VSS Myth Fact or Fiction?
10-20-2004, 09:48 AM
#1
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VSS Myth Fact or Fiction?
As you can see i am a transplanter. Now the question: Is VSS needed to make the engine run right? I know lots of things like fans, and fuel are looked at it in MPH. I think the myth is that timing and fuel supply are controlled by VSS. Thoughts, or references would be most helpful to me. for the sake of conversation we are talking about ODB1 LT1's.
Thanks
This is the statment i am trying to figure out if accurate or not
Thanks
This is the statment i am trying to figure out if accurate or not
I've done considerable programming on my LT1 and came to the conclusion that although you can turn off the VSS signal diagnostic, code 97, the ECU needs the data to work properly.
While it won't give the code 97, it will give you another code that tells you you've got other problems. The result is poor running in all conditions, but without an engine light on most of the time. The check engine light came on while decelerating on mine. While troubleshooting mixture, spark advance, egr, etc, I determined some of those functions NEEDED speed input.
I went round and round with this a few years ago when I put the LT1 in my *** with the original ****** 3 speed automatic. I finally spoke with a GM engineer I met (lost his number years ago, doh!) who confirmed the LT1 needs speed input to calibrate the spark advance, AF ratio, and IAC among other things.
While it won't give the code 97, it will give you another code that tells you you've got other problems. The result is poor running in all conditions, but without an engine light on most of the time. The check engine light came on while decelerating on mine. While troubleshooting mixture, spark advance, egr, etc, I determined some of those functions NEEDED speed input.
I went round and round with this a few years ago when I put the LT1 in my *** with the original ****** 3 speed automatic. I finally spoke with a GM engineer I met (lost his number years ago, doh!) who confirmed the LT1 needs speed input to calibrate the spark advance, AF ratio, and IAC among other things.
Last edited by 944v8inDFW; 10-20-2004 at 09:59 AM.
10-20-2004, 11:27 AM
#2
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Location: Houston, TX
Posts: 477
Re: VSS Myth Fact or Fiction?
If you are running an 4l60e, you need it... if it's a M6 or an older non computer controlled tranny, then you can do away with the VSS. The PCM uses the VSS to determine if the car is moving or stopped - it doesn't care about vehicle speed (except for fan control and A4 functions).
You will lose the benifits from the PCM's 'throttle follower' function (I haven't had any problems due to this ... adjust your TB blades until you have a relatively low IAC count at idle and you're set). If you are using a closed loop program, you'll probably be limited to only one long term and short term cell ... so make sure your tune is good! Of course, if it's an open loop program, this is a non-issue.
You will lose the benifits from the PCM's 'throttle follower' function (I haven't had any problems due to this ... adjust your TB blades until you have a relatively low IAC count at idle and you're set). If you are using a closed loop program, you'll probably be limited to only one long term and short term cell ... so make sure your tune is good! Of course, if it's an open loop program, this is a non-issue.
10-20-2004, 06:58 PM
#4
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Re: VSS Myth Fact or Fiction?
No trans controlled by the PCM here and fact is one car has a PCM4Less tune! On my workup sheet i said no VSS so does that mean that one is programmed correctly? I am running closed loop with a MAF
thanks
thanks
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