Noisy rpm signal

[z0tya]

I have a cosworth yb with 36-1 vr, wastedspark config. It has a bullet proof config in my racecar. Now the engine need rebuild. and I put into a Ford Sierra to running in. The vems run on 1.1.27 with v3 harness.
Now I have a noise problem. At first start I have some trigger error , but after I move another place the coil and spark wires. So the trigger error end. But I have very noisy rpm
At 1200 it is boing up and down about 40 rpm/min intervall, and it is reamain at higher rpm. At cranking the rpm signal clear and stable.
I try to move vr sensor cable and ignitions some kind of different place , but no result.
I put some log here:
www.cosworth.hu/misc/noisyrpm.zip

Have you any idea?

Thx

[rob@vems.co.uk]

My first thought is that if the engine has been put in another chassis then you need to check and double check the grounding - especially on a rusty old Ford
Also the 1.1 releases before 1.1.4x were all for Audi triggers, so its perhaps not a good idea to work with that firmware.  Either go back to 1.0.78 which is super stable for 36-1 or to the stable 1.1.5x releases.

[z0tya]

I am totally disappointed.
Yesterday we worked about 4 hours on the car but no positive result.
I changed the grounding. Wired new gnd cable from battery to engine block, to cyl head, to chassis. The vems get the gnd from this point. Thick wire from batt to chassis and vems gnd from this point.
We put another space the coils, it got new gnd cable.
Vems get 12v from batt with his own wire. We use the v3 harness, and we never see similar this.
We changed yesterday from a similar setup: coil, injectors, ecu: no result.
We saw the vr sensor with scope but no noise.
We try to fire the car w/o alternator.
With 1.1.27 and 36-1 vr we run 4 car with no problem until this terrible problem.
See the log:


and the other:


There are some good period in.

Today I will try the 1.1.56 or 58 but I am not trusting.
Please give any ide, maybe help us....

[z0tya]

Our fault: bad vr sensor polarity....
(we programed with this cable a Scorpio dohc and replaced the vr pin)