well, it happened AGAIN tonight. This phantom RPM limit again cost me another win at the track. It should have been an easy win but the car did the fuel cut (rpm limit) on the launch.
sweet35th mentioned earlier in the thread about GM having some acceleration/RPM limit. Could Ford also have something similar we don't have access to the table for yet?
Something similar to this GM acceleration limit?
http://www.hptuners.com/forum/showth...tion-Threshold
Check the Reverse RPM limit.
Eric Brooks
HP Tuners, LLC
My Reverse limit is 5000Originally Posted by Eric@HPTuners
Reverse Limit is 5000 for me too Eric.
I've attached another log from this weekend. This is a burnout where I caught the RPM limit triggering twice. Granted it's not during the launch where I'm also seeing it, but I feel like it's probably the same mechanism triggering them
You have to run the log at a slow speed to see it, but I see it trigger just as the RPM drops below 4,000 (RPM was dropping as I was reducing throttle), after the RPM limit and I felt the fuel cut, the RPM's dropped to 2800 and I gave it more throttle and it triggered again as the RPM was coming back over 3,000 (the RPM Limit occurred at 3200 RPM's)
First RPM limit at time 5.563, second RPM limit at 5.874.
from this log, I'm guessing, but it looks like the transmission isn't following the gears properly. it knows its in 2nd then you let off and it goes to unknown- 05 thinking it should be in fifth. The RPMS are too high for that so it limits them. Probably trying to satisfy its anticipation logic. I would make sure your speedo calibration is setup properly. If you are running slicks make sure you compensate for the tire stretch while its rpms increase.
Looking at your launch log its also sitting still not sure if its in 1st.
maybe hidden limits based on anticipation and inferred gears.
To the others having this problem on launch, how are you doing your burnout?
I had been placing the shifter in 1, manually upshifting to 2, manually to 3, and then rolling out of the water. I stopped before staging and put the shifter in D.
I then switched to staring in 2, shifting to 3, and then rolling out. Again I stopped and put in D before staging.
On the log I posted, I remember I accidentally went 2, 3, then D on the burnout. Could this play into it?
Since my original post I have not have the problem resurface. I did not change my tune at all, but did lower my 2-step to 3200. I also changed my burnout procedure.
I now start in manual 3 do a short burnout and roll out. So no shifting during the burnout. Again the car is placed in D before staging.
Not sure about everyone else, but I am on a transbrake. Now I'm wondering if this limiting is due to something in the transmission monitoring. The transbrake is applying 1st and 3rd gear at the same time, then releasing 3rd to allow launch. Does this create confusion for the ECU as this scenario (trans in 1st and 3rd simultaneously) is something that was never considered by system designers?
These are some good thoughts Murfie.I attached the log with the launch. Take a look at time 1.532, That's where the RPM limit occurs right after I launch and I'm showing 4MPH.
Some other info, I have transmission anticipation logic shut off. But I've also had the RPM limit with it turned on. I have 28" slicks with 721 revs per mile. That's also what I have vss revs per mile set to.
use vid: disabled
VSS/P Rev - trans: 40.00
Gears 4.10
N/V Base 40.00
N/V Min Learned 30.00
1-5 gears set at 7300 RPM limit
Reverse: 5000 RPM Limit
Max Accel: 100 (I also tried up to 200)
Can you take a look at my latest log? It shows "unknown: 1" but this right at the launch and the RPM limit occurs at 3500 so I would think it should be nowhere near the 7300 Limit I have the trans limits set at? I've thought about just raising the VSS tires per rev to a really high number like 761 just to trick the VSS into thinking I'm going slower than I really am in case this is some hidden acceleration limit.
I do my burnout right in D. I will try out your theory too. It's strange because I wouldn't think the burnout should affect launching the car a full minute later. I run off a 2-step (no trans brake). But I don't think it's related to the 2-step or the transbrake. I had a friend that races the same year 11 Mustang GT come up to me at the track and out of the blue ask me if my car has ever taken a dive on the launch. It was something he's experiencing he was wondering about and I had never told him before about my RPM limit issue. So I'm positive he's experiencing the same thing. He runs footbrake and stock tires.
