Magnus

iTrader: (4)

I know what it does. .... But what is its main purpose. What does the PCM use this signal for?

My 97 didn't have one from the factory, but 98+ cars do.. Do you guys fab these up with your conversions or just not use it?

Speartech

iTrader: (14)

The PCM uses the signal to adjust idle speed based on whether the car is in gear or in park/neutral.
As soon as the PCM "sees" the car go in gear it drops the idle speed by around 100 rpm to prevent jerking going into gear, and to prevent tugging at the torque converter.

It can be considered as optional on a swap. As long as the line is left open the PCM will always assume the car is in gear, and will drop to lower rpm when the engine is started. This also causes a much quicker rpm rampdown on a cold engine start.

Some aftermarket wiring harness companies that have no clue as to how the PCM works will wire this line to ground which makes the PCM think the car is always in park or neutral. On some applications this allows some diagnostic tests to be skipped (EGR, purge, etc.) so that these items can be left off without setting a code. The problem is that the idle is too fast then, and the car wantts to pull a little when sitting still, as well as other issues.

The PNP signal line has been around about as long as fuel injection, so if your 97 was an automatic, it should have had it.

Magnus

iTrader: (4)

Thanks for the reply John.. very informative..

I swear I've looked up and down my wiring schematic and PCM pinout diagrams.. and I don't think the 97 3.8 A4's come with them.. I know GM put them in the 98+ 3.8 A4's though..

I think I'll just let the car think its it gear all the time now.. It's fine as is.. but that may need to change when I do the lumberjack cam.

Now.. to finish this walbro install and fuel gauge problem.

Speartech

iTrader: (14)

Maybe they did it some other way. I don't do much with that engine or PCM, so I don't know that much about it. You should be fine without it on the LS1.

Pro Stock John

iTrader: (34)

if you have a A4 you have that.

Magnus

iTrader: (4)

I'm almost 100% positive I don't john.. I've looked all over.. I've mapped out my entire V6 harness.. I have all the pinout diagrams and PCM diagrams..

and it's just not there... and there are no extra unacounted wires.

Pro Stock John

iTrader: (34)

Are you sure it's not tied into the reverse lockout feature.

Magnus

iTrader: (4)

It's not. Now that I think about it.. the V6's idle never really changed between park and gear... not like I know the LS1's do.

Speartech

iTrader: (14)

I think you're right Keith. I pulled the wiring diagrams for a 96 3800 Camaro and I don't see any P/N switch there either. I would guess you probably have the unused locations on your shifter switch down in the console, so it could be hooked up fairly easily, but as I said earlier, it doesn't make a huge difference either way.

67ls1CamaroProject

So, how does this work on a 6 speed car? My other post will show that I am stalling when selecting reverse. I know the RPM's are being dropped too much and hence the stall. What does the PCM do for a stick car when selecting reverse?

Magnus

iTrader: (4)

You push the clutch in.. engine disengages from the transmission.. the rpm's change depending on what gear you select even with the clutch disengaged?

I don't think the PCM knows what gear the M6 is in. I'm no M6 wizzard though.