VSS singal and the PCM
 

Simple question for those that know the JECS tuning well.

is the VSS signal at all interlaced with the PCM in controller open/closed loop and AFR during engine operation?

Re: VSS singal and the PCM
 

A simple question, but not necessarily a simple answer.

The VSS signal is used to determine whether the car is stationary (< 3km/h) or moving. The ECU uses different AFR calculation for stationary and moving. But I haven't looked into it enough to say what the difference are.

I hope that helps.

Phil.

Re: VSS singal and the PCM
 

Mainly curiosity on my part as there is a member of another forum who is stating that the JECS computer, without a VSS signal, will be stuck in a "limp" mode and will have lean AFR's and loss of power. I'm not discrediting what he's saying, however on my past WRX with the EG33 swapped into it I recorded none of these happenings and didn't have a VSS hooked up. Car made more power than my WRX did in stock trim and was far from any limp mode.

Again mostly curiosity, as wiring in the VSS from the car is just as easy as cutting the wiring out and can be done either way in a jiffy.

Wonder if LAN could put some light on the subject if he sees this thread.

Re: VSS singal and the PCM
 

That would be me.

The code 33 puts the car into permanent open loop, and leans out the entire powerband even more than the stock 15afr region.

I logged with revscan, and my timing values were gone along with my fueling. Changing anything with an safc was futile, for the ecu would not accept a damn thing. I richened the safc to the max, and the afrs stayed rock solid.

I should note that the limp mode I speak of isn't necessarily conventional 4500rpm ceiling, with stalling, etc. You can rev to the sky with it.
The ecu only references the open loop system is all, and backs off considerably. It's a good failsafe.

Re: VSS singal and the PCM
 

Hahah Figured you were on here and would chime in. I'm wondering if something was either wrong with my JECS, or if the thing had been chipped or modded. I never did open the case up to find out. I should ask the new owner if he can swing by with the car for me to check.

Somewhere I have the dyno sheet and logs on file from when I tested my car on the dyno at the shop. AFR's were nowhere near the 15.xx mark like you mentioned, which makes me think even more that it was chipped.

It does make sense, just was a curiosity thing on my part as my old car seemed to have been a diamond in the rough on this topic, knowing full well that I purposely deleted all VSS wiring to the computer and left the WRX computer to send the signal to the dash cluster from the swap.

Either way good to know for possible future endeavors with the stock programming. :)

Re: VSS singal and the PCM
 

There were at least 4 different types of JECS ECU hardware during the 1990's and a multitude of different firmware versions for each type. Even the low-volume SVX has at least 7 different ECU firmware revisions that we know of.

All the JECS ECUS are similar, but it is entirely possible for two ECUs to differ on something like this. Particularly if they are from different years or markets.

The only way you can ever really know is to try it and see. Then fix, or find a workaround for, the problems you encounter.

Re: VSS singal and the PCM
 

I have tested this on c3, x3, m7 jecs