1G 90 Tach issues

[badbird]

I have recently purchased DSMLink v3 for a 1g from a prior owner, everything appears to be fine with the ECU, got the disc and cable, as well as a GM MAF adapter for future use, etc. My vehicle is a 1990 Eagle Talon TSi AWD, I am running stock 1g MAF (it is hacked). To make a long story short, I took out the ECU that was installed into the car that I thought was "stock" but after plugging in my new ECU with link found out otherwise.

After doing some research I had a non EPROM ECU from a non 90 DSM. The one I have that is now in the vehicle is a 90 ECU with DSMLink v3 installed, the main issue going on upon install was when I held the gas down a little bit, the tach would jump and the car would "buck" in very early rpms so I did not bother driving it to prevent problems.

Turns out that the bucking issue was solved when I switched pins 6 and 14, they were already previously switched by the previous owner of the vehicle before to run the newer ECU and get the tach to work, so I switched them back to stock configuration in their respective places. The ECU with DSMLink started the car just fine, runs clean and does not buck anymore at all, however my tach is now not working correctly, it responds to throttle, goes backwards when in higher rpms sometimes and jumps from none to 3k or so often.

I have since parked the car and not driven it because I feel this is causing the knock to be read due to the car thinking it is at a different rpm then it really is. I checked the noise filter, and to see if someone switched the tach power transistor and piggyback to a newer than 90 model and had no luck finding any to be a non 90 part. I have no idea what is causing this and really need help to get the car to respond correctly with the tach.

Any knowledge or insight is well appreciated. Thanks in advance

 

[jbeaton9292]

This has been cover many times the tach will not work as you have it there is a board you must buy its only like 12$ and it gets added to 2 wires on the ECU and makes tach work again

I cant remember who makes it I'm gonna find it and order it later today as I have the same problem

Your other option is to do a complete harness swap to a 91+ (this mean body and engine harness) included in this you will have to change to the later model coil and PTU and this will cost a lot more than that small circuit board to fix the problem

Here I did a quick google search and this is our answer

Don't worry I knew it was out there already so ###### slightly easier to find

DSMChips.com | DSM ECU Chips Enhanced by Keydiver

If you look more on their site there is also an internal version but I would rather not be soldering on the ECU board but to each his own

Disregard where they have them they are no longer around anymore I didn't know that.

 

[badbird]

@jbeaton9292 I appreciate the help, but I must have written something that was misunderstood, my dilemma was someone prior to me already placed a 91+ ECU into my 90 Talon and the computer I purchased with DSMLink v3 (which is a 90 ECU model correct for my year vehicle). I read about the whole transistor and many tach issues you mentioned above, also about the DSMChips.com solutions for tach to display.

I cannot find the external element placed on my harness anywhere ( DSMChips.com | DSM ECU Chips Enhanced by Keydiver ) or any modifications done to my transistor, etc. to have made the 91+ ECU work in my car from the previous owner.

The pins 6 and 14 were already switched in my harness and would not let the car run without bucking when I installed my 90 ECU with DSMLink v3. I switched the pins back to stock after realizing someone already switched the pins in the harness for a newer computer.

My car runs smooth and idles well, even drives good, I just cannot match rpms with the needle, it jumps, stops and sometimes goes down when the car is being driven not at idle.

Could they have switched just the tach gauge from a 90 to 91+? If so what is the difference and would that make this issue come up?

Thanks

 

[1990TSIAWDTALON]

Are you certain that you have a '90 dash cluster? The speedometer should read in increments of 5's instead of zeros....like 5, 15, 25, 35 etc on the speedo if its a '90. They are the only year that read in increments of 5. Check that to make sure you have the original instrument cluster.

 

[badbird]

Are you certain that you have a '90 dash cluster? The speedometer should read in increments of 5's instead of zeros....like 5, 15, 25, 35 etc on the speedo if its a '90. They are the only year that read in increments of 5. Check that to make sure you have the original instrument cluster.

Yes, for sure have a 90 cluster, unless switching the actual tach gauge in the cluster from a 90 to 91 would cause this? I am certain the cluster is a 90 like you said, it goes in increments of 5.