More Pi RPM Woes

[4mulaGuy]

Hi again. This time I am posting in the right area. (this was from a post in General Classifieds)

To recap... I have a (new to me) RF99 VD (Pinto) with a Pi system 2 dash - the RPM box was not connected. With help from ApexSpeed members, I got the RPM to read using the HT connection (I got NOTHING using the LT). So yeah, progress.

I reads, but there must be a huge amount of noise, because the display is pretty jumpy and flips to redline and more then back. I adjusted the sensitivity - I turned it until it read nothing, then adusted it up until it was the most stable. But it is still not great. I don't know how I could rely on it.

For the HT connection, I simply ran a wire about 8 inches long or so and wrapped it about 5/6 times around the coil wire. I tried moving the RPM box closer to the coil wire and I tried moving it farther away. I even tried wrapping the RPM box and lead wire in foil and grounding that to the chassis (as a sheild). Still not a very stable RPM display. I tried keeping the RPM box away from the coil and other ignition cables. I even tried disconnecting the MSD.

What am I missing / doing wrong? For as expensive as the Pi System is, you'd think it would work well and be simple to do.

- Rob

[David Ferguson]

First, the most obvious thing -- doesn't the MSD box have a tach output? (The MSD-6A, does according to the manual I downloaded from http://www.msdignition.com/ignition_4_6200.htm ) If so, you should wire that directly to the Pi RPM input, bypassing the RPM Adapter module. It's likely that MSD's multiple sparks probably confuse the Pi RPM Adapter.

If you must use the RPM module, then here are some things to try:

- Experiment with the number of turns of wire you put around the HT lead. Try from 4 to about 10 (I know Pi recommends 5 times, but you'll need more turns the thicker the insulation on the wires), try reversing the direction of the wrap.

- Make sure you have the filter setting correct for your engine (9 for HT with 7500 RPM 4-stroke)

- In the dash configuration, Make sure the RPM configuration is set to Type "D".

- You might try turning on the spike filter in the RPM configuration, set it to 7. (this is unlikely to help, but if you get real close, this might be the final piece).

- If all that fails, we might be able to supply a filter that will clean up the signal.

David Ferguson
Veracity Racing Data
ferg@veracitydata.com

Oh, if you don't have a Pi System 2 Manual, I can send you a PDF copy.

[4mulaGuy]

Thanks David. I will take a look at the MSD and see if it has an output for RPM. Are the output specs of devices like the MSD all compatible with the input specs of the Pi system? I just don't want to fry the thing and end up having to buy a whole new dash. Thanks again.
- Rob

[David Ferguson]

If it would make you feel better, you can use the LT attachments on your RPM box. However, Pi specifically says in the System 2 manual you can directly attach ECU-type tach signals.