The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support Kiggly Racing
Please Support STM Tuned

90 model dead tach.

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
I've searched multiple times and have read about the little noise filter. However I read that someone just jumped the wires and the tach worked.

So, is the noise filter required?

I also read that there was an attachment/sensor on the stock 90 TB that is required to make the tach work. Is there truth to this?

Most of the threads I found were dead and hadn't been updated with a fix so I'm asking here.

Thanks for looking.

------------------------------UPDATE [FIX]------------------------------

So today Sep 19th, 2011, I have found what I've needed to know for many many days. And this is VERY good news for the 90 guys.

This fix is so simple that it's mind boggling.

Ways to fix it WITHOUT A NOISE FILTER.

Items needed:

3-4 inches of 18-22 gauge wire.
Two MALE quick slide 22-18 gauge electrical connectors.

Now, to do this, you'll need a pair of wire strippers (or use your teeth, your choice) and wire crimpers.

1. Assemble everything you'll need. Ensure you know where the noise filter harness is in the car.
2. Take your wire and strip off about 1/2" on both sides.
3. Take the two connections and REMOVE THE OUTER CASE. I took a pair of pliers and yanked on the male side and locked the plastic part into a vice. A pair of pliers should also work. Take care to not crimp down on the wire crimp part yet.
4. Attach the two naked connections to the wire.
5. Bend the wire as shown in the picture below.
6. Slide wire into the noise filter harness plug.
7. Make sure it's tight, if not then secure it to the plug somehow.
8. Start the car and make sure the tach works.

It took me about 10 minutes to do this, but I have a good mechanical knowledge and background. Even a complete idiot should have this done in no more than an hour.

Notes:
1. The stock noise filters resistance measure 2.3 kilo ohms.
2. The wire resistance measured .2 kilo ohms.
3. I did not need to ground the wire for this to work.
4. I did not go on an extensive test drive to test this out, but the tach DID function throughout the entire RPM range.

If any questions, give me a buzz on here. Good luck DSMers!

MODS: can you please reflect the title to show resolved or say "Fix included" Thanks! It wouldn't let me do it myself.

Pictures.

You must be logged in to view this image or video.

Items needed. I used house wire as it's very sturdy and fit just right. You'll see the parts to the left and assembled to the right.

You must be logged in to view this image or video.

My noise filter and area of the plug. Right behind the intake manifold. If your noise filter is still attached then it's only a 10mm bolt holding it on.

You must be logged in to view this image or video.

Fix bent to fit into the connection nice and snug.

You must be logged in to view this image or video.

Fix installed and working.

Now if you are wanting to be SUPER right about this, then install a 2.3 kilo ohm resistor on the line and see if that works. I didn't need to.

-Brando
 
Last edited by a moderator:

1990AWD

Supporting VIP
8,539
20
Apr 27, 2009
Langham, SK_Canada
The noise filter is needed for the tach to work. It plugs into the harness below the intake manifold, right beside the knock sensor plug and it has to be grounded to something. The throttle body also needs a ground, stock is a little tab that goes on the TB bolt and a screw on the top.
 

tsiman1995

Probationary Member
4
0
Jul 17, 2007
new castle, Pennsylvania
Might also want to try the power transistor also, since it also sends signal for the tach.
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Sorry I was still confused to it.

Turns out that I could NOT find that plus that is around the knock sensor area behind/under the intake manifold.

What I did find was on my old coil pack that i had removed, I found the filter wired up all goofy like. Now that I've addressed a lot of issues and the car is running really good, I though tomorrow was the time to fix the tach.

I could REALLY use that picture or a more detailed clarification on how you fixed yours sk8. Sounds like you're one of the only ones who's figured it out.

Thanks for all of the help. The car is coming along nicely.

Just to clarify.

1. My car didn't at the time have the noise filter installed on it. I'd removed the old coil pack that it was attached to without realizing it was on there. Car still ran great but not I have to figure out how to get that thing off and onto a good coil pack.

