1991+ Eprom in a 1990

[jdmtrav]

I have searched for this and it seems like it had been I found the tach adapter from DSM Chips, but I also read that you have to switch out coilpacks and a few other things. Do I really need to get a 1991+ coilpack or can I just use the adapter only? Thanks for any help!

 

[buddahboost]

I would like to know this too. I almost got a 93 EPROM for my 90 until I heard I need a tach adapter

I thought You only needed to switch like 2 wires cause they are different...

 

[steve]

You always have to swap 6 and 14 when you mix 90 and 91+ ECUs.
The tach adapter for the 91+ ECU is so you don't have to change the 90 ignition system just modify the ECU and plug it in.

 

[jdmtrav]

Thanks a ton Steve!

 

[Michael