Tach. not working Please try to help

[icedearth15]

Hey, I need some help for a wiseman, or someone who has ANY idea of how I fix my problem. My problem is I have a 5-Speed, and a tach (who would have guessed) and ever since I had the car the tach has never worked, but will sometimes jerk around (I mean not very often at all). I have tried to install a autometer tach with no sucess...tried taping the RPM source at the ecu and the coil pack....I didnt find any signal. So is there a part by the coil packs that has gone bad...I have no idea where the RPM signal comes from. If someone can lead me into the right direction I would really appericate it...after all tuning the car with an AFC and no tach cant be fun.

 

[Lordpaxin]

The actual RPM junk is located inside the Power TR unit. the black square connector on the back of the intake manifold.
its says Power TR Unit on it, and have a wide plug, wtih about 4-6 wires commin out of it.

my JDM had a seperate cirucuit for the RPM signal, and it was a smaller black square on the coil pack itself.

try borrowing a TR unit from a friend. and see if it will chance anything.
I have the JDM tr unit, but it work work for you.

 

[Mike1992]

could be TR Unit, Coil Pack, Or maybe you got a wrong year gauge cluster 90's wont work in 91-94 and vice versa, my tach didnt work for a while until i swapped my cluster out.

 

[icedearth15]

I will try swapping out the power TR Unit. Before I bought the car the past owner had a 1991 6-bolt put in for some reason (I have a 1990), I guess he thought because the valves where bent the whole engine was garbage. So I will also try swapping the gauge cluster out....any other suggestions would be great.

 

[Mike1992]

when he did the swap did he change the engine wiring harness also?

 

[icedearth15]

I couldnt tell you.....a shop did the swap for him. He didnt know much about the car, and seemed like an ass to me. I am going to swap out the power tr unit with a buddies and see what comes out of that. Thats for the help

 

[Morphius]

Originally posted by Mike1992
could be TR Unit, Coil Pack, Or maybe you got a wrong year gauge cluster 90's wont work in 91-94 and vice versa, my tach didnt work for a while until i swapped my cluster out.

The clusters are identical. You simply had a bad cluster.

 

[Mike1992]

you are wrong my friend, the tach signal is different or something in the setup between coil/tr unit from 90/91-94. I tried 3 diff. 90 clusters and was proved to be what i read was right. So i ended up buying a cluster outta a 91 laser off ebay and things all worky now!

 

[Morphius]

Originally posted by Lordpaxin
The actual RPM junk is located inside the Power TR unit. the black square connector on the back of the intake manifold.
its says Power TR Unit on it, and have a wide plug, wtih about 4-6 wires commin out of it.

True. On 91-94 cars.

Originally posted by Lordpaxin
my JDM had a seperate cirucuit for the RPM signal, and it was a smaller black square on the coil pack itself.

Because it is from a 90 car.

Originally posted by icedearth15
ever since I had the car the tach has never worked, but will sometimes jerk around (I mean not very often at all).

Originally posted by icedearth15
Before I bought the car the past owner had a 1991 6-bolt put in for some reason (I have a 1990)

You answered your own question as to why this is happening. They didn't change the coil pack and power transistor when they did the swap.
First you need to get a coil pack from a 90. It has a module as Lordpaxin stated, on the backside of the pack.

Here is a pic:

 

[Morphius]

A 90 also has this additional noise filter seperated from the power transistor. Be sure to plug this into your wiring harness or else you'll get no signal.

Pic of this filter attached to the bracket on the underside of the intake manifold. You can see the length of wire and connector.

 

[Morphius]

That then plugs into the body harness. Notice the plug/wire near my thumb.

 

[Morphius]

Originally posted by Mike1992
you are wrong my friend, the tach signal is different or something in the setup between coil/tr unit from 90/91-94. I tried 3 diff. 90 clusters and was proved to be what i read was right. So i ended up buying a cluster outta a 91 laser off ebay and things all worky now!

I see your car is a 90.

What year are your coil pack, power transistor, and ECU from?

 

[Mike1992]

wiring front to back is all 91 along with motor, thats how i found out 90's clusters dont work in 91, even the dash harness has a few more wires in 91.

