Stock tach doesnt work, but tach works on SAFC

[ShadeTreeDSM]

1990 gsx My stock tachometer doesnt work and hasnt worked since i got the car over 2 years ago and its driving me nuts, trying to figure out why it doesnt work, tried alot of things, searched the forums, searched google. I have a SAFC and its showing my rpm's properly. So why doesnt my stock tach work if the safc is? The noise filter isnt connected and still i get a reading from the coil pack to make the SAFC get a reading. ive tried another cluster, i do have a 92-94 power transistor and coil pack in my car, i was looking at the schematics for the tach and i see that there is a TACH connector on the firewall on our cars, i was wondering could i get a tach signal from that ? I need some input on how to get this working, i know people switch from 90 to 91 ecu's, but i dont want to do that, my 90 ecu is already epromed. and i dont see why you would have to switch the pins to make the tach work anyways, pins 6 & 14 control idle speed and maf signal so what does that have to do with tachometer ? Mitsu doesnt make noise filters anymore, can i get a noise filter off any car? HELPPPPPPPPPP

 

[williamsoa]

After reviewing multiple links; I think the noise filter is bad. I have the same problem with my car; I am getting noise form the coils and when I taped into B-60 white wire, I am getting no signal. This week I am going to see if the dealership sells noise filters; if they don't sell them any more, I guess I am going to the junk yard.

 

[donniekak]

Do you have a 1990 ecu?

 

[1990AWD]

it's almost guaranteed to be the lack of a noise filter. go to a wrecker, get one, plug it in and mount it onto the intake manifold by the ground wire.

 

[tsi1991awd]

OK I'm confused....you say the noise filter isn't connected (which it needs to be for the 90 tach) but then you go to say you have a 91+ coil pack in the car. With the 91 coil pack, your tach won't work whatsoever without modification to the ECU, since you have a 90 ECU. If you have a 90 coilpack and PT in the car, get a new noise filter and ground it to the intake manifold stay or on the hole at the back of the manifold. Noise filter is the problem 90% of the time. But as I said, if you're using the 91+ coil pack, it won't work. Go to DSMChips and see what needs to be done to get it working.

 

[williamsoa]

I have an AEM stand-alone. 1990AWD is on point. I am going to the J-yard today and post my results this weekend. The more I think about the problem I do think it is a bad noise filter since I am not getting a signal from the stock tach wire, my dis-2 didn't work, and I am getting noise from my coils.

 

[MattUnderwood]

Okay maybe I am just an idiot, but what are we calling the "noise filter" is it the like 2 inch metal piece that connects right at the intake manifold and then has a plug that I believe goes to the knock sensor? If so then thats what is wrong iwth my car as well, I've just been going by ear and by ecm link for my tach.

 

[williamsoa]

No, it is not the knock sensor. Yes it does have a connection that is routed underneath the intake manifold; the noise filter looks like a metal rectangle (underside filled with a black epoxy) that is bolted to the support underneath the manifold. The support has the metal hose junctions for your purge hose to your canister and the hoses that connect to your throttle body.

 

[MattUnderwood]

No, it is not the knock sensor. Yes it does have a connection that is routed underneath the intake manifold; the noise filter looks like a metal rectangle (underside filled with a black epoxy) that is bolted to the support underneath the manifold. The support has the metal hose junctions for your purge hose to your canister and the hoses that connect to your throttle body.

No I didn't mean it was the knock sensor, I said I thought it plugged into its connector but wasn't sure. But I was thinking of the right piece. But this is the piece that fixes the tac issue?

 

[williamsoa]

I will find out this weekend when I replace it . . . if I can find one in the local junk yard.

 

[MattUnderwood]

I gotta go find one at a junk yard or maybe go without one for a few days until I get paid and get one from the junk yard. What did cars past 90 do instead of having the noise filter? Like where did they install it or what happened?

 

[williamsoa]

After experimenting and swapping out the noise filter. This is what I found out. . . that didn't solve the problem. After re-reading the service manual I found out that in order to read the pulses off of the B-03 (noise filter connector) or A-54 (engine speed adjustment connector) only the computer and standard tach can read the signal because the signal is coming off an OR gate. After market tachs require you to tap directly to the (-) side of the coils for the signal which is either the yellow/green or yellow/black wires coming off the coils. I plugged my tach into both connectors and could not pull a signal; I am assuming that the signal comming off these connectors is 5v square wave vs. 12v off the coil. IF you wanted to pull the same signal going to the ECU you can tap into the #2 connection of the noise filter because it is the same signal. You can test the signal coming out of these connections with a fluxmeter-type tachometer. It is similar to a multimeter that mesures the pulse coming from the coils. I hope this explanation helps.

 

[Colt4G63 also]

You guys are running a '90 tach, so you should be getting your tach signal from the "Tacho Interface" via a noise filter.

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The "Tacho Interface" comes mounted directly to the '90 ignition coil, and is a little box that looks like this. The 90 tach absolutely won't work without it.

You can still run your PT's tach signal to your '91 plus ECU directly, but your tach want's to see the signal from a '90 style coil pack, via the metal filter mounted on your IM. The '90 coil has a square four pin plug, instead of your '91+ style triangular 3 pin plug.

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[DIRQUIN]

OK, I have searched a lot. Cant get a strait answer. I have a 90 gsx. Using a 91 + ecu. Without changing the cluster, what can i do to keep my cluster and still have a tach? It doesnt work properly now. Bounses all around and as soon as i touch the pedal it drops to 0. Help.......

 

[DSM_IKE]

I have the same issue with mine as well.. I have changed the cluster with no help. Im not sure if the coil pack was ever changed or if i even still have that noise filter on mine.. Ill do some looking tomorrow though and find out.