Last edited by dbb2797; 07-27-2016 at 10:40 PM.
Things I see: your throttle starts to close just as the car starts moving. this is right after releasing the trans brake. the engine indicated torque spikes over 450ftlbs. Then your limit kicks in. VCT goes in to stability mode. If you do not already have trans torque truncation disabled raise any value less than 600 or disable it. I see you have 4.10 rear gears so in first at 450ftlbs multiple that by transmission first gear 4.17 and rear gears 4.10 you get 7693 ftlbs. Theres probably some slip and loss but you will still be over the 7,376ftlb engine combustion stability limit. I would raise that up to if you have not already.
Just FYI, I updated the values for Trans Commanded Gear, so that PID should now report properly (in tomorrow's build).
Eric Brooks
HP Tuners, LLC
I do have trans torque truncation disabled.
Ahh, I do still have Max Brake Torque under Engine combustion stability set to 7,376. So I'll raise that up too.
I'll do another log next weekend. Getting married this weekend so I can't hit the track. But next week I'll try raising the VSS tire revs, raising the max brake torque, and datalogging with the updated version of HPT to get the correctly reported gears.
Thank you both Eric and Murfie!
congratulations dude!
little update and info on my end. Moved my Reverse RPM limit to 8k, thought it fixed it. Made 10-12 clean passes then it showed up in 3rd round of a $7500 to win race. Read through the replies and upd my combustion stability limit as that was still 7365. Not sure I was meeting that as I'm not logging an engine torque value currently. Someone mentioned about an acceleration rate limit, have a hard time thinking that would be an issue as i'm only cutting 1.58-1.63 60's. As I mentioned before I hadn't seen this in a burnout, then I thought about it. Before I was running a line-loc for the burnout I would occasionally have a loss of power in the burnout. Never logged the burnouts, but I'm guessing it was this. With the line-loc I've never had the issue. My burnout procedure is manual, starting in 1st, shifting to 2nd then 3rd and rolling out. I will try to communicate with Eric and come up with something to test by this Wednesday's Test n Tune. This is such a pain to sort out as its so random, I'm going to try to make it act up. Seemed like the shorter cool downs between passes makes it more common. Given this, I'll try to get it to repeat, might try a lower launch rpm and anything Eric recommends. I'll report back, Glad to see a few people working together to sort this out! Congrats on getting married Dbb2797!!
Looking over these logs again I see that your torque numbers are very high. I have seen phantom limits from improper torque tables many times. I suspect you look at your torque to load table. Im attaching two pictures to compare your torque/ load to stock torque/load.
This first picture is stock foot brake launch. As you can see the engine torque(torque/load tables) and ETC torque(driver demand table) follow the same general path.
Foot Brake launch.PNG
This is the trans brake launch of one of the logs. In it you can see the enigine torque and ETC torque do not follow the same general path.
Translaunch.PNG
I suggest redoing these tables and keeping them both going in the same general direction for given load and RPM. Also keeping the torque values lower and raising the load values that correspond to the torque values helps avoid torque limits.
I logged the event last night with a lot of the torque data. I'm using LiveLink and my X4 to log. First thing I wanted to check was that my engine flywheel torque wasn't over my driver demand at release of the button. It is not, its worth mentioning that when the button is released you will get a torque spike as the engine hits converter stall speed.
First thing that happens is the Transmission RPM limit drops to 3235.82 RPM, Then .020 sec later Torque source 4 pops up. I'm also logging Torque Based RPM Limit, this also goes to 1 as torque source moves to 4. The throttle angle desired moves to 2 when the TQ Source 4 occurs. when throttle angle desired goes back to 85, you get some spark/fuel source changes, which I'm guessing is a result of the ecu recovering from the torque error.
