Just as the heading asks. I'm wondering if the PCM not getting a signal from the VSS affects the way the car will run. I'm not sure if any of the tuning tables take into affect the VSS. This is on a M6 car btw.

 

some times ago I had a VSS fault at one of my Fiero's....

okay, the SES comes on and the engine cut off during a stop, because the ECM don't commanded the IAC Valve in the correct way...... Idle with no rolling car was fine, only from driving to slow down was a problem....

after fixing the bad VSS (gear was brocken off ) normal driving and stopping returns...... hope this help you

btw: with no VSS signal your cruise control don't work!!

I think there is no affect during normal driving, because the VSS is not involved in tuning tables.

 

That is what I was wanting to know. Thanks.

 

I know on 93's if the VSS isn't functional, the car won't use all the fuel trim cells. It uses 17 for idle and all part throttle and...can't remember for wot.
But I know we couldn't tune it without the VSS working.
Maybe the 94-95's are different?

 

I know that my car was using cell 16 for idle, 17 for part throttle and decel, and 18 for full throttle. That was in open loop though.

 

Ah, the 93 I did wouldn't go into closed loop without the VSS...that's what it was. When you mentioned cells 16, 17, and 18 being used that sparked the ole memory.
Are you sure your car is going into closed loop?

 

No, not definitely. Now that you say that, I don't see how it would have been. I logged the car yesterday and it was hot and never got out of cells 16, 17, or 18. I didn't even think about that. I just thought since it was getting hot and the program allowed it (low enough temps for closed loop) that it was going into closed loop. I knew it felt better with the automatic, but I thought it was because the stall was absorbing most of the surging. That sucks. Either pay hundreds of dollars for the converter box or just tune in open loop.

I'm going to look at the log from yesterday to make sure.

 

The VSS will affect they way the car comes back down to an idle when you come to a rolling stop. Without VSS you PCM thinks the cars is stopped all the time. The target idle speed and the 0% tps moving idle speed are different.

Steve

 

I'm not following. If the car has no VSS, then how does it know the car is moving, utilizing the 0% tps moving idle speed? Or, are you saying that since it can't utilize that the 0% tps moving idle speed, it won't idle when coming to a stop? If so, why would it have a problem with just using th e target idle speed at all times? I do have problems with it idling sometimes when I come to a stop. The rpms fall down to like 500, but the IAC isn't maxxed and the car never dies.

 

the ECM meters the engine load (MAF and / or MAP)! It's higher if the car is driven.....