ratty RPM signal from MSD + Racepak????

[entropy]

TFA's lakester has a pretty vanilla set up: NA 383" crate motor + TH350
MSD Streetfire HEI distributor + Racepak IQ3 monitoring the usual stuff. 
We don't really need all the data we collect, but i just like knowing what's going on.

By having good grounds and moving sensor cables away from ign wires, all channels are mostly clean. 
All except RPM...  It's useable (when the scale is exaggerated) but i'm not happy with it.  The dist cap has a "Tach" port which we are using.
My bikes had clean RPM signals so i expect our lakester to have one.

We've tried a shielded tach cable = no change. 
Also tried MSD's GMR inductive pickup (PN 8918) = no change
Talked to MSD & Racepak tech people = very friendly & helpful but no change yet

Next step is to mount an MSD Digital Ignition Control (PN 6425) which MSD tech says should cure our RPM blues AND it's give us a rev limiter.  I wouln't stress over this issue if i didn't have an extra year to get ready for SW/WOS.
I'm guessing that it's me doing my normal dumb azero stuff, but i'm determined to solve this.

Does anyone "out there"  have an MSD + Racepak set up?  Experience?

karl

[kiwi belly tank]

Not with that same setup Karl but have had all sorts of Racepak issues coming from plug wires that I cured with Mallory Pro Shield wire covers.
  Sid.

[entropy]

hey Sid, do you mean this stuff?
http://prestoliteperformance.com/pro-shield-insulated-sleeving.html

i'm a dumbazero, but wouldn't you have to make up ign wires to put the sleeves on???
karl

[NathanStewart]

Noisy tach signals from MSD products is pretty common it seems.  I know that doesn't help you but don't think that you have an unique problem.  We see the same thing with customers using our AQ-1 logger. 

[entropy]

Noisy tach signals from MSD products is pretty common it seems.  I know that doesn't help you but don't think that you have an unique problem.  We see the same thing with customers using our AQ-1 logger. 

Nathan, thanks so much for your info, it does make me feel better to know that I'm not alone.  I often generate my own problems through ignorance and/or lack of attention to detail.
      My pal Randy put an oscillosope on the MSD distributor Tach output and it was not a sq wave, rather it was a burst of sinewaves.  My IQ3 Racepak does generate a noisy RPM from that burst, but i'm told that Racepak is looking for a sq wave.  The MSD GMR inductive pickup i tried also generates a sine wave burst and gave the same noisy Racepak rpm trace as the MSD distributor tach output.
     MSD install sheets say the tach signal of the Digital Ignition Control which i am installing (PN6425) is "a 12V square wave signal with a 22.5 degree duty signal"
I am optimistic...
Karl

[jdincau]

Here is what the tachometer output signal from our MSD6520 ignition looks like on our AQ-1 logger.The Tach Output Terminal produces a 12 volt square wave signal with a 30° duty cycle according to the manual.

[NathanStewart]

There's a chance you're on the wrong wire.  The tach signal should be a square wave and I've verified that it is one on their CDI boxes at least with an o-scope although it's a "dirty" signal.  An AC sine wave sounds like you've tapped into the actual VR position sensor inside the HEI distributor.  I've also personally tested the MSD GMR pickup and while it didn't output a perfect square wave, it did output a good falling edge signal that didn't cross 0v so I find it odd that you're seeing a sine wave out of the GMR as well.  Maybe try putting the GMR on one of the spark plug wires from the distributor to a plug.  Not questioning your buddy's o-scope usage but if he's seeing sine waves on signals that should be square, he may have a probe grounding problem.  

[NathanStewart]

Jim's image is a good example of what the captured RPM signal looks like in the AQ-1 software coming from an MSD CDI box - pretty fuzzy.  I unfortunately don't have a good example of the raw signal to post.   

[entropy]

I'll see if i  can get Randy to reply to this discussion.  I know less than nothing about this stuff.  I'm just in love with my Racepak and want it as perfect as I can get it.  I hope this isn't like"The Birthmark" a story i read in high school

We did get a sq wave from the GMR by putting it around a wire with 9V, tapping it. 

