03 montero sport 3.5L..no codes but upon checking coil 3-6 not giving sparks.. swapped coils .. coil good.. running on 4 cylinders so poor idle and sluggish acceleration.

anybody has any ideas how to proceed?

 

Since you determined that coil is good - then the issue is somewhere with the wires on the primary side of the harness. Do you have any signal on the harness connector on primary side of the non working coil? If not, you have to trace wire all the way back to PCM. It's possible that you have a wire break or short somewhere. If your lucky, it will be somewhere not too far along the harness. Alternatively, it can be at any point further down. Start by checking the wires on top of engine. If all good there, get a wiring diagram and test to see if you have signal coming out of PCM to the harness side of the wires to the bad coil. If no signal - some sort of PCM issue, if signal present, but not getting to coil - trace more harness wires.

 

thanks.. i guess you are right about the PCM/ECU.. if there are sparks in the other coils then there must be no signal from the ECU to the one in question.. any ideas how to fix that?

 

Figure out where the issue is exactly. Then we should be able to come up with solution.

 

Might be a bad ignition switch. I had a problem with the contacts, maybe they are not securely fixed at worst wire break. If the ignition coil does not have a spark, it's time to check its wires. Use a test light to check the continuity on the signal wire and power wire on the ignition coil. If both wires are functional but the coil fails to produce a spark, the ignition coil or the ignition control module is bad, otherwise, replace the ignition coil on this site https://davesoilchange.com/coils-for-5-3-vortec/ you can see the best coils for 5.3 vortec,I use QYL.


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