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Crank Frequency to identify a "Fish-bite" (synced with Power-Probe)

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3 years 6 months ago - 3 years 6 months ago #43271 by Chad
(Disclosure: This vehicle was not repaired, and my theory was not proven.)


I, recently, had a Dodge Ram with an intermittent "fish-bite" type misfire/shudder. I could not find anything in scan data that indicated a misfire, nor transmission slippage. I decided to scope the Crank sensor and go for a test drive. With my Power-Probe connected to Channel C, every time I FELT the misfire/shudder, I pulsed the Power-Probe to make a visible marker in the waveform.Then, I went back to the shop and applied a Frequency Math Channel to the Crank signal. Zooming in on the Power-Probe pulses, I noticed the Crank Frequency increased, just before the pulse. This allowed me to determined that what I was seeing was, in fact, what I was FEELING. And what I was feeling was transmission slippage, not a misfire. If it had been a misfire the Crank Frequency would have decreased, just before the Power-Probe pulse.




drive.google.com/file/d/14Ddjb8UwDNyZO8Y...qCl/view?usp=sharing

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 3 years 6 months ago by Chad.

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3 years 6 months ago #43275 by Matt T
Looks like an upshift at 13 seconds so the event immediately after it may have been normal. And if I'm right about the upshift this is happening in at least two gears.

How consistent the events look I'm wondering if they're being commanded. Maybe the torque converter being unlocked then locked back up.

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3 years 6 months ago - 3 years 6 months ago #43276 by Noah
What a good idea to use the Power Probe to mark the the waveform in real time.

I'm interested to see more of these as you them.
So your thinking the increase in crank frequency is the momentary increase in engine RPM during the transmission slip?

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Last edit: 3 years 6 months ago by Noah.

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3 years 6 months ago - 3 years 6 months ago #43279 by Chad

Matt T wrote: Looks like an upshift at 13 seconds so the event immediately after it may have been normal. And if I'm right about the upshift this is happening in at least two gears.

How consistent the events look I'm wondering if they're being commanded. Maybe the torque converter being unlocked then locked back up.


Torque Converter Lock-up was, definitely, in my mind. But, when I looked at the wiring diagram for this 8-speed transmission, it offered no help. Scan data didn't, either. The problem was pretty persistent. But, I wouldn't say CONSISTENT. With the exception of it always being on a mild acceleration, it was quite random.

When I checked the Transmission Fluid (being an 8-speed, it has a song and dance routine that you have to go through to ensure proper Temperature/Fluid Level. With the vehicle, and fluid, at the proper temperature, when removing the "Fill/Level Check Plug", Transmission Fluid is supposed to just drip out. If it streams out, you should let it drain until it just drips. If it doesn't drip, you add fluid until it DOES drip. That is the proper fluid level.), instead of "dripping, or streaming, out" It POURED out, with a velocity that told me there was PLENTY more to come. I took a sample and replaced the plug.

When I talked to the customer and recommended a Transmission Service, he was not happy. He said that he had, just recently, had the transmission serviced at the Dealer. He informed me that they admitted to him that they "had a problem" with the procedure. At this point, I showed him the fluid sample that I had taken. I, also, open a NEW quart of the 8 and 9 speed Transmission fluid.



I, also, noticed lots of particles in the fluid, which I can only guess is clutch material according to some reading I have done. They are kinda hard to see in this picture, but the fluid was full of it.



The last I spoke with the customer, he was going back to the Dealer.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 3 years 6 months ago by Chad.

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3 years 6 months ago #43280 by Chad

Noah wrote: So your thinking the increase in crank frequency is the momentary increase in engine RPM during the transmission slip?


That is what I believe. Sadly, I did not, and can not, prove it. :(

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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3 years 6 months ago #43283 by Matt T
Did a little experimenting with the event around the 18 second mark. Looks to be flaring about 100 rpm then dropping back down when "whatever" corrects. Since Chad has now confirmed it's a newer 8 speed I've got another possible explanation besides the torque converter. The TCM might be detecting slip and increasing line pressure to stop it.



