944Hybrids: 924/944/968 and 928 V8 Conversions
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Mon Jul 08, 2013 3:56 pm by Admin

For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Speedometer wire

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Post  lsporsche Wed Oct 21, 2015 8:18 am

Firstly, I have searched! I don't believe advanced search is working correctly though, I type in "VSS" with no results, but type in "speedo" and get a result that has "VSS" in the title of the topic. Anyways, I'm going to use the TPC VSS, wiring it into the LS pcm makes sense and seems straightforward. I also have a wire coming out of the PCM labeled "VSS" to wire up to my speedometer. My question is, where does this wire go? I found info on the tach, but haven't found any on the speedometer. At first I was under the impression the factory Porsche VSS would still operate the speedo but have been told that it won't. This is for an 85.5 n/a 944. Appreciate any help!


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Post  spence Wed Oct 21, 2015 11:55 am

The speed sensor in the 944 transmission still operates the speedo. There's only one VSS wire needed, and thats the input from the VSS sensor. All the VSS sensor does in this conversion is tell the ECU when the car is moving. It has nothing to do with the speedo in our cars.

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Post  lsporsche Wed Oct 21, 2015 12:05 pm

Ok, thank you! Thats why I'm not finding any info about it! So no VSS output wire is needed from the LS pcm correct? Want to verify before I remove it for the second time. Lol


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Post  gdopnt Wed Oct 21, 2015 10:02 pm

The VSS sensor from TPC should be connected to the VSS labled wire at the LS1 PCM

Simply put,

I'm not a professional tuner but I have HP Tuners and from what I've slightly figured out is this. The VSS tells the PCM the speed of the car, period.  Which as far as the cooling fans go is a simple thing - the PCM will turn them on and off at 35MPH. When the car is moving it could stall at low speeds.  It will tell your idle control valve to open a bit because your throttle is closed (your clutch in or your out of gear coasting to a stop sign).  On a cold start the PCM has Milli seconds to figure out the motor is cold as well car not moving before you go to start it, the idle control valve opens more for a cold higher idle.  Idle is not controlled with a screw don't turn the one on the throttle body.  there are tire size calculations to correct your PCM speed as well. if you have emissions - it tells the emissions system your moving down the road off the throttle and to add exhaust gas to the intake air to fill the cylinders to conserve fuel. this is a small part that will effect your tuning latter. the PCM will trigger a pile of codes for what car it is set for and what your not using in the 944 for instance, transmission, emissions. You can reset them all you want but there coming back. One of them could be your VSS. In the HP Tuners program you have to disable them. You will have to decide on your own but if you have purchased the VSS and installed it I would connect it and save trouble shooting time latter.

This is a quote and the one big thing about VSS.

Throttle Cracker is a set amount of airflow that references MPH and RPM once activated. If your table says it needs 1.0 grams/second of airflow at 2200RPM and 20MPH, then the IAC will open up a certain number of steps by referencing the IAC Effective Area table, which converts desired airflow into actual IAC steps. The throttle cracker will remain active until it reaches its deactivate speed. Then, it will decay based on its decay rate. This is often the table that causes RPMs to hang while coming to a stop since it usually doesn't reach its deactivate speed until 2mph.

This is the purpose of the VSS.


Throttle Follower is airflow added based upon the throttle position percentage and its rate of change. When it exceeds the % change value in a 12.5ms time span, the follower will be activated. If it's increasing, the Throttle Follower values will be added to the desired airflow, which will open the IAC in the same manor as stated above. Once the change in TP% has stopped, the decay delay timer starts. After the timer is done, the follower is then decayed out at the rate listed in the Follower Decay Delay table until it reaches 0 or the TP% reactivates the follower. If TPS% is less than or decreasing by the % change, it will bypass the delay and decay the follower immediately.

simply put - if your were racing this could be used to control the drop of RPM when shifting gears.

all based on VSS.


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Post  lsporsche Thu Oct 22, 2015 6:05 pm

Good info! I appreciate it. I'll definitely be running mine, I still have the 2 twisted wires in the harness that go to it. I was just making sure none of that was used for the speedometer gauge on the dash.


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