2. My aftermarket throttle body does still have that little grounded wire to the closed position switch.

3. I was unable to find that noise filter on the only other 90 turbo I was able to locate. I'd removed the coil pack from it previously and it was not on that pack like it was on the one I removed from my own vehicle. This is why I wasn't aware of my removing it as I was in fix it mode.

Again, thanks for all of the help.
 

hazmat6135

Proven Member
121
0
Oct 22, 2010
canton, Ohio
the filter they are talking about is bolted to the bracket on the bottom of the intake manifold. everyone takes that bracket off so it gets moved. i have mine bolted on top of the manifold in the extra screw hole for the wiring harness cover. works great. you just need to find it then ground it and your good
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
The 90 model car I was working on still had that bracket and I looked all over it and still couldn't find it. I have my old coil pack assembly with the noise filter (tacho adapter) and a new coil pack. I'm going to see what I can't do to get that tach working today!

And for the first time EVER, I will post up pics on how I fixed it, what I did to fix it and how others can fix it, this is, ofcourse, if I do manage to fix it.

I found a few other posts about people running a different wire and just completely negating that noise filter so that is the route I'm going to go.
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
I am not sure if I have a 90 or 91-94 cluster so that is a possibility.

It's never had a working tach.

I'm going to attempt to splice the yellow signal wire into the white CAS wire today to see what happens.
 

thomcasey

Proven Member
949
28
Dec 16, 2009
Indianapolis, Indiana
I am not sure if I have a 90 or 91-94 cluster so that is a possibility.

It's never had a working tach.

I'm going to attempt to splice the yellow signal wire into the white CAS wire today to see what happens.

AWD cluster for a '90 should have the MPH gradient as follows (5, 15, 25, etc... FWD models have 10, 20, 30, etc...). 91 and later have 10, 20, 30, etc...
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Damn, my hopes was going good as I was thinking I needed a cluster and was on the prowl. Now after reading that.

My cluster does go by 5's. 5, 15, 25, 35, 45... etc.

Turns out I have TWO coils with the tach interface so I'll modify one of them for the fix above and keep the other stock incase it doesn't work.

Thanks for the warning before I wasted money.

Before I try this, I would like some extra input.

I got the yellow wire no problem, but the white wire, that is where I'm having the issue.

Do i splice into the white wire from the CAS OR the white wire from the transistor harness?

Also, to I add the yellow wire to the white wire or do I cut the white wire and run it straight through the yellow wire.

Please give me the solution before I start and kill a perfectly running car.

Also, when this issue is fixed I will make a new post with pictures and a How To: so others can fix the same problem WITHOUT a new thread.

Thanks!
 

19Eclipse90

DSM Wiseman
5,278
1,145
Sep 29, 2003
OKC, Oklahoma
Mind sharing some of those posts?

I'll leave these quotes here:
As discussed in many threads, the 90 cars generate their ignition pulse signal at the tach adapter on the bottom of the coil pack. That's why they have a 4 pin connector vs the 3 pin connector on the 91+ coils. The extra pin is the ignition pulse signal from the coil pack. That wire runs to the unique 90 noise filter where it splits, the unfiltered signal going onto the ECU pin 109 and the filtered signal to the gauge cluster to drive the tach...
...The 90 gauge cluster is driven from the output of the noise filter. You need to retain it unless you swap to the later cluster...

If there is a way to bypass the filter, I'd like to know as much as the next guy. But over the span of seven years of looking for a reason as to why my tach wouldn't work and then if there was a way around the noise filter, I found nothing. Ended up getting a noise filter and, voila!, my tach worked.
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Try tapping into the power transistor all white wire (pin 4) and connect to your tach input. If you're using the dash tach, you can unplug the tacho interface filter (unique to only a 90) and connect to the single white wire (not the 2 white wires together) on it's harness connector. Can't guarantee this will work but according to the diagrams it's the way to go (if the pulse width, and peak voltage level are compatible).


