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Old 10-29-2008, 10:43 PM   #1 (permalink)
The Fridge
EcoModding Lurker
Join Date: Oct 2008
Location: Colorado
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Fuel injector kill switch for '05 Scion xB

This is how I added a fuel injector kill switch to my '05 Scion xB.
The kill switch works beautifully except that you have to hold it down for a second or so while the engine stops spinning.
Otherwise it just fires right back up if you let off the kill switch too soon.
This car has the 1NZ-FE 1.5 liter engine, but I imagine that many small toyota engines will be similar.

Here's a 'shopped schematic showing the circuit for the fuel injectors.
Starting at the lower left, the battery provides the +12 volts which then goes through a fuse, the keyswitch, then the main junction block and finally divides to provide common hot for all four injectors.
The other side of the injectors goes to the ECM which switches current to ground for each injector in its turn.
-Notice that the 'EFI relay' does not switch the voltage to the injectors on or off.

My goal is to find a place to switch open the wire that provides this common hot to the injectors (thanks Hobbit).
This wire is black with a red stripe so I first searched for it at the main junction block - that turned out to be bloody impossible.
Then I went under the hood and popped off the plastic cover on top of the engine - ready to look at the wiring harness to find my wire.

Here I have just begun unwrapping the tape from the wiring harness.
The four arrows point to the connectors on top of each injector.
I was hopeful that the funny looking thing in the middle of the harness would be my junction of wires, but it turns out to be the common hot for the ignition coils.
It didn't help that these wires are also black with red stripe.

Almost done unwrapping, here is the left side, I will unwrap as far as the double white lines.

And the right side...

I am preparing to cut the four injector common hot wires.
I couldn't find where the single wire split to become four, so I decided I would risk cutting all four and joining them together. (turns out this worked fine)
The injectors each have two wires. All injectors have the common hot which is black with a red stripe.
The second wire is a unique color for each injector and must not be cut.
Because the four common hot wires originate from one wire, it is ok to reconnect them as one which I have done to make the job easier.
I will mark each wire on either side of where it is to be cut so that in the event of a problem it will be easier to re-connect them properly.
I ultimately made my cut by the semicircle on the left.

Here I have cut all four wires, joined each group together (coming and going) and joined them to the wire I will lead inside the cabin.
this is a solder joint that I wanted to do well.
I used an electricians copper crimp collar to join them mechanically, then soldered it carefully so it made a good solid connection.
Before this step, (after I made my cut) I had to un-thread and re- arrange some of the wires I had cut to make them lie closer together on the wiring harness.

Here I am sealing and insulating the connection.
My method is as follows:
-Smear silicone grease over the connection and inbetween the wires leading into the connection.
-Squirt a little grease into an over-long piece of heat shrink tubing.
-Shrink the tubing and fold the extra end over.
-Cover this with another larger diameter piece of heat shrink to hold the folded end closed.

Here I am beginning the process of re-wrapping the wiring harness.
I have secured everything roughly in its place prior to final covering with tape.

Done, ready to button it up under the hood!
The arrow points to my new wire taped on top of the harness.
I changed the brightness in the upper left to show where I led the wire into the cabin.
Leading the wire was actually quite a pain, I had to carefully bend a coat hanger and poke it through.
Once I was sure it went the right place inside, I taped the wire to it and pulled it through.

Here's the relay behind the glove box.
I included a connector that I can use to bypass the system in the event of trouble.

Here's the button switch on my shifter.
This is a temporary mount and from using this I know I want it lower down.

Here are two schematics showing the original configuration (left) and the modified version (right).

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