Zoomed in you can tell the truck is an 8 cylinder.



And for "Bonus Footage" :silly: how I got it to display in RPM.



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3 years 6 months ago #43284 by Matt T

Chad wrote:

Noah wrote: So your thinking the increase in crank frequency is the momentary increase in engine RPM during the transmission slip?


That is what I believe. Sadly, I did not, and can not, prove it. :(


You probably could prove it by 'scoping CKP and the transmissions Output Speed Sensor. Also 'scope the Input Speed Sensor if the tranny has one. With this being an 8 speed it probably does.

Then apply the maths to all three traces and see which sensors flare up and which don't. If ISS and OSS both stay flat during a CKP flare the slip is in the torque converter. If ISS flares but OSS doesn't it's the tranny.

Looks of that fluid the tranny may well be spanked and that's probably why the owner took it to the dealer in the first place. And because they appear to have screwed the "transmission service" up they might end up eating this one.
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3 years 6 months ago #43293 by Andy.MacFadyen
Putting a small drop of the transmission on blotting paper or other absorbent paper overnight might be interesting.

" We're trying to plug a hole in the universe, what are you doing ?. "
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3 years 6 months ago #43295 by Andy.MacFadyen
Putting a small drop of the transmission on blotting paper or other absorbent paper overnight might be interesting.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



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3 years 6 months ago #43297 by Tyler

Noah wrote: What a good idea to use the Power Probe to mark the the waveform in real time.


Definitely a great idea! Probably pretty easy to rig up with the cigarette lighter adapter. Maybe I'll find an old adapter and wire it to a momentary switch...

When I talked to the customer and recommended a Transmission Service, he was not happy. He said that he had, just recently, had the transmission serviced at the Dealer. He informed me that they admitted to him that they "had a problem" with the procedure. At this point, I showed him the fluid sample that I had taken. I, also, open a NEW quart of the 8 and 9 speed Transmission fluid.


I had no idea that stuff was green. :silly: What year was the truck?

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3 years 6 months ago - 3 years 6 months ago #43301 by Chad

Tyler wrote: What year was the truck?


2014

I had no idea that stuff was green.


Expensive, Too!:woohoo:

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 3 years 6 months ago by Chad.

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3 years 6 months ago - 3 years 6 months ago #43304 by Chad

Matt T wrote:

If you add some filter, it makes makes the wave much more pleasing to look at.




"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 3 years 6 months ago by Chad.

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3 years 6 months ago #43305 by Matt T

Chad wrote: If you add some filter, it makes makes the wave much more pleasing to look at.


Much better definition of cylinder contributions too. You can really tell that truck wasn't misfiring with the filter applied.

And thanks for showing me how to apply filters :) I found that "Crank" feature poking around after a failed attempt to filter frequency.

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3 years 6 months ago - 3 years 6 months ago #43307 by Tyler

Chad wrote: 2014


I gotta watch out, then. :ohmy:

EDIT: Oh, it's a ZF product. OF COURSE it has its own special fluid.
Last edit: 3 years 6 months ago by Tyler.

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3 years 6 months ago - 3 years 6 months ago #43309 by Chad

Matt T wrote: And thanks for showing me how to apply filters :) I found that "Crank" feature poking around after a failed attempt to filter frequency.


You're welcome. :)

I am learning that applying filter to Math Channels is a trial and error process. At least, for me it is. I don't have the science down, yet. Sometimes, I get a better picture adding filter to the Math Channel Equation. Other times, I get a better picture leaving the filter out of the Math Channel equation, and applying filter to the Original (Crank) signal, instead. Other times, I have used a combination of filtering on the Crank signal AND in the Math Channel equation. Sometimes, it takes a lot of filter. Other times, just a little. But, no matter which way it goes, TOO MUCH or TOO LITTLE can make the whole frequency trace disappear. Also, overriding and changing the Min/Max seems to have an affect on the Math channel. No two waveforms seem to have the same filtering settings that produce the best image.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)
Last edit: 3 years 6 months ago by Chad.
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