'Sticking' speedometer on tuned 2012 GT Auto?

[KrisR]

This is a copy/paste from another thread, sorry about that.

I searched but didn't see this issue come up...

The 2012 GT A6 I just bought has a strange occasional issue. Background, the car came with an SCT X3 with 3 Bama tunes in it, Using the '91P' tune at the moment. Waiting to hear back from Mike Rousch who tuned my old car to get setup with new tunes for this one. Only other mods are 3.73s and an offroad x pipe.

Occasionally, when accelerating from a stop, the speedometer will 'stick' at zero and the car will not upshift at the 'normal' time into 2nd, it hangs 1st gear out way too long. Then suddently the speedo will jump up to 20-25mph or whatever and the car will shift into 2nd, then third, etc, then act normally until I stop again, in which case it will sometimes do this stuck speedometer event again, but most of the time it doesn't. Is this Bama tune related, or something else going on? I assume that it's not just the needle itself, as the car won't shift, which leads me to believe its a speed sensor or tune related. The car runs and shifts perfectly otherwise. Strange. My old 2011 never did that, and I had Bama tunes for a bit.

I switched to another Bama tune that was previously loaded into the handheld, I'll try that one tomorrow and see if the problem remains.

 

[KrisR]

Bumping this. Problem has resurfaced. Now running Mike Rousch tuning instead of Bama, so I don't believe it's tune related.

Issue seems to occur only after 'cool' restart, like letting it sit for an hour or two after driving it, but never after sitting overnight. It happened a couple times yesterday, and even threw up the 'wrench' light. I happened to be datalogging while it happened. This time, I was driving at around 40mph, could feel the car 'miss', wrench light came on, then it drove fine afterwards. Datalog shows vehicle speed dropping from 40ish to around 20mph, then jumping right back up within 1/2 second or so. It happened a couple other times in the log too. Also of note during the first event, throttle angle and load spiked up and right back down again, so that seemed to be related. Throttle angle values look pretty erratic in that datalog overall, lots of spikes and dips, not a smooth linear curve. I did a subsequent log with the engine off, key on, sweeping the accelerator up and down slowly and the throttle angle looked perfect in that log, smooth as can be, except it dips to zero and back to 7* when fully released.

Throttle body? TPS? Output shaft speed sensor? Something else? It drove 100% perfect this morning all the way to work after a cold start, as it always does.

 

[KrisR]

Here's a quick pic of the datalog showing vehicle speed. Notice erratic 'dips'. The spikes in the other parameters around the 99-second mark are throttle angle, load as a fraction.

 

[KrisR]

Last night I did a datalog of the car not running, ignition on. Did a bunch of slow and fast 'sweeps' of the throttle angle pressing on the gas pedal, datalog showed smooth operation, no glitchiness or spikes. I guess that might suggest the pcm taking control when it's getting a bad signal from elsewhere?

 

[eighty6gt]

I would be looking at where the ECU gets its speed info. Is it not the ABS system? You may need to consult with Ford on this one.

edit: I wonder if this is tech? Sure looks like it!

 

[KrisR]

It wasn't really 'tech' when I posted it initially, and I know how strict the 'tech' rules are, so I posted it here. Feel free to move it, mods.

There's an output shaft speed sensor inside the trans that is what the pcm uses to determine vehicle speed, I believe.

 

[Exley]

Are you able to flash it back to stock? That would eliminate the aftermarket tune as a potential issue.

 

[KrisR]

Upon researching, it looks like TSB 13-6-8 shows similar symptoms, and the fix is replacing the 'Molded Leadframe' in the 6R80 trans. I guess the Raptor / F150 guys are having this issue. Same trans. Maybe I'll be covered, I don't know. My car was a manufacturer's buyback...