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Discussion Starter #1
Hi....I have a 99 3.5HO that is giving me fits. One of the cylinders is not firing. The plugs and coils have been replaced, and there is voltage getting to the coil pack. I even tried swapping plugs and coil pack out of this cylinder, and still nothing. Fuel injector is working as well.

Any ideas?:banghead:
 

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Is that a swapped out engine from another year Trep 3.5? 1999 didnt have 3.5 yet i dont think, lol im just curious.
 

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How do you know the injector is working? Did you test the compression in the cylinder or try swapping another injector and coil pack from a known good cylinder to see if it works in that one?
 

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Discussion Starter #5
How do you know the injector is working? Did you test the compression in the cylinder or try swapping another injector and coil pack from a known good cylinder to see if it works in that one?
Used the stethoscope method. Coil pack is brand new, but swapped it anyway. Same with the plugs.

Had a shop check the compression when I 1st got the car, and they said compression was good and consistent on all cylinders.

Also ran a can of Seafoam through it....no changes.
 

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Did you compare the sound of the injector to the other ones? Sometimes they will still click but faintly.

The compression should be checked now, it may be different from when you got the car.
 

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swap the injectors to make sure that they work.
 

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Hi....I have a 99 3.5HO that is giving me fits. One of the cylinders is not firing. The plugs and coils have been replaced, and there is voltage getting to the coil pack. I even tried swapping plugs and coil pack out of this cylinder, and still nothing. Fuel injector is working as well.

Any ideas?:banghead:
Getting voltage to the coil is one thing, but the coil is controlled on the ground side by the ECM. I would disconnect the connector from the ECM and check for continuity from the coil of the lazy cylinder to the ECM connector. Also check that same wire for a short to ground. Before disconnecting the ECM connector be sure to disconnect the battery FIRST or damage to the ECM could result.
 

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Do a balance test on the injectors, its quick. See if its holding and compare how fast it releases the pressure.

Bring it to a shop to hook up a lab scope to check the spark.. I had a little injector tester for bench testing, pretty neat.. just gotta listen to the solenoid ticks, doesnt check the spray pattren though
 

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Discussion Starter #10
Thanks for all the input.

I am going to try swapping injectors today as well as doing a continuity check on the wiring on the ground wire to the coil pack.
 

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Discussion Starter #11
Well it finally shot me a code 304. Never showed until today. Wiring is showing continuity, and the Seafoam didn't clear up the miss. Picked up a new injector and will install it in the morning.
 

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Discussion Starter #12
Well it finally shot me a code 304. Never showed until today. Wiring is showing continuity, and the Seafoam didn't clear up the miss. Picked up a new injector and will install it in the morning.
Update: Put in a new injector------still misfires.

Put the plenum back on and idle went up to 1200 rpm. Pulled the plenum back off and found a tear in the gasket. Replacing that tomorrow.

Would a previous small (and less noticeable) vacuum leak at the plenum have caused a misfire????? Previous idle RPM was 700-750 RPM.

Also, took it out for a spin and it threw a flashing CEL at me. I was taking it up to 3000 rpm and when brought down to idle the light turned off. Checked it with the key dance and got a 304 (this was last night). Did the same thing today with the flashing CEL, but NO CODE with the key dance. :banghead:
 

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If your idle was at 700-750 , you probably did not have a vac leak, until you took it apart.
The flashing CEL means you are about to destroy one or both cat converters.(do not operate the engine except for testing purposes , shut 'er down immediately if you still get the flashing CEL) Probably from unburned fuel getting into your exhaust due to the mis-fire, or from an excessively rich mix. It could be that the lean condition caused by the vac leak is causing the 'puter to pour in more fuel.
If you no longer get the 304 code , then you may be on your way to happiness after you replace that leaking gasket.
 

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intake manifold gasket tear can certainly cause misfire as it lets in too much to burn the fuel.
 
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