The signal for the Tach comes directly from the white wire on the transistor pack. On my car with AEM EMS the tach goes stupid on the two step and rev limit due to it being a ignition cut limiter and not fuel so the tach signal from the transistor pack gets cut and a 0RPM signal is sent out but the engine is really spinning at 5500rpm or 8000rpm depending if its my rev limit or 2step. Its just really stupid to see that tach sweep from 8K to 0 and back up to 8 and 0 in less than a second. My solution for this was to cut the white wire off the transistor pack and jump the CAS yellow wire (crank signal) to the transistor pack white wire. That way it just goes off the crank signal. It is a direct square wave signal from the transistor pack out to the cluster and the CAS is a square wave output that is mechanically driven.

These are the two I found off hand.

They both pretty much say the same thing so this is what I'm going to attempt.
 

19Eclipse90

DSM Wiseman
5,278
1,145
Sep 29, 2003
OKC, Oklahoma
The only thing those two quotations have in common is that they both say there is a white wire on the power transistor.

Take this for what it is worth: there is no white wire on the '90 transistor unit. That white wire on a '90 is pin 3 on the coil pack. With all due respect to those two posters, that simple fact works to discredit their information in my eyes.

luv2rallye admits he's not positive it will work. Sam doesn't specify that what he did was for a '90.

Keeping everything else the same, a '90 tach will not work in a '91+ car, nor will a '91 tach work in a '90 car which might (I'm not an electrical genius so I'm not absolutely sure) imply that they do not use the same signals. Just some food for thought.
 
Last edited:

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Hell, whats the worst that can happen? My tach doesn't work? LOL

The white pin on transistor pack I believe is dedicated to the tachometer but it goes through the filter first. By doing this, the filter is eliminated and you get a working tach.

I'll probably try it out tomorrow.
 

19Eclipse90

DSM Wiseman
5,278
1,145
Sep 29, 2003
OKC, Oklahoma
Consider me a bit pessimistic: cutting into the CAS wiring can potentially leave you with a non-running vehicle (although it's easily reversed).

Did you miss this part? Or is there a reason you keep saying the white wire on the transistor?
Take this for what it is worth: there is no white wire on the '90 transistor unit.

The tach signal on a '90 comes from the tach gate which is on the coil pack. The '91+ models integrated this into the power transistor which is why those later transistors have more wires -- including the white wire on pin 4 as referenced in the two quotations you provided.

This is the tach gate (signal source):
You must be logged in to view this image or video.


This is the tach filter:
You must be logged in to view this image or video.
 
Last edited:

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Damn, I actually thought the gate you showed was the filter. Well F' me randy....

I say that filter on a vehicle at the yard. I'll make damn sure to grab it next time.

Thanks a million!

Man it's crazy how when you're actually awake you see different things. I worked on the talon for about 8 hours yesterday and was beat when I was going back through this thread.

So the way I'm reading it now is that the white wire on the CAS is the fix, IF it is a fix at all.

I'll try it because I have 3 vehicles and one being down will not hurt me. If it doesn't work then I'll just solder the cas wire back into a whole piece and reply saying it didn't work. That should help nip this rumor in the butt.

This thread is probably the best one I've found on this subject. It's nice to have all the appropriate info in one place.

Please NEVER delete those pictures! That is a piece of gold right there.
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
I didn't get the chance to get to it today as I was busy installing another interior into my car. Tomorrow I'm going to work with a shop so when I get off work, I'll give it a shot and see what happens.

Found a filter. Going to install it today and hope for the best.
 

obsidian

Proven Member
394
5
Jun 25, 2007
New Orleans, Louisiana
Well I got the filter installed. Guess what?

The bastard works. After all that heartache I could have just grabbed that little guy and been done with it.

Now! I have another theory. Why can't we just jump the leads in that connector? Has anyone tried this before? It's such a simple thing to try. I never even saw this connection in my engine bay (still not used to it as this is my first 90 model) and had to hunt for it even when I knew what I was looking for. The P.O. tucked it under the main harness. If I'd have seen that before I could have been attempting other fixes.

So, has anyone tried to just jump the leads?
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Top