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.

does any one think if you could put the switch on only two cylinders, you could have a button to run on 2 or 4 cylinders?

You could do it, and yes it would cut fuel to two of your cylinders but....

It would be a very unsatisfying experience and I recommend against it strongly.
-The engine would run rough.
-The power loss would be substantial, not only are you losing half your power, but your engine will still be working just as hard to pump air into and out of the two dead cylinders.
-The mixing of air from the two dead cylinders into the exhaust stream could drastically affect the readings your cars ECU gets from the sensors, causing the ECU to attempt to adjust the fuel mixture to compensate.

I'm sure some others around here can come up with more reasons why this is a bad idea.

you are possibly right about it being a bad idea, just figured it might help while in iddiling.

A search will reveal that the running-on-two-cylinders idea has been beaten to death, and that there's pretty much no practical way to do it, unless one was willing to make a custom cam, exhaust manifold, and ECU map to specifically use those dead cylinders as an air pump.

Just switching off the injectors is a sure-fire (no pun intended) way to make your car run awful, and probably get worse mpg.

Just a quick update...
My mileage shot up when I learned P&G.
My last 5 tanks: 40.76 US MPG, 39.216 US MPG, 40.937 US MPG, 48.14 US MPG, 44.934 US MPG.
The last 2 tanks are the P&G ones.
CMPG mileage log

P&G is great. Congrats on the great mileage. :thumbup:

The real problem is that this won't actually save any fuel unless the car is set up to know how to do this. If you turn off 2 cylinders, the car's O2 will see FAR to much oxygen in the exhaust stream. It will assume the car is running super lean, and will richen the mixture. This will dump twice as much fuel into the two running cylinders. All the extra fuel and air will then burn in the cat, and will probable reduce it to a puddle of molten metal under your car.

The GM pickups that do this shut off the valves on the side that isn't running, thereby reducing pumping losses for those cyclinders, and not messing with the O2 sensors.

you could always use something like this

i always though these buttons would be cool as an engine kill + push button start

http://pix.crutchfield.com/products/...100-o_dmt.jpeg

Quite good idea actually.. but could be improved on
 

This is a very interesting idea actually.

Depends on the engine of course as to how big the benefit is
and what the driving conditions are. I just drive around town
up and down hills, so i would expect an increased benefit
from this rather than a decreased benefit.

Vibrations - if the lubrication system in a engine is working
really well then you wouldn't expect to get more vibration.
Actually, you might expect less. No explosion/combustion is
more likely to make the engine run smoother.

At lights and when the vehicle isn't moving, one doesn't
need more power. Being stuck at lights is a total fuel
waste.

This system could be improved by hooking the switch so
that it automatically engages after a certain engine
temperature and when the car is in neutral gear.

so for me it is :thumbup:

Good write-up Fridge. This will likely help me complete my own fuel cut-out. Are the ignition coils and injectors all wired separately?

I must be a little slow, why would you want to shut off the injectors?

Dosn't the ECU shut them down when coasting?

I know that even in a 1982 Camaro the injectors shut off after 5 seconds of rolling with a no throttle condition, and come back on as soon as you take off.

Rick

The engine will shut down the injectors when coasting with an automatic or the manual in gear, but that will also use the rotational force of the engine turning to "brake" the car. By putting the transmission in neutral and shutting off the engine, you are able to coast longer. You can key off and then back on, although this turns off other stuff as well (and you have the same caveat - turn back on too fast and the engine keeps running).

I have the xA and the schematic looks similar. The single 15A fuse that powers the injectors also supplies power to just about everything else in the ECU. In fact, that fuse feeds the ignition switch, so it would be the equivalent of taking the key completely off - no acc power either. I am not sure if I'm going to try and follow the black/red wires back to where they're joined or not; I may try and cheat and follow the black/red wire out of the ignition switch.