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Ron, ASE Certified Technician
Category: Mazda
Satisfied Customers: 36024
Experience:  35 years as a automotive tech
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Trouble shooting a 94' Miata with weak spark on cylinder 4.

Customer Question

Trouble shooting a 94' Miata with weak spark on cylinder 4. Swapped coil, plugs, wires, coil harness, checked grounds, and still weak spark. Swapped coil plugs with on another and the misfire stays on same cylinder. Also changed injector on cylinder 4. Good compression on all cylinders, also changed ECU.
Submitted: 1 year ago.
Category: Mazda
Expert:  Ron replied 1 year ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

The coil is fired by the driver in the ECM (computer) and if you are sure the coil checks okay the the next thing to do is check the circuit from the coil to the ECM. If the wiring checks okay then you are likely looking at a bad driver in the coil. See the wiring diagram in the link below for reference.

Customer: replied 1 year ago.
I have already figured it out and in my statement I said that I changed the ECU as well and it did not change the problem. Turns out it was a low output signal voltage from the cam angle sensor to the ECU which was giving me a low voltage reading for the signal to the coil on #1&4. I was able to figure this out yesterday at about 4:30 pm so I would like a refund please
Expert:  Ron replied 1 year ago.

Glad to hear you got it resolved . You can request a refund by contacting customer service and they will process it for you.

Customer: replied 1 year ago.
Thank you for your time
Expert:  Ron replied 1 year ago.

Your very welcome and thank you as well.