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Fuel Pump Rewiring
Well, after some discussion with Bruce Lewis and 2 nights of studying the shop manual, I figured out how to rewire the fuel pump for better operation on the TurboII. Why rewire the fuel pump? - Even on a car with a new alternator, new battery, new battery terminals, and clean electrical connections (mine) I saw as low as 10v to the fuel pump with a load on the system (lights on, stereo cranked, heater on, etc.) - The fuel pump should, under boost, be seeing at LEAST 12v. Reduction in voltage=reduction in fuel flow=bye-bye motor. Considerations when rewiring the pump... - First off, it should operate as normal. You turn on the key and go; no extra switches, etc. - The fuel pump resistor circuit should continue to work. This drops the fuel pump voltage to 9v at idle and cruise to improve fuel economy. - The safety switch in the air flow meter should continue to work. The airflow meter, when closed, turns off the fuel pump. So, if you roll the car, you won't be pumping gas out of the car at 30-40psi making a big fireball :). Some caveats about doing this job - 1. This is NOT EASY. If you are comfortable with 12v electronics (you've wired up a few stereos) you should be able to do this. You need to test everything as you go along. If this doesn't work, your car will not run. If you really hose it up, you could have inadequate fuel pump voltage. I WILL NOT TAKE ANY RESPONSIBILITY - you broke it, you bought it. 2. I'm also assuming that you know all the standard procedures for wiring stuff - solder your connections, heat shrink tube or electrical tape all bare wire, etc. 3. Just take your time with it. It's really not that hard, but there's a lot you have to keep in mind. It took me the better part of an afternoon to do, most of which was double-checking and triple-checking my theory on how stuff is going to be hooked up. OK, so how do you do it? You'll need - - a 12v automotive relay (Radio Shack - "30 Amp Auto Relay", cat #275-226) - about 15 feet of 12 gauge wire - an inline fuse for the 12 gauge wire - about 20 feet of speaker wire (you need two wire runs to the back of the car, and speaker wire has 2 wires) - various crimp-on connectors (to connect to the relay and positive battery terminal) - electrical tape OK, first off let's run the wire. The speaker wire needs to start at the airbox location in the engine bay and end by the driver's side rear shock tower. The 12 gauge wire needs to come from the postive battery terminal to the same spot (don't hook it up yet! :) Hook the inline fuse between the positive terminal and the 12 gauge wire - you always want the fuse close to the battery. I used a 15 amp fuse, and it seems to be adequate. You might want to run both wires at the same time - makes it a little easier. Next, it's time to move the resistor and relay. Remove the airbox. There's a metal bracket that has a relay and a aluminium box that looks like a heat sink. It connects to the wiring harness with a large round white connector. Inside the connector should look like so - ____--____ | - - - | | - - - | ----------- Let's label these wires, as per the shop manual. Diagram below is on the relay/resistor side: ____--____ | E C A | | F D B | ----------- OK, cut the connector off the wiring harness. Leave enough slack on both sides of the cut - we'll be re-splicing the connections in. Connect the speaker wire to C and D (one wire to C, the other to D). So, now you've got your resistor and relay with a cut off connector. Move to the back of the car. Remove the driver's side rear speaker assembly and the plastic trim above where the jack goes. Pull the covering on the side of the hatch area forward. On the side of the shock tower closest to the rear of the car is a wiring harness with a white connector. This is the connection for the fuel pump. There's 4 wires there - 2 for power and ground, and 2 for the fuel level sender. On the fuel pump side of the wiring, the two topmost thicker wires are power and ground. I believe power had a white stripe and ground is just black. You might want to test it first and make sure you've got the right wires. Cut both of them about 6 inches down from the connector - you might need to cut off some of the covering around the wires. Time to hook up the relay. Here's what you want to do - use the power lead that normally comes into the fuel pump and the ground on the car side of the wiring harness to turn the relay on and off. Run the 12 gauge wire from the battery terminal into the relay. The relay has 4 connectors. Two are for power and ground to activate the relay, and the other is the circuit that the relay activates. The lead that normally activates the fuel pump should go to switch the relay on, with the opposite connector going to ground. The output from the fuel pump resistor relay (see below) goes into the 3rd connector, with the lead to the fuel pump going to the final connector. Time to wire up the resistor relay. Take the wires from terminals A and E and splice them together. Take the wires from terminals B and F and splice them together. Attach the speaker wire you ran from the front of the car to terminals C and D (one to C, the other to D). Run a wire from the relay (the opposite terminal that the 12 gauge wire is on) and attach that to terminals A and E that are spliced together. Run a wire from the spliced terminals B and F to the fuel pump positive lead. You can ground the fuel pump separately or just attach it to the same ground wire it used in the past on the harness. After you get the fuel pump resistor relay wired up, make sure to put it in a spot where it has plenty of "breathing room". It gets REALLY got and can melt the insulation off wiring (as Bruce found out). I nylon-tied it in the area where the antenna motor is; it's just got metal around it, nothing meltable. OK, go back to the front of the car. There should be 4 extra wires where you cut the resistor relay off. Splice the wires that were on A and B together, and the wires that were on E and F together. This lets the signal from the main fuel pump relay travel back to the fuel pump area, and it activates the relay there to bring the new 12 gauge wire online with the pump. Time to test it. Get a jumper wire and jumper the fuel pump check connector - it's a yellow two-prong connector on the passenger's side shock tower in the engine bay. It might be buried a bit, so keep looking. After jumping the connector, turn the key to "On" (don't start it) and go back to the hatch. You should hear the fuel pump running. If not, check your wiring for good connections. Yes, this is a VERY complicated procedure, and you have to keep a lot of things straight. If you have a shop manual, turn to pages 4B-70 and 4B-71 - there's a really nice diagram of the whole setup there, along with a diagram of the fuel pump resistor relay. This job took me just a Saturday afternoon. The prinicpal of the idea is moving the fuel pump resistor relay near the back and splicing a relay carrying a REAL voltage into the equation. This method keeps all the factory safety features (air flow meter cutoff, check connector, etc.) It also allows the resistor to function properly. When the relay for the resistor is open, all the current goes through the resistor and is dropped to ~9 volts. When the relay closes, it makes a path with no resistance through that part of the circuit, and we all know that electricity takes the path of least resistance. Results? Well, I'm now seeing over 13v at the fuel pump with no electrical load at wide open throttle. With stereo cranked, headlights/foglights on, AC blowing, etc. I see about 12.5 volts. Sweet! If any part of this is unclear, please let me know. It's a pretty complicated procedure with a lot of wire-deciphering, and I think I got the gist of it down. This procedure is VERY necessary with upgraded fuel pumps and fuel pressure regulators as Bruce Lewis found out - the stock wiring just can't deliver enough current. Hopefully this $10-20 mod will help save some modded engines out there! :)