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Tachometer jumping when off throttle
Hi! '94 Tracker, 1.6 TBI:
I've been playing with a programmable ignition module from JayCar. I run out of this into a CDI module from the old days ('74 maybe). When I first put this in, it ran fine, but I noticed the tachometer would stutter when I let off the throttle (coasting). When I stop, it would be smooth. It's gotten to the point the tach stutters while driving, and the engine's cutting out!
My question, where does the tach get its' signal?

The distributor module is putting out a 5V P-P square wave. That normal?

This programmable ignition has this signal and a vacuum line. You can program the advance/retard on a 15X15 matrix of Vacuum and RPM. The output of this goes straight to the CDI, and the CDI to the coil primary. It's a 300V pulse from the CDI.
Yesterday the tach and vehicle ran fine. Today it quit on the street and would only crank. I think the CDI quit, but would that drop the tach? Is there something sensing the coil output, like an aftermarket tach would attach to the switching leg of the coil primary? I have the output of the igniter disconnected from the coil. I know if the ECU or whatever doesn't see the distributor signal somehow, the injector will not work.
I disconnect the CDI and connect the igniter to the coil -, and the + to the coil +, like stock, and it works. I don't bother disconnecting the JayCar module from the dizzy.

Note: When this setup is working, gas mileage goes up, pinging is gone, and response is better.

Another note: When the igniter 'fires' the spark, it's the release (positive going edge) on the coils' negative that makes the spark. This CDI puts out a negative 300 volt pulse. Could that be the problem? Where is the noise suppressor connected?
no idea why you are doing this?? (slept 3 nights ,woke and i think, your EGR is dead, missing , and you are trying to hide this fact>?)
I have no clue as to what is missing on this engine>? (from stock)
no idea at all how you wired CDI up. make a diagram.?
no idea what model, Jaycar box you have they have many.
zero, inputs on that..
I can say no side kick needs such a device. ever. (unless turbo'd or force induction or other wild modifications to engine and mode of combustion)
yes, 5vdc square wave is the CMP. in distrib. 100% normal , have the scope photos, all sensors. (that swing)
the CMP is an open drain (collector) hall sensor, with the PULL-UP resistor in the ECU side, to 5vdc, (near) (cmp runs injection timing and spark , and is not optional)

deleted, i deleted my guessing.. what is there and reasons for doing all this.
(all non stock guessing>?..gone.)
i can't help you with out knowing what you have now and where you going with it and why do this? (my guess engine is missing some major parts, like EGR)

warning , that 300 volt CDI pulse is very bad for any stock part on that car. ECU and all other related parts. igniton coil, ignitor, , cmp, etc.
sorry, left out a key fact....
Pinging #1 cause is a dead EGR
the EGR must work in this engine, if not, under load it sure can PING like mad.
but for the EGR to work the CAT must be in-place or the EGR modulator goes dead.

the EGR lowers combustion temps greatly.
it keeps exh, valve cooler too.
and better MPG. (tad)
and with full advance , more power.
the ECU is tuned perfectly for a working EGR.

all G16's ping if the EGR is dead,
under load. (event timed perfectly)
the EGR stops that and stops the hug NOX pollution, ( in fact this is how VW just got in trouble, for fibbing on the NOX)
some version (not in USA) there may be no DTC code 51. warning you of dead EGR, so just PINGS as your clear warning..
all ours give 51, or P0400 (1996+)
and some JDM engines, have no EGR at all.. and a matching ECU.... this is the hard way to defeat EGR but is illegal here.. just saying this to be complete, EGR wise.

ping list:
EGR dead or weak. (cat mission or rod'ed out , blown out,,etc)
head milled way too much causes huge CR increases.
huge carbon build up on top of piston and or combustion chambers (caused by running in limphome mode)
Timing way off on cam or spark (usually this retards, due to cam belt slip so....?)
crank pulley marks off, (internals slipped)
engine running lean (lean likes to ping) nice ring to that. (this and mix of above)
does this help?

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