Help with scope pattern
Not looking for help with the actual diagnosis on this. I already know what is wrong. I was just wondering how to prove it with a scope. I am by no means an expert with lab scopes. I work at a dealer where swapnostics is the norm because time is money and everybody needs it yesterday. Not saying I agree with that philosophy, but I digress. I want to improve my meager skills with a scope.
Anyhow, I have a hemi with a misfire, only happens at higher rpms. Can duplicate in neutral. I scoped the coil primary on #5 and #7 for comparison. I can see a definite difference, but here is my question. What exactly am I looking at?
Rick great files and thanks. Because these files are in a SnapOn VSS extension format many won’t be able to offer help. If you can save them in another format (PDF maybe jpg) and update post we can help more. I don’t have my SnapOn program on my phone. Looking forward to offering some help.
Can't view them either. Try another format.
You're connected to the ignition coil primary circuits, correct? Which trace is #5? For what it's worth, you'd get much more usable information out of your capture with Peak Detect on, and at a faster time base. 10ms, preferably. That'll dramatically increase the amount of detail in the capture.
channel 1 is cylinder 5, sorry. And thanks, great advice, exactly the kind of thing I am after.
No worries! Can I take a shot in the dark and guess broken valve spring? Based less on the capture, more on the symptoms.
I would say good guess, but sorry, that's not it. I got it with my initial guess but I want to be able to see the problem, not guess.
Was the fix a coil? If I remember correctly the negative spike at the end of the dwell saturation looks like a coil short to ground.
It was not, although the truck came in with 8 fresh coils and 16 shiny new plugs
I think the other thing I've seen with a drop in the signal is the pcm coil driver faulting. What was the fix?
👍 I would've never guessed by the scope pattern. Good job.
Me neither,LOL. The intake lobe was wiped so that probably explains why it resembles a lean condition
This 2016 Charger 5.7 with a P0301 would only misfire on hard acceleration and during WOT. The blue CH A is COP1 primary winding volts. The red CH B is the starter amps or relative compression. The green CH C is a pressure transducer in the intake manifold near the throttle body and it shows cylinder 1 with a repeating weak vacuum pull.
Great stuff, Ray. You are light years ahead of me. I have read enough of your posts before to realize that. Thanks
Key thing to remember here, RZ, is that the mobile specialist will use the scope to find evidence that the shop needs to sell tear-down (or a new engine). The FLS and the WPS are gonna be what shows breathing faults better than an ignition trace. They likely won't know if it's a lifter or a lobe till it's taken apart, but they know it's a breathing fault, and that plugs and coils will NOT fix…
Thanks, Geoff, great points. I am just trying to learn and grow as a tech. I always want to gain knowledge and become better. I initially suspected the cam on this because as they say, this is my second rodeo. In other words, I have seen this a few times. I wanted to find the simplest method of accurate diagnosis. The scope led me to believe it was either the cam or injector problem. I stuck my…
Sounds like the borescope is the simplest method of accurate diagnosis. But if you want to avoid disassembly, you will need more attachments for the scope. Ray has done a bunch of examples with putting a WPS on the exhaust pipe and a WPS on an intake vacuum source. You'll see both inhale and/or exhale faults that way.
Pico and pressure transducer are on my wish list. We have been told that FCA is going to send us a Pico as an essential tool but that has yet to materialize
GM dealers got them a couple years ago, but the only accessories (I'm told) are the NVH kit, to pinpoint vibration issues. I guess that is their main customer satisfaction issue. "Easy" enough to just tear apart engines to find those type failures ;-) I suspect when you've torn down the exact same engine a half-dozen times you can get pretty fast? Out here, time is not money. Money is money…
every cam lobe I've had wiped out the roller bearings go out in the lifter
Yep, that's what caused it. I have one in the shop right now that wiped a lobe but did not misfire. Set a dtc P219a, Bank 1 air fuel ratio imbalance. #3 intake rocker wasn't even moving during cranking, but it only set the 1 code
The yellow trace appears to have high rise in the kv during the burn or spark jump....the rise in the kv usually is a lean condition..as the spark burn begins every thing is ok...the voltage is jumping thru the gas particles and suddenly there is no conductive particles left to burn (air/lack of compression) and the spark kv has to rise to be able to continue to the other side of the spark plug…
I was thinking it resembled a lean condition also. There's a little more to it, I just wish I knew what was showing it
As mentioned, use peak mode and you will have something more usable. At the same time, know that you may still need more. Let me suggest as well that you set your time base shorter. You can always zoom out, but you can't zoom in further than your time base. Attached is a Hemi primary with peak on and a tighter time base. I also set the voltage for what I was looking for. As for swaptronics…
Thank you, that is extremely helpful
Aloha Jim. I have a Pico now, but used to use a MODIS (the 20lbs one). What exactly does Snap-On peak-detect do? I hear it mentioned in diag videos sometimes too. Think SMP will let you loose on your own webinar class soon? ;-)
Hi Geoff, Take a look at the scope specs table at the end of the doc here: snapon.com/display/1068/B….pdf The information applies to the original Modis for the most part. See the sample rate per sweep column and footnote 3. Basically with Peak Detect off, the effective sample rate is directly related to the time sweep selected. The longer the time sweep, the slower the sample rate. With…
Oh! OK, cool, got it, thanks.
Thanks, Jim. I am not against swapping parts, I just don't want to rely on that. I see way too much of it
This capture was taken during a steady 1500 rpm brake torque. The secondary on the left shows the spark burn voltage rising high because there is no fuel in the cylinder. The secondary on the right shows a good spark burn voltage.