You should use the latest firmware, 1.26, but that is not what is causing it.

So it disconnects when you connect the load cell? Sounds like the load cell is shorting the power supply. Can you recheck the load cell connector? Also measure the resistance between 0V and 5V on the load cell connector (when disconnected). It should be 300-400 ohm. When connected you should see 5V between 0V and 5V.

@admin

Loadcell is working (giving data) when engine is not running but cuts USB if I plug it in sensors to blue box when engine runs.. or direct after start up. Win 7 say com port 4 is not working . usb also go down when engine run and aux 1 is connected...lamda signal

After I stop engine I just disconnect USB from laptop and connect again and USB is running getting data from aux 1 and rpm and loadcell...untill I start engine...USB cuts of.

I reinstalled the USB art inifile and upgraded to latest firm....no different??

Is it a standard car, or a car with a special ignition?

Maybe you have a ground problem. If you disconnect all Aux sensors and any other connections you may have to the car, does it help? 

Its a VW aircooled engine on my dyno stand, sep 12 v battery to the engine and grounded stand...Bosch red coil ignition ...sitting about 1 m from blue box together with laptop, powersupply and stepper drive.

Load cell disconnected 364 ohm and 4,96V connected motor running. It seems like USB is up only when RPM is connected to blue box and engine running. 0 ground is together with lamda and blue box. I also think it is some kind of disturbance from engine running ...but??  Tried to have cables away from ignitioncables but no changes..sending a photo

More photo 

With aux 1 lamda and loadcell disconnected the USB is up and running with the motor running. Connect them to blue box while motor runs...Usb goes down ...no comunication!

Is there a effect when disconnecting the AC adapter from the laptop ?
(so the laptop runs only by battery)

It sounds like electro magnetic interference. 

Here are a few general tips on chasing electro magnetic interference problems:

• The most common source of disturbance on non-standard engines is the ignition. These can be extremely noisy. Dynomite dynos has a good guide, check it out: https://dynomitedyno.com/tech-corner/rfi-troubleshooting/ and follow the tips
• Variable frequency drives and power supplies can also be very noisy. Try for example with the stepper power supply off
• Ensure cables are routed away from noisy electronics (ignition and high current carrying cables) and as a second priority that they are as short as practically possible
• Move the instrument box away from noisy electronics
• You can ground the box, but only if there is no other ground in the system. You must avoid ground loops (i.e. two electrical paths to ground). A loop will generate currents from the electro magnetic radiation. Take care for external sensors, is the sensor's 0V is grounded? Then you already have 1 ground in the system, and must not add another
• Shields shall be open in the sensor end and connected to the YourDyno box shield input in the other end (otherwise, same problem as above). The load cell and RPM sensor are correctly made like this, but if you add your own sensors or modify the cable on the RPM sensor or Load cell, then ensure the shield is only connected to the YourDyno shield input

Let me know if you are stuck after checking the above, I can call you and we look at it together.

Posted by: @harald-bergthaler

Is there a effect when disconnecting the AC adapter from the laptop ?
(so the laptop runs only by battery)

Tried that ..no effect.

So I located the EMI disturbance the loadcell. When motor runs and the loadcell conneted USB dropps directly after start, so I routed the loadcell cable way out from all metal and connect to blue box...USB then stays on, but cable closer than ...approx 100-150mm to the metal, USB dies.

Another change since last time it all worked is that I replaced all rubber housings to COPPER tubes and pressure tube is running close to loadcell..se picture. Its def. related to spark noice! But I dont whant to reeroute the coppertube...so what can I do?? By just moving the laptop and all the electronics away ...more than 1 m ..didnt help.

Thanks for all your help, Im going up to the mountains this coming week riding snowmobile...no electrical interference up there..but will continuing faultfinding after new year when back.

Curius how to protect Loadcell and wire from it to bluebox...Il read mail up there to...so Happy New Year to you all!

@yhakan  Like @admin stated the ignition is one major source of EMF.  If you haven't already checked this,  are you using different plug wires on the  engine since you last used your setup?  I have seen a number of problems with interference from plug wires that have improper EMF suppression (solid core wires, etc.) Especially on the AC VWs we see.  I had a 2276 I/C turbo that one big name brand of wires majorly interfered with the crank trigger/sensor signals to the ecu.    EMF from an ignition system can wreak havoc for sure.   MSD super conductor wire has worked well for me in our EFI set ups but you will have to custom make these for the stock socket style cap  or buy the tower adapters.  Just a thought. Have fun up there and  Happy New Year to you as well!

@turbo-dub

Yes I use different ignition cables now, yellow siliconcables. But I realised that Im using "non resistor plugs" Bosch W 8 AC....mabe thats no god??

Should try NGK BR5HS instead! Should be simular to the Bosch but with resistor!

Thanks!

@yhakan  I always run the NGK plugs in all the VWs we see here.   You could try the resistor plugs but ill bet the cables are your issue.  I saw the same interference issues with the NGK plugs and the Taylor cables.