DL-1 getting dodgy RPM feed from coil negative terminal

[evanbottcher]

Hi folks,

I have a wire running from the coil negative terminal to the high voltage RPM input (rH) on the DL-1. Another wire from the coil goes to my rev limiter/shift light (works perfectly).

I'm getting data, but it doesn't seem remotely accurate. Climbs slowly to 8000rpm, then drops and spikes up and down around 1000rpm. Not remotely related to engine speed.

I've read the knowledge base sections here & here:
http://www.race-technology.com/wiki/ind ... RPMSensors
http://www.race-technology.com/wiki/ind ... sionPickup

I have the earth (rG) connected just to a chassis earth - should I try running a lead to an engine earth?

Please tell me I've just got something totally wrong.

thanks,
Evan.

[evanbottcher]

Here's a screencap of analysis - RPM at the bottom.

http://picasaweb.google.com/lh/photo/dq ... directlink

[jlucas]

Hard to say. Signal strength? interference?

Do you have another option? fuel injector trigger wire? ECU feed?
If not, you might have better luck with the MSD GMR pickup.

[Support]

..or, if you have fuel injection take a signal from one of these... that works very well.

Best regards,

Andy

[jlucas]

fuel injector trigger wire

echo?

[evanbottcher]

Thanks guys. Unfortunately I don't have injection or an ECU - this is a 1978 Alfasud Ti race car running carbs and basic electronic ignition. Can I run a shielded wire from the coil -ve to reduce interference?

Does it sound like I've got it wired correctly? Coil negative to rH ?

thanks,
Evan.

[osborni]

Either a shielded wire or a twisted pair wire might help.

If that doesn't work you could run a hall effect sensor to pick up a bolt head on the clutch or accessory drive.