Wiring an injector cutoff switch

[HeadlesNorseman]

This is just some basic question/theory i have regarding an injector cut off switch.

The car is a 1990 civic, with the throttle body DPFI injection

Disclaimer: i am very experienced with automtive/especially honda wiring, so im not scared and i can diagnose and fix anything i mess up

Question on theory: I assume fuel injectors operate by recieving a 12 volt positive signal, constant, and the ECU then switches the ground as its pulse width mod. Interupting which one of these would be best? how many amps are used to operate the injectors? i have a 30a relay and a 20a switch wired up and ready to go. This is where im stuck!

My car only has 2 injectors, like a 2 barrel carb: a constant and a "full throttle" injector

Now... each injector has 2 wires listen in its ECU pinout, but i can not figure out which is which. they just say A5 manin injector with A7.

It is my understanding that if you cut off this signal, the ecu does not like it very much. And with personal experience, it DOES NOT like the key being switched off. Will be hard to restart, CEL, and erratic idle for a moment.

The real question, do i interupt the ground for the injectors, or the constant 12 volt signal? and do i want to do this at the injector itself or at the ecu?

[wagonef8]

I would interrupt the 12v constant ....on the ECU they go by pairs A1 and A3 and A5 and A7 cant remember the colors but I know they are yellow and red you will have to switch them all I think it be easier to do on the plug on drivers side by fire wall since it goes back to single wire to each injector

[some_other_dave]

Can't you find an exposed bit of the connector to test with a voltmeter?

Do the wires all come from the ECU? I think I recall that in the MPFI that my car had the hot wires actually came from a relay and not from the ECU at all. (I could be confusing it with a different car, though.)

A wiring diagram would be a big help, too. Do you have access to one?

-soD

[wagonef8]

My bad I got all mixed up ...the wires I described are the grounds to the ecu

[Cobb]

On the newer hondas with injectors you cut the yellow black wires as the ecu grounds them out to make em work.

[Occasionally6]

Re. current draw on the injector circuit: less than 30A. The switch doesn't matter if you are using the relay; the switching side of a relay draws only a fraction of an Amp. You should be using a relay with diode protection of the switched circuit.

Either the ~14V (alternator charging) or the earth prior to the ECU will work. My personal preference is for the earth side.

It's usually easier to make connections near the ECU. It's clean and all the wires are accessible and in the same vicinity as each other.

If you have an issue with the ECU not liking the injector disconnected you can put a dummy "injector" in the circuit, in parallel to the real injectors, and switch to and from that. The dummies could be injectors, or at least the solenoid windings from them, junkyard sourced.

This problem is part of any propane fuel conversion so you might get some answers from a shop local to you that does such work.

[Mista Bone]

Honda DPFI is it's own crazy animal....

[pete c]

I would like to do the same for my '09 Sonata. 4 cylinder, 5 speed.

Any recommendations on the best way to do this would be appreciated.

[Cobb]

See if you can find a wiring diagram and what color are the injector wires to start, the copy the switch aspect.

Originally Posted by pete c

I would like to do the same for my '09 Sonata. 4 cylinder, 5 speed.

Any recommendations on the best way to do this would be appreciated.