Fishinfool98 Posted January 26, 2022 Report Share Posted January 26, 2022 (edited) 2012 Limited with 3.5 154,000 miles Engine developed a miss fire on #1 replaced plugs, coils and injectors. Still had misfire. sent out pcm. Get new pcm and replaced with another set of coils… still has misfire. Start ohm testing wires and find that I’m getting readings on multiple wires on each coil with all the coils and injectors disconnected, disconnect the engine to ignition harnesses and the issue goes away…. Test the ignition harnes and I have 5 wires that ohm test together. In desperate need of a wiring diagram! Any help greatly appreciated. Edited January 26, 2022 by Fishinfool98 Quote Link to comment Share on other sites More sharing options...
Perblue Posted January 27, 2022 Report Share Posted January 27, 2022 6 hours ago, Fishinfool98 said: Start ohm testing wires and find that I’m getting readings on multiple wires on each coil with all the coils and injectors disconnected, disconnect the engine to ignition harnesses and the issue goes away…. Test the ignition harnes and I have 5 wires that ohm test together. The 2 wire coil packs will all have constant voltage at the same time, the pcm is the ground. When the coil pack loses ground that causes the coil to fire. Coil On Plug Ignition: The Wired Differences (siu.edu) Coil-on-plug (2-wire) - primary voltage (picoauto.com) "This principle starts with a magnetic field being produced, as the coil's earth circuit is completed by either the contacts or the amplifier providing the coil negative terminal with a path to earth. When this circuit is complete, a magnetic field is produced and builds until the coil becomes magnetically saturated. At the predetermined point of ignition, the coil's earth is removed and the magnetic field collapses. As the field inside the coil's 250 to 350 primary windings collapses, it induces a voltage of 150 to 350 volts." I would suggest a compression test and coolant exhaust gas test, unless the one with no voltage is for cylinder 1 then start there. 3 Quote Link to comment Share on other sites More sharing options...
1004ron Posted January 27, 2022 Report Share Posted January 27, 2022 (edited) Perblue - "it induces a voltage of 150 to 350 volts" - isn't there a zero missing? Edit/correction: that would be the induced voltage on the primary. Edited January 27, 2022 by 1004ron 1 Quote Link to comment Share on other sites More sharing options...
Fishinfool98 Posted January 27, 2022 Author Report Share Posted January 27, 2022 The #1 has no power! The plug has not been fired at all. No voltage shown at all on the coil Quote Link to comment Share on other sites More sharing options...
WWWPerfA_ZN0W Posted January 27, 2022 Report Share Posted January 27, 2022 since you have replaced the pcm and coils, that leaves the wiring harness. ohm test the wiring harness for breaks. what misfire code were/are you getting? 1 Quote Link to comment Share on other sites More sharing options...
enigma-2 Posted January 27, 2022 Report Share Posted January 27, 2022 The five wires that ohm together are connected at a junction point and come from the battery junction box. Furnishes + voltage. As WWWPERFA_ZN0W stated. Look for corrosion or insulation failures. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.