Here is my problem...I have a 3.4 DOHC with a 4T65E trans. The first trans installed had no 4th gear and no lockup...looking it up online I found all kinds of threads talking about non hardened splines a common problems with this model trans.. not wanting to deal with a teardown I opted for a replacement trans.the one I got is a known good trans..I drove the car before it was pulled and everything worked fine in the donor car (97 monte 3.4 dohc) but I installed it in my 88 GT and I have the same problem...no 4th or lockup. Only codes im getting is slow o2 and vss no output. Will a bad vss cause a no 4th gear problem? Also my speedo works fine I would think it runs off the same vss signal. Any ideas?

Exactly what VSS code number are you getting?

If there is a VSS sensor problem and the PCM is not setting a valid VSS signal, it could cause a no 4th gear / no TCC problem. The slow O2 sensor code should not be affecting the trans at all.

I assume you have the speedo running off the PCM 4k PPM VSS output. If so, and if the speedometer is working fine, then we have to assume the PCM is receiving a valid VSS reading from the trans mounted speed sensor. However, I would still like to know exactly what VSS code number you are getting.

One of the other things that could cause a no 4th gear / no TCC issue would be if the PCM isn't programmed for the correct gear ratio (final drive) for the transmission you are using.

Do you have any way of getting scan data out of this PCM?

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 11-19-2013).]

I have phonedawgs harness and you just reprogramed my pcm cant remember the exact code im getting ill see if I can find it. Said something about turbin shaft if I remember right

Edit PO717 code

[This message has been edited by 701GT (edited 11-19-2013).]

quote Originally posted by 701GT: I have phonedawgs harness and you just reprogramed my pcm cant remember the exact code im getting ill see if I can find it. Said something about turbin shaft if I remember right Edit PO717 code

P0717 is for a missing transmission input speed sensor (ISS) signal.

Unplug the PCM from the harness and measure resistance across pins C1-7 and C1-46 - you should get 800 or so ohms to 1500 or so ohms. IF not, check resistance across pins S and V at the transmission round connector itself (on the transmission, with it unplugged). If you don't get the resistance spec at the transmission, there is an internal problem (bad wiring inside the trans or bad input speed sensor). If resistance is in spec at trans but not at the PCM, there is a PCM wiring harness problem.

If everything checks out (harness and trans), you could have a bad PCM.

Also, these two ISS wires must be a twisted pair all the way from the transmission connector to the PCM connector and cannot be routed near any spark plug wires. Interference on this circuit can cause problems.

Let me know what you find via email because I may not come back to this thread.

-ryan

------------------
OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 11-19-2013).]