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.

  • Join the Community!

    DSMtuners is a massive archive of DSM information - but more importantly, it's a COMMUNITY! Join in and participate with other DSMers, and invite all of your DSM friends to make this place their home. Chat with others, create a build thread, post questions and answers. Get involved! Logging in will also remove many of the advertisements, along with this notice. ;) It will also allow you to view images in threads.

Please Support ExtremePSI
Please Support Rix Racing

Tach doesn't work correctly

My1GLaser

Proven Member
1,565
31
Dec 4, 2006
Bartow, Florida
My tach is 300 rpm off at idle and about 1200 off at Redline. What could be causing this? I have been having this problem for a couple months now. It is consistent and hasn't changed at all over time. I did a total rebuild on the car and everything seems to run fine, except for a few idle sputters here and there. I am comparing the info to the RPM in DSMlink, which I have been emphatically told is correct. Please help, it is hard to drive this thing at WOT while looking at the tach and doing addition, or trying to watch my laptop log.
 

My1GLaser

Proven Member
1,565
31
Dec 4, 2006
Bartow, Florida
Yes, thanks. I read it before, but there was never a reply with the part number. I need something to go on here. I have no idea what to look for, and there isn't anything on the throttle linkage. It might be somewhere on the maniflod, but not in the "normal" spot. I did have to reroute both original harnesses, but used a plain accel cable to get rid of the cruise control. I need a clearer description, part number, picture or some idea of how it is wired so I can follow wires to see if it is somewhere. What feeds the tach its signal that this thing "filters?"
 

wvturbo2

Proven Member
1,166
1
Jan 25, 2006
Huntington, West_Virginia
My problem is that my rpms jump all around at 3-4k They start jumping around and if i get it on it they go down to 0 and back up. Wtf?
 

mjboehm

Proven Member
229
3
Oct 18, 2006
Fort Myers, Florida
i am have the same problem with my talon my tach is off by 300+/- rpms but i have an avc-r hooked up and i get a perfect reading off the screen of the avc-r thats how i know my tach was incorrect any info would be great
 

dsmdreamin

Proven Member
58
0
Jan 15, 2007
Spanaway, Washington
when i put a 91 ecu in my 90, it did the same thing, i would hit about 3-4k and it would drop to zero, check the ecu, they have different ways that the tacks hook up.
 

wvturbo2

Proven Member
1,166
1
Jan 25, 2006
Huntington, West_Virginia
I was told to cut pin 109 i think and it would solve my problems, but I never cut the wire. I'm kind of afraid to do it, but maybe I'll man up and try it out.
 

luv2rallye

DSM Wiseman
8,095
952
Jun 7, 2003
Minneapolis, Minnesota
I need a clearer description, part number, picture or some idea of how it is wired so I can follow wires to see if it is somewhere. What feeds the tach its signal that this thing "filters?"
If you have the original '90 ignition (coil, PT, ECU, tach noise filter, harness) the dash tach gets its signal (via a white wire) from the tach noise filter which gets its signal through another white wire from the coil pin 3 (which also goes to ECU pin 109). All other years are different.
 

luv2rallye

DSM Wiseman
8,095
952
Jun 7, 2003
Minneapolis, Minnesota
I was told to cut pin 109 i think and it would solve my problems, but I never cut the wire. I'm kind of afraid to do it, but maybe I'll man up and try it out.
Better not do that or your fuel pump won't work. ECU uses signal on pin 109 to know engine is running/cranking so it will turn on fuel pump. That is why just turning key to ON with engine not running/cranking does not power the fuel pump (safety measure).
 

My1GLaser

Proven Member
1,565
31
Dec 4, 2006
Bartow, Florida
Rallye,
I do have the all the original ign system. Thanks ALOT for that info. I will check out the wiring this weekend.

As for this point you made, it gives me an idea and a question.
Better not do that or your fuel pump won't work. ECU uses signal on pin 109 to know engine is running/cranking so it will turn on fuel pump. That is why just turning key to ON with engine not running/cranking does not power the fuel pump (safety measure).

I lose all fuel pressure within a few minutes of the car being shut off, and I wish that the fuel pump primed for a second or two just before cranking. Can I run a signal wire to pin 109 from the fuel pressure solenoid, so that it gets power with "key on, car off?" I know it has power in key on, but its 12v. I guess I could just probe the pin 109 source wire under the hood and find its voltage and get a matching "key on, car off" source (in case its 5v) Just double checking with someone who knows these cars...this is my first DSM.
 

luv2rallye

DSM Wiseman
8,095
952
Jun 7, 2003
Minneapolis, Minnesota
Sorry that won't work. It's looking for pulses that come from the OR gate on the coil primaries.
If you're losing fuel pressure that quickly try first replacing your gas cap and second checking for a leaking FPR.
 

