Testing Fuel Injectors on 2.9L V6

[Demersus]

Hi all,

Just finished installing a rebuilt 2.9L in my 1990 Ranger Custom. Had to troubleshoot a no-start situation. Went through everything and narrowed it down to a fuel delivery issue. EEC, relays, fuel pump/pressure, spark and compression all look good. I even did the electrical pulse test on the fuel injector connectors and all seems normal. So I pulled the fuel rail and injectors to inspect and test them. When I do a direct 12V test on them individually, I cannot really hear or feel the solenoid clicking. I think I can hear a very faint clicking in some of them, however. I've swapped polarity as well with no noticeable difference.

Is this a valid way to test an injector? Should I expect a fairly audible and obvious "clicking" when I energize one with direct 12V?

I also measured resistance across each, and they fall within 14.5 - 15 ohms. That sounds low, but they're all in the same range. The rig ran prior to the overhaul, so it's strange that all six would fail. So it makes me feel like I'm not testing them properly.

What has your experience been with similar issues?

 

[Terry]

Did you hook up the frame ground?

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[RonD]

11-18ohms is correct for Ford injectors, they are low impedance injectors.
How long have the injectors been sitting?
Could they be plugged up inside?
You can put a rubber hose on the end and then add power to see if you can blow or suck air thru the hose, won't be easy to blow air thru, small opening, but there would be a difference between open and closed.

An injectors electrical connection has no polarity, there is just a coil of wire inside, like a relay or solenoid, when power is passed thru the coil of wire, in either direction, it becomes an electro-magnet, this pulls up on and opens the needle valve allowing fuel to flow out, when power is cut a spring pushes needle valve closed.

With a no start I would have first added fuel manually to the intake, gasoline or Quick Starter(ether), if it started and died then I would check spark plugs after cranking engine a few times, just to confirm they are dry, so no fuel coming in.
I would they cycle key on and off a few times and push in on the Schrader Valve pin on the fuel rail, so see if I have fuel pressure.

PCM(EEC) gets fuel injector timing from the TFI module, the PIP wire tells PCM the distributor's spark timing, if this PIP signal isn't making it to the PCM, then the PCM doesn't even know you are trying to start the engine.
PIP is where PCM gets RPM reading and injector timing.

When key is turned on all the fuel injectors get 12volt power(red wire), but they are not Grounded so stay closed.
The PCM Grounds the injectors to open them.
2.9l PCM will use Batch Fire injection, so PCM Grounds 3 injectors on each 1 revolution of the crank, then Grounds the other 3 injectors on the next revolution, just alternates based on PIP #1 TDC.

 

[pjtoledo]

electrically the best way to check an injector is with an Ocilloscope. with that you can see the actual voltage drop pulses, the are very short duration.
without a 'scope there are a couple of different ways.

with an older needle style volt meter put the leads on each side of the injector, not running there is no volts, running there will be small pulses/wiggles on the meter.

other way is to use a digital meter with peak hold feature, put the leads on each side of the injector. when the injector is idle there is no current flow, thus no voltage drop. when the injector fires there will be a quick voltage drop, the meter should pick up that pulse in peak hold.

there is a way to physically test an injector, bear in mind spraying gasoline is sort of dangerous. do this outside, lots, lots of ventilation !!!

I put a 3" piece of air hose on the injector, with a male quick connector.
poured a teaspoon full of gas in the injector, hooked the hose up to an air hose dialed down to 40 psi. keep this pointed down, you don't want the gas flowing back into the main hose.

hit the injector with 12volts and observe the spray. do quick taps or strikes of the 12 volts.
if you have an old distributor with points use that as your switching 12volts by hand spinning the distributor.

have fun, and no smoking!