1G 90 Tach problems, getting angry!

[NeMiZiS]

Well I have jumped on a couple of different threads, about this same subject.
But I finally decided to start my own, because not every problem is the same.
I have replaced the noise filter.
Got one from Mitsubishi graveyard.
Just put in a new 90 5 speed cluster, that is in working order.
Still no tach, now I'm assuming the only thing it could be at this point is the tach filter?Which I'm confused about.
The tach hasn't worked since I got the car, except one time the power transistor got unplugged and after I plugged it back in, the tach worked for about 35 seconds?WTF
So what should I do next?
Replace this tach filter too?
I just don't want to run an aftermarket tach, unless I absolutely have too.
Thanks in advance...

 

[banishedmunk]

Assuming this is on a 90 car. The tach adapter is on the coil pack you may want to try another coil pack now if this is in a 91+ car with 90 components then there are a few pins in the ecu that must be switched pin 6 and 14 to be exact.

 

[NeMiZiS]

Yes it is on my 90 talon tsi.
I guess I'm going to buy a new 90 coil pack.
It will have the tach filter built in?
I was told when I bought the car it had a different motor.
Possibly it doesn't have a 90 coil pack on it.
If I just go to the parts store, can I get a 90 coil?
Or will they try and sell me a 91-94 style?

 

[steve]

The thing on the coil pack isn't a tach filter but the tach gate, it's the source for the tach signal, gating the outputs of the power transistor together. So when the coils are firing you should see a pulse train from it all the way back to the gauge and ECU.

If you have an automotive multimeter that reads RPM you should be able to make sure the signal is being generated and trace it back to the gauge. If you don't, perhaps the best you can do is check the wiring for continuity end to end and swap parts.

 

[NeMiZiS]

Ill check to see if my meter read RPMS.
If it does, which wires on the coil pack should I be testing for a reading?
At this point I don't care if I just have to buy a new 90 coil, to make it work.
Thanks for your help so far, I really appreciate it.

 

[steve]

If your asking me which wires I have to assume you don't have the wiring diagram and what you've done so far is just swap parts.

The tach signal on a 90 is pin 3 on the 4 pin coil pack connector, the white wire.
It runs to pin 2 on the noise filter, which also runs to the ECU pin 109.
Pin 1 (also white) on the noise filter runs to the gauge cluster for the tach and the body of the noise filter is grounded.

 

[NeMiZiS]

Well I do have a Chilton's and a Haynes, they probably have the wire diagrams in them.
I honestly didn't even think to look.
I'm just so used to getting on Tuners, for my info.
I really do appreciate your help.
I don't have a meter that is specific for automotive, so it doesn't have a RPM reading.
But I'll try to get a hold of one.
Thanks again, for all of your help.

I'm going to take a look this weekend, I'll get back and hopefully get it figured out!

 

[NeMiZiS]

OK well I went ahead and replaced the coil with a brand new 90 coil pack.

New coil, new gauge cluster and new "used" noise filter.
Still no tach!
Now I'm going to get a hold of a Meter, that can read RPM's.
Thanks for the help so far steve, I'll post back when I can get a reading on the wires.

 

[white92talontsi]

Are you 100% sure that you have a 1990 Instrument cluster in the car?

Also since you said it did work one time when you unplugged and plugged the PTU try wiggling the wires at it and have someone watching the tach at the same time to see if it tries to work.

 

[NeMiZiS]

Yes it is a 90 cluster, the MPH goes by 5 increments.
I will try wiggling the wires at the PTU and have some one watch the tach.
I'm going to really check out all the wires too, make sure nothing is damaged.