What is the voltage to fuel injectors?

I just replaced my fuel injectors. One of the cylinders was not running. All was fine before. I am getting spark but doubt I am getting fuel to it. I have voltage on the plug that goes to the injector. However, I do not know if it is the right amount. It also seems to vary when I checked at another plug.
Thanks
BSD

What reading did you get?

I believe it's +12VDC, but A) I'd have to check and B) it's a pulsed voltage, so you'll have trouble getting a good reading with a voltmeter - you're better off trying to read injector pulses with an O-scope.

If you get a steady voltage (a quick check can be done with an analog voltemeter - watch for needle "tics",) then there is a problem somewhere that merits investigation. No voltage - no signal from the driver, and find out where it's getting lost.

Since the injector signal is supposed to run a duty cycle of 30-80%, you really should use a 'scope to read it...

5-90

Using my multitest - and I am not to sure of how to use it - I came out with about a .90 on one blade and .14 on the other blade. (I had the tester set on the 2 volt setting) I pulled some of the other ones off and they read around 1.20 on one blade an .14 on the other blade.

Does the voltage have to be at a certain point to trigger the injector?

The quick way to tell if it is the injector or the drive coming from the ECU is to swap the connectors from an adjacent cylinder. It will still run, but you can then see if the same cylinder is still misfiring. If it is, then you have a bad injector, otherwise, the drive is faulty. That can range from a bad connector, to bad wire, to bad ECU. I have seen more corroded connectors on the ECU causing problems than virtually anything else.

You don't say what year, but if it's a 91-up, the ECU switches the negative side of the injector. Each injector should have +12 volts at all times when the ignition is on, relative to ground. If the voltage is not +12 at each injector, there is a fault in the harness or the positive supply, which comes from the ignition (exactly where I forget, could look up, but it's fed as I recall from one of the coil supply wires).

If it's a pre-91, and if I'm reading the fuzzy little schematic I have correctly, the ECU switches the positive side, but presumably the impulse should be pretty close to +12 volts at each injector. I say "presumably" because past experience with a bad wiring harness on a 93 suggests that the injectors won't fire reliably if the voltage drops more than a couple of volts. If the impulses are very short, it might be pretty difficult to measure because many meters will not respond quickly enough. If there really is a question on the voltage you might need to find someone with an oscilloscope to get a definitive answer, as 5-90 suggests.

The ASD relay supplies 12+ to the coil, O2 sensor heaters and the positive side of the coil within the injector. The PCM sends a ground signal to the heaters to turn them on and through the monitoring of the crank and cam(distributor) pickup it will pulse a ground to the coil and to each injector through the other wire. You can tell the difference on the wire. All the injectors will have one wire the same color, this one is the 12v+ from the ASD relay. The other wire is the ground from the PCM. It is only grounded when the PCM want the injector on. with the engine running voltage changes but the PCM monitors this and adjusts injector pulse width accordingly. one wire on each injector should be equall to battery voltage and the other will be 12v+ untill the PCM grounds it and it fires. (very short interval) Use a noid light not a test light. A digital multi-meter might not be fast enough to sense it...................

gptherezonlyone said:

The ASD relay supplies 12+ to the coil, O2 sensor heaters and the positive side of the coil within the injector. The PCM sends a ground signal to the heaters to turn them on and through the monitoring of the crank and cam(distributor) pickup it will pulse a ground to the coil and to each injector through the other wire. You can tell the difference on the wire. All the injectors will have one wire the same color, this one is the 12v+ from the ASD relay. The other wire is the ground from the PCM. It is only grounded when the PCM want the injector on. with the engine running voltage changes but the PCM monitors this and adjusts injector pulse width accordingly. one wire on each injector should be equall to battery voltage and the other will be 12v+ untill the PCM grounds it and it fires. (very short interval) Use a noid light not a test light. A digital multi-meter might not be fast enough to sense it...................

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I must add here, however, that the dedicated injector and harness tester I used did not catch a low voltage at a connector caused by resistance in the harness. There was voltage enough to light the tester, but not enough to fire the injector once it heated up. So if a harness problem is suspected, I'd check the wires themselves with an ohmmeter.

The above information is correct for 91-up. We're still not sure what year we're talking about here, so remember if it's a pre-91, the ECU sends a positive signal to the injectors, which share a common ground, rather than the other way around. Because of this, you cannot use a voltmeter to test the wiring, but can test at the injector plugs with an ohmmeter for resistance to ground, etc. and can still use the noid light or injector tester for basic firing tests.

Sorry, its an 89. I think I will first try switching injectors around to make sure it is not the injector. If that does not solve it, I will check the electrical. However, I am a bit doubtful that it is electrical since it was running fine before I changed them out. One thing that I am curious about, do the Ford injectors require more voltage to fire off than the OEM?
BSD

I didn't catch that you switched the injectors and then the problem started. If the injectors were not new, it is not uncommon for an injector to stick. My stroker did the same thing. I added a can of BG44K to the fuel system and the injector started working within an couple of miles. Most additives don't do squat, but BG44K does wonders, and it shoud for $18 a can.

old_man said:

If the injectors were not new, it is not uncommon for an injector to stick.

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THey were take off's - taken off new crate engines that were being upgraded - not technically. But close enough to be considered such. As to teh injector sticking, the palce I bought it on suggested tapping it to get it going. It did not work so they are sending me a new injector. I tried putting my old injector in but it leaked like a mad dog.
GAB