Testing a Coil with No Access ?

You can look at primary ignition voltage by grabbing the coil control circuit with scope at the PCM. The coil driver is still in the PCM on this model. Gives you beautiful primary picture.

Thanks Caleb that's good to know. I was actually thinking of doing that but Bossman was kind of rushing me so i went with my gut and got lucky this time. I definitely have to scope more ignition waveforms and research more about it.

The boss was rushing a diagnostic ? The boss has an attitude problem. Has the boss provided you with diagnostic training?

I wish they offered training. Most of the techs here ive noticed don’t understand electrical or don’t like troubleshooting. They read codes and change parts. when that doesn’t work they send it to the dealer So that’s One of the reasons I’m trying to educate myself on how to troubleshoot

Hi Aaron. Good for you for asking the question and being motivated to learn! As Caleb alluded, grab a waveform from the primary ignition, since it is essentially mirrored in the secondary. I recommend spending some time saving some good and induced fault failures on some ignition systems using both primary and secondary ignition systems. Despite seeing the common elements of the ignition…

Martin, These days, “everybody and his dog” is at it with their own channel, posturing as scope gurus. However, if you can find some works by some of the older guys like John Thornton, Bill Fulton, Jim Morton, Mac Vandenbrink (RIP), Gary Goms or Bernie Thompson and the like, you will find that they were writing about and presenting a lot of these now “super hero” revealed techniques, long…

Hi John! I hope that you are keeping well. Yes, it seems that what was once old is new again and everyone is a “guru”! Of course, this is not to say that there are not any new “gurus”, but much of what surfaces has been around for many years. Perhaps current and new tool technologies allow for improved viewing and analysis, but if Leornado da Vinci had been born a hundred years or so later…

Hi Martin, I am sure you recall the early days. Back when the big cabinet scopes cluttered many shops. They were bulky, time consuming and a pain to detangle and connect all the cables. Half the time the user manuals were nowhere to be found, so maybe one guy in the shop knew how (hopefully) to read the patterns well enough to be good at using them. Of course, many were often quietly shoved…

Hi Glenn. Yes, I too learned on the old Allen and Sun big box “engine analyzers” that had a cathode ray tube scope sitting atop a cabinet full of gauges, dials and buttons! Vacuum testing was built in, condenser (capacitor) testing and a whole lot more. For ignition system diagnostics, the old scopes could not be beat by early DSOs and the like. I still have my old Tektronics 222a portable scope…

Hi Martin, I still own a bear 200 engine analyzer and a Snap-On Counsellor. They still come in handy a few times a year at this point for older vehicles. They work well for the classics. Recently, I had an 86' Ford F250 that had been to a couple of shops, it was the last of the carbureted monster 460 CID's. I figured out the issue with the truck and the owner was happy to pay me. It had a bad…

Hi Glenn. I still have the scope from an old Sun analyzer that had been stripped for scrap. It still works just fine, although I cannot even lift it unassisted from the roll cabinet on which it currently sits! One day in the spring I'll bring my '71 GMC into the shop for a scope session! Back on campus we do still have a couple of Counsellor IIs in storage, that still work. Ah, from my days…

Hi Martin, We are going back down memory lane. People might think we were crazy to ever get into this industry. In reality though, I've never went without work to provide for myself and my family. I still use a lot of my old test equipment. I know eventually it will give out someday, I'll cross that bridge when I come to it. We've come a long way from the big CRT scope days down to handheld…

Thank You I will definitely look up those ppl you mentioned. Ill take any advice and training I can get.

Hi Aaron, I also suggest you check out Wells Automotive Electronics on You Tube. They have some very informative troubleshooting videos. Oh No! It's Ohm's Law Pacific Time - Bing video

I'm not sure you can scope Primary ignition on Smart Coils ???? … Dumb coils you can I forget what's on a 2015 coil wise , maybe they are stupid coils ..if anything we'll get a discussion about it …. And going in and finding the problem visually is never undermined , I've done that after 2 days of inconclusive testing

Good question, is it like scenario B or C? diag​.​net/file/f2x1se1t6…

In this capture, the blue channel is a distributor 2 wire inductive pick up coil on a Toyota COP. It shows the COP secondary with the injector disconnected, during a 1500 rpm brake torque. The COP secondary winding has to produce more kv to force the spark to arc across the spark plug's air gap to the plug's ground terminal, with no fuel molecules in the combustion chamber to act as a…

It was a 2 wire coil so from my understanding you can still get primary waveforms on them. Yea I was just curious as to what others would have done and if what I did was a good procedure.

