Tach trouble after installing a pertronix ignitor

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Sgreg

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I am a new Tiger owner and I inherited a Pertronix Ignitor system in my distributor. The car runs great and no more points maintenance will be needed. The rub is after installing the Pertronix parts in the distributor, the tach now reads nearly double actual RPM. Worked find with the old points and condenser installed. Has anyone faced a similar problem after installing a Pertronix system ??? I have a feeling it has something to do with the resistence in the wire going to the tach but that's only a guess. What is the cure ?? Comments would be appreciated.
 
michael-king

michael-king

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There are a few tech tips about this.. though i thought its normally the MSD/Crane igntions that cause the issues not the petronix.

This option uses a modified tach:

http://members.shaw.ca/tsmit/tachmod/tachmod0.html

To Hall does these mods. You can modify it yourself. The module has a voltage input that the output pulses using a Pertronix distributor module the tach module will sense its current pulses correctly and give you a proper reading.
 
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Sgreg

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Holy Cow, Batman !!! Is it really that bad ??!!! I have an MBA not a degree in EE. I was thinking maybe I have a wire that needs to be moved to a different post but redoing the tach and inserting a module is downright scary to contemplate. Thanks for the help and I hope I can find an easier and less expensive solution. I might even go back to points. Hate to, but I probably drive more by tach than speedometer. It was accurate before the modification I understand.
 
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cadreamn67

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Just some thoughts from left field. I seem to recall that usually the problems with electronic ignitions and our OEM tachs is there is not enough of a pulse signal coming back from the coil to trigger the tach's circuitry. Here it sounds like you are getting two pulses for every one you should be getting. I do not see how it could be relevant, but are you sure you have a correct Pertronix unit for a 8 cylinder and not a 4 cylinder (i.e., Alpine) motor? Just seems strange you are getting twice the number of pulses reflected back through the power wire that runs through the tach to the coil. Were it me, I would have a friend confirm the installation of the Pertronix wiring is correct. Good luck, and please keep us posted on the ultimate solution. We all learn from each other.

Cheers, Gene
 
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S

Sgreg

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cadreamn67 said:
Just some thoughts from left field. I seem to recall that usually the problems with electronic ignitions and our OEM tachs is there is not enough of a pulse signal coming back from the coil to trigger the tach's circuitry. Here it sounds like you are getting two pulses for every one you should be getting. I do not see how it could be relevant, but are you sure you have a correct Pertronix unit for a 8 cylinder and not a 4 cylinder (i.e., Alpine) motor? Just seems strange you are getting twice the number of pulses reflected back through the power wire that runs through the tach to the coil. Were it me, I would have a friend confirm the installation of the Pertronix wiring is correct. Good luck, and please keep us posted on the ultimate solution. We all learn form each other.

Cheers, Gene
Click to expand...

Gene, I like your logic. Makes sense. I did not buy or install the unit. So I just figured the previous owner who was meticulous about maintenance wouldn't screw up that bad. But maybe he did. Worth checking. I am going to call Pertronix tomorrow for a discussion of the problem. I emailed them and did not get a well defined answer.
 
S

Sgreg

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The previous owner said this was a common problem with Tigers and Pertronix ignitions. Since 33 people have viewed this thread and only a couple have replied, guess it isn't so darn common after all. Time to unhook the tach till I have a solution other than a $160 rebuild of the distributor. :D

Hope the Pertronix techie can help !
 
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cadreamn67

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608
Just another thought from the outfield. If all else fails, you can probably still make your current set-up read correctly. You just need to adjust the tach. The tach for the Alpine (4 cylinder) and the Tiger (8 cylinder) have the same electronics behind the dial face. In fact it was not uncommon for Tiger owners in the past to replace their broken Tiger tach with an Alpine one and get one that reads to 7000 rpm. You could also swap the dial faces to retain the OEM look.
The key is a potentiometer (variable resistor) on the circuit board that can be adjusted to calibrate the tach. Thus the Alpine tach, which would normally read twice as fast as it should in a 8 cylinder application, can be adjusted to read properly in a Tiger. Properly is a relative term, since all tachs of that vintage are only really accurate at one point in the rpm range. Most people would calibrate for around 3000 rpm. At other points, it is going to be reasonably close.

Best regards,

Gene
 
S

Sgreg

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cadreamn67 said:
Just another thought from the outfield. If all else fails, you can probably still make your current set-up read correctly. You just need to adjust the tach. The tach for the Alpine (4 cylinder) and the Tiger (8 cylinder) have the same electronics behind the dial face. In fact it was not uncommon for Tiger owners in the past to replace their broken Tiger tach with an Alpine one and get one that reads to 7000 rpm. You could also swap the dial faces to retain the OEM look.
The key is a potentiometer (variable resister) on the circuit board that can be adjusted to calibrate the tach. Thus the alpine tach, which would normally read twice as fast as it should in a 8 cylinder application, can be adjusted to read properly in a Tiger. Properly is a relative term, since all tachs of that vintage are only really accurate at one point in the rpm range. Most people would calibrate for around 3000 rpm. At other points, it is going to be reasonably close.

Best regards,

Gene
Click to expand...

Gene, thanks for those thoughts. That would be a solution for sure. I sort of wonder if my unit guts have been swapped. Food for thought.
 
cobrakidz

cobrakidz

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Did you ever get your tach to work? I have the pertronix and mine is opposite, it reads way too low. thanks.
 
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chirodoc

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Tachometer calibration

Tiger Tom was testing and calabrating tachs at SUNI. I assume he is still doing this at Uniteds or at his shop. Call him !

Edit by Admin Rick: FYI "The" Tiger Tom is User "tigertoms" on this forum. Not registered user tigertom.
 
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Warren

Warren

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Do over

I had a local speedo guy Pauls in Redondo Beach do the guts conversion. I had sourced the info to D.I.Y. on Tigers United or was it the old S.T.O.A,?

Well it does seem to work fine and really retains the original flavor and patina of the car but at $175.00 it was a rare time when I paid to have something done on the car, I could do myself.

The next time I'd go for the Autometer route with the new face by Paul.

I am not sure but the speedo guy told me the white pick up wire that does a loop coil to gauge then back to coil to pulse ignition just does not have enough mojo left due to the resistance.

I still have a little related gremlin when the dash lights are on the tach drops a 1000 rpm or so. I suspect this is a ground problem and since the car hardly goes out at night is down low on the to do and behind the honey do list.
 
hottigr

hottigr

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Warren, you might try 2 loops around of the white pick up wire- that has worked for some.
 
Warren

Warren

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Bruce

I have the white wire and its cute lil connector in the tool box. Since my guts were replaced I have a new single wire which replaces the single white wire loop . Cobrakidz may have this solution , unless you suggest I run another direct lead..
 
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Coolvt

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I think the more common complaint with Petronix is an erratic tac. That's how mine is......at a steady speed, get a constant reading on tac. Speed up and the tac jumps all over the place. Planned to get tac rebuilt to solve problem, but haven't gotten around to it.
Mark L
 
at the beach

at the beach

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In the SCF Tiger I have an electronic Porsche tach with a custom Tiger type face. It never worked too well with the MSD but has been perfect with the Petronix 3.

bt,
at the beach
(but about to tow north)
 
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Moondoggie

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Duke Mk1a said:
In Korea now....be back in December for leave. All I have now is work, golf, running, lifting and drinking soju.
Click to expand...

Is it in that order or can you mix it up a little bit ......... Does your private email still work ??? I would like to stay in touch .....

Moondoggie
 
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