[JrZook]

After reading many posts regarding the VSS and now that i have a G16B that had a VSS as an input to the stock ecu, I raise the question of what does the VSS control on the engine?

Now from my understanding I believe that the VSS is a direct input to the ecu as some form of EGR solenoid trigger, opening up the EGR valve at cruise speeds. I believe this to be the case as the original 1.3 in the sierra had no speed sensor as such, although it had 4th and 5th gear switches to control the EGR solenoid valve. The 1.6 does not use these switches so the only input to cruise speed is the VSS, hence the conclusion that the VSS is used as an input to the EGR solenoid valve.

Anyone else got input or can confirm this?

Cheers Dan

[Damo]

I guess there is one way to find out. Give the ECU the signal it would be expecting at speed (spin up the VSS with a drill maybe?) and see if you get a voltage on the EGR solenoid. I'm guessing that you're right, but it doesn't necessarily mean that EGR is the only thing the ECU uses that VSS sensor for.

[Hybrid]

I cant confirm anything but the 3.8L commi motors used in lux conversions need the VSS as it controls fuel reduction during deceleration and the like. Without it they chew through the fuel. I can't remember if it also put the computer in limp mode. Either way it might have a similar role in the g16.

[JrZook]

Hybrid wrote:

I cant confirm anything but the 3.8L commi motors used in lux conversions need the VSS as it controls fuel reduction during deceleration and the like. Without it they chew through the fuel. I can't remember if it also put the computer in limp mode. Either way it might have a similar role in the g16.

This is interesting, cause i woulda thought a decrease in engine speed and increase in manifold vacuum (map sensor) or decrease in intake air flow (maf sensor) would be alot more responsive in terms of working out weather the engine is deaccelerating and hence to cut fuel.

[Gwagensteve]

I think the issue with deceleration is that if the car is moving, it's kept fuelled a bit richer than if it's stationary to provide crisper throttle response.

However, none of these factors address the best reasons to keep the VSS-

A) You'll get a check engine light if the ECU sees prolonged load without a VSS signal

B) If the check engine light is on anyway, you won't know if you have developed another problem.

C) You can't get an engineers cert on a car with a fault code showing (ie the check engine light is on)

D) If you disconnect the Check engine light to "ignore" the VSS fault, you might as well run a carby. One of the huge advantages of EFI is the on board diagnostics.

Just some thoughts.

Steve.