How to drive an injector

[mic*]

Hi all,

Was wondering if anyone can suggest any ways possible to drive an auxillary injector with a factory ECU?

Aquamist make this thingy that can tap an injector signal, drawing "less than 10mA" from the line. Does this sound like some sort of electromagnetic induction device?

Can anyone delve further into the electronics of tapping an injector circuit? If you just wired one in series, i imagine flow would be divided relative to resistance. In parallel the ECU would not like the current draw?

Thanks.

[mrshin]

Depends on a few things...
How many injector channels are there on the original ECU? If it's old school and there's only one, chances are the ECU won't mind and extra injector in the circuit, provided the current draw isn't too high. An ECU with a dedicated channel for each cylinder will probably have less tolerance if one channel has a much greater loading.

'Tapping the injector circuit' is not anything amazing, it's just using the existing pulse to trigger another injector driver, which has it's own transistor to carry the additional current. Think of it as being (sort of) like a high-speed relay.

[jonra23]

Jaycar make a kit that will let you run an extra injector and also to tune it to run at different ratios if you need.
Kit is KC-5384 Digital pulse adjuster kit, also need another kit KC-5386 to adjust ratios.
http://www.jaycar.com.au/productView...Max=&SUBCATID=

have used the same kit to alter air fuel ratios on rb30det, reasonably easy to build.

[mic*]

Depends on a few things...
How many injector channels are there on the original ECU? If it's old school and there's only one, chances are the ECU won't mind and extra injector in the circuit, provided the current draw isn't too high. An ECU with a dedicated channel for each cylinder will probably have less tolerance if one channel has a much greater loading.

'Tapping the injector circuit' is not anything amazing, it's just using the existing pulse to trigger another injector driver, which has it's own transistor to carry the additional current. Think of it as being (sort of) like a high-speed relay.

So on old EFI ECU's the comp pulses all injectors simultaneously, even with multi-point injection? Ie they are all wired in parallel on the one circuit. I did not realise this.

Its a gen3 1G...

[JustCallMeOrlando]

The 1G has two injector drivers, it drives 3 at a time. It just sits on the back of the valves when fired on the exhaust stroke and gets sucked in next time the valve opens.

[mic*]

So how do you think the ECU would like four?

Also what should the base fuel pressure be? And what size are my injectors (gen3 1ggze)?

Thanx for all the help.

[JustCallMeOrlando]

Not entirely sure. 4 per channel might be alright, you might have to suck it and see. Base fuel pressure is around ~40psi isn't it (?). As for your injector size, nfi. Gen2 1G are 285cc and Gen3 are 315cc.

[Ben Wilson]

Jaycar make a kit that will let you run an extra injector and also to tune it to run at different ratios if you need.
Kit is KC-5384 Digital pulse adjuster kit, also need another kit KC-5386 to adjust ratios.
http://www.jaycar.com.au/productView...Max=&SUBCATID=

have used the same kit to alter air fuel ratios on rb30det, reasonably easy to build.

I'm using one of these to drive the fuel injector for my water injection, it works like a charm.

[o_man_ra23]

I shouldnt like to load up the ECU any more than it already is, based purely on the amount of heat required to run it. Most ECUs are placed in kick panels, above gloveboxes, and anywhere else that has no ventilation, but cant be seen (boxes arent aesthetically pleasing to the average motorist). Sooo... the less current draw through the ECU the better. I should imagine the Jaycar kit to have a high input impedance, and therefore would not affect your ECU's power output more than a few milliamps (stuff all really), and as they are configurable, it can be used to tune the car, rather than just throwing on an extra injector that will solve one problem, and cause another. The Jaycar kits, developed by the team from the Silicone Chip magazine tend to be quite robust and reliable when put together properly. I would recommend using a device such as this to control the injector, rather than risking an overload on your circuit, which would have either disasterous concequences, or it would use huge amounts of fuel and cause the car to run pig rich, and be less powerful than it could be.

Cheers, Owen

[brett_celicacoupe]

if your worried about loading up the ECU too much, you could have it so that the water injector is ONLY piggybacking off the ECU when you have your foot flat to the floor....or close to it. this way the ECU wont be loaded up with an extra injector for prolonged periods of time... unless ofcourse you drive like a lunartic

maybe just mount a button on the floor.....or even tap a wire from the TPS if its possible. it should also let you use the water sparingly as its likely you will be using a water contatiner similar to the size of a windscreen washer bottle?

[mic*]

Yeah Brett your on my wavelength.

Was gonna put a 10psi N.C. Hobbs switch in the parallel injector circuit... Or else invest in the jaycar thingy...

To date i have a 7Lph vapourising nozzle. It was running on the 10psi Hobbs switch i have, but after fixing the ABV "overboost" leak, 10psi came on WAY EASY and i was drowing it when i opened up the throttle at low revs. I switched to a 15 psi switch and started cooking teflon off the charger...

[jonra23]

The Jaycar will let you tune your water injection based on injector duty, at low injector duty cycles(low load) conditions can set water injector pulse to 0%, at higher duty cycles can as required.
There is 128 points of calibration that you can adjust up and down.
If you want i can scan a couple of the pages from the book that i have on that explain how it works and how to tune and pm/ post.
The control box only needs to be plugged in when tuning, can be used with Jacars boost control kit as wsell.

[o_man_ra23]

if your worried about loading up the ECU too much, you could have it so that the water injector is ONLY piggybacking off the ECU when you have your foot flat to the floor....or close to it.

This can still fry the ECU if not done properly. Without opening the ECU box, finding out what transistor they are running, the thermal efficiency of the heatsink, the ambient temp where its slotted, and the loading on the trannie, you dont know how close to popping it may be. Always, if in doubt, play it safe. Otherwise you will be searching the forums for a new ECU, and after that, you will be buying the Jaycar kit, or other external driver which you should be buying in the first place. A mistake here could be quite costly, can you afford the cost and the downtime??

Just a friendly warning from a concerned engineer. Brett, you will learn probably in third year that you need to over-compensate for possible mistakes.

Cheers, Owen

[mic*]

This can still fry the ECU if not done properly. Without opening the ECU box, finding out what transistor they are running, the thermal efficiency of the heatsink, the ambient temp where its slotted, and the loading on the trannie, you dont know how close to popping it may be. Always, if in doubt, play it safe. Otherwise you will be searching the forums for a new ECU, and after that, you will be buying the Jaycar kit, or other external driver which you should be buying in the first place. A mistake here could be quite costly, can you afford the cost and the downtime??

Just a friendly warning from a concerned engineer. Brett, you will learn probably in third year that you need to over-compensate for possible mistakes.

Cheers, Owen

My sentiments exactly Owen. I have one question that will probably decide for me; If people upgrade to larger injectors on a factory ECU, wouldn this be doing the same thing, Ie drawing more current?

If the above is true, I intended just to splice into the wiring of an injector at a neat point in the loom and "suck it and see"...

[jonra23]

when replacing injectors it is important and normal practice to get injectors with same impedance so as not to overload ECU