2 cylinders not firing, 1 code-knock sensor

misfire
infiniti
sensors
sparkplugs

#1

I have a 96 infiniti that has no spark from cyclinders 2 and 3. I have swapped out the ECM with one from the recovery yard and still have the same issue. I have traced the wiring from the coil pack to the ecm for both cylinders and found that the voltage to these is only .08 (all the rest are .14) when the engine is running. The only code that comes up is the knock sensor… no misfire, no cam sensor, nothing. What am I missing here? I have also swapped coils to see if it was a resistance issue but that did not work either. What could cause the below normal voltage on these two cylinders, and how probable is it that two ecms have the same issue? ( I think the ecm is not the issue, as I find it hard to believe that both have the exact same issue).

Please help, dealer wants 1750.00 to replace complete wiring harness before they will even look at the problem!


#2

Did you check the continuity of the wires running between pins 2 and 3 of the ECU and there respective coil connections on pin 3 of each of the coils?


#3

Since theres no misfire codes, you gotta wonder if this is an ignition problem or possibly low compression in those 2 cylinders.
Like Cougar sez check the wiring & see if you can find your missing voltage.

If it’s good do a compression test. This might solve this little mystery. It’s barely possible.

If you’re sure the plugs are not firing then disregard this post.


#4

I checked for continuity between pin3 of the coils and the respective pin on the ecu, but I did not check pin 2 and pin 3 on the ECU. Should there be continuity between the two pins on the ECU, or are you saying to check the continuity between pin2/ECU to pin3/coil and then pin3/ECU to pin3 coil? Basically what I am saying is that I checked for continuity between the two coils in question (pin3 on each) and the correlating pin on the ECU. Like I said, I get .08v at the ECU on each pin and .08v at the coil on those in question. Other coils/pins get .14v at both ends.


#5

Do you actually KNOW that spark isn’t occurring, or, are you ASSUMING? Did you stick a spark plug in each ignition coil spark wire (or, “tube”) , ground the spark plug side electrode, and watch for spark? Inductive lights, and timing lights, can flash without the spark actually going through the spark plug center electrode.

“Volts” is not a unit of resistance. Ohms is a unit of resistance.

The ECM (engine computer) does NOT supply voltage for the ignition coil on #3 wire on any coil. The ECM, from terminal #10, supplies voltage (power) to ALL the coils on the brown/yellow wires. The ECM causes the spark plugs to spark by making and breaking, repeatedly, the circuit from each #3 coil wire. Each time the ECM disconnects the circuit from ground, the ignition coil fires. So, it’s a constant make, break, make, break, make, break.

I’m assuming you have the V6 engine. What model is your Infiniti?

The brown/yellow wire, at each coil, should show 12 volts dc. The ignition key needs to be in either RUN, or START (check your manual). The black wire goes to ground. Make sure there is the 12 volts dc on brown/yellows, and that each, and all, the black wires go to ground.
You can back-probe the ECM terminals #18, #19, #20, #22, #23, #24 for spark control ON/OFF with the engine cranking, or running. The voltage should swing up and down, if it’s not averaged by your multimeter.


#6

Good job on the wiring check. You did the right check by making sure you had continuity between pin 3 and the ECU. The next step would be to check the power side of the circuit. See if you have 12 volts on pin 1 of the coil connection.