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1G Tach Question

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So I realized in order for the circuit I built to NOT fire all four spark plugs at the same time I needed to add some diodes. I also figured I'd make the diagram a little clearer. So in this diagram the ground on the left represents pin 54 on the ecu, the ground on the right represents pin 55, and the ground in the middle represents the output to the tachometer. The switches represent the ecu actually switching the coils on.

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and here's what it looks like with one of the switches closed (note the red LED is off)
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Why are you tying the 2 gates together? Shouldn't they be driven independently by the ECU pin 54 and 55?
 
@1990TSIAWDTALON and @19Eclipse90

Marty, Brian sent me this photo from the 1990 FSM. It's our answer to what's inside that tach noise filter module - the diagram on page 8-71. It is just a resistor and a capacitor configured as a low-pass filter like I drew here in post #43.

One leg of the capacitor goes to ground. So all we need to do now is measure the values, for which I guess we would need a known good one to measure! But we should be able to measure it the same way as in post 43, where the wire end "3" is the leg of the capacitor that goes to ground.

If I were to make one at home I wouldn't try to put it in a metal case. I would probably wrap it up in self-fusing silicone rubber tape (X-Treme Tape for example) and have the 3 wires sticking out of it. The #3 wire would go to ground, the other 2 would make the connections to the harness. I'd probably bolt the ground wire to the firewall anyplace handy. Or whatever!

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Since many have been known to have there eyes roll back into their heads at the first glance at a schematic I've zoomed into the Noise Filter and where the signal comes from the Tach Gate on the coil and splits, into the filter and on to the cluster, the other branch runs directly to the ECU.

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I am so thankful that we have members on here that don't just leave stuff hanging, they finish the thread with solutions. That is what is so good about our group, you guys (and gals) all ROCK!!!
 
Just thought I would post this for anybody who has one of these little 1990 "tach filters" out where you can get at it with a multimeter that measures capacitance. This is the thing Marty showed in post #4.

This is how your meter should react to it, if the thing is a resistor and a capacitor as proposed in post #21.

You would make these 6 measurements: 3 resistance, and 3 capacitance.

I did this with a known resistor and a known capacitor put together as shown in the diagram, and wrote in what the result of each measurement was.

So anyway, this is how we could probably find out what's inside without taking the thing apart and probably wrecking it. I would measure mine but I can't even see it - hiding somewhere under the intake manifold I guess.


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Following this as a guide, here's the measurements of the units I have on-hand, most I have verified to function in my vehicle.

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Sample #3 (in the below picture, it is marked 7 and you can see the marking on the top face) is a bit different than the rest so I removed it from this list. It showed a creeping resistance between pins 1-2, but the same readings for all other columns. I think this is the only one I haven't trialed in my car and not real certain where I got it from. Its case is marked / stamped with "HMC" (presumably, Hyundai Motor Company, I believe this one came from a 1990 Hyundai Excel) and had some printed on lettering that disappeared when I tried to clean the unit up.

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From this list, I know for a fact that samples 1 and 2 are from 1990 DSMs (right-most, with longest leads). Samples 4, 5, and 7 (left-most, with brackets) were from either late 80's / early 90's model Colts.

So nominal resistor value is likely 2200 ohms and I'd have to say 2 nanofarads for the capacitor based on these measurements.
 
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Following this as a guide, here's the measurements of the units I have on-hand, most I have verified to function in my vehicle.

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Sample #3 (in the below picture, it is marked 7 and you can see the marking on the top face) is a bit different than the rest so I removed it from this list. It showed a creeping resistance between pins 1-2, but the same readings for all other columns. I think this is the only one I haven't trialed in my car and not real certain where I got it from. Its case is marked / stamped with "HMC" and had some printed on lettering that disappeared when I tried to clean the unit up.



From this list, I know for a fact that samples 1 and 2 are from 1990 DSMs (right-most, with longest leads). Samples 4, 5, and 7 (left-most, with brackets) were from either late 80's / early 90's model Colts. I'm not sure which of Sample 3 or Sample 6 came from a 1990 Hyundai Excel, but one of them did.

So nominal resistor value is likely 2200 ohms and I'd have to say 2 nanofarads for the capacitor based on these measurements.

Cool! Wow that is exactly what we needed. Especially good for having several examples of the module and getting the same result from them.
Your meter giving an "OL" instead of just creeping on the Resistance 1-3 and 2-3 measurements, I think is OK. The idea is that it's invalid to expect a single stable number for resistance there. So I guess it's just a matter of how your meter tells you that it's an invalid measurement. Right? Or wait, since the capacitor is so small (it's a lot smaller than the one I used in post #43) it would "fill up" very fast and then you'd have infinite resistance to DC, therefore "OL".
I'm so glad you did this! Now it would be cheap and easy for anybody who wants to build their own, to do it.
 
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