My1GLaser

Proven Member
1,565
31
Dec 4, 2006
Bartow, Florida
There is a white wire from coil 3 (closest to firewall) to the "tacho interface." There is another white wire that runs from the other side of the tacho to the harness end of coil pack. That harness runs to the large harness for the Transistor. I don't know if the white wire goes to the transistor then the ecu or just thru that "bundle" of wires and straight to the ecu.

The question of whether or not it goes to the transistor before the ECU is so I can eliminate or include the PT in the troubleshooting. That damn thing is expensive!

Is this "tacho interface" the noise filter that you are referring to? It is bolted to the back of the coil pack. I do see one other white wire coming out of coil 3 (both wires are more like off white, which I guess is a 17 yr old white wire?), but it goes straight to the coil harness plug and into the same bundle of PT wires.
 

luv2rallye

DSM Wiseman
8,095
952
Jun 7, 2003
Minneapolis, Minnesota
There is a white wire from coil 3 (closest to firewall) to the "tacho interface." There is another white wire that runs from the other side of the tacho to the harness end of coil pack. That harness runs to the large harness for the Transistor. I don't know if the white wire goes to the transistor then the ecu or just thru that "bundle" of wires and straight to the ecu.

The question of whether or not it goes to the transistor before the ECU is so I can eliminate or include the PT in the troubleshooting. That damn thing is expensive!
I don't have a 90 so I can't tell you what harnesses the wires physically go into or what the device order is when a wire goes to multiple places. But I do have 90 wiring diagrams and I can see that none of the tacho interface wires go into the PT. As my post #8 states, coil pin 3 goes to one side of the tacho as well as ECU pin 109. The other tacho side goes to the instrument cluster pin A12 (tach). The tacho casing must be grounded (bolted to engine or something directly bolted to engine like a coil pack) or it won't work properly (is this your problem?).

Is this "tacho interface" the noise filter that you are referring to? It is bolted to the back of the coil pack. I do see one other white wire coming out of coil 3 (both wires are more like off white, which I guess is a 17 yr old white wire?), but it goes straight to the coil harness plug and into the same bundle of PT wires.
yes
 

steve

DSM Wiseman
14,087
1,133
Feb 3, 2002
Boulder, Colorado
This is the noise filter
You must be logged in to view this image or video.


While it's no longer necessary to change all of the 90 ignition system to allow it to work with a 91+ ECU, http://www.ecanfix.com/~mdhamilton/ecuconversion.html is still a great (and perhaps only) reference on the unique wiring found on '90 DSMs.

This is the tachometer sender on the bottom of a '90 coil pack, shown with a 91+ coil pack for comparison.
On the 91+ cars the tachometer sender is part of the power transistor module.
You must be logged in to view this image or video.


Steve
 

xtreme-elements

Proven Member
139
1
Jan 4, 2007
eighty four, Pennsylvania
HOLY MOLY..... FINALLY!!!! OF ALL THE POST I READ ON THIS SUBJECT (1990 TACH DONT WORK..) SOMEONE FINALLY SHOWED A PIC OF THE PARTS... THANK YOU steve DSM Wiseman I LIGHTENED THE AWD UP BY GETTING RID OF ALL THE UNNESSECARY BRACKETS AND STUFF.. WELL THE BRACKET FOR THE MANIFOLD TO ENGINE IN BACK HAD THE NOISE FILTER ON IT AND I PITCHED IT.. GOT ONE FROM JUNK YARD.. WALA... TACH WORKS AGAIN THANKS
 

Colt4G63 also

Proven Member
3,393
49
Jul 23, 2008
Tonawanda, New_York
There is a white wire from coil 3 (closest to firewall) to the "tacho interface." There is another white wire that runs from the other side of the tacho to the harness end of coil pack. That harness runs to the large harness for the Transistor. I don't know if the white wire goes to the transistor then the ecu or just thru that "bundle" of wires and straight to the ecu.

The question of whether or not it goes to the transistor before the ECU is so I can eliminate or include the PT in the troubleshooting. That damn thing is expensive!

Is this "tacho interface" the noise filter that you are referring to? It is bolted to the back of the coil pack. I do see one other white wire coming out of coil 3 (both wires are more like off white, which I guess is a 17 yr old white wire?), but it goes straight to the coil harness plug and into the same bundle of PT wires.


That wire doesn't go to the PT on a 90, it splits and goes to the tach via the filter
You must be logged in to view this image or video.
, and the other branch goes to the ECU.

If you are runninng a 90 ECU, 90 coil (with tacho interface), 90 PT, and a 92 tach, (your car is a 92 right?) there's your problem right there.

You need to install a 92 PT to support the 92 tach. It has a square plug with a PITA wire retainer clip on the 90, and a nice easy ovalish plug with the squeeze lock retainer on the 91+ PT. The important part is the one extra white tach wire on the 91+ PT. Run that straight to your tach input, and run the tach wire from your tacho interface straight to your ECU pin 109 and NOT to the tach. I just went through all this with my car.
 
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 Raven Fabrication RixRacing RockAuto RTM Racing STM Tuned VR Speed Factory

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Top