Injector Grounding through ECM? - Hemi Truck Club
 
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Old 08-14-2016, 04:53 PM   #1
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Injector Grounding through ECM?

HI I was over on a jeep forum but no one really seams to know anything about a Hemi over there.

so I just got a 05 grand cherokee limited hemi 4x4 168k miles, it has a engine problem.

CODES-
p0300 multiple cylinder misfire
p0308 cylinder 8 misfire
p0520 engine oil pressure sensor out of range
p0208 injector 1,2,3,4,5,6,7, or 8 control
p2302 ignition coil No 1 secondary circuit insufficient ionization

I have replaced plugs, wires, coil packs, pulled valve cover to inspect springs and everything, did a compression test. Nothing mechanical that I can find is wrong.
#8 plugs were dark and wet with some oil when I pulled them.

After probing around with multimeter I am showing that #8 injecter ground (to pcm) is just ground and not pulsing.
It is just showing 12v through it all the time.(constant spray) The other injectors do not do that, they bounce around on the mulitmeter (as they fire)

It runs rough and when I unplug #8 injector the idle does not change. (100% fuel to 0% fuel) I thought it would change the idle.

Is this a bad ecm?

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Old 08-14-2016, 04:59 PM   #2
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Im going to jump #1 injector input from ecu to also ground #8 and see if it runs better. 1 is right before 8 in firing order so that would be the next closest bet.
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Old 08-14-2016, 05:48 PM   #3
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That's an unusual problem and I believe will require a scanner or a O scope. If the PCM has a continuous ground on the injector than the injector is most likely fried. They cannot take the constant current. I've been told you can hear injector click, but I've never been able to hear one. But I don't hear a lot of things. How about with the engine running squirt a spray of water on the header port to see if it is hot as the others to determine if it is firing?
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Old 08-14-2016, 06:39 PM   #4
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Swap no. 8 injector with no. 1 injector to see if it's a bad injector or ground on the no. 8 circuit.
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Old 08-14-2016, 07:38 PM   #5
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ok I think the ECM is taking a sh1t.
I jumped #1 injector ground to #8 ground. It worked for about 30 seconds. Now no power to #1 so I might have blew that one up. Its running worse.
But anyway
I went and grabbed a diode test set for the injectors. No power to #1, #6, or #8 injectors. I do not know if the injectors them selves are actually bad but they sure are not getting power.
It has to be the ecm at this point. Injectors are controlled by ECM. So if injectors have no power ECM is the cause. correct?
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Old 08-14-2016, 07:56 PM   #6
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Old 08-14-2016, 08:44 PM   #7
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No, the injectors and coils have a common power source controlled by the ASD relay. The PCM controls the ground side of the coils and injectors. Also the ASD shuts the power off to the injectors and coils in about 3 seconds if it doesn't have a sense signal that the engine isn't turning over.
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Old 08-14-2016, 08:47 PM   #8
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That would effect ALL injectors and coils if the relay was bad. (Common power source)
Im looking how they are individually controlled as only 3 dont have power.
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Old 08-14-2016, 08:56 PM   #9
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If you unplug all the injectors and then measure for power and any of them don't have power then it's between that plug and the harness supplying power.
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Old 08-15-2016, 05:15 PM   #10
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Unplug the connector and check for power at plug every injector should have one 12v leg. The grounds are pulsed thru the computer. If you have no noid light opperation it's likelythe pcm took a poo on you.
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