I asked MSD tech which wire to use as source on my specific MSD distributor, he was very clear to use the one labeled B+, which goes from the base of the dist to the cap.  That wire and the tach wire both had a packet-like signal very unlike a sq wave, but I don't think it wend negative

I am very hopeful that my new ign controller (it is CDI) will have a sq wave

[ronnieroadster]

My data system is made by Computech I also have had a huge problem getting a clean ignition signal for data. I tried shielded cable wiring for the tach signal and I also relocated the wiring so its was not near any possible ignition source plus i replaced the plug wires with MSD 8.5 Spiral after doing all that the ignition reading on the screen still looked like a coarse saw blade it was total junk for reading. 
   After being completely frustrated with this problem a final suggestion from Computech to add an MSD Tach Adapter Magnetic Trigger part number 8920 in line with the same source used to operate the tach which always worked perfectly. After adding the Tach Adapter now the tach signal for data is clean the simple wiring of the tach adapter solved the problem. I wonder if it would solve yours?

[kiwi belly tank]

hey Sid, do you mean this stuff?
http://prestoliteperformance.com/pro-shield-insulated-sleeving.html

i'm a dumbazero, but wouldn't you have to make up ign wires to put the sleeves on???
karl

So you have a SBC with no plug wires, ok!
  Sid.

[entropy]

hey Sid, do you mean this stuff?
http://prestoliteperformance.com/pro-shield-insulated-sleeving.html

i'm a dumbazero, but wouldn't you have to make up ign wires to put the sleeves on???
karl

So you have a SBC with no plug wires, ok!
  Sid.

hahahahahahahaha
I am asking you about making up a set of ign wires as opposed to buying a kit, installing the sleeves as ea wire gets made.  I would think that the factory with special equipment would make a much superior set of wires than i could assemble. from components.  If making up a high grade set is routine, then i would like to put it on the list of stuff to do this winter.

BTW:  my googling on protective sleeves talked more about heat protection than noise suppression
Karl

[entropy]

Ronnieroadster,
Thanks a million!
In looking at the MSD instructions, it seems that the tach adapter 8920 works in conjunction with a MSD 6AL ignition control.
Excellent info.  I am 1/2 way through my install of my new 6AL, so if the signal is still noisy after the install, i have a path forward.
Very much appreciated
Karl

[BVCBR]

Karl,

I work at MSD and would be glad to try and help you sort your problem out. You can send me an e-mail jwagner@msdperformance.com

If you are using the TACH post on the HEI, it is not a conditioned square wave. It is just a tap off of the ignition primary side of the coil. It will be a very ugly signal. Some tachometers were built to be able to use that signal with the circuitry internal of the tachometer. Feeding that signal into another device that is expecting a 5 or 12 volt square wave signal will not be happy, as you have found.

The TACH adapter is a possible option, but they can vary quite a bit and may or may not work for certain applications.

The GMR pickup also is hit and miss. It works great on some ignition system, not so much on others. It is a fucntion of the amount of current and duration that determines if it works or not.

Send me an email and we'll figure out the best way for you to get a good RPM signal.

JW

[rtbain]

Really appreciate the comments and suggestions.  Karl already gave most of the information but I can add a bit.

The scope is pretty new to me so the possibility of operator error is large.  It’s a Tektronix TBS1052B.  Probes were calibrated to the scope.  Readings were taken using a good negative source as ground reference (the vehicle is negative ground).  Will figure out how to do screen shots and post later.

MSD Streetfire HEI distributor tach lead had a pretty ugly signal.  While the measuring technique could be off it looked more like an unconditioned signal rather than a probe grounding issue.  But it will be rechecked to make sure.

The GMR inductive pickup (PN 8918) was bench tested using a 9vdc battery and a straight piece of wire.  It produced a clean square wave on the bench.

Once connected to the “BAT” terminal of the MSD HEI distributor (as per MSD instructions) the output of the GMR was read once more.  The signal mimicked the HEI tach output closely.  My thinking is the HEI does not draw enough current to make the GMR operate reliably.  But that is a guess.

The tests will be re-run with pictures showing test set up and scope screen shots.