Keeping it simple
Hey guys, I have several simple case studies I am going to post back to back. I'm mostly doing these because I love using the scope lol. I know for most guys this content will be old news. However I also know there are many guys like me who are still learning, so here goes. Got called to this shop. I was told" we have replaced the #7 MDS solenoid 3 times with a Mopar and we can not get rid of the P1417". This code sets if if the PCM does not see the #7 cylinder immediately contribute 100% after it has reactivated the cylinder from a V4 event. The PCM also disables the injector control circuit until the code is cleared. This code will not clear unless you disconnect the battery cables. It is very important to get the P1417 cleared before further diagnosis to ensure you aren't chasing your tail. Also I have to thank Eric O from the South Main Auto Youtube channel a few months back for this information. Anyway disconnecting and reconnecting the cables cleared the P1417 and we now have restored injector pulse. I can tell there is still a misfire. I go on a quick test drive an immediately I get a flashing MIL and P0307 and the car has a dead miss. I dont know why the MDS solenoid was replaced to begin with. To rule out a solenoid problem I command the #7 solenoid with the scanner KOEO and hear a nice solid click similar to another solenoid. Ok cool moving on. Next I just listen too the cranking cadence. It sounds great. I was confident enough with my ear to move on without a relative compression test. Next I grabbed injector and coil amp draw for #7. They looked great. Did not see much of a pintle bump on the injector but the shop had already swapped the injector and it was the same waveform compared to the #5 injector so moving on. Here is that screenshot.
Next I grabbed a secondary pattern on the control side of the coil while using a 10:1 attenuator.
Wow, there is our problem lol. I am not very good at secondary yet but I like it and so I want to use it as a diag tool. I think to myself " it looks like the spark never reached the cylinder". I pull the coil up and can hear the spark banging away. Pull out the coil and I dont see any leaks in the boot. This engine has 2 plugs per cylinder. I pull the plugs and well, I think we found the problem lol
Some of the worst plugs I have ever seen. Now I begin to understand why my secondary waveform looks the way it does. There is really no gap to close because of the fouling so the spark just instantly grounds or shorts out?? Ill take any professional input on that statement. I tell the shop to get me 2 new plugs and I do a quick in cylinder while I am waiting on the plugs since I have time.
The compression looks nice and even and I am happy with the 11 psi vacuum at idle. This translates to about 22 inhg at idle which is perfect. The new plugs arrive, I put them in and get another secondary, the results speak for themselves.
Anyway this was quick but I had fun using different tests using many different methods to accurately pin point the issue. The vehicle has been driving for over a month no issues. I really dont know how those plugs got that way. The injector wasnt even spraying because of the P1417 code. The plugs were brand new Boschs. I dont know if they were the wrong plugs so they didnt last ??!!
Nice work! Crazy they went through all that work but never checked a plug.
Awesome post Caleb thanks for sharing can’t forget to test the secondary very often overlooked
I see plugs like that out of the Chevrolet trucks with the AFM 5.3L engines. Thanks for taking the time to post this.
I'm laughing so hard at "replaced the #7 MDS solenoid 3 times" that I can't keep reading!
great case study . sounds like KISS Keep It Simple Stupid in short tell the other shop
Caleb, Nice & simple write up! After all these years, I am just now learning to use my scope. Need to master the basics before heading off into the weeds. Thanks, looking forward to more, Davie
Thanks for the informative write up. Very cool. Sorry if this sounds like a dumb question. What do you mean when you say you grabbed a secondary pattern on the control side of the coil? If you're connected to the control side wouldn't that be primary? Alex
On coils with the driver in the ECU the secondary bleeds into the primary. Thats the best I can tell you. You have to have a good scope too catch it tho.
Would a faulty ignition coil waveform look similar to your bad spark plug waveform?
I'll give you a faulty coil when I get my laptop out. But the best thing to do is not memorize how failures look but rather in the words of Mac Vanderbrink"analyze don't memorize ". That being said. I'm just starting myself with secondary. So I'm no expert, but practice makes perfect.
Any sources I’ve seen call it the primary voltage pattern: picoauto.com/library/automo… Primary voltage at the primary winding, secondary voltage at the secondary winding. Keeping it simple, right?
So guys I'm not really sure how to answer the question about primary versus secondary. To me it's so simple that I'm not sure if I'm missing something in you guys questions. Nonetheless I'll answer what I think is being asked. I have added this crude illustration. diag.net/file/frhlcmzis… So yes I am using the primary voltage too view the secondary. And the primary voltage is visible on…
youtu.be/Z2YYrERTX6E watch this video it explains the difference
So, you are trying to split the coil operation timewise. Typically, this is done by talking about the Dwell time (left of firing line), and the Burn time (right of firing line). images.app.goo.gl/DTX8LuiV2QQRiL… During the Dwell time there is current flowing through the Primary winding, but none in the Secondary winding; and the opposite happens during…
Thanks for clarifying that. For whatever reason I haven't had any luck getting a pattern that looks like that on my scope when back-probing the control wire to a COP unit. The pattern I get looks more like a current ramp than a secondary ignition pattern.
Hi Alex: It sounds like you are looking at the IC control. In effect, you are looking at the voltage side of a current ramp. If you see it, you know the coil is charging. You can also measure the time to saturation and extrapolate if the coil is shorted. Don't like the view? Zoom in and turn your scope upside down. :) HTH, Guido
Thanks Anthony. How should I connect my leads to obtain a primary (secondary mirror) pattern on a COP unit? Maybe I'm connected correctly but my scope just won't do it?
Hi Alex: On that type of system, there really isn't "an easy way" to do what you're asking since the IGC is internal (4 wire COP). If memory serves, Ray made a post in the last few months addressing a way to do so. I suggest going through his posts to see it. Usually, the quickest way will be to use an extension secondary lead. HTH, Guido
Thanks! I'll check check out Ray's post. I appreciate the useful info!
I want to apologize guys for my response about primary and secondary. I was aware that I was using the primary voltage. However I misspoke when I said the secondary bleeds thru into the primary. Brandon Steckler helped me understand that what I thought was secondary is actually still primary voltage but the part that looks like secondary is a very small mirror of the real secondary. Anyway so…