is the vss a must to have hooked up or can i pogram it out? ive been reading up on this for a while and i have read a load of battle stories getting the vss to work after an engine swap. i dont need it for my speedo i have my old ecm in the car and it still works. my question is does my obd1 ecm need the vss signal. is it a must??

 

In short, no the ECM does not rely on the VSS signal if you are using the ECM out of a car without VSS...

 

im using a obd1 ecm for engine managment and a 730 for the speedo. i think you answered my question.. i do not need the vss to run the obd1. correct?

 

AFAIK there are NO ECM's that don't have a VSS input.
The ECM and the code it runs was designed from the 'gitgo' to incorporate vss into it's calculations.

The ECM uses the vss signal for various functions relating to fuel mixture, DFCO ,ECS and TCC control, etc.

With that being said, you can get it to run fine without vss.
To do that you will need to set the flag in the chip to tell it you don't have a vss.
This is in the "ECM Switch Table".

Actually it just causes the ECM not to output a failure code for the lack of vss signal.

That's in the $8D mask for your 730 ecm. BTW, the 727 ecm uses the exact same Memcal as the 730.

BTW, I'm running TPI with a 727 ECM in my '73 Super Cheyenne.
I have no vss on it but I'd really like to have one.

 

The ECM doesn't have any way of knowing how fast the car is going, other than the VSS. That includes the 730. It doesn't have a foot that it can stick out and feel how fast the ground is passing by, or something else to do that job for it.

 

I have an old tennis shoe on a rope that I throw out.
This substitutes for the vss I don't have. Sort of like ships used to do.
And the term for speed called the "knot" was born.

Seriously, they'll run fine without a vss input.
They'll run BETTER with a vss input.

 

if the vss is programed out how would it make it run fine rather than better?