Richard Hill Posted April 18, 2019 Report Share Posted April 18, 2019 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. Quote Link to comment Share on other sites More sharing options...
cj Posted April 19, 2019 Report Share Posted April 19, 2019 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) Quote Link to comment Share on other sites More sharing options...
Adamw Posted April 19, 2019 Report Share Posted April 19, 2019 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. Quote Link to comment Share on other sites More sharing options...
Richard Hill Posted April 19, 2019 Author Report Share Posted April 19, 2019 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. Quote Link to comment Share on other sites More sharing options...
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