LT1 OBD2 pcm questions...
LT1 OBD2 pcm questions... Ive searched everywhere, and posted in both the LT1/Lt4 and auto trans sections to no avail. Maybe someone here can help..
-How does my 96 TA's pcm 'know' when Ive moved the shifter out of park or neutral and into a drive gear?
-Or does it even care whether its in gear or not?
-Dont the M6 pcm's use the VSS at least partially to determine whether the engine is under load or not?
Just trying to figure out whats different in how a M6 pcm does it and how a a4 pcm would do it. My wiring diagrams show a difference in hard wiring, mainly in the PRND switch on the A4 cars. That switch seems to be 3 in one; park/neutral safety, reverse lights, and one more undetermined circuit with 2 wires that get connected/disconnected based on switch position. I have no diagram that illustrates the internal workings of the switch and I dont have one to experiment with.
Im guessing/hoping that these two wires (orange and black) are the answer to my questions.
Thanks in advance,
Justin
-How does my 96 TA's pcm 'know' when Ive moved the shifter out of park or neutral and into a drive gear?
-Or does it even care whether its in gear or not?
-Dont the M6 pcm's use the VSS at least partially to determine whether the engine is under load or not?
Just trying to figure out whats different in how a M6 pcm does it and how a a4 pcm would do it. My wiring diagrams show a difference in hard wiring, mainly in the PRND switch on the A4 cars. That switch seems to be 3 in one; park/neutral safety, reverse lights, and one more undetermined circuit with 2 wires that get connected/disconnected based on switch position. I have no diagram that illustrates the internal workings of the switch and I dont have one to experiment with.
Im guessing/hoping that these two wires (orange and black) are the answer to my questions.
Thanks in advance,
Justin
Joined: Nov 2001
Posts: 1,707
Likes: 33
From: Anderson, Indiana
The VSS is used for lots of things. Imagine coasting down a hill in 2nd gear with your foot off the gas. With no VSS signal the PCM would be saying "why the hell is the engine idling so fast?"
The orange and black wires are the P/N position switch. The input from that circuit changes the idle speed between in gear and out of gear to lessen torque converter "tug".
The orange and black wires are the P/N position switch. The input from that circuit changes the idle speed between in gear and out of gear to lessen torque converter "tug".
__________________
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
Originally Posted by Speartech
The VSS is used for lots of things. Imagine coasting down a hill in 2nd gear with your foot off the gas. With no VSS signal the PCM would be saying "why the hell is the engine idling so fast?"
The orange and black wires are the P/N position switch. The input from that circuit changes the idle speed between in gear and out of gear to lessen torque converter "tug".
The orange and black wires are the P/N position switch. The input from that circuit changes the idle speed between in gear and out of gear to lessen torque converter "tug".
As I was doing the nice break-in on the rear and th400, I just had those two wires connected as I did when I originally swapped from the 4L60E to the t56. The idle characteristics were really weird and the pcm seemed to have a hard time with me engaging a drive gear with the TH400. So the PCM was thinking I was in park/neutral when I was going into any other gear.
So basically I need those wires to connect through a relay or something when Im in park or neutral, and disconnect in any other position.
I had another question along with this one that never got answered either... Maybe you can help
If I have the WSS hooked up instead of a trans VSS, will I have issues with a zero speed signal while the car is on the dyno?
Thats just something I would like to know, as my thinking it would be a problem led me to just go ahead and purchase the correct GM parts to adapt a VSS to my TH400.
Thanks Again!
