Unicarriers (& Nissan) MU1 F2A35LV:
#3 cylinder not firing

Codes 27& 34. #3 coil wasn't a oem. Replaced all 4 and plugs. Cleared codes and engine starts up. No codes but 3 isn't firing. Checked voltages and on all 4 cylinders at plugs and are the same. Won't fire #3. Changed out crank and cam sensors. Cleared any codes and won't fire 3. Any help much appreciated.

Model number is a mu1F2a25LV.
  • Posted 11 Nov 2020 05:30
  • Modified 11 Nov 2020 05:31 by poster
  • Discussion started by ron_k
  • North Dakota, United States
4kliftman
Showing items 1 - 8 of 8 results.
Thanks for the final update, glad you got it going. I've had coils burn up due to plug gap becoming too large but never heard of it taking out the driver'/ecm. And yeah, its crazy how some trucks just don't like aftermarket parts
  • Posted 18 Nov 2020 02:18
  • Reply by Triggs
  • California, United States
Final outcome was the driver output from the ecm. Voltage was present on the wire to 3. Wouldn't fire the coil. Another tech stated to disconnect driver output and jump from 2 since it was the same stroke, After that coil fired. Ordered new ecm and replaced. Run learn steps for throttle and fuel. Started u it and run. No codes. All cylinders firing normal. These engines require OEM parts just like everything nowadays. Keeps aftermarket out of the picture. We all knew someday it was coming and it's here. A simple terminal now makes the difference in choice of parts. Thanks for the info!
  • Posted 18 Nov 2020 01:52
  • Reply by ron_k
  • North Dakota, United States
4kliftman
Thanks for the info. Ended up clipping the signal wire from the ecm and running direct. Didn't change the no fire. Run a jumper from cylinder 2 to 3 and coil fired. Then went down to ecm and run a jumper from there to 3. No fire. Ordered a ecm as no signal was being output. Figured the driver went bad due to a aftermarket coil and plugs were installed before I was given the repair. Will update the outcome. Thanks again for all the info from everyone.
  • Posted 15 Nov 2020 11:46
  • Reply by ron_k
  • North Dakota, United States
4kliftman
There are no drives to be replaced when you change a coil. One of the wires in the plug is a signal wire that has 1-2 volts when cranking over and running. I would say that there is a bad wire at the connector. A lot of times the wire will be broken but the outside wire covering is still holding the wire in the connector. This is a common problem due to light wiring being used in the harnesses.
  • Posted 15 Nov 2020 11:10
  • Reply by mwjski
  • Montana, United States
The voltage and ground is there on all 3 wires. I've learned that there are drivers for the coils that should be replaced along with coils? Is this correct?
  • Posted 11 Nov 2020 07:04
  • Reply by ron_k
  • North Dakota, United States
4kliftman
So the spark plug isn't receiving voltage...
You will need to find a wiring diagram and trace #3 coils wiring back to ecm, there is most likely a break.
  • Posted 11 Nov 2020 06:38
  • Reply by Triggs
  • California, United States
Yes. Have moved that coil to others and fires on that cylinder but not on 3. Compression is good. Even laying on top of motor no fire. Tried multiple plugs and different coils. No spark on 3. The voltage is 14 on the wiring to the coil. Negative is there as well but it fires a negative from the ecm correct? For spark?
  • Posted 11 Nov 2020 06:17
  • Reply by ron_k
  • North Dakota, United States
4kliftman
You're saying #3 spark plug is receiving voltage from the coil but doesn't spark..??
  • Posted 11 Nov 2020 06:07
  • Reply by Triggs
  • California, United States

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