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Topic: 2.3: Where do the injectors ground? (Read 2626 times) previous topic - next topic

2.3: Where do the injectors ground?

I ask because I want to wire in an injector kill switch for better engine braking, which is good for mpg and decelerating in the winter.

My idea is to have the ground for the injectors run through a momentary switch/button. Since the injectors open when grounded, I can push the button (maybe mount it on the back of the steering wheel, somewhere I can hit it without looking for it) and essentially have manual decel fuel cut down below 2000 rpms. Sometimes I dont get fuel cut at all on decel so this would be helpful anyway.

I want to put the switch inline with the ground so when I hold the button down it interrupts the ground and causes the injectors to stay closed.

Can anyone help me out with this?
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #1 –
You have it all wrong, the injectors fire(open) when grounded which is the EEC's function... They are supplied a continual 12v, which is what would have to be interrupted to preform injector shut down as you want...

2.3: Where do the injectors ground?

Reply #2 –
Quote from: TurboCoupe50;292958
the injectors fire(open) when grounded which is the EEC's function...



Exactly thats what Im talking about, I want the switch to keep that ground from happening thus keeping the injectors closed.

Pins 58 and 59 on the LA3 are for "Injector bank" 1 and 2 respectively, are these for +12v or grounds? I thought all injectors fired simultaneously as well?
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #3 –
Nope, they're "bank fired" to reduce fuel consumption.  There's no point in firing an injector while the piston is somewhere between compression and exhaust stroke, but firing them in pairs was more efficient than re-designing the EEC which was originally designed to fire only two injectors.
 
But, what you want to do is either open the TWO wires going back to the EEC to interrupt the grounding done by the EEC, OR, much easier, drop the single 12V feed to the injectors.  The grounding is done by open collector outputs which turn on to ground the injector to open it.  If you open the 12V circuit feeding the injectors, they will not open, and you'll get a total shut-off of the injectors.  HOWEVER, don't be surprised if you start seeing Lean indications from the O2 sensors if you do that.  The EEC is designed to keep some fuel flow to the cylinders for cooler cylinder temps and lower emissions of NOS.  You may introduce some lean miss problems on your plugs too.  Spark plugs don't like to be fired with nothing to burn.  Who KNOWS what will happen when you let go of the switch and the EEC has really cranked on the injector pulses.  You may get some really nasty results in the catalytic converter which will get red hot when lean, just like it does when rich.  Dump fuel rich exhaust in there (when you first let go), and it's liable to give you a very nasty surprise under the car.  Throttle chop is exactly one of the things EFI eliminated by having the IAC go wide open until you get below a certain RPM, and keep some fuel going in there.  Throttle chop makes some nasty pollutants.  Not that I'm a tree hugger, and I too like good engine braking.  That's what kinda brakes I learned to drive with.
:birdsmily:
(X2) '86 Thunderbird, 3.8L CFI, C5 Tranny
 
'92 F-150, 5.0L EFI (SD), M5OD Tranny, 3.08 Dif
 
'70 VW Beetle, 1780cc, twin Solex 43's.

2.3: Where do the injectors ground?

Reply #4 –
leme see,,

you gain control of your injectors by either way already explained
you are on snow along the highway
you hit your kill switch just a little too long
engine dies
power brakes gone
power steering gone

or...
you hit your kill switch and the car dies for a moment but recovers
during recoverey the eec will compensate for the loss
vac pres is low during the high rpm recovery
eec compensates by surging the fuel
vac to power brakes is low
car seem to leap forward out of control
brake pedal seems non responsive during stopping
engine may surge like this a couple times

meanwhile, your 40 feet behind another car with this dangerous distraction.

you would be better off insuring the rear brakes are adjusted real well and practice to feather the brake

2.3: Where do the injectors ground?

