Ring Support
	Just like you took them off of the old pump.
	Lubricate O-Ring and Reinstall Pump
	Put a little WD-40 or some other lubricant on the o-ring before reinserting the pump into the housing. Failure to do this may cause the O-ring to tear upon reinsertion.
	Reconnect Wiring
	Connect both the positive and negative wires to the new pump.
	Install Pump Inlet Filter
	I used a small socket to press the clip back into place.
	Reinstall Pump Lower Support Bracket
	Reinstall the bracket and make sure the screw is on tight. Don't strip it!
	Reinsert Pump Assembly Back Into Fuel Tank
	Maneuver the assembly back into place. Make sure to hold the fuel vapor return line out of the way and take care not to bend the fuel level switch float arm. Align the holes in the pump with the studs on the tank and drop it down.
	Tighten Fuel Pump Assembly Nuts
	The service manual doesn't list a torque spec for these bolts, so use common sense. They're pretty small studs, so snug them up, but don't crank on them.
	Reinstall Fuel Hose and Tighten Upper Connection
	Reinstall the hose and rotate it to tighten the upper connection. The torque spec for this connection is 25 ft-lbs. Don't ask me how to get a torque wrench in there. I just used my finely-calibrated fingers to tighten it to 24.924 ft*lbs. Or was it 24.925?
	Reconnect Lower Fuel Hose Connection
	Put it back just like it came off. The torque spec is 22 ft*lbs. Again, I used my digital torque wrench. Digital. Get it? ;-)
	Reconnect Fuel Pump Wiring Harness
	Stick it back on there and make sure it clicks to indicate a solid connection.
	Pressurize System and Check For Leaks
	Perhaps the easiest way to do this is just to start the car. I chose to use my datalogger's fuel pump test feature to turn on the pump without starting the car. This allowed me to listen for leaks without exhaust and engine noise. Another way to test only the fuel pump is to connect to the battery's positive terminal the blue test connector between the battery and the firewall. Only once you're sure there are no leaks should you proceed.
	Replace Fuel Pump Access Panel
	Replace RHS Cargo Tray and Spare Tire