Bouncy tach w ms2 / seq shift light

[revolutionary]

Part one; Since we put MS on Lewy's 240z (w SBC - thanks again Scott for the on-track tuning) last year, the tach hasn't been acting right. We ran the ignition back on the MSD for a while and it did fine but running with MS controlling spark the tach is jumpy as hell. It is on the neg side of the coil so I'm guessing it is freaking out the timing as well but I haven't put a timing light on it to check. What do you think? Noise? Something not wired right? It seems to run aok.

Part B; We are going to install a sequential shift light and the 'guru' that has been fiddling with it for the last two months can't seem to figure out some way to make one work. I haven't looked into it yet but figured there may be someone on here that can give me a head start before I jump in.

[CDMBill]

Re: Bouncy tach w ms2 / seq shift light

Which ignition box is it? I'm driving my shift light (Stewart Warner Ultra something) straight from the ignition box tach output (the offroad version of a 6AL) and factory tach with an MSD Tach adaptor. The EMS handles all of the spark control as the distributor is locked out. Both run smooth and track with the MS software "gauge" on the laptop. I think good clean engine grounds are key to low noise and a clean signal.

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

Part one; Since we put MS on Lewy's 240z (w SBC - thanks again Scott for the on-track tuning) last year, the tach hasn't been acting right. We ran the ignition back on the MSD for a while and it did fine but running with MS controlling spark the tach is jumpy as hell. It is on the neg side of the coil so I'm guessing it is freaking out the timing as well but I haven't put a timing light on it to check. What do you think? Noise? Something not wired right? It seems to run aok.

Part B; We are going to install a sequential shift light and the 'guru' that has been fiddling with it for the last two months can't seem to figure out some way to make one work. I haven't looked into it yet but figured there may be someone on here that can give me a head start before I jump in.

Where does the MS get it's tach signal from, negative side of the coil? that's a noisy place to get a signal and there are a ton of suggested mods to do this... but if you're controlling spark, then you are likely getting signal from the VR sensor in the distributor? or is it a halls sensor in the distributor?

give me a little more detail and I'll help you figure it out. Tach noise is a common problem but one that usually can be solved pretty easily.

-scott

[revolutionary]

Re: Bouncy tach w ms2 / seq shift light

CDM, the MS box is controlling spark, MSD is not in the car.

It is getting tach signal fron the neg side of the coil.

Ignition signal is coming from a stock MSD pro billet dist.

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

CDM, the MS box is controlling spark, MSD is not in the car.

It is getting tach signal fron the neg side of the coil.

Ignition signal is coming from a stock MSD pro billet dist.

I am confused...

the MS can't be controlling spark if it's getting it's tach signal from the coil... or are you saying the car's tachometer gets it's signal from inside the car?

First concern is the MS tach signal shown in megatune. If that's bouncing then we have something to worry about. If it's just the tachometer in the car, that's less to worry about. Let us know!

[revolutionary]

Re: Bouncy tach w ms2 / seq shift light

The tach is getting signal from the neg side of the coil. The MS is getting signal from the dist.

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

The tach is getting signal from the neg side of the coil. The MS is getting signal from the dist.

gotcha, so is it the tach in Megatune, or the tach on the dash, that's wandering? sorry I am so confused rofl.

[Matt Cramer]

Re: Bouncy tach w ms2 / seq shift light

Could you take a data log and check it for a bouncy tach signal there? You can upload it here or email it to me if you need some help checking it over.

[revolutionary]

Re: Bouncy tach w ms2 / seq shift light

The tach on the dash is bouncy. I didn't datalog the signal at the MS but when Lewy gets back from Cali (helping with some Pinks car) We'll check into that. It doesn't run like it's bouncy though!?!?!?!?

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

The tach on the dash is bouncy. I didn't datalog the signal at the MS but when Lewy gets back from Cali (helping with some Pinks car) We'll check into that. It doesn't run like it's bouncy though!?!?!?!?

Which coil (and ignitor?) are you using? is this an HEI config?

[revolutionary]

Re: Bouncy tach w ms2 / seq shift light

MSD Blaster 2 and a pro billet msd dist.

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

Are you using an MSD box, or a VB921 ignitor - what's between the MS and the coil?


I'm thinking you might have your spark output inversion incorrect... or dwell settings, if you are using a dumb ignitor.

[revolutionary]

Re: Bouncy tach w ms2 / seq shift light

No msd box in the car at all. The ms ALONE CONTROLS spark. sorry for the caps lock.

[dieselgeek]

Re: Bouncy tach w ms2 / seq shift light

No msd box in the car at all. The ms ALONE CONTROLS spark. sorry for the caps lock.

Triple check that your dwell settings and "inversion" are correct.


Good way to test the spark output inversion is to disconnect the coil signal wire from the MS, power it up but engine not running, the signal wire should NOT be providing a ground. Check it with a small test light real fast (don't sit there with the light on for more than a second or so, Matt Cramer is probably going to get on here and say "you told him to do WHAT?" lol)

If you want to be more proepr make a simple LED tester - a simple LED and a small resistor - and test it that way. If the light comes on, then you know the coil was trying to charge when the engine isn't running, thus the inversion output needs changed in "spark settings"


The next thing I'd check is that you have the right dwell for that coil setup. Matt Cramer, distributor 7 VB921 guru, can you help?


Also rev, for what it's worth, in this case I'd usually recommend an MSD 6A box, that way you don't have to worry about dwell and burning up an ignitor or coil. And you have a nice stable tach output,

-scott

[Matt Cramer]

Re: Bouncy tach w ms2 / seq shift light

I'll need a copy of the MSQ file and a data log, but I'll be glad to help. Email me them at [email protected] if you don't have a place to host them.