FYI/Model Train transformer & Injectors

[Bruce Allert]

Quite a few posts back I'd asked how to get a fuel injector to open safely so a cleaning fluid could be pressured through it. I received several answers and one of the "Brads" said it took (I think) 2.2 volts to open the injector long enough to clean it without harming it.
While wandering in Good Will I came across an old train transformer with the rheostat dial that allows you to move the train backwards, forwards, slower or faster. It also had AC & DC connections. I bought it for $3, took it home & hooked it up to a volt meter. I was able to dial 2.2V DC! I Connected it to an injector & stepped back while flipping the switch! The injector opened! I went ahead and pressured some cleaning fluid through it and saw the stream was good so I did all the injectors like that. It seemed to work. I used a hand pump for the pressurizing due to not having access to a fuel pump & pressure regulator to pump the fluid up to 29#'s. Anyone have any thought on this apparatus?
bruce

[rich]

Great idea, I had a friend build a injector clening machine once. I can't remember what he used to open the injector but I remember he used a Volvo fuel pump with no regulator. His theory was the higher pressure would clean better.

[GWN7]

Now all the old Lionel stuff I have will come in handy

Great idea

[bowlsby]

Great idea!

I seem to recall that the voltage for the 2.0L injectors is 3 volts

and that the resistance is 2.4 ohms.

[Racer Chris]

Two "d" cells will give you the required 3 volts.

I made an injector tester a number of years ago. I got a VW fuel injection pump and attached the inlet to a coffee can. The outlet went to a 914 pressure regulator, with a pressure gauge after that. I hook up an injector to spray back into the coffee can so the fluid recirculates. I can vary the pressure and witness the effect. The setup has two switches to turn the pump and injector on and off. I use a car battery to power the fuel pump. A couple of bottles of cheap injector cleaner and I'm ready to go.

[Bruce Allert]

Chris, sounds like a nice job & that's exactly what I had planned but, without the fuel pressure regulator and pump I couldn't wait! I just got the PR and am waiting for a cheap pump to pop up then I'll do a similar set up.
bruce

[jamcleod]

this is good info!!! i'm trying to hook up a FI tester by making a fuel system: fuel pump, pressure regulator, hoses, fuel rail with pressure gauge; but none of my swap meet fuel pumps work: all leak or don't pull gas out of can. in the next room i have an HO scale railroad with.... transformer. thanks for the useful info!!!

[anthony]

If they leak, pull the cover off and replace the o-ring.

[pbanders]

The voltage requirements of operating D-Jet injectors are somewhat complex. The injector is a solenoid. The coil has an inducatance of about 4 mH, and an internal resistance of about 2 to 3 ohms. The ECU drives the injector through a circuit that has a series 6 ohm load resistor, and a parallel RC circuit.

When the driver transistor turns on, about 12 V is applied to the series combination of the 6 ohm load resistor and the injector. You might think that the voltage drop across the injector would be determined by the series resistance of the injector (e.g. 12.2 * 3 / (6+3) = 4 V), but you'd be neglecting the inductive reactance of the coil. When a step voltage is applied, the reactance is essentially infinite at first, so all of the 12.2 V is dropped across the injector.

Why did Bosch do this? Because they wanted a very fast opening time for the injector so that the pulse width would determine the injected quantity w/o an indeterminate phase at the beginning of the pulse. Using this peak voltage approach permits the injector opening time to be only about 0.1 ms.

Once the field is built in the coil, the inductive reactance drops near zero, and the voltage drop across the injector is now determined by the series resistance of the injector, so it's about 4 V or so.

In building a test bench, you don't have to be concerned about the injector opening time, so you don't need the peak voltage. You want to limit the applied voltage to about 4 V or less. Why not apply 12 V? Because it requires a series 6 ohm power resistor to prevent the voltage drop across the injector from exceeding 4 V, and limiting the steady state current to tolerance of the injector. Otherwise, w/o the load resistor, 12V may overload the injector and damage the winding.

Using two D-cell batteries can work, but be aware, you're supplying about 1 A, which will kill the D-cells quickly. I'd suggest going with a bench source that can supply between 3 and 4 V at at least 1 A. If a model train transformer can do this, then it should work fine.