Variable reluctor circuit, Step 51, h: C31

[ironwill11]

I am working on the Input section construction and on Step 51 Variable reluctor cirucuit, substep: h.
The directions say
"Install and solder C31 {399-4329-ND, 0.1µF, 104 marking OR 399-2017-ND, 0.001µF}. This is located as the 4th cap in the row of "vertical" capacitors above the text "Bowling" in the copyright notice.
Note: A 399-2017-ND 0.001 µF capacitor should be substituted if MegaSquirt will be receiving higher frequency tach inputs. The smaller capacitor helps to maintain the signal integrity and timing. This 0.001 µF capacitor is especially useful for high tooth count wheels including all crank wheels that have more than one pulse per ignition event such as the popular 36-1 or 60-2 missing tooth crank wheels."

1.) My kit only came with the C31 0.001µF capacitor. Do I just assume that is for my application (GM 4.3l TBI injection)?
2.) I am installing both circuits Hall/optical and variable reluctor like the instructions recommend. I am not sure but thinking that the hall/optical circuit should be done like in step 50a, as I have a 8 pin GM HEI distributor. Does anyone know if this is correct?

Thanks for any help
Will

[Bernard Fife]

Will,

1) Yes, you can use the 0.001µF cap. The HEI will be a relatively low frequency input. High frequency inputs refers to crank wheel with lots of teeth (60 - 2 teeth, for example). However, the value of the capacitor is not that very important for a low frequency input. That is, too high a value will mess with the high frequency input, but too low a value shouldn't affect a low frequency input. So your vendor has apparently decided that the 0.001 value can be used for both situations.

2) Yes, 50a is what you want to do.

Lance.

[trakkies]

I am working on the Input section construction and on Step 51 Variable reluctor cirucuit, substep: h.
The directions say
"Install and solder C31 {399-4329-ND, 0.1µF, 104 marking OR 399-2017-ND, 0.001µF}. This is located as the 4th cap in the row of "vertical" capacitors above the text "Bowling" in the copyright notice.
Note: A 399-2017-ND 0.001 µF capacitor should be substituted if MegaSquirt will be receiving higher frequency tach inputs. The smaller capacitor helps to maintain the signal integrity and timing. This 0.001 µF capacitor is especially useful for high tooth count wheels including all crank wheels that have more than one pulse per ignition event such as the popular 36-1 or 60-2 missing tooth crank wheels."

1.) My kit only came with the C31 0.001µF capacitor. Do I just assume that is for my application (GM 4.3l TBI injection)?
2.) I am installing both circuits Hall/optical and variable reluctor like the instructions recommend. I am not sure but thinking that the hall/optical circuit should be done like in step 50a, as I have a 8 pin GM HEI distributor. Does anyone know if this is correct?

Thanks for any help
Will

If you look at the circuit of the VR input as given in the schematics section of the manual, you'll see there are other component differences too. If you just fit the components by their position numbers on their bags, you'll likely not have noticed. That schematic should really be updated to reflect the kits supplied today.

[ironwill11]

Thank you for your help. I've set it up and although the tach signal is bouncey (within 100 rpms) it is working. I think I should install capacitor C12 to try to smooth the signal.

Will