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Discussion Starter #1
Engine has miss. #4 injector does not make any difference when unplugged or spark plug wire pulled. Also, mass air flow sensor had no affect on engine when unplugged. Snap on engine analyzer shows coolant temp sensor fault, mass air flow @ 0 volts. Plug reads 12 volts.on 1 pin. 0 on other 2 pins with key on. Replaced #4 injector, mass air flow sensor-no change.
 

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Replaced #4 injector, mass air flow sensor-no change.
I assume you have already checked...
that the cyl 4 plug is sparking?
the cyl 4 injector power supply and control signal?
the cyl 4 compression?


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Discussion Starter #3
Have spark, good compression, 12.2 & 3.8 @ injector connector. All ecu fuses @12 volts engine fuse block.
 

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12.2 & 3.8 @ injector connector.
And what about the injector control? Is the ECU attempting to fire the injector?



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Disconnect the injector and connect a 12V bulb across the injector harness connector. Erase the misfire trouble code, then start the engine. If the ECU is firing the injector the bulb should blink while the engine is running.

On most engine management systems once a misfire code is logged the ECU will switch the injector circuit off in the effected cylinder to protect the catalytic converter from damage. So the light might only blink for a short period of time then stop once the misfire is recognized by the ECU.



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Discussion Starter #8
Disconnect the injector and connect a 12V bulb across the injector harness connector. Erase the misfire trouble code, then start the engine. If the ECU is firing the injector the bulb should blink while the engine is running.

On most engine management systems once a misfire code is logged the ECU will switch the injector circuit off in the effected cylinder to protect the catalytic converter from damage. So the light might only blink for a short period of time then stop once the misfire is recognized by the ECU.



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Discussion Starter #9
Found an ecu fuse on engine fuse block reading 12v on one leg and 0 on the other. Replaced fuse and now #4 is firing. Engine is running somewhat better but is still trying to cut out in drive. Could the trouble codes I was getting be causing the rough idle? MAF and Coolant Temp sensors.
 

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Could the trouble codes I was getting be causing the rough idle? MAF and Coolant Temp sensors.
Hard to say when you don't tell us what the codes are?
But yes, if the ECU doesn't like the look of the MAF or ECT signals I'm sure that could effect how the engine runs.

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Discussion Starter #11
Drove it about 500 miles last week. #6 cylinder now is missing. Has no effect when I pull injector wire or spark plug wire. All ecu fuses read 12 volts in both legs.
 

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Discussion Starter #12
Injector connectors 2,4, & 6 all read 12.2 & 3.8 volts on the connector with ground to battery. They all read 0 with key on and dmm connected to both pins at same time and also reversed. Any ideas? Still have a miss on #6 cylinder. Injector is not firing. There is spark and compression.
 

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Injector connectors 2,4, & 6 all read 12.2 & 3.8 volts on the connector with ground to battery.
As I suggested earlier, you can use a 12V bulb to check that the ECU is controlling the injector. If the power supply is good and the ECU is supplying the ground pulse to control the injector, then it can only really be a fault within the injector itself...assuming the misfire is in fact due to a lack of fuel in the cylinder.

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You can listen to the injector with a screwdriver handle in your ear and the tip against the injector. Run the engine and compare the sound with a good injector. Of course that won't tell you if the basket filter in the injector is blocked.
 

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Discussion Starter #15
As I suggested earlier, you can use a 12V bulb to check that the ECU is controlling the injector. If the power supply is good and the ECU is supplying the ground pulse to control the injector, then it can only really be a fault within the injector itself...assuming the misfire is in fact due to a lack of fuel in the cylinder.

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Can I use a dmm on the disconnected #6 injector connector with engine running to see if it gets any reading? Don't have a test bulb on me at the moment. Also, changed the injector to a known good injector and no change.
 

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Can I use a dmm on the disconnected #6 injector connector with engine running to see if it gets any reading?
That's not really a good test, because the injector on time is so short that a dmm wont be able to measure the voltage properly. You really need an oscilloscope to measure the injector signal voltage.

ca7922303 said:
Also, changed the injector to a known good injector and no change.
If the injector is good and it's power supply & control are both good, that surely means your misfire can't be due to a fuel delivery issue.

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Noid light shows injector #6 is firing.
As I said, if everything relating to the injector is good the misfire can't be due to a fuel delivery issue.

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