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4L60E A/T won't shift from 1-2 w/o letting off gas pedal...


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#1 96WhiteTransAm

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Posted A week ago

1996 Trans Am with a 4L60E A/T. Problem started to happen on Friday. Saturday did a filter/ fluid change. No metal shavings, and what I would guess is a normal amount of 'grey goop' around the magnet on the bottom of the pan. Problem persists. I've got to get it up to about 2800 RPMs and just under 20 MPH before it is ready to shift, but it will not do so until I let off the gas pedal completely, then step back onto the gas pedal and it'll shift into the next gear. If I do this smoothly it almost feels like there's no problem at all. Once I get it past the initial shift, it accelerates as it should.

 

I've taken it down to 1 on the shift knob and once it hits the point where it should upshift I throw it into 2. Nothing unless I take my foot off the gas. However, if I keep my foot on the gas and move the knob from 1 to 2, then 2 to 3, then it will shift without having to take my foot off the gas.

 

Any ideas? Could the 1-2 shift solenoid have gone bad?



#2 JoePeek

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Posted A week ago

Sounds like it could be the throttle position sensor or the car speed sensor. These two things are main inputs that the PCM uses to command a shift. Either the 4L60E is getting the command to shift, but it doesn't (i.e. -something is wrong inside the 4L60E like a shift solenoid), or the PCM is not telling the 4L60E it needs to shift, which can happen if the PCM is getting bad data from the TPS or speed sensor. I would start with the TPS since when you let off the gas, you change the voltage the TPS is sending to the PCM which makes the 4L60E shift.


Edited by JoePeek, A week ago.


#3 Injuneer

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Posted A week ago

Scan the PCM for codes. It records codes for the trans, and some of them do not turn on the SES light.

Use this code list, unless you have downloaded the 1996 factory service manual

Scroll to bottom and click on OBD-II Trasmission Codes

http://shbox.com/1/Dtcs.htm

1994 FIREBIRD FORMULA

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381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

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#4 96WhiteTransAm

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Posted A week ago

Thanks guys. My brother has a scan tool. Hopefully I'll get my hands on it tomorrow.



#5 JOE68

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Posted A week ago

take it for a drive with the scanner hooked up and watch sensor data and trans data to see if it calls for a shift



#6 96WhiteTransAm

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Posted 6 days ago

Engine codes pulled. Came back with a P0100 code, which is a MAF sensor malfunction. I doubt that would cause the issue I'm having with it not upshifting. As of now, I've pulled the negative battery terminal and the two fuses to clear the ECU.

 

Something I forgot to mention, this issue first occurred on Friday when I stepped on the gas pretty good, and it felt like my right rear wheel lost traction/slipped. The ABS light came on and that's when it dipped down into first. I pulled off to the side and turned off the car to look at the tire. Looked fine. When I fired it back up the ABS light did not come back on.



#7 Injuneer

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Posted 6 days ago

Which dash light came on.... with ABS only the applicable lights are "ABS INOP" (system fault preventing ABS activation) and "LOW TRAC" (ABS active)? Or do you have ABS + TCS option? That adds a "TCS OFF" light.

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#8 96WhiteTransAm

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Posted 6 days ago

It was the ABS INOP. It hasn't come on since, though I'm guessing it caused my tranny to go into 'limp mode' because of that?



#9 Injuneer

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Posted 6 days ago

Don't think so. Can your scanner pull ABS codes? (Unfortunately you may have cleared the codes stored in the EBCM). There are descriptions in the 1996 factory service manual showing the actions taken when a code sets. Free download of the factory service manual - link in a pinned thread at the top of the "Fourth Generation...... Forum" topic listing.

Again, response is based on car having ABS only. ABS + TCS (EBTCM) is a bit more complicated.

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#10 96WhiteTransAm

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Posted 6 days ago

The scanner I was using is an Actron CP9180, which is a pretty basic scanner. However I just remembered about and found a Vetronix Mastertech MTS 3100 scanner out in our warehouse which I believe reads a whole lot more. I'll have to mess around with it some after I get off work, as it's been several years since I used it last.



#11 JoePeek

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Posted 6 days ago

Not to break into the good troubleshooting logic going on here, but couldn't help but think that if the VSS was bad it would make ABS issues since the wheel speeds, front to back would not match each other, and a bad VSS could keep the 4L60E from upshifting. I am not thinking that a hunch, or a comment like this takes the place of a good scan or a more logical problem solving process approach, but was just trying to think how could you tie together an ABS light with a transmission that didn't want to upshift. 


Edited by JoePeek, 6 days ago.


#12 96WhiteTransAm

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Posted 6 days ago

Okay guys a couple things I learned on the drive home today:

 

1) I found out it will shift into another gear without releasing pressure on the throttle at about 4700-5000 RPMs after a few seconds, depending upon how aggressive I push it.

 

2) Live-reading on the TPS% with the MTS3100 scanner seems to be true. It was at 0% at idle and jumped up to 100% when I went pushed it to the floor. All readings in between seemed accurate. I'm not sure if that has any bearing on whether or not I'm dealing with a bad TPS, though.

 

3) Also live-read, Ign. timing stays consistently at -45-47° when opening up the throttle before it finally shifts into the next gear.

