RX-Ben

iTrader: (7)

I'm doing an LS1 hybrid and using a LCD gauge panel, which needs a VSS input (racepak). Does the PCM need the VSS input or does it simply process the signal and send it on to the speedometer?

Thanks
Ben

horist

if it's an automatic (4L60E) then the PCM needs to know how fast you're going as the shift points are both speed and RPM driven (speed and TPS normal, speed and RPM when 100% TPS)

if it's a stick shift you could prolly get away w/out providing a VSS signal... so long as stuff like CAGs is turned off or any 6 speed stuff that is controled bys peed

RX-Ben

iTrader: (7)

sounds good. CAGS will be off and I don't know of any other controls the PCM has over the T56.
I'll try splitting the wire at first and run one to the PCM and one to the speedo, but this is good to know in case that doesn't work out.

Thanks
Ben

gameover

many features of the PCM are speed related such as idle control, spark mode transitions, O2 sensor, fan control etc. I wouldn't go running it in a car with no VSS and expect great driveability.

RX-Ben

iTrader: (7)

That is an even better reason to put in it.

Anyone know how many pulses per revolution the VSS puts out?
I guess another way would be- how many "teeth" are on the trigger?

Thanks again.
Ben

Speartech

iTrader: (14)

40 teeth on a 4L60E
17 teeth on a T56

The biggest problem I've seen on swaps with no VSS is idle instability and/or stalling after coasting to a stop.
Picture a car coasting down hill with no VSS. The PCM sees 0% TPS but high RPM. Since there is no VSS the PCM doesn't know the car is moving; it just thinks the idle speed is high and needs to be brought down, so it runs the IAC all the way in. Then when you finally stop, the IAC can't always recover quick enough causing a crazy speed fluctuation and sometimes a stall.

It will also set a code and turn on the MIL if not programmed out (no VSS, high idle speed).

I always use a VSS unless it's just not possible.

BLK02WS6

iTrader: (2)

So on a TH400 swap, you absolutely have to do the sensor to input speed? I was thinking if it only drove the speedo, I would skip the cost and drive by rpm for the little street driving I do. Guess I gotta do the sensor huh?

Speartech

iTrader: (14)

Not absolutely. You can try it and see how it does. We've done several rock crawler off road applications without a VSS and haven't had any complaints yet. A VSS is highly recommended though.