Forgot your password?
Posted May 14
Posted April 20
Hmmm. Lots of folks looked, but no one had replied, so figured there was no interest.
Thanks for asking.
It is complex.
First, there is no trans problem. This is normal power train-drive train behavior on this car.
Indeed, as counterintuitive as it may seem, the input shaft does briefly speed up - just before being abruptly halted, since the car is stopped for the shift.
It is a real-time race condition playing out inside the different computers. Multiple events are playing out in parallel, very fast.
Both the ECU and TCM are separately and independently seeing and acting upon similar and different asynchronous signals, some of which are high-frequency reporters.
The ECU sees the TRS and knows he has to increase RPM for the impending shift change and load on the engine, but the TCM sees the TRS and knows the trans is stopped.
Meanwhile, the ECU is seeing and processing - and converting - the crank signal. But, the TCM does not see this directly. It gets a converted (PWM) signal from the ECU, after the fact. Kinda like seeing the sun as it looked seconds ago.
Meanwhile, the TCM is seeing the high-frequency-reporting (input shaft) pulse gen signal, which the ECU does not see. And, the TCM sees this directly. So, the TCM knows what is happening to the input shaft, slightly before the ECU's (delayed) converted crank signal (for the torque converter) arrives.
Meanwhile, the TCM has activated the valve body's solenoids seeing its version of the TRS signals, and the hydraulics are unfolding within the trans. And, importantly, shifts into D and 2 and L take longer than shifts into R, because there is a pressure build-up for the kickdown servo's activation for these. This trans and TCM take a two-step sequence to entering D and 2 and L when stopped, which is part of what is called creep. But, there are actually two creep states. (I have another post on that - if anyone wants to help on that.) Anyway, the trans and TCM take a one-step sequence for R, where there also is creep, but not with different creep states (unlike the forward gear shifted positions).
Thus, there is slightly more time for the inversion to play out shifting into D and 2 and L, than R.
So, the ECU commands more fuel for the shift load for D - there is minimal load in P (no clutches nor brakes are applied), thereby increasing the TC's speed causing the impeller to drive the turbine faster driving the input shaft faster mere moments before and while the trans is taking action to stop the input shaft's rotation - which it does, since the car is at a stop for the shift.
And, after commanding the VB's shift solenoids, the TCM grabs its input shaft pulse gen status (which it had to convert) and then grabs the delayed arriving ECU's converted crank signal - where the engine speed already has changed, and then the TCM places these values into the OBD-II protocol message and sends them to the scanner, which does as he's told: displays the un-aligned engine and input shaft speeds.
Thus, there is no actual inversion. It is an illusion, explained by the real-time computers, trying - as best they can - to keep up with the real-time rapidly-unfolding events … which are not waiting on the computers to keep pace/catch up.
P.S. There's actually more to this - with some fascinating corollaries, when they get thought through, including the layout of the gear shift lever positions (P/R/N/D/2/L) and the inverse situation shifting from D to P … and 2 to P … and L to P … and R to P.
By the way, I am finishing writing my second book on these cars. The first is already in the AACA Library and Research Center, thanks to Matt Hocker.
Posted April 18
Would you please see this post?
Posted April 18
Edited April 18 by Car guy in Virginia
(see edit history)
Any transmission specialists on the forum?
Why does the TC housing/impeller and Engine speed (and turbine and input shaft) on these cars briefly gain speed when transitioning from gear-uncoupled in P (transmission in neutral) to gear-coupled in D - when at a stop?
The turbine/input shaft on these trannies are turning in P, and halted once in D (due to the car being at a stop).
So, the rotating turbine/input shaft are transitioning from clutch-/gear-uncoupled (no gears nor clutches engaged, no loading on the turbine/input shaft) in P … to clutch-/gear-coupled in D (D's rear clutch gets engaged connecting to the forward sun gear, but there is no power transfer possible since the turbine gets back-stalled due to the car being at a stop).
O'scope clearly shows the input shaft briefly speeding up (for 16-40 ms or so) during the end of the shift from P to D, and immediately before the input shaft is stalled/halted.
And, the manufacturer's scanner shows the same.
And, this happens in P to D …. and P to 2 …. and P to L. And, the engine speed also appears to be briefly speeding up in each, at the same time.
What is causing the energy gain?
What is causing the turbine/input shaft to briefly speed up before they stop?
Posted April 17
Elantra '96. The two simultaneous signals are the live shift controls. They are in C. And, yet, when creeping, the pulse gen ratios align with 1st gear's spec ratio.
misterc9 do you have insight on these early Hyundai ATs? Can you explain what's happening in the trans when it's in creep?
Posted April 16
Edited April 16 by Car guy in Virginia
(see edit history)
When shifting from P to D, why do the AT's input shaft RPMs briefly invert higher than the Engine's RPMs, before settling to 0?
This is for an early gen Hyundai electronically-controlled 4-sp AT being AACA restored.
Posted April 15
Edited April 15 by Car guy in Virginia
(see edit history)
Posted April 15
Anyone know this answer?
Posted March 11
This is for an AACA restoration that is underway.
SM states C is in 2nd gear.Yet, KD switch remains closed …. and …. gear ratio matches 1st's.Why is the ratio not 2nd's?
in Cars For Sale
Posted January 20
This is a non-starter in this case, being an air filter assy. (It is a special air filter.)
Posted January 8
Thank you! Had tried the forum and FB previously. Emails to the other clubs all bounced.
Posted January 6
They didn't have, but they checked their dealer system to try to find it at other dealers - which was helpful; no other dealers have the part.
Still thinking some Datsun or Nissan club or owner out there has one or more of these parts.
Posted January 5
Thanks! Will contact them.
Posted January 3
Still looking for anyone who has a '91-'95 or '96-'98 Elantra who can check a couple of Vs on their OBD-I 12-pin data link connector and OBD-II 16-pin DLC.
Still seeking this new or NOS Nissan part.
VCM air filter assy
Pictures in post #1
Please contact if you have ... or if you know where they can be obtained.
Posted December 18, 2019
Yes, that's the place. Thanks. When I had been there before, didn't have success. But, will keep it in mind.
The place on the west side of 29 immediately off the road down the hill into the woods, south of C?
Posted November 30, 2019
I have obtained every gen 1 and gen 2 U.S. Elantra SM/ETM from '91-'95 and '96-'99.
But, I'm still looking for anyone who still has a '91-'95 or '96-'98 Elantra who can check their OBD-I 12-pin data link connector for me and OBD-II 16-pin DLC for me, in the companion post to this.
Still looking for anyone with a '91-95 or '96-'98 Elantra who could check a couple of their data link connector pins for me.
Posted November 13, 2019
Is there a wire under the black wire on your Hyun-2 adapter picture? On the bottom row far right?
If so, what color is it?