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2001 Lexus 3.0L- Ignition Coils Wired Backwards - Misfire Under Load

Robert Diagnostician Oldsmar, Florida Posted Latest Edited

Case Study

Driveability

2001 Lexus GS300 3.0L (2JZ-GE) 5-spd (A650E)—JT8BD69S110121530

Misfire Under Accel

MIL On

Well just wanted to share what happens when 2 wire ignition coils are wired backwards and how to spot them. This vehicle came from another shop who gave up on it. The primary current on two of the three coils was quite odd and those 2 coils were the ones misfiring under load.

We removed the throttle body and found the harness was starting to crumble and come apart. The coils, wires and plugs were all recently replaced. I decided to rewire the coils because of the harness issues I was seeing. Then I came across two coils that were wired wrong. Someone had replaced two of the connectors and switched the wires. I have never seen this happen before but I bet its more common than I think. So i will post up the current wave forms before and after of the coils. The vehicle did not misfire at idle or light acceleration. Only when you got on it is when it would just break up.

Another thing, this vehicle was also setting a code for the accelerator pedal position sensor. I swept the accelerator position sensors and tps and did not see any drop outs. After the coils were wired correctly we cleared the codes and the acceleration pedal position code has not returned. That code was previously setting shortly after the misfiring events so it may have been related. The capacitor for the coils mounts just back from the TPS sensor so maybe it had something to do with it. Hope this helps someone along their journey.

Cyl 1 Ignition Coil Primary Current

Cyl 2 Ignition Coil Primary Current (Reversed Polarity)

Cyl 3 Ignition Coil Primary Current (Reversed Polarity)

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Interesting

Thanks

James Instructor

Boucherville, Quebec

James Default

Seen this before on a 2006 or so Hyundai . The good or should I say properly wired coil would not even hit current limiting by the PCM driver. The badly wired one would hit current limiting with almost a vertical ramp before it did.

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Chad Mechanic

Chandler, Arizona

Chad Default

That is pretty cool! I have always wondered what the waveforms would look like when a COP coil is wired backwards sense you are going from a step up transformer to a step down transformer, if that is even correct. Do you have any captures of the primary ignition waveform of one the coil wired backwards by chance? Thank you for sharing this!

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Robert Diagnostician

Oldsmar, Florida

Robert Default

Yes I do and here it is #3 was wired backwards and #1 was normal the extra spike on #1 I believe has something to do with capacitor not sure . all the captures i shared were at idle not actually misfiring. It misfired under loads and higher rpm driving it when the demand for spark was greater.

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Dmitriy Analyst

Toronto, Ontario

Dmitriy Default

Robert, the scope settings you are using do not seem to be correct for capturing the primary voltage waveform. As per Picoscope guide: picoauto.com/library/automo… diag.net/file/f53oe8453… This is captured while using 20x attenuator; if using 10x attenuator, that one should be selected.

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Robert Diagnostician

Oldsmar, Florida

Robert Default

Late reply but this was captured with 20:1 attenuator yes

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Chad Mechanic

Chandler, Arizona

Chad Default

Awesome! I was curious what they looked like at idle. Thanks for sharing Robert!

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Stephen Technician

Gallatin, Tennessee

Stephen Default

Hi Robert, I’m trying to reverse analyze the voltage waveforms to understand what the scope was showing. Can you tell me how the scope was connected to the coil? Is that a 2 wire coil? What type of scope lead was used? Was there an attenuator? Thanks,

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Todd Technical Support Specialist

Brooklyn Park, Minnesota

Todd Default

Shooting from the hip: I'm visiulizing 4 things. - There is a clamping diode diode that turns on so it flows lots of current suddenly. - That current causes the driver to go into "current limiting" quicly preventing a strong build of the magnetic field. - The weak magnetic field causes weak spark (also the spark is fireing from the ground to the center electrode). - The weak spark is…

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James Instructor

Boucherville, Quebec

James Default

That was my guess as well, On the Hyundai I had there was no spark at all if remember correctly

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Olle Instructor

Albert Lea, Minnesota

Olle Default

Most of the COP coils have a high voltage diode in the secondary circuit. Having the primary circuit wired backwards could certainly cause some odd problems. Conceivably even a total loss of spark.

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