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Q: I have Engine code P0304 which I was told " Misfire on that cyl.. on 2001 Jeep Grand Cherokee

I also have while trying to drive my JGC a flashing Engine light (which I was told is a cat getting ready to fail or has failed... Total loss of power while driving, I can only drive like an old man out for a sunday drive. I replaced the ignition coil pack and it didn't help.
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Flashing light means you have a misfire that may damage the cat. conv. if not repaired, not a failed/failing cat! These are possible causes for code PO 304: ignition misfire on # 4, injector blockage or defective injector, no injector pulse to # 4 injector, low compression or gross vacuum leak at # 4 cyl. Check to see if anything has chafed wire insulation to injector 4. ie throttle linkage/bracket etc. This imisfire or dead cylinder is the reason you have no power! Also the reason for the flashing light.
By now the amount of money you have spent would have been spent by taking it to a professional to have it diagnosed it properly.
The loss of power by now is because you drove it to long with the check engine light flashing. You probably do have a bad cat by now.
You do need to do a basic compression check on all 6 cylinders. If it's not mechanical than it's electronic.
For your information.. I stopped driving the Jeep as soon as this problem started.. I'm not a complete moron.. and two I am a Mechanic. however my main focus is Suspensions not Engine performance! and three I don't have access to a diagnostic system !
I know I've never implied you were a moron . You say you are a tech, but you don't focus on Drivability. You must work around techs that have those abilities. You are going to have to have the right equipment.
Let me get on my soapbox. That is the major problem in the Automotive Repair Industry, People(customers) just don't understand the investment to repair automobiles. It's not just the equipment but the training. I myself have spent thousands of dollars. Then you have people that can't seem to understand that you won't warranty the job if you bring you own part. This whole industry has gone to a HELL in a hand basket. I'm sorry that I have bored you all.
I replaced the plugs, Coil railpak and am in the process of removing the exhaust as we speak, only bebause I have the flashing light while under accel, and the book indecates thats a signal the the cats are failing...
STOP YOUR WORK!!! Read next suggestion! Cat. is not the problem! Cannot cause code PO304 or flashing light!!

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