Being that the Transmission RPM limit changes to 3235, I'm thinking this is where our problem lays. Why is it doing this? I've glanced through stuff looking for a limiter with that value, didn't find one. What I did just stumble across is low/reverse max VSS. This is set to 2.5mph. looking at the log again the speed sensor resolution at the lower mph seems to be poor. In this particular log the MPH goes from 2.42 to 5.34 instantly (crossing that 2.5mph threshold) as this happens the trans rpm limit changes at the same time. My current thoughts are that the 3235 rpm number is what ecu calculates the trans rpm needs to be at 2.5 mph based on the gearing/tire info I have applied. This raises the question, why does the ecu think the low/reverse clutch still needs to be applied? Thought I came up with is that we are applying this "externally" on the trans brake and for some reason the ecu still sees that clutch is applied for a brief amount of time after the button is released. Or maybe the engine rpm is above what the ecu calculates it should be at 2.5mph (possibly do to a higher stall converter) and it applies the limit?
On another thought, if I make 5 passes back to back. The VSS reads different every time, some times going from 0 to 15 with nothing in between, sometimes its smooth. If this low/reverse VSS max is what is causing our issue, the VSS inconsistency may explain why we can make several passes without issue. Good news is this should be easy to test. I'm hoping that if I lower this value I can get the problem to repeat. Hopefully raising this limit will cure our issues..
Sorry if I appear to be rambling through this as I was working out my thoughts and ideas as I was typing. I'll play with this a little on the street/parking lot tonight as long as I am able, and I'll report back. I'd like to know your thoughts on this!
firstpass.csv
Awesome info ForcEng!
Interesting log. With HPT scanner you can increase the polling speed to help with the data resolution. Looks like its getting an update every tenth of a second. HTP scanner can get up to every hundredth.
The first thing that pops up as a limiter is the trans RPM 3235 RPM. I can swear I ve seen this number before. This triggers a torque based engine limit. After that Torque source, Fuel source, and Spark source change to correct the limit. Torque source goes to RPM limit, Fuel source goes from OL power to what I guess is injector cut, and Spark source goes from borderline to i guess torque control. This brings the Engine RPM back down below the 3235 limit and the sources go back to normal.
3235RPM in first gear would trans late to 12-18mph(depending on what it think your rear gear and tire are) or 776 output shaft speed.
Have you tried disabling the toque based TCC control?
Thanks for the well wishes on the wedding everybody! I made it through to the other side. Wow was that stressful lol. ForceEng, awesome job with the log. You caught our rpm limit nemesis in action. Murfie, a great suggestion. I will try disabling that tonight at the track and see if it helps. I can create the RPM limit on the burnout every time so I should be able to see immediately if it's going to work.
Well, after about 15 passes without this limiter popping up, it mysteriously appeared in second round of eliminations today. Needless to say it cost me the race. Looking forward to a fix for this!!!!
I need more testing to confirm, but raising the VSS low/reverse max up to 10MPH seemed to shift the MPH up that the RPM limit occurs at when I'm coming out of my burnout. I think that's a good thing in that when launching, it should reduce the possibility of hitting it. I only got 3 passes in to test. I also shut off torque based TCC control and raised the revs per mile to 726 for my 27.6" tires. Something strange was then happening at high RPM's. I was hitting an RPM limit at about 7200 RPM. My trans RPM limits are set at 7400 RPM so I wasn't sure why I was hitting it. Then my laptop died and I couldn't tune or data log any more
I agree Enginerd_Rob. We need to get this figured out. It's causing too many losses at the dragstrip.
A couple questions...
1. Do these cars get the VSS reading from the OSS sensor in the trans or from a wheel sensor(s) in the ABS system?
If the VSS signal is from the front wheels, and we lift the front wheels (wheelie) on launch, could this explain the erratic VSS readings as the car starts moving? I know my car does pull the drivers side tire off the ground on launch.
2. Could the trans rpm limit of 3235 be occurring due to trans control not liking the difference between TSS and OSS while on the transbrake? I found a tech manual for the 6R80 that shows an error generated (P0722) under these conditions:
"Sets when not in Park or Neutral, engine RPM greater than 3000, input shaft speed greater than 2800, throttle position greater than 10%, output speed less than 200, all conditions met for 3 seconds".
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