 

I'm not sure if this info is helpful at all. Hopefully it is. I have no experience with this matter. Also, no codes popping up as yet.



#13 Injuneer

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Posted 6 days ago

If you didn't do it this way, you should examine the TPS sensor reading by rotating the throttle slowly from closed to wide open, watching for spikes and/or dropouts. The PCM codes for TPS are based on readings outside the normal limits at the extremes of rotation.

I would have to examine the ABS code charts to see if there is one that sets based on differences between front and rear wheel speeds. or mismatch between the VSS reading and the wheel speed sensors. Most of the codes I am familiar with are related to sensor circuits, but there are a lot I have never looked into. I see cautions in low level documents like the Owner's Manual regarding problems due to significantly different front and rear wheel diameters. But the ABS activation appears to be highly related to a wheel speed sensor indicating the wheel rotational velocity is approaching zero, indicating incipient lockup. Limited on time right now to get into it in depth.

This is not a simple problem. My general lack of knowledge on automatic transmissions is also a factor.

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#14 96WhiteTransAm

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Posted 6 days ago

If you didn't do it this way, you should examine the TPS sensor reading by rotating the throttle slowly from closed to wide open, watching for spikes and/or dropouts. The PCM codes for TPS are based on readings outside the normal limits at the extremes of rotation.

 

I did the best I could do with this, at times having to consider I had cars in front and behind me that I had to take into account. I stepped on the pedal as slowly as I could manage from idle to WOT at least once, and readings on the TPS% seemed accurate. No spikes or dropouts. Makes me think maybe the solenoid(s) went bad on my drive back home Friday and not the TPS, especially since it will shift, just not 'til an exceptional RPM is reached.


Edited by 96WhiteTransAm, 6 days ago.


#15 Injuneer

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Posted 6 days ago

You can test the TPS sitting in the driveway key on/engine off, while watching the throttle blades move..... :D

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#16 JoePeek

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Posted 6 days ago

The two shift solenoids do not directly control shift timing. They just get a signal from the PCM, (or they are not getting a signal from the PCM) So they are either ON or OFF. Just for reference, in first gear both the 1-2 and 3-4 solenoids are ON. Second happens when the first solenoid goes to OFF, third happens when they are both OFF. Forth gear hits when the 1-2 solenoid comes back on. So if your transmission IS shifting, the solenoids are working. Furthermore, if the transmission shifts from 1st to 2nd, AND shifts from 3rd to 4th, then the 1-2 solenoid is working. The best way to zero in on this is first determine if the transmission shifts into second when the 1-2 solenoid wire goes cold. You can do this with some kind of scanner that can monitor transmission stuff, or find the 1-2 solenoid wire (I think it is a green wire) on the 4L60E wiring harness and tap into it with a voltmeter or test light. If the transmission shifts when the light goes out, the solenoid is working good, and that will also confirm that it is the PCM that is just not sending the signal to shift. Is there an adjustment slot for you TPS sensor to "fine tune" it's starting point. Check with a volt meter to see if you are getting about .5v at idle and 4.5v at wide open throttle, The readings don't have to be exact, just in that neighborhood is OK. The TPS sends a signal to the PCM telling it how far you have your right foot into the throttle. As we all know, if the PCM thinks the gas pedal is pressed down more it will hold the transmission in gear longer. So if your TPS is sending too high of a signal because it is going bad, or is out of adjustment the PCM will "think" you have your foot into it more than you really do and delay the shift. 



#17 Injuneer

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Posted 6 days ago

TPS "adjustment" generally isn't an issue in the LT1. There are no adjustment slots on the sensor. The PCM reads the actual closed throttle TPS voltage at "key on",and as long as the value is between ~ 0.30 volts and 0.90 volts, it sets that value as 0% throttle position (TPP). Then it appears to add ~ 4 volts to the closed throttle voltage to set the 100% TPP. Then it prorates between those values to determine actual TTP. The shift tables I have seen in the factory manual are TPP vs RPM.
  • JoePeek likes this

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#18 96WhiteTransAm

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Posted 5 days ago

I read the TPS% on the scan tool again, this time with the key in the On position and engine off. It was pretty consistent from 0% all the way up to 100%, but how quickly should this reading pop up on the scan tool? There's about a 3 second delay from when I step on the throttle to the tool displaying the respective TP percentage.



#19 KeyKeeper

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Posted 5 days ago

Dont want to barge in, but are you 100% sure its not skipping a gear?  like a 1-3 upshift?  Have you tried to shift if manually?  Do you have ALL 4 gears? Does the scan tool have a data stream you can view the trans solenoid commands?  Need to know if the PCM is commanding the shift and its just not happening or if its not getting the proper data to command the shift at a given time.


I prefer to drive short distances....1,320 feet at a time

 

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#20 Injuneer

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Posted 5 days ago

As far as the TPS, read the voltage rather than the percent. If the scan tool doesn't offer that option, skip the scan tool and use a volt meter to measure the voltage between the black wire and the blue wire in the TPS harness connector. Measurement should be instantaneous.

Derrick/Joe - keep the input coming regarding the trans operation. I'm too weak in that area.

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg





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