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Richard Hill

Communication problems

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Hi, 

I have a storm running a rover V8, all was fine until I installed a relay coil to drive the tacho (on a spare ignition output).  Since then I have continuous failure to connect to the ecu with comms dropping randomly, lots of failed to store messages.  As soon as I turn off the tacho function the problems seem to stop.  Is there a recommended way to use the relay coil to drive the tacho without the interference with the comms? 

Thanks, 

 Richard. 

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How close is your relay to the usb cable? also, does the usb cable run parallel to the tacho wire for a long distance before or after the relay? 

High frequency switching can cause a bit of EMF interference, which is quite likely to propagate along the tacho wire. If wires run parallel, intereference can jump between them - ie from the tacho wire to your USB cable.

I'd try moving the laptop/usb cabling away from the rest of the wiring first. Failing that, try getting a usb cable with a ferrite choke on it (the inch long metal blocks around the cable near one or both ends)

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I've done the tacho relay trick on quite a few cars over the years and never seen it cause any interference, so its a bit odd.  There are not normally any special tricks required.  Is the relay just a common automotive type with a coil of about 100Ohms?  If you had a spare regular aux it might be worth a try connecting it to that - the flywheeling diode may quieten it down a bit.  I have had some tachos that dont work when connected to a normal aux but work when connected to an ignition aux.

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Yes, it's exactly 100 Ohms, I will try a normal aux out, but at the moment while tuning I have the tacho turned off.  We will turn it back on when we've finished tuning. 

Thanks. 

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