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Injector connector constant power, no key, short to ground

  I have one injector that will not stop spraying, #4. When I probed the connecter with out the key on there is power there. I smell fuel at the exhaust. Aren't injectors wired in pairs, so if it's a short to ground would it be on two injector, connectors? I ran about a mile with the injector runing open will I need to change the oill ? Can I run the car for 6 miles with the injector unplugged to get it home? 


2005 dodge neon 2.0

Having power to the injector with the key off may be normal as most systems run the return side of the circuit through the ECU and no current flows in the circuit until the ECU commands the injector to turn on. Did you compare other injectors also to what you found on that one? There could be a problem with that injector circuit inside the ECU and it is allowing current to flow. As far as turning on a second injector I don’t think that is going to happen since injectors are turned on individually as far as I know. There are ignition systems that fire two plugs at a time. If the injector really is being turned on all the time I suggest you disconnect the electrical connector to it so the injector can’t turn on and allow fuel to flow.

What @cougar said.

They very likely switch ground as that’s actually easier to do, electronically. If you see power across the coil of that particular injector all the time, you may have a pinched wire that’s now shorted to ground, for instance.

More than likely the driver in the computer for that injector has failed.

The injectors are provided with constant voltage. It’s the job of the computer to ground each injector at the appropriate time thru the drivers in the computer.


With the key off measure the resistance from the low side of the injector to ground.
If it’s really low like less than 100 ohms there’s the problem.
Then disconnect the computer. Measure resistance again.
If the resistance is still low there’s a pinched/shorted wire.
If it’s high now the problem is in the computer (bad driver).

Are we 100% sure its an electrical problem? Could it not simply be a defective injector that either has a broken internal spring or just won’t close for some other reason?

@Cougar my 1994 Tercel injectors are fired in pairs. I believe my 1995 Corolla was the same way. I believe that all current cars have sequential injection, though.
But you guys are right about the injectors. The PCM provides the ground.

 UPDATE: Hi, There are no breaks in the injector connector driver (ground) wire to the PCM. I check the connector for injector pules, light stays on all the time. I disconnected the fuel rail and turned the key on. That injector sprays for 4 seconds each time I turn the key on. Can the injector cause the ground  driver to the PCM to go bad, sometimes? I moved over the #4 injector and the code didn't follow. #4 Injector works in the other cylinder. Car runs rough on three cylinders, with injector #4 unplugged. Should I change the injector along with the PCM just to be safe?

I haven’t been getting your answers

I don’t think people will email you because we’d all be duplicating effort and it will not help people that may have this problem in the future. That’s what this forum is for.

So - just to clarify - that injector stops spraying when you turn the key off, sprays for four seconds when you turn the ignition on and sprays all the time (no pulses) when the engine is running?
That spraying for four seconds is part of the system priming. It turns the pump on but it is not supposed to open the injectors to spray inside the cylinder.
It sounds like the PCM has a short to ground on that driver or, inside the PCM, whatever drives that driver is active all the time. I’d try to make sure that wire to the injector has absolutely no short to anything else. On that connection, you should see rapid pulses when the car runs and nothing when the car is not running.
If you see a solid ground connection there at all times, that PCM may have an issue.

An injector is a coil, from an electrical point of view.
A coil that has a voltage applied to it and then when you turn it off, it fights to sustain its electric field. It wants to retain that charge and as the field collapses, it generates a fairly large very fast pulse of the opposite polarity (a phenomena called “Back EMF”).
Depending on the coil, that voltage could be several hundred volts but just a couple of microseconds in duration.
That reverse voltage could potentially zap the driving electronics. It may not damage them immediately, but all this zapping will age them prematurely. To circumvent it, coils should have a diode across them to short that collapsing voltage. No doubt your injector has that diode across it somewhere but, if that diode goes bad, you could do damage to your new PCM as well.

Long story short: Providing that’s the cause of your PCM dying, I’d replace the injector as well - just to make sure.

It does sound like the ECU is damaged. One thing you can do to possibly verify that is to check the resistance to ground on the injector wire going to the ECU for the suspect injector. It will most likely show a low resistance when compared to the others. I suggest you set your meter for the diode test position to make the measurement. You can use a working injector pin for a reference to a good reading if you want to.

Thanks @db4690 for the info about the injector pairs.

 Cougar,  I got 12 ohms on each injector. I switched a good injector with the problem injector and it did the same thing. ( trouble code said open circuit, wiring problem ) Can a bad injector still run? I may just replace it, maybe it shorted the PCM driver? I opened the wiring harness and there are no shorts in driver wire. Can I test the driver at the PCM for free? I rechecked for injector pulse at the connecter while running the car. after about 3 minutes still no pulse, just a solid light. I get pulses on the other three injectors. Thanks for the help.

There should only be two wires on each injector, one hot wire and one that seeks ground through the PCM. The hot wire should be the same color to all injectors, but the ground seeking wire should be a different color for each injector.

With power off, unplug the harness from the injector and check the resistance of the pin on the harness (not on the injector) that the ground seeking wire is attached to and a nearby ground. Check a couple of plugs. There should be no continuity. If there is a low resistance on the wire for the #4 injector only, then the driver transistor in the PCM or the wire to it has shorted out. If it is low or high on all the ground seeking wires, then test again but with power on, but before you conduct this test, do a voltage check on each ground seeking wire to make sure there is no voltage on the wire, this is to protect the meter.

If you get a voltage on on wire only, the the issue is still with the PCM. If no voltage present, all wires should read high resistance to ground. If the #4 only reads a low resistance to ground, the problem is still in the PCM, but the issue may be something other than the power transistor.

If the #4 only reads a low resistance on the first test, unplug the PCM and retest. If it is still low, then the problem is with the wire and not the PCM.