Explorer 5.0L Tachometer

[Big Slim]

I bought an old SW tachometer and bench tested it and was calibrated so is working fine. it does not match OBD value when on the truck. have 98 explorer 5.0 with edis. i have the brown/yellow wire from the computer into the tach as the signal. this is suppose to give the same type signal as normally off the coil? or does this need something special for tach to work? EFIguys video seem to imply that this wire should work as is.

 

[lars]

How far off is it? Modern electronic tachometers normally count pulses. I imagine yours does as well, though I'm not familiar with SW tachs. My Autometer tach works fine, connected to what ever I connected it to ages ago. If yours is looking for an analog voltage or current, that could be the problem.

 

[Big Slim]

its acts like it is getting stuck. but varying it on the bench was as smooth as can be. seems pretty close at idle. but then never got above 2k last drive and certainly did rev it up. maybe CPU signal is lower voltage than from a coil and doesnt work well with the older tachs?