EFIDynoTuning Forum

I have a 4R70W swap with a Precision Industries 3200 stall (honestly not spec'd to my current power level) that I run unlocked. I suspect my converter is either too loose, inefficient, or my transmission is slipping. I've felt a somewhat steady decline in acceleration performance each time I take my car out - some of this can be attributed to hotter weather or me getting used to my car's power level.

I don't think its an issue with the motor - I gauge this by the data logged amount of air this sucks in via the MAF and commanded Fuel / AFRs being pretty consistent with all other factors fairly equal. I figure if its making less and less power these values would also go down.

I've started by looking at data logs of MPH vs RPM. With these values I've calculated somewhere in the neighborhood of 15-20% driveline slip approaching the top of 2nd gear, and when it shifts into 3rd, there's a calculated 34% driveline slip. This was calculated using TCI's converter slip calculator. I don't know if this is the most accurate way of calculating slip just because of a potential delay between logged RPM and MPH values.

I found PID's for Output Shaft RPM (NOBART) and Speed Ratio Across Torque Converter (SPD_RATIO). I started logging these now but didn't get a good run in, I reached about 5400RPM in 2nd where it showed a value of 0.81 for SPD_RATIO. Does this mean 19% converter slip? Or is the way this is calculated make it a potential transmission slip as well?

Curious if these methods are fairly accurate to measure driveline slip, if so seems I need to investigate my transmission/converter. I already have a new triple disk converter on order so I can lock it up reliably, I'm hoping there's less concern on the trans.

Thanks!

yep spd_ratio is slippage

yep 19% slippage

its stupid to not lock the converter as soon as it shifts in to 2nd

then just use the tcc slip tables to set your desired stall speed

Thank you - yea I currently have a single disc lockup converter, once I have the triple disc in I will be locking it up more.

After converter stall, I assume an efficient converter should approach 5-8% slip even when unlocked, just by virtue of the fluid coupling. This is well beyond the stall RPM and still seeing about 20% slip. Hoping the new converter built to my specs cures this.

no if its unlocked thats nornal

OK now I am stumped as to where my issue may be. I thought I was having a converter issue but now I think it may be something else. I was fighting a sluggish lockup in 2nd with the old converter, and what I felt was too loose of a converter in general.

I've completed my converter swap with new triple disc lockup converter. The car drives great, shifts normally, power seems to be put to the ground now. Now I'm fighting no lock-up issues, particularly in 2nd gear. At some time this car would shift into 2nd and lockup right away.

I've data logged BCSDC for a quick drive and I'm noticing it staying mostly at 0 in 2nd gear, occasionally I can see it climb into 30-40% and feel it start to lock but then it goes back to 0 and it doesn't seem there's rhyme or reason to why duty cycle goes up or back to 0.

In 3rd gear, duty cycle goes to 100% and I can feel it hard lock.

Based on the tune I can't see the reasoning for this, 2nd Gear lock schedule looks like attached (I've left these functions stock), Slip tables for 2 and 3 I've zero'd out.
I hope I'm not trying to track down a nightmare electric issue. BCSDC a commanded value by the EEC am I correct? Trying to figure why its not commanding expected values.

yeah bcsdc is whats commanded

thata only one peice theres a bunch more

make sure the tcc slip min to lock function isnt set too high

and kick up the tcc slippage dueing shift function as well so it doesnt unlock so far if need be

Thanks I'll take a look - to confirm my strategy has these

SR_HL - Converter Clutch Hardlock Speed Ratio Min - right now this is at .80, I should try a lower val?

I also have SRLUMN which is labeled "Speed Ratio Max to Unlock Torque Convertor" stock value is .650

I got lockup to respond at factory points using the duty cycle table:

FNDCNOCAP - Converter Clutch Dutycycle for No Capacity. Boosting these values higher got it to lock hard, maybe a bit too hard.

There's another similar table that I couldnt figure out what it was affecting as it didnt seem to respond to changes

FNDCNOSLIP - Converter Clutch Dutycycle for No Slip

I started with changing that one figuring the description made more sense to change, but it didnt do anything.

Anyways looks like I'll be messing with these and other settings to get it right.