TDI Cruise Control Possible Solution?

So for the past few days I have been thinking of how to get a VSS signal into the ECU for a vehicle running a mechanical speedo such as a MK1.

I set out to see how many pulses the VSS puts out for each wheel revolution. Spinning the output shaft of a Mk3 CTN box I get 7 or 8 pulses per revolution. It appears the ECU(actually the cluster) reacts of a change to 0v, because the high voltage was only like 0.16.

From there, I put the numbers in Excel, using a typical Mk1/2/3 tire OD of 22.5".

First column is speed, second column is pulses per minute if its 7 pulse per rev, 3rd column is pulses per min if 8 pulses per rev.

10 1045.754963 1195.148529
20 2091.509925 2390.297058
30 3137.264888 3585.445586
40 4183.019851 4780.594115
50 5228.774814 5975.742644
60 6274.529776 7170.891173
70 7320.284739 8366.039702

SO, my idea. Rather than go thru the hassel of trying to install a hall effect, what about driving the speed input pin with the tach output pin???
Tach output alternates between ground and some elevated voltage.

So as similar format, actual engine RPM in 2nd and 3rd columns would simulate MPH in the first column. 2nd column is if VSS is 7 pulse per rev, 3rd column is if 8 pulse per rev.

10 522.8774814 597.5742644
20 1045.754963 1195.148529
30 1568.632444 1792.722793
40 2091.509925 2390.297058
50 2614.387407 2987.871322
60 3137.264888 3585.445586
70 3660.14237 4183.019851


So pretty much any RPM you would consider using the cruise, is a speed that the ECU would consider plausible. Only issue I see(assuming it works) is that if you set cruise in 4th, then switch to 5th, you need to reset your speed, not hit resume unless you want to speed up like 15 or 20 mph.

I could mount a hall effect to count CV bolts(6 pulse/rev), but this would be cleaner, and I do not have to worry about the sensor.

Thoughts?

this might be what your looking for? http://www.fastforward.ca/vehiclespeedsensors/speedpulsvw.html

been using the tach signal as a surrogate speed input on my truck for over six years ... however the signal "as is" is too fast for the ecm and you'll get a signal input too high
code unless you modify the signal with a pulse divider box such as a dakota digital speedo adapter

what year and pa/german mk1??

if 82+ german/mk2+ the factory cruise goes in the back of the speedo head.. via those 2 weini bitty screw holes.. just 2 wires a ground and what ever your sending a signal too..

if not german with screw on cable 81-84pa.. i know a guy who has cut the metal thats in the way out and installed the sensor when adding factory cruise to a mk1... but he a precise kind of guy and wanted factory cruise in his mk1 gti and his tdi-m caddy

now the round eye cluster ive not messed with..

The Volkswagen Industrial engines from the 90s had the tach signal fed into the VSS-in on the ECU. Idle is around 28Hz, and redline is 150Hz both are within range of the CCS system.

The correct frequency for Volkswagen ECUs up to 2005 is 1Hz per km/h, so 100Hz is 100km/h - most ECUs are limited to 250km/h

If you have a 1980 or later MK1 it should have a spot on the back of the speedometer that you can knock out and install one of my Speedpuls VSS


If you have a pre 1981 or one of the US made ones that don't have a hole at the back of the speedometer then you would need a universal speed sensor


If you need to calibrate that signal, then my latest VSS Korrekt is the ticket - both 12V and 5V outputs and can adjust from 0.10 to 10.0X for perfect speed representation if you are using something like ScanGauge or Torque to show your speed.