MSD/tach query

[Alan L]

I don't know if the brains trust can answer this , but I have enough faith to post it.
I have a Leask MSD switch on my WUR. I just installed a 2nd MSD switch to run the CSV at high revs in case I am still short of fuel after tweeking the 007 Fuel head.
But it seems the tach circuit can't support 2 MSD switches, tach and shift light. Anyone tried this path? My tach drops out with both MSDs hooked in. Either one of the MSDs is fine, but both = no tach.
I am about to contact MSD to see if there is another option, but based on response to last query (nil) I am not holding my breath.
Regards
Alan

[mark houghton]

Hmmm....must be some kind of impedance thing (I'm absolutely no help, I know). One would think you could daisy chain two switches, but...?

I suppose you could use just one switch (the one on the WUR) and let it actuate the cold start valve as well, but your rpm set point probably wouldn't be where you wanted it (probably looking for around 6k+ for the CSV actuation, and somewhere around 4500-5000 for the boost enrichment delay). So, scratch that idea!

[Tonger]

I also have a MSD RPM window switch and the tach display can bounce around sometimes. The problem is likely that the MSD box has a relatively lower impedance on the input side and the CDI box cannot drive enough current to support the MSD boxes and the tach simultaneously.

My fear is that the MSD boxes will stop working and cause the WUR to become overly rich. For this reason I purchased (but haven't yet wired) a Tach Adapt that I will use to drive the MSD rpm inputs. I called the guy that developed this and the input side of Tach Adapt does not require much current. I would hook the output of the Tach Adapt to both MSD rpm inputs.

Tach Adapt Website

The Tach Adapt guy was really helpful over the phone, good luck!

[Alan L]

Originally Posted by mark houghton

I suppose you could use just one switch (the one on the WUR) and let it actuate the cold start valve as well, but your rpm set point probably wouldn't be where you wanted it (probably looking for around 6k+ for the CSV actuation, and somewhere around 4500-5000 for the boost enrichment delay). So, scratch that idea!

Hi Mark - precisely - I am trying to minimise the fuel dump, not exacerbate it. Another issue is the MSD switch is rated for 1.5 A. The CSV alone is drawing 2A.
Thanks for the link Tonger - looks useful. Will follow it up.
Alan

[Alan L]

Just ordered a tach adapter from Bob. As the forum states in the link from Tonger - the guys service is awesome. Had a reply and Q/A session with him in no time. (Whats the bet I don't hear back from MSD)
He is not sure if it will work - never used it this way - but money back if no good.
Can't ask for more than that. Will keep you posted on this and the CSV bit if I can get it working as intended.
The brains trust wins thru again. Thanks guys.
Just got my engine running after top end tear down, heads replaced etc, and it fired and purred on first turn of key, and no leaks. Yahoo. Racing next w/end.
Alan

[JFairman]

Summit racing digital programmable rpm switches are half the price of the analog MSD ones that look like they were designed in 1970 by a teenager and work much better. No stupid rpm "pills" or any of that obsolete crap... you program them.

I have two of them, one for the same thing you're doing and one for a shift light and there's no tach problems. Being digital they probably steal less of the skinny black/purple wire tach trigger signal than the old MSD ones.
They do what they do by grounding whatever you hook up to them at the rpm you program.

[Alan L]

Thanks Jim. If the current attempts don't work, I will follow that path. Sounds hopefull. You need to understand we don't have any of that stuff available here in NZ - it is all internet order - even the MSD single step rpm switches. So sometimes I just have to take what I can source. What I could get was a 2 stage MSD switch unit. I figured it must work as a single stage at least - I only wanted a bit to activate the CSV. Wrong, as far as I can figure . Doesn't look like it can even do that. It will be F/S soon.
Regards
Alan

[JFairman]

If you use an rpm switch like the Summit Racing one that grounds devices at your programmed rpm to open the cold start valve you would have to wire the rpm switch to trigger a small 12 volt automotive relay. Then wire the relay so it sends 12 volts to the CSV when the rpm switch triggers the relay.
Around here generic 12 volt relays are less than $10. Most auto part stores have them and I'm sure Summit has a selection of them.

That way the CSV will continue to work as it originally did and you will also be able to trigger or open it with the rpm switch.

FWIW, here's a couple programmable rpm switches Summit sells. They have a RPM window switch too.

Summit Racing® RPM-Activated Switches with Digital Readout SUM-830450-1 - Free Shipping on Orders Over $99 at Summit Racing

Summit Racing® RPM-Activated Switches SUM-830449-1 - Free Shipping on Orders Over $99 at Summit Racing

[930/66]

I hade a Problem with the non digital RPM window Switch from MSD in combination with my Zeitronics ZT-II, tach was good but the ZT-II incorrect display.



I could solve the problem with the digital MSD window switch:



I remove the digital window switch in the next time, my new turbosmart ebc can make that job.

[JFairman]

Here's the digital rpm window switch Summit Racing has.

Intellitronix RPM-Activated Window Switches N3210 - Free Shipping on Orders Over $99 at Summit Racing

I never used one but it looks like a good programmable one and the price is lower than the others.

[mark houghton]

Originally Posted by Alan L

Thanks Jim. If the current attempts don't work, I will follow that path. Sounds hopefull. You need to understand we don't have any of that stuff available here in NZ - it is all internet order - even the MSD single step rpm switches. So sometimes I just have to take what I can source. What I could get was a 2 stage MSD switch unit. I figured it must work as a single stage at least - I only wanted a bit to activate the CSV. Wrong, as far as I can figure . Doesn't look like it can even do that. It will be F/S soon.
Regards
Alan

That will teach you to live in the land of Oz. In the opulent U.S., we get pissed off if we don't get everything we think we deserve....which is why the rest of the world doesn't think too well of us. Thank God for the internet....you can get what you need eventually.

[Alan L]

Originally Posted by mark houghton

That will teach you to live in the land of Oz. In the opulent U.S., we get pissed off if we don't get everything we think we deserve....which is why the rest of the world doesn't think too well of us. Thank God for the internet....you can get what you need eventually.

Nope - not even. Head south from Oz then hang a turn East. Eventually you get to NZ. Next stop, South Pole.
Got a reply from MSD - to tell me the 2 step rpm module I bought is actually a rpm limiter. Nice. I have the instructions and doesn't matter how many times I read them, I struggle to find that statement. Says 'provides the ability to switch between 2 different rpm modules'.
Never mind, Bob's tach adapter is on the way.
Regards
Alan