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Registered
Join Date: Jul 2001
Location: mt. vernon Wa. USA
Posts: 7,738
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Bob, I don't know how I missed this thread.....I've emailed you with a few questions regarding a current project.
regards, al
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[B]Current projects: 69-911.5, Previous:73 911X (off to SanFrancisco/racing in Germany).77 911S (NY), 71E (France/Corsica), 66-912 ( France), 1970 914X (Wisconsin) 76 911S roller..off to Florida/Germany RGruppe #669 http://www.x-faktory.com/ |
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louis
Join Date: Oct 2015
Posts: 3
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Registered
Join Date: Nov 2007
Location: Fullerton, California
Posts: 365
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Does the engine management system provide a tachometer signal?
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Registered User
Join Date: Jun 2011
Location: Darien, CT
Posts: 56
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Hi,
I have just replaced a 3-pin CD ignition with a MSD ignition and Tach Adaptor P/N 8910 on my 69T, but I am getting quite a lot of needle bounce. Is this something your unit can fix or does it sound like the MSD part is defective? Thanks, JP
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69 911T 2.4S |
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Registered
Join Date: Nov 2007
Location: Fullerton, California
Posts: 365
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Common problem with the MSD adapter driving these old VDO tachs. You should use the discrete tachometer output from the MSD and send that to my TACH-ADAPT unit. It will then convert that low voltage square wave tach signal to one with a narrow high voltage leading edge that is needed to trigger your '69 tachometer.
Last edited by Bob Ashlock; 09-09-2018 at 02:13 PM.. |
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Registered User
Join Date: Jun 2011
Location: Darien, CT
Posts: 56
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Thanks Bob. I don't quite understand the point of the msd tach adaptor then. Or was it designed for the later tachs that don't need a high voltage pulse...but if that is the case isn't the low voltage tach signal what the msd generates in the first place? Confusing issue.
In my old system, the tach was driven by the high voltage CD output from terminal A through the Intermediate Unit. I guess you are saying the msd tach output won't work with the Intermediate unit. Talking about tachs, I have a question on the RPM Transducer which is not used with carbs except for the 911T USA version. I don't have the throttle valve compensator system anymore so the RPM box is not doing anything, right? JP
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69 911T 2.4S |
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Registered
Join Date: Nov 2007
Location: Fullerton, California
Posts: 365
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As I understand it, the MSD adapter is basically is a toggled inductor that puts out a pretty high voltage spike with some undamped resonating pulses. Some tachs respond to those extra pulses and bounce around. The old VDO tachs are sensitive to this. Your 1969 VDO tach wants to see ONE solid high Voltage pulse, greater than around 80V. (Later VDO tachs from August 1971 will respond to the low voltage MSD signal.)
The intermediate unit circuit (which shapes the CDI discharge signal) will not work if it is connected to the coil (as it was from the factory) because the coil signal now has multiple pulses from the MSD. The unit I make takes the low voltage MSD tach signal and provides a nice single, narrow pulse that the old VDO tach likes. The RPM transducer (aka speed relay) modulates a fuel control solenoid on the Zenith Carbs. (And the MFI) Essentially, shutting off fuel to the idle circuits when coming of throttle until rpms drop into the lower ranges, somewhere around 1500 (off the top of my head). A good thing to avoid overrun rich mixture that contributes to smog and possibly some popping in the exhaust. If the fuel control solenoid is missing then the transducer is not providing this benefit. |
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Registered User
Join Date: Jun 2011
Location: Darien, CT
Posts: 56
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I discovered some interesting things in preparation for installing your system which I ordered from our host. The pro who installed the msd tach adapter had routed the points signal through the Intermediate Unit to the tach wire which had been cut, in other words, open circuit. How the tach worked at all I don't know. I then tried putting the points signal direct to the repaired tach line and it works, but not 100% so I am keen to compare with your TA. I will keep you posted.
JP
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69 911T 2.4S |
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Registered User
Join Date: Jun 2011
Location: Darien, CT
Posts: 56
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Tach Works Great
Hi Bob,
Well, I am pleased to confirm that my tach is now working correctly. Thank you for providing this valuable product. Don't know what is in the MSD Tach box but it weighs a ton compared to your neat little device. For the record my VDO Tach had a date stamp of 8/67 and a "1" at the tach connection, so definitely one of the older models which need a higher voltage pulse to work. At the same time I cleaned up the electronics panel now that I don't need the Intermediate Ballast Unit and also the RPM Sensor since the throttle valve compensator disappeared some time ago. Finally figured out what those two modules were for. Here is pic of installation ![]() I'll be sure to pass on the good word. JP
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69 911T 2.4S |
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Registered
Join Date: Nov 2007
Location: Fullerton, California
Posts: 365
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Thanks JP! Glad to see you got everything working properly. I have over 1000 of these units now in service.
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Speed Metal Army General
Join Date: Apr 2012
Posts: 408
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Ive had one for a few years. Good stuff!
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Almost Done
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can you develop one for speedos :-)
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Registered User
Join Date: Aug 2008
Location: Mallorca 9treffen
Posts: 316
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I need one of this !!!
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Registered
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I have Bob's TachAdapt too, I converted to the MSD Street Fire and lost use of my tacho after the install.
Pleased to say my tacho works again with this little device, thanks Bob!! |
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Almost Done
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now if someone could invent a similar box for the speedo signal from the transmission, i would be a happy camper...
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914-6Werkshop
Join Date: Dec 2009
Location: Wilmington, DE
Posts: 3,110
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Get a gps antenna.
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All used parts sold as is. |
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Almost Done
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How does that gps unit work? Any specific supplier?
Tx |
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Registered
Join Date: Oct 2007
Location: East Coast USA - Tysons, VA
Posts: 1,216
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Testing a tach
Hi, Bob. I have a 1972 VDO 911 tach that doesn't seem to work. I'm not sure if is the tach itself or the car. Is there any way to simply bench test a VDO tach to see if it even works before spending more money on a separate device? Any advice will be highly appreciated.
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Almost Done
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your best off getting professionally tested and adjusted at same time..you have lots of choices of shops on west coast..your lucky
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