I think diagnosing an inaccessible coil, coil circuit, or driver issue is a must when you have a dead (steady misfire) miss under all loads (unless you already know it’s a mechanical issue) IMO a “fish bite” miss is always related to a secondary fault: insulation leak, carbon track, excessive resistance, or a coil fault. I like to stress the suspect coil with an adjustable spark tester and a…

I like to stress the suspect coil with an adjustable spark tester and a spray bottle if there‘s a plug wire involved rather than setting up a scope, particularly in situations where you’ve gotta find an EWD and start some dissassembly process to get to a specific circuit. All that said, if it’s a “fish bite” you’re going to have to get to the coil no matter what so let’s spend our time getting…

😀 I appreciate the comments. Apparently I can take off my flame suit and put it back in the closet.

For intermittent “fishbite” misfires, I can usually capture the misfire while doing 1500 rpm brake torques, with the scope is set at 500 ms/div or 1 sec/div. In this capture, the vehicle is a 2010 Buick 3.6 with intermittent “fishbite” misfires under load and I'm doing brake torques. The blue channel shows a good spark plug burn time and the red channel shows the misfiring spark plug.

Same here Rusty. I still have a bottle of “Hi Volts” spray kicking around here at home in one of my cabinets. It was great for those insulation break down type failures and faster than any scope hookup. Of course, there are many instance where this approach may be beaten out by using a DSO, but not in this case. FYI, here's a spark plug that was damaged by careless installation on the rear…

LOL When the traffic is backed up ya need to take the breakdown lane to get to ground. Excellent example BTW. Before we had the luxury of misfire detection, finding the offending “hole” in a fish bite misfire could be a real challenge, even with the engine analyzer. I’d typically do a wet brake torque and look/listen for the arc but most times that vehicle would get new secondary stuff and…

Before we had the luxury of misfire detection, finding the offending “hole” in a fish bite misfire could be a real challenge, even with the engine analyzer. Indeed, Rusty Many years ago, the librarian at our local high school brought her '80s vintage Ford F150 truck in for a loss of power complaint. Her description of how it performed seemed to indicate an ignition misfire. Although it passed…

Hi Martin, As you pointed out if the shop had replaced the PLUG and the WIRE that would have solved the problem. Doing one, or another just means the misfire is coming back. The engineering speak that GM addressed in a TSB, I think from the 80's on that, was a “breakdown of the silicon dielectric interface.” The coils used to start to arc at the output terminals on those vehicles, as well as…

Exactly Scott. It was the norm to replace both components, as you well know. It was just the series of “comedy of errors” diagnostics at the two previous shops that led it to me for the final fix. The second shop had replaced the coil since it was arcing by that time, but for some unkown reason hadn't looked at the spark plug. Once those boots suffer from any arcing, they become rock hard and…

Aaron! You have asked a good question which many of us have faced many times. The accessibility to coils and injectors can be a challenge based on engine design and access. If a technician can not access the ignition coil he is left with only a could of options. One is to access a suitable connector(if available) inline or to go to the PCM and access the wiring. As an FYI Stellantis(FCA) is…

Mike Presutto(sp) posted, a few years ago, a kind of voltage drop(I think) method. Ground the scope to battery negative. Connect scope probe to the engine block. It won’t show a secondary pattern but will show the difference of intensity of the coils. I wonder if probing the coil’s ground wire would enhance the “waveform”?

You were not guessing , it is called tear down and inspect for visual investigation. It is not your fault that the coil is not readily accessible. Familiarize your self with the “tear down and inspect” legal procedure so that you can get payed for your time if you are forced to work flat rate. Your boss would scapegoat you if that coil replacement did not fix the misfire​.​And…

Aaron, You got an advantage when there is a specific cylinder misfire code. When you have a P0300, no freeze frame, and don’t have a live misfire data list… I like to check cylinder misfire history in mode 06. This works well in most Fords, and seemingly all CAN vehicles. Document all of the misfire test data before your first road test. Then recheck again before you turn off the key. The…

Hi Aaron, Here are some misfire identifications I have learned/identified/utilized over the years that may help you. Others can chime in here with more details, that is why we are here. 1.) A steady misfire is any that are consistent at all RPM ranges. A cylinder that is not contributing fully. Often called a ‘dead miss’. A failed coil or a leaking valve is typical. 2.) A misfire ‘under…