Bad injector

'88 Z-24 2.8 multiport has a steady miss at idle, but it seems to go away as soon as it throttles up above idle speed.
I suspected a coil pack and changed it but that didn't change the way it
runs.
When an injector goes bad, is that the way they behave? Or do they just suddenly go dead altogether? I did run a bottle of STP injector cleaner through in a tankful of gas, didn't change anything. Can an injector pass the resistance test but still be bad?
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snipped-for-privacy@webtv.net (Gomer Einstein) wrote in

it
injector cleaner is a good thing for PM. it rarely, if ever, will unclog a nozzle.if resistance is within specs (meaning magnetic coil is still a functioning circuit) pull injector and bech test it, hell, take it apart and learn how it works. apply voltage while on bench. you should feel and hear a sharp 'snap'. if 'snap' is observed the injector has did its electrical job. there is still the plumbers job of the part tho. meaning being clear enuff to pass liquid from one side to the other.......kjun
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Just because an injector electrically work on a bench, does not mean it's clogged. Don't forget about all the upstream wiring and ECM.
Steve
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nodding in agreement!......i was assuming he/she had boiled it down to actual 'injector wont pulse with current applied'. very inexpensive way to diag loom end of injector connector is a small lamp from blue point that plugs in to conn. and flashs as injector is pulsed...had mine over twenty years and still verifies electrons are either there or not. if not, could be related wiring or injector drivers in PCM......kjun
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The ECM has been replaced in this car. I was curious as to how injectors commonly fail, i.e. since this steady miss only occurs at idle and disappears as soon as throttle is applied. It's as though the injector is slow to open and won't open at all until pulsewidth is sufficient to give it time to get open. IOW, when they fail, do they begin to function more "slowly" and then finally not at all--or do they just quit?
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Quite possibly the latter. But as another poster suggested, have someone plug what's called a *noid light* into that injector's circuit & see if it's firing at idle. That will give you a starting point. s
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snipped-for-privacy@webtv.net (Gomer Einstein) wrote in

when an injector coil fails it produces no magnetism to lift the pintle resulting in dead cyl. in all rpm ranges. i have run into inj. that would pulse normal and still not deliver enuff fuel to fully fire the cyl. it WOULD be most noticeable at idle but still give ok driveability at throttle up rpms. clogged outlet nozel. also have had same symptom and found bad cam lift on intake valve of affected cyl. resulting in poor mixture..a handheld digital pyrometer would be handy to diag. this. compared to other known good cyls. the exh. temp on the exh. runner would be low if rich and high if lean. i dont have accses to one anymore, have to rely on the old 'ball of spit boil off' method. not near as accurate but entertaining to the newbies that werent taught it in shop class ;-)................of course there are always the intermittant probs that drive us all nuts. u could easily swap the prob inj. to a known good cyl. and see if prob swaps in parallel................kjun
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