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.

http://i69.photobucket.com/albums/i4.../mod_schem.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/eng_inj.jpg
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.
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http://i69.photobucket.com/albums/i4...nwrap_left.jpg
Almost done unwrapping, here is the left side, I will unwrap as far as the double white lines.
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http://i69.photobucket.com/albums/i4...wrap_right.jpg
And the right side...
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http://i69.photobucket.com/albums/i45/jvnn/prep_cut.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/soldered.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/seal_up.jpg
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.
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http://i69.photobucket.com/albums/i4...rappingjpg.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/done.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/relay.jpg
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.
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http://i69.photobucket.com/albums/i45/jvnn/shifter.jpg
Here's the button switch on my shifter.
This is a temporary mount and from using this I know I want it lower down.
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http://i69.photobucket.com/albums/i4...mod_schem2.jpg
Here are two schematics showing the original configuration (left) and the modified version (right).

Any feedback from doing this kill switch yet?
Anything you like or dislike about it?

I did something very similar, only I found the single wire that led to all four injectors, so I didn't cut and splice all 4.

Mine kills and restarts very quickly.

If you want to get really fancy, replace the entire stick-shift knob with something like this...

http://gallery.me.com/benhdvideoguy/...12215010400003

The black switch now kills my fuel injectors, and the blue one will be for economy-boosting grappling-hook launchers.

I'm very happy with it!
It works exactly as I expected it to.
I wouldn't say it kills instantly but that's not the fault of this design, you just have to hold it long enough for the engine to stop spinning.
I do want to mount the little pushbutton lower so I don't touch it unless I am intending to.
It isn't really a problem, but it's annoying to have it under my fingers during normal shifts.

A grappling hook sounds nice, but what I really want is a compressed air cannon to exact revenge on annoying drivers.
I think the perfect ammo would be the plastic Yoplait yogurts.
Imagine one of those spreading over the window of somebody's car!

I don't mean to rain on the parade... But it seems to me like you went to a lot of work that could have been avoided, by simply interrupting the injector fuse at the fuse block... If the xB doesn't have an injector fuse at the block, though, feel free to ignore my ignorance... :)

And I don't know how you hold the stick, but I usually drive with my hand around the circumference, and would therefore install the switch into the head of the shifter knob. Just my $.02

I couldn't find any fuse on my truck specific to just the fuel injectors. At least on mine, it was just one wire to cut and splice for the kill switch.

True, one is better than 4. Too bad you have a pre-OBD-2 truck, as I have the service manuals for the ODB-2 Dime series, and it shows the injector fuse in the diagram. :p

BTW, did you just install your switch, or is some of the fuel log showing switch use? Also, have you experienced any re-starting hiccups? I know you said it restarts good, but my fathers Bravada, (though it is the 4.3), usually starts up again ok, but every once in a while it'll just crank forever before it restarts. 20-25 seconds worth.

Check out the first schematic in my OP, On my car the 'EFI relay' does not switch the voltage to the injectors on or off. It does have an injector fuse, but that also controls power to several other items. I wanted to cut the injectors only.

I seem to lay my palm over the top of the shifter and let my fingers hang down the front.

I can't make out what else is going on there, is the middle fuse the one that cuts the injectors? And it looks like that goes into the ignition...

And I believe they call that the crows foot method. :p

BTW, how's bump-starting on it, or have you tried that yet?

The xB bump starts quite easily-- I do it regularly, usually at about 25-30mph in fifth.

I do need to look at the wiring diagrams and see if there's a better way to hook up a kill switch. I do not doubt the effectiveness of this method, but I'd be happy to avoid opening up the engine wiring harness.

Jams: yeah it was kind of a pain, but it's done now except for a better mount for the pushbutton...

Atomic: Yeah the middle fuse is the one, I didn't want to open the circuit at the fuse because there's several other things that take power from the circuit which I don't want to speculate what effect it might have to cut them out.

And bump starting - a piece of cake.