VSS signal to a '91 - '93 ECM

[sspeedstreet]

So I know the VSS signal controls the speedometer through the ECM. The VSS also tells the ECM when the wheels stop turning (at least on my 5-speed) allowing the engine speed to drop to idle. Does the ECM use the signal for anything else?

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[robertisaar]

vehicle speed is used in a LOT of internal calculations....

the 4K PPM the ECM outputs from the VSS signal is also used for various modules, such as ABS, the DIC/DIS fuel economy calculations, cruise control....

[sspeedstreet]

Thanks for the reply. I should have been more specific. This motor is in a Fiero, so none of those you list affect me. Is the PPM count referenced for engine management, like spark timing or fuel delivery, etc?

[robertisaar]

well, depends what you're referring to, the VSS input or VSS output.

if you don't have anything that runs on the 4K PPM output from the ECM, then you don't need it connected anywhere.

the VSS input is used for a lot of calcultations though, fuel and spark related.

[sspeedstreet]

The VSS sender in the transmission sends a signal to the ECM. Does the ECM use that signal to calculate for fuel and or spark values?

[robertisaar]

since you're running a 5 speed, there are a few less items that depend on it, but highway spark. AE fueling, idle fueling, CCP, DE fueling, DFCO, EGR, ESC, launch mode, idle spark, RDSC are all the ones i can think of off the top of my head that effect either spark or fuel based on vehicle speed input.