Computer ground to injectors - 1992 Mitsubishi Mighty Max

The voltage for fuel injectors go hot with the key on. The computer switches the ground on and off, check voltage and ground.
If the computer doesn't ground the fuel injectors, you'll have voltage on both legs.
If computer doesn't see rpm signal, it won't ground the fuel injectors. If no rpm signal check the crank sensor and ignition module, plus wiring circuits. Don't replace anything unless your testing points in that direction.

with the key on there should be 12volts to the injector. the other wire on the injector is the ground side and it is grounded by the computer when it receives a signal from the cam sensor to know when to fire, ground circuit, to activate the injector. you need to check the wire from the injector ground side to the computer for an open circuit. if its good then it may be an injector driver problem inside the computer.

No pulse means the injector ground side is absent, since you have power to the injectors. The ground wire goes into the engine computer to be internally grounded for the pulse. You can test the injector ground side with a test light, as a verification of it not having pulse. If it really has no pulse, but it has correct voltage to the injector solenoid, then you have a bad injector, or a bad ground wire to the pcm, or a bad pcm.

Use a test light with a ground clip and a needle-type probe. Unplug the injector connector and note which is the power wire terminal and which is the ground wire terminal. Clip the test light lead to the POSITIVE battery post, and put the probe into the injector's ground wire terminal. Now have someone crank the engine over and watch for a blinking light on the tester. If you have a blinking light, the injector ground side is working right, so check if voltage to the injector is correct, or if you have a bad injector. If you have no blinking light, then no pulse is correct. You will need to check the ground wire to the computer before assuming a bad computer. I think they are called quad drivers inside the computer that control the injector grounds.

Best way to check that ground wire is, first, take off the negative battery cable, then pull off the computer connectors, then use an ohmmeter to check resistance of wire from injector terminal to the pin on the computer's connector. Low resistance, low ohms, means the wire is good. ...But first I guess you will have to find the pin-out diagram for the computer, where and on which connector that ground wire goes in at. There's around a hundred or more wires going in, so color coding, tracing by the color of the wire would be a royal pain. Good luck, Scott.

check for power and ground at the injector harness plug. the computer supplies power all the time with the key on then when the car Is running the computer grounds the circuit to allow the injector to function. if you have no power then you will have to check the wiring to find the open. if you have no ground side then you will have to check the ground circuit at the computer. if there is none then you may have an injector driver gone bad. if you have ground at the computer but not at the injector then check the wiring between the two.

Check the grounds from the rear injectors to the computer. On a bank fired system as yours, all 3 injector grounds on each bank splice together before they go into the computer. Check wire continuity from injector to the computer connector with the ohmmeter.

So, it's the injector circuit. There is a 10 amp injector fuse in the fuse block, on left side, 4th one down. Check this fuse. It supplies constant power to both injectors, on the red wire to injector 1, and a white wire splice from this to injector 2. A steady 12 volts anytime key is in on, run, or start. You can check this with a test light or voltmeter. Ground the test light and probe injector connector's red wire on injector 1, and the white wire on injector 2-both should be hot with key on.
This may be why the noid light didn't blink. The noid light must have this steady power signal, and when the computer internally grounds the injector ground circuit for a split second, you get injector pulse-or a blinking noid light.
You can check the ground circuit separately with a test light also for each injector. Place the ground clip of test light on the POSITIVE battery post, and probe the blue (ground) wire on injector 1, the engine must be cranking over, and the test light should be blinking. Do the same for the green wire on injector 2. If the test light is blinking on both ground wires, with engine cranking-the ground circuit is good. You are sending power down the ground wire to computer, and when the computer grounds the circuit, the tester will light up-it will blink because the computer only momentarily grounds the circuit to cause pulsing of the injectors.

Are you sure it's not the fuel pump? I would be checking fuel pressure-the injectors need fuel under high pressure against them so they will spray out when pulsed.
What year is your Isuzu, and what size engine? Multiport injection has a higher pressure requirement than throttle body injection.
There should be a fuse for the injectors, check that. With key on, not start, the injectors would have power to them on the "injector drive circuit". In other words, constant power is supplied to the injectors when the key is on. The other wire at an injector is the ground wire. The ground wire goes into the engine computer. When the computer internally grounds the injector wire for a split second, the injector is energized and fuel is able to spray out.
Post back if you need help checking the injector circuit-both the power side and the ground side. You can check both with a test light.

Well, here it is anyway: ground a test light and probe the injector connector. With key on, one terminal should be hot-the drive circuit. Now move the test light lead to the POSITIVE battery post, and stick the test light probe into the injector terminal that did not light the test light-the ground terminal. Now have someone crank the engine over. If ground circuit is working, the test light should be blinking-meaning the computer is properly grounding the injector circuit. If both tests are good-a steady light on the power side (key on) and a blinking light on the ground side (engine cranking), the injector circuit is good.

There should be an injector fuse, under the hood. Might check if the fuse itself has power to it. When key is on, injector circuit should have power.
Ground is only good when the computer (ecu) internally grounds the injector to pulse. To check the grounds, clip a test light onto the battery positive post and stick the tester probe into the ground side of one injector connector. When the engine is cranked, the test light should be blinking-the computer is grounding the circuit every time the light blinks.

Check the injector fuse. With key on, injectors should have constant power available to them on one wire. The other injector wire is ground wire. With constant power to injectors, all it takes to pulse the injectors is for the computer to ground the injector ground inside the computer for a split second, and pulse occurs, causing fuel to spray out the injectors.
So if injectors aren't working, either the injector drive circuit (the power to injectors) or the injector ground circuit is lost. You can buy a cheap "noid light" at any auto parts store, and check the injector circuit. Just plug the light into the injector connector and crank the engine over. If the light is blinking, circuit is good. If no light, the circuit has a problem, either on the drive side or the ground side.
Here's a way to check the ground circuit separately. Use a test light clipped to the Positive battery post. Probe the ground wire terminal of the injector connector while the engine is cranked over. The test light should be blinking-meaning the computer is grounding the circuit normally and would be causing the injectors to pulse, if power is available to them.

For fuel injection, usually the ground is inside the engine computer. The computer grounds the circuit for a split second to pulse the injectors. When key is on, the injector circuit has constant power to the injectors. When the computer grounds the circuit internally, the injector coil is energized, or pulsed.