Question about 1991 Chevrolet Camaro

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No run problem

With the key turned on i have power to both sides of the injectors.where should i look for the problem.

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  • radv6 Sep 03, 2008

    it was a shorted injector.changed it and fixed the problem.

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If the organization is as in most cars, the injectors ae controlled by individual transistors located in the ECM/ECU (computer).

Since the injectors are controlled by pulse action from there, having voltage on both sides of the leads is normal I would say if the engine is not running.
The typical arrangment is that one side of the injector coil is supplied with 12V if the ignition is turned on and the other side of the coil is grounded under control of the computer but only for a few milliseconds at a time, nothing that you can measure with a meter.
If you were monitoring the low side of an injector with a meter, you might see a slight decrease in the reading but that's all.
If even that small decrease is not present, then the computer has probably failed and it is no longer grounding each injector when required.

Posted on Sep 02, 2008

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No injector pulse 4 cyl 93 f250 460


if you have a $5 test light, you could find the problem. just know that all eight injectors have a constant voltage applied to them anytime the key is in run or start. and also that 4 of the injectors share a common ground, they have their ground wires spliced together before the ground wire enters the pcm to be internally grounded. and the other four injectors are the same- their ground wires splice together. so your four that don't pulse have lost either the power to them, or the common ground wire for the 4 may have broken. or lost connection.

it is easier to check the power side first, so clip a test light lead to the negative battery post or cable, turn the key to on,and probe each injector connector. one of the terminals at all eight injectors will be the power wire, and it should light up the test light. if all eight injectors have power to them, you know it must be a ground side problem. if you find that 4 injectors have no power to them, look for a broken splice in the power wire to all injectors. back in those days, injectors were "bank fired". one side or bank of the engine all had the injector grounds spliced together, so all injectors on one bank fired (pulsed) simultaneously, and then the other bank was fired or pulsed. that was good until sequential injection matched the pulse to the cylinder ready to fire, more precise, and in the modern systems each injector ground has a separate ground inside the pcm. no more splicing of the ground wires, and having bank fired engines.


when the pcm grounds the circuit, the injector coil is energized and the injector opens to spray fuel out. so the injector has constant voltage to it. only when the circuit is grounded is that power applied across the injector.

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1 Answer

Engine only firing on left bank rtf. Side no. Fire will start and idle


Check for spark on the side not firing. If there is spark, the injectors on the right side may have a problem in the wiring to them. Older multi port injection systems used a "bank fired" approach: all the injector grounds on one bank splice together before they go into the computer to be pulsed.
All of the injectors have a steady voltage applied to them when the key is on. The same color wire to all injectors is the power wire, it is a fused circuit, the fuse is in the power distribution box, and is hot in run or start. When the computer internally grounds the injectors, pulse occurs and fuel is sprayed out. Check if the right side has power to the injectors with key on, use a voltmeter or test light. To test an injector circuit, purchase a cheap "noid light" from a parts store. You plug it into an injector connector, then crank the engine over. If the noid light is blinking, the power and ground circuit is good for that injector.

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Where is the fuel injector relay fuse on a 98 ford expedition


In the Power Distribution Box-the fuse relay block under hood- it's on the driver's side.

it is fuse # 24, a 30 amp green fuse. This fuse is only hot in run or start, so with key on, the fuse sends power to the PCM Power Relay (also in the power distrib. box), turning the relay on so power goes to the fuel injectors, among other things..

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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.

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1 Answer

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You said you hear the pump come on, then said fuel pump not running ???
Check the fuse for the pump, preferably with a test light to verify power is there. Key must be in on position. If the fuse is powered, feel for the fuel pump relay to click when you turn key to on. Put your finger on it while someone turns key to on. If it clicks, check for power at the tank connector on the pump wire, while the engine is cranked. If power there when cranking, the pump must have failed and needs replacing. If the relay clicked with key on, and no power at the pump wire at tank while cranking, then check wiring from relay to pump connector-the fuel wire may have broken.
If the relay doesn't click when key turned on, check for the power feed for the pump at the relay terminal. If the relay has power available to be transmitted to pump, then the relay's signal from the computer or the ground side of the relay's coil signal (from the computer) may need checked.
If the pump is working, and you have good pressure in the lines, check the injector circuit. Also a fused circuit, so check the fuse first. The injector should have a steady voltage signal to it with key on. The injector only has two wires, the power wire and the ground wire which goes to the computer. When the computer momentarily grounds the injector circuit, the injector "pulses", causing fuel to spray out the bottom.

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1 Answer

No signal to fuel pump or injecters


Pressure in the rail indicates the pump is working.
When the key is turned on, the pump will come on for about 2 seconds to pressurize the fuel system. Then pump will shut off and not come on again until the engine is cranked. When cranked or when running, the pump will be on full time. To check if the pump is getting a signal, the engine must be cranking over. Or you may pick up that 1 or 2 second signal when the key is first turned to on. Is this the way you checked for power to the pump? How much pressure are you getting at the rail? Any pressure at all means the pump put it there.
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If you got a steady light on one wire, then check the injector ground circuit. Move the testlight lead from ground to the positive battery post. Now probe the injector connector's wire that did not light the testlight, while someone cranks the car over. If working right, the testlight should now be blinking, meaning the computer is properly grounding the circuit for injector to pulse. If both tests pass, the injector circuit is working right.
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If it is similar to Quest, the fuel pump runs for 5 seconds when you turn the key to ON. Then, unless the engine is running, the pump shuts off. It runs when the key is in START position though. Can you hear the pump run for 5 seconds when you turn key to ON? Listen carefully for the hum of the pump in the tank.
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