Bad shifting due to 0.04V dither? - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 10 (permalink) Old 08-13-2017, 11:35 PM Thread Starter
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Bad shifting due to 0.04V dither?

I'm still having issues with my '95 7.3. (Basically, the PCM is randomly shifting the transmission out and back into 4th with the TC locked. When I say randomly, I mean very randomly: sometimes once in a 100 miles, other times chronically, with no relation to weather, temps, incline, driving conditions, etc.)

According to FORScan (using a high quality ODBLink SX USB cable) some sensors are showing a 0.04V dither (this is with the engine off, van immobile)

I've already replaced the PCM ($$$) to no avail.

I'm truly lost as to what to try next. Any suggestion would be welcome. I'm about ready to drive this thing into a canyon.
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post #2 of 10 (permalink) Old 08-18-2017, 10:56 PM Thread Starter
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Re: Bad shifting due to 0.04V dither?

Update: I captured a couple shifts and the voltage spikes with the MLPS co-incide with the temp gauge.
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File Type: jpg shift 2.jpg (23.1 KB, 4 views)
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post #3 of 10 (permalink) Old 08-19-2017, 01:14 AM
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Re: Bad shifting due to 0.04V dither?

Pics are WAY too small to make out any detail; by "temp gauge", do you mean EOT? If so, I'd seriously consider replacing it.
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post #4 of 10 (permalink) Old 08-19-2017, 07:20 PM Thread Starter
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Re: Bad shifting due to 0.04V dither?

I uploaded full sized photos. This site resized them for whatever reason. It makes the photo attachment option a farce.

The image shows the TR_V and TFT_V roughly mirroring one another and spiking. When they go up by an appreciable amount, the PCM shifts the transmission out and back into 4th with the TC locked.
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post #5 of 10 (permalink) Old 08-19-2017, 07:25 PM Thread Starter
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Re: Bad shifting due to 0.04V dither?

So it seems the site doesn't like png (or even .jpg, but instead needs .jpeg to avoid resizing). Let's try this again using old formats.
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File Type: jpeg shift 1.jpeg (611.6 KB, 10 views)
File Type: jpeg shift 2.jpeg (287.3 KB, 7 views)
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post #6 of 10 (permalink) Old 08-19-2017, 10:08 PM
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Re: Bad shifting due to 0.04V dither?

If you resize them to something web-reasonable (say, 1024x768) before uploading, the site doesn't resize them to something even smaller.

So "temp" refers to tranny temp? Hmm, just a WAG, but perhaps the tranny temp sensor is flaking. Or a connection issue with the harness down to the tranny. Sorry, I'm not familiar with the automatics. I forget which sites he's on, but look here and on the other Ford-related truck sites for a guy name Mark Kovalsky. He's Mr. Ford Automatic Transmisson; the guy has Type F running through his veins. Those correspondences between voltage, tranny temp and the shifting might mean something to him.
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post #7 of 10 (permalink) Old 08-20-2017, 12:27 AM Thread Starter
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Re: Bad shifting due to 0.04V dither?

Quote:
Originally Posted by madpogue View Post
If you resize them to something web-reasonable (say, 1024x768) before uploading, the site doesn't resize them to something even smaller.
Not true. In fact my screen shots were smaller than that. I'll attach another screen shot which shows the very odd rules of this site. All I did was convert from the lossless png to a lossy (harder to read test) jpg then rename it to jpeg.

Quote:
Originally Posted by madpogue View Post
So "temp" refers to tranny temp? Hmm, just a WAG, but perhaps the tranny temp sensor is flaking. Or a connection issue with the harness down to the tranny. Sorry, I'm not familiar with the automatics. I forget which sites he's on, but look here and on the other Ford-related truck sites for a guy name Mark Kovalsky. He's Mr. Ford Automatic Transmisson; the guy has Type F running through his veins. Those correspondences between voltage, tranny temp and the shifting might mean something to him.
Don't know him
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post #8 of 10 (permalink) Old 08-20-2017, 01:29 AM
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Re: Bad shifting due to 0.04V dither?

Quote:
Originally Posted by ballo View Post
The image shows the TR_V and TFT_V roughly mirroring one another and spiking. When they go up by an appreciable amount, the PCM shifts the transmission out and back into 4th with the TC locked.
The entire problem could be the TR voltage going up. The PCM sees this as you moving the shift lever from D to 2, so it downshifts. If it isn't a spike from an alternator problem it's a failing TR sensor. This won't set any codes until the sensor gets really, really bad. The only fix if this is the problem is a new TR sensor.

Quote:
Originally Posted by madpogue View Post
Mark Kovalsky. He's Mr. Ford Automatic Transmisson; the guy has Type F running through his veins.
Not true. It used to be MERCON V, now there is MERCON LV running around in there.
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Mark
Former Ford Automatic Transmission Engineer

“The good thing about science is that it's true whether or not you believe in it.” ― Neil deGrasse Tyson
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post #9 of 10 (permalink) Old 08-20-2017, 02:13 AM Thread Starter
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Re: Bad shifting due to 0.04V dither?

MLPS sensor was the first sensor replaced (NAPA part) and no behavior changed.
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post #10 of 10 (permalink) Old 03-05-2018, 10:08 PM Thread Starter
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Re: Bad shifting due to 0.04V dither?

So I've been going through various diagnostic schedules in the service manual and came across a possible problem. The voltage to the tranny temp sensor is a little out of spec. It measures at 4.61 volts instead of 4.75 - 5.25 volts (I'll try to attach a photo). I tested it with two high quality meters, but using the same leads. Could this be my problem? The PCM has already been replaced in an attempt to fix my tranny issues.
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