Reply #5 –
Quote from: jcassity;293024
leme see,,

you gain control of your injectors by either way already explained
you are on snow along the highway
you hit your kill switch just a little too long
engine dies
power brakes gone
power steering gone

or...
you hit your kill switch and the car dies for a moment but recovers
during recoverey the eec will compensate for the loss
vac pres is low during the high rpm recovery
eec compensates by surging the fuel
vac to power brakes is low
car seem to leap forward out of control
brake pedal seems non responsive during stopping
engine may surge like this a couple times

meanwhile, your 40 feet behind another car with this dangerous distraction.

you would be better off insuring the rear brakes are adjusted real well and practice to feather the brake

As long as it's in gear(manual tranny), vacuum, P/S, etc is not affected... On a automatic what you say is possible, as the engine could stop spinning...

The braking system on a TC is electrically actuated(electric motor) no vacuum is applied, so it would make no difference there, even if the engine were stalled...

I can't see a issue with firing the spark plug with no fuel... I've read some EFI systems do just that on deceleration above 2000 RPMs to conserve fuel... Cadillac did it on the 8-6-4 V8 by stopping valve action, the plugs continued to fire...

2.3: Where do the injectors ground?

Reply #6 –
Quote from: TurboCoupe50;293034
As long as it's in gear(manual tranny), vacuum, P/S, etc is not affected... On a automatic what you say is possible, as the engine could stop spinning...

The braking system on a TC is electrically actuated(electric motor) no vacuum is applied, so it would make no difference there, even if the engine were stalled...

I can't see a issue with firing the spark plug with no fuel... I've read some EFI systems do just that on deceleration above 2000 RPMs to conserve fuel... Cadillac did it on the 8-6-4 V8 by stopping valve action, the plugs continued to fire...


maybe i should have noticed his sig before i commented.

lack of experience on the tc, didnt account for the brake system type., my mistake.

as for the plugs,, some 4cyl 2.3 with 8 plugs fire 4 in the exhaust headers.  makes sense they wouldnt really need fuel to carry out thier duty.

2.3: Where do the injectors ground?

Reply #7 –
Yes I couldnt really see anything bad happening so as long as the ignition is on I have power brakes, and Im not too worried about steering manually. And as long as im in gear the engine should be turning.

Our engines already cut fuel on decel above 2000 rpms (or are supposed to).
Its pretty easy to notice with a manual trans, cruse along at 55 and drop to 4th, you should feel a drag on the engine. At around 2000 rpms that drag will suddenly go away.

All I really wanna do is be able to make that drag happen on demand and below 2000 rpms.

For an automatic as long as the TC is locked it shouldnt stall.


So you guys think it would be simpler to interrupt the +12v going to the injectors? Is that in the fuse panel? How much current runs through there?
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #8 –
Power is fed from the IRCM(EEC relay) to the red wire(s) feeding the injectors... Easiest would be on the injector harness...

2.3: Where do the injectors ground?

Reply #9 –
Which pin from the IRCM is for the injector power then? What color is the wire?
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #10 –
The feed from the IRCM feeds several places, you'll have to tap into the harness...


Quote from: TurboCoupe50;293048
Power is fed from the IRCM(EEC relay) to the [COLOR="red"]red[/COLOR] wire(s) feeding the injectors... Easiest would be on the injector harness...

2.3: Where do the injectors ground?

Reply #11 –
So there is a red wire in the injector harness that splits and feeds all  four injectors?
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #12 –
According to the EVTM, there is one power connection(red) on the injector harness that junctions into separate feeds for each injector... Dunno how close to the plug this junction is, you'll have to look...

2.3: Where do the injectors ground?

Reply #13 –
I wonder if it could be in the plug itself.
93 Festiva L, 193k miles, BP+T/G25MR swap, T3 50trim .48/.42, SRT FMIC, Capri electronics/Rocketchip, 2.5" exhaust
bests: ET 12.86, MPH 110.25, 1.92 short
02 Subaru Impreza WRX, 129k miles
97 Subaru Impreza Outback Sport, 236k miles

2.3: Where do the injectors ground?

Reply #14 –
Not much chance all four wires could be crimped into the terminal in the connector... I'd look for a dog knot near the plug though... Possibly could tap into the feed side of the plug instead of the injector harness itself...