Electrical VSS question

[Mcmahst]

I swapped an 87 TBird 5.0 drivetrain into a 73 Mustang and as part of that swap, I did not include the VSS sensor.mI was going over my notes and stuff regarding the wiring harness I made, and I found a note I wrote that said, I don’t need the VSS because I did not bring the cruise control over as part of the swap. Am I wrong; do I need the ECU to see that input? I’m starting to second guess that decision since I cannot find where that original note idea came from.

 

[AeroCoupe]

VSS is used for two things which are cruise control and strategy in the ECU. If the VSS is not hooked up the cruise will not work and some have experienced stalling. Here are the ECU wiring diagrams for the various years of Mustangs:

86 - 88 non-California cars

88 California cars - 91 (early)

91 (late) - 93

You can see that on the mass air cars (88 California -93) Pins 3 & 6 are for the VSS sensor and on the non-mass air cars (86-88 non-California) they do not have it.

With all of this being said you used a motor, wiring harness, and ECU from an 1987 Thunderbird 5.0 so it was a non-mass air car and non-HO. Best place to get information on those cars is here:

Fox T-Bird/Cougar Forums - Index

Fox T-Bird/Cougar Forums - Index

foxtbirdcougarforums.com

 

[Mustang5L5]

Speed Density cars do not use the VSS for anything other than cruise control. My '88 (originally SD) didn't have factory cruise, so there wasn't even a VSS on the car.

If you convert to mass air at all, you would need the VSS for the ECU, but if you are still running the t-bird speed density ECU than it is not required.

 

[Mcmahst]

Thank you gentlemen, I now remember. I’ll hang on to the VSS in case some day I go MA.

 

[Willybill32]

Speed Density cars do not use the VSS for anything other than cruise control. My '88 (originally SD) didn't have factory cruise, so there wasn't even a VSS on the car.

If you convert to mass air at all, you would need the VSS for the ECU, but if you are still running the t-bird speed density ECU than it is not required.

I converted my ‘86 to MAF using the Ford Motorsports kit. My ‘86 didn’t have cruise control, hence no VSS, and the kit instructions didn’t say it was necessary. I’m not aware that I’ve ever had an issue with not having VSS.

 

[FastDriver]

If you pull the VSS out of an MAF car, it'll still work, but since it always tells the computer you're going 0 mph, you will not have the buffer the EEC builds in when coasting down to a stop. Anyone that has the VSS will notice that the computer adds a little RPM that finally settles when the car drops under 5mph. That extra RPM buffer is nice to have, because it reduces the chances of the car from stalling and helps the car settle back down to idle softly.

I'm still a newb with the A9L programming, but this is what I've inferred so far. There may be more.

 

[Willybill32]

If you pull the VSS out of an MAF car, it'll still work, but since it always tells the computer you're going 0 mph, you will not have the buffer the EEC builds in when coasting down to a stop. Anyone that has the VSS will notice that the computer adds a little RPM that finally settles when the car drops under 5mph. That extra RPM buffer is nice to have, because it reduces the chances of the car from stalling and helps the car settle back down to idle softly.

I'm still a newb with the A9L programming, but this is what I've inferred so far. There may be more.

@FastDriver, thanks! Interesting that I've never had an issue with the idle dropping down or stalling. Recent mods (HCI, headers, etc.) resulted in an issue with "jerking" at idle speeds...wonder if the VSS would help with that.

 

[General karthief]

@FastDriver, thanks! Interesting that I've never had an issue with the idle dropping down or stalling. Recent mods (HCI, headers, etc.) resulted in an issue with "jerking" at idle speeds...wonder if the VSS would help with that.

The 'jerking' at low RPMs likely is caused by the duration on the cam, valve overlap, JMO.
Installing a VSS will not help in this case

 

[Willybill32]

The 'jerking' at low RPMs likely is caused by the duration on the cam, valve overlap, JMO.
Installing a VSS will not help in this case

@General karthief, thanks. The cam has always been the prime suspect. It’s an E303, wish I would have gone with a newer design…

 

[General karthief]

What gear you got in the back?

 

[Willybill32]

What gear you got in the back?

3.55

 

[General karthief]

Good choice

 

[Mustang5L5]

I converted my ‘86 to MAF using the Ford Motorsports kit. My ‘86 didn’t have cruise control, hence no VSS, and the kit instructions didn’t say it was necessary. I’m not aware that I’ve ever had an issue with not having VSS.

The issues that would arise from not having it is that the vehicle may stall when coming from a stop. So if you notice the car doing that on occasion you would likely want to add it.

But on the 89+ MAF cars it is referenced by the ECU

 

[Willybill32]

The issues that would arise from not having it is that the vehicle may stall when coming from a stop. So if you notice the car doing that on occasion you would likely want to add it.

But on the 89+ MAF cars it is referenced by the ECU

Funny…that’s never been an issue.

 

[Mustang5L5]

If it’s not an issue, don’t worry about it. Just keep it in back of mind in case you ever notice the stalling out.