inaccurate rpm reading (msl attached)

[teRcel]

this was logged while revving the engine... it's a paseo engine using the 12 tooth/1missing gear.... tried adjusting it as good as we could with a scope but still the results aren't all that great.... what could improve the "issue"? is it bad to have the pick up in the distributor cap and the coil could cause too much noise ????

i'll try and get a log while driving tomorrow.....

you can see the rpm issue at 1426 and 1443....

[Matt Cramer]

Does the glitch happen all the time at that RPM, or just occasionally?

[teRcel]

quite frequently.... more then 50% of the time... in the new msl it's a bit clearer as there are more logs of it happening.... sometimes its drops down to zero and other times more like half way... i didn't use to have that issue before.... but since then i added an MSD box.... could that make it an issue because the voltage is stronger and also causing more noise in the signal???

[Matt Cramer]

MSD boxes are known for being electrically noisy. Where is the MSD box grounded? How about the MegaSquirt?

[teRcel]

the msd box is grounded to the head on the intake side on a bolt right by the distributor...

the megasquirt is grounded right on the ground cable of the battery....

[patrickbrown]

MSD offers a noise filter (part number 8830). I added one to my MSD 6AL equipped car prior to going EFI. I had a lot of noise in the radio and this cleaned it up nicely.