Coil ramp question

Rudy Technician California Posted   Latest   Edited  
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2008 Lexus RX350 3.5L (2GRFE) 5-spd (U151E)
P0304 P0354

This vehicle has a bad coil. Simple enough diag,and I was showing another tech how to coil ramp the coils. I amp clamped the fuse that feeds the coils and injectors (same fuse) and to my surprise the coils did not look out of sorts, the vehicle was actively misfiring

However the IGF signal clearly shows the lack of coil firing event. Whats is occurring here? Why doesn't my amp clamp reflect a bad coil? The coil pattern looks like it peaks slightly higher on #4,but not across the board,nor does it look shorted(IMO) (You'll have to load the BIN file to take a closer look at the coils)

Yellow=Amp clamp

Green= synch cylinder# 2 (FO is 1-2-3-4-5-6)

Red= IGF (tapped into #6)

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Jim Mobile Technician
Pennsylvania
Jim Default
 

What I go OVER and OVER in my ignition classes is "The A,B.C,D of ignition. "A" - Where does the power for the Primary come from ? "B" - Where does the Primary get switched or interrupted at ? "C" - Where does the Secondary begin at ? "D" - Where does the Secondary go to ? My mentor beat this into my head MANY years ago and it still works today. What I would be checking on the vehicle you have…

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Ricardo Diagnostician
Michigan
Ricardo Default
 

Jim, so what you inferring is maybe a cracked spark plug , or shorted/opened windings on secondary but wouldn't any of those circumstances affect the primary current ?

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Jim Mobile Technician
Pennsylvania
Jim Default
 

YES, It sounds as though "A" and "B" and good, just that "C" isn't going to the current place.

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Would issues in the secondary path cause the IGF signal to disappear?

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Jim Mobile Technician
Pennsylvania
Jim Default
 

NO, basically IGF is the signal that says "A" and "B" did their job, It doesn't mean the "C" went to the correct location.

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Dmitriy Analyst
Ontario
Dmitriy Default
 

But the IGF signal is missing — the red trace at 350ms mark on the waveform does not go to ground, right?

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Rudy Technician
California
Rudy Default
 

Dmitriy- As I understand the IGF, as taught by Dan Marinucci, that signal comes from the igniter and signifies whether or not the coil fired. If the IGF signal is missing,its almost certainly a bad coil. Even with a stray secondary, the coil is still firing and I believe you will still have an IGF signal.

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Rudy Technician
California
Rudy Default
   

Jim- Im not sure I understand. Are you saying the coil is not the problem? Because a new one fixed this vehicle. What I am mostly trying to understand is why didnt the amp clamp display a faulty coil,even with the vehicle actively misfiring?

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Ray Diagnostician
Ontario
Ray Default
 

An ignition coil has 2 windings, a primary coil winding and a secondary winding. After the primary coil winding amperage draw stops, the primary coil winding's magnetic field collapses and then the COP's secondary winding creates the high voltage to force the burn voltage to jump the spark plug gap, to the plug's ground terminal. So a problem in the secondary voltage may not show a problem in…

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Geoff Diagnostician
Hawaii
Geoff Default
 

Hey Rudy, I had a class once that said Toyota used three different methods for determining IGF over the years. (Sorta like the way they kept changing their EVAP system). All my books are at the shop and we're all laid-off right now. Inductive kick was probably one of the methods, as opposed to current, sorry my memory isn't better.

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Sherman Service Manager
Georgia
Sherman Default
 

If I am correct the fuse that powers the injectors and the ignition coils is a IG2 7.5 Amp that goes to IG2 relay, so what you are measuring is the relay coil side. I tried that once before and got the result as you. Amp clamp connection will have to be made at the engine wiring harness near the to the ignition coil.

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Rudy Technician
California
Rudy Default
 

Sherman- I saw that ,so instead I went with the INJ 10A fuse,it is on the power side of the relay.

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Sherman Service Manager
Georgia
Sherman Default
 

So Rudy, you are measuring injectors and ignition coils if you are amp clamping that 10 amp fuse INJ fuse which supply power to 2 different legs 1 for the injectors and the other for the coils

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Rudy Technician
California
Rudy Default
 

Sherman- That is correct.(you can see the smaller injector "spikes" in my waveform) It is sometimes unavoidable, but should not interfere with the coil current measurement. (at least it never has on other vehicles that Ive tested this way.

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Jonathan Educator
California
Jonathan Default
 

Rudy; Good afternoon Sir, I hope all is well. Comparing the two coil patterns Coil #4 doesn't show a Current Limiting Plateau on the top like the others in your waveform. I created a side by side image of the two coil current waveforms, I hope this helps.

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Rudy Technician
California
Rudy Default
   

Jonathan- I saw that but wasnt sure if that was an issue. Are you certain the other "good" coils have that plateau? It seems to me that 2 and 5 look similar. I wanna say not all coils on every make have such a plateau? I think some are limited by the ECM and not circuitry in the coil.

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Dmitriy Analyst
Ontario
Dmitriy Default
   

Rudy, there are two things that jump out at me on these waveforms: - IGF signal missing at 350ms mark; - Injector pulse missing at 415ms mark; IGF signal missing can mean a few things: - the igniter fails to respond to IGT signal; - wire that carries IGF signal is broken; - IGF circuit has failed; - a combination of above; The primary current waveform suggests case 1 is not an issue…

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Randy Diagnostician
California
Randy Default
 

That is what I suspected. Thanks for the link

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Joseph Technician
Pennsylvania
Joseph Default
   

Good eyes Dmitry!! I had an '09 corolla yesterday, current ramp looked good to me as well. It had a p0352. I replaced the coil along with all 4 plugs. The plugs were brand new, but were autolites. Im new to using scopes. I did not check the igf circuit, so i cant confirm that was the case w/my vehicle. The way Bat. wire is set up, you should be able to get the feed voltage to all coils by…

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Bob Owner/Technician
Massachusetts
Bob Default
 

Dmitriy, I was searching for information on how IGF is created and I came across the same case study. It looks like Rudys case is similar to Matt's. The vehicle had a coil with a bad IGF circuit. The cylinder misfire was due to the injector being shut off by ecm strategy. It would have been interesting to see a secondary pattern at the same time. You probably would have seen that the coil was…

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Douglas Engineer
New York
Douglas Default
 

Dmitriy nice catch on the difference from Matthew's broken wire case and the fix being a new coil! Intentional injector shut downs can be tricky to catch but I learned that you can look for injector signals at start-up prior to the PCM shutting them down to validate an intentional shut down case and then work backwards from there. Nice Job!

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Rudy Technician
California
Rudy Default
 

Dmitriy- Excellent find and observation!! I think you nailed it! It makes perfect sense. This issue isn't with the coil windings,but rather with the IGF circuit itself,leading to the injectors being shut off and subsequent misfire. Thats why my current ramp looks like a normal firing coil,because it is!! Yes a new coil fixed this vehicle, I did do swaptronics prior to installing a new coil…

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Caleb Diagnostician
Indiana
Caleb Default
 

Hey Rudy I was dont have ATS software so I could not view the file. And not to take away from all the excellent responses. However just wanted too mention that the amperage waveform does not have to "look bad" for the coil to have failed. I know that sounds like stating the obvious but its true. Especially when dealing with coils that have an internal driver or igniter or whatever its called (…

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Rudy Technician
California
Rudy Default
 

Caleb- Thanks for the observation. You can download the ATS software for free(same as Pico) and load and manipulate waveforms. I dont have a Pico,but I have the software just for that purpose.

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James Owner/Technician
Pennsylvania
James Default
 

Thanks for the download

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Brandon Diagnostician
Pennsylvania
Brandon Default
   

just an annotation describing the chain of events. The missing #4 IGF signal was the cause of the missing #4 injector ramp

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Joseph Technician
Pennsylvania
Joseph Default
   

I think what is hard for me to figure out is the igt circuit. Is it safe to say that it takes 360 degrees of crank revolution for the coil to receive the trigger from the pcm to fire the coil?

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Philip Educator
California
Philip Default
 

Rudy, IGF is magic! Of course, I'm kidding. Suffice to say that Toyota has some pretty sophisticated ways of deciding if a coil fired. Almost always your method works perfectly to identify the bad part. But every now and then something like this happens and we scratch our heads and say to ourselves "How does it know not to deliver an IGF when I can't see a thing wrong with it?" The explanations…

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Rudy Technician
California
Rudy Resolution
 

I want to thank everyone who provided input, hopefully some of you learned from this unusual issue as I did.

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Interesting
Michael Diagnostician
Illinois
Michael Default
 

looks like maybe somebody already replied about the injector. Sorry about that.

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Michael Diagnostician
Illinois
Michael Default
 

Hi Rudy nice catch. Got a suggestion for you next time when you get into a similar situation. The method you used to find the misfire was great. I believe the reason why you don't see anything obvious on the primary current ramp is because of the sample rate possibly. So next time after you find the culprit only use 1 channel at the fastest deep record time or use one channel on scope A rolling…

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Ray Diagnostician
Ontario
Ray Default
 

A COP has 2 coil windings, a primary coil winding that draws amperage and when the current stops, the collapsing lines of force thru the secondary winding, creates the kilo volts that will arc across the spark plug air gap to ignite the air fuel ratio in the cylinder. To find misfires, on 3 or 4 wire COPs, the COP's secondary should be used to diagnose the spark plug burn times. When the PCM…

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Michael Diagnostician
Illinois
Michael Default
 

Thanks for sharing. Maybe Rudy will do some more captures of a coil on plug primary,secondary,and current at a fast sample rate to see some better detail of the waveform.

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Ray Diagnostician
Ontario
Ray Default
 

These captures are from an 07 Camry 2.4 In the first GIF, I'm doing a 1500 rpm brake torque to stress the ignition system CH A is the COP secondary and the spark is arcing across the spark plug's air gap for a good 1ms. CH B is the COP primary coil winding amp draw. In the second GIF, CH A is the IGT which controls the length of time that the primary coil winding is grounded CH B is the coil…

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Samuel Technician
New Jersey
Samuel Default
 

I was sitting back waiting for someone to say the IGF was faulty....The IGF acts like a supervisor to confirm the Coil is doing the job. There is an EXCELLENT short video by a Toyota Technician on Toyota 4 wire coils. The youtube channel is called Voltage Drop Diagnostics and his name is Pj Walter. The video is SUPER thorough and after watching, you will think, OMG, I cannot believe how simple…

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