 

[BISHILVR]

the tach in 90 clusters will only work in 90 cars, 91-94 will work in all 91-94 only.

 

[Mike1992]

Originally posted by BISHILVR
the tach in 90 clusters will only work in 90 cars, 91-94 will work in all 91-94 only.

Thats what I meant!

 

[BISHILVR]

yeah....i know, just setting the record straight

 

[icedearth15]

Thanks alot for the information....I am now going to start looking for a 90' coil pack (with the transistor of course). And see what happens. Thanks all--I will keep you updated

 

[91awd]

Before you do that I would do what Morphius said and make sure that the noise filter is plugged in. We did an engine swap in my friends 90 and we didn't put that little bracket on the back of the intake manifold back on wich had the noise filter bolted to it. It took us quite a while to figure out that that is why his tach didn't work. He bought a used one for $10 plugged it in where Morphius showed you and his tach started working.

 

[Morphius]

Originally posted by 91awd
Before you do that I would do what Morphius said and make sure that the noise filter is plugged in. We did an engine swap in my friends 90 and we didn't put that little bracket on the back of the intake manifold back on wich had the noise filter bolted to it. It took us quite a while to figure out that that is why his tach didn't work. He bought a used one for $10 plugged it in where Morphius showed you and his tach started working.

^^^ ditto to that. Funny you should mention that, because I did the EXACT same thing about 5 months ago when I did an engine swap. It's all too easy to overlook plugging that in.

You should also check the part #'s on your ECU and see what year you have. That could make a difference on what you need to get.

 

[Morphius]

Originally posted by BISHILVR
the tach in 90 clusters will only work in 90 cars, 91-94 will work in all 91-94 only.

Here is where and why I think the clusters are the same. Below is a pic of a 1990 cluster. Notice the point to the left where the wire harness plugs in and to the right you see two screws marked Tach and Ground. The runners that go from those screws (or posts for the tach) to number 10 and 11 on the plug. (10=ground, 11=tach postive)

 

[Morphius]

Below is a pic of a 1991 cluster. Again, notice the point to the left where the wire harness plugs in and to the right you see two screws marked Tach and Ground. The runners that go from those screws (or posts for the tach) to number 10 and 11 on the plug. (10=ground, 11=tach postive)

Are they not identical?

 

[Mike1992]

ok now that youve gone and tried to prove me wrong, go look at the wiring on the dash behind the clusters, the 91 will have more wires in the slip plastic things that slide into the cluster

 

[Morphius]

Originally posted by Mike1992
ok now that youve gone and tried to prove me wrong, go look at the wiring on the dash behind the clusters, the 91 will have more wires in the slip plastic things that slide into the cluster

Well, the harnesses are over locked up in the shop and I won't be back over there tonight to investigate. That may well be true, but in regards to the connectors and the mating PC board on the cluster, the PC board/connector have the same pin #'s for the tach.

Are you sure that it's not actually the ECU outputs that are different 90 to 91-94? (ie the reason they are not interchangable) I'm looking for the link now......

 

[Morphius]

Mike1992,

Before you switched clusters, did the tach not work at all, or did it work but read low/high?

Reason I ask..... I measured the resistance of the two tachs and they differ by 60 ohms. I wonder if it's acting like an aftermarket tach. Usually an aftermarket tach will have 3 resistors you can leave or remove. Depending on which ones you leave/remove the tach will read correctly for a 4, 6, or 8 cylinder engine.

They quite possibly removed a resistor somewhere else and then had to make up for it internally in the cluster.

Being curious, I'm going to throw the 91 cluster in my 90 to see what it does later in the week.

 

[Mike1992]

when i had the 90 cluster hooked up with my 91 wiring and all the sheebang, all the gauges worked great except the tach, its didnt do anything, it didnt move at all. I cant remember how many more wires there were in the 91 dash harness compared to the 90 but from what i remember between 1 and 3. Where the wiring plugs slide into the back of the cluster, in 90 the drivers side wiring socket has a blank slot where theres a wire for sure in 91, i wanna say its the tach wire, but after looking at your pics, kinda seems like both clusters should read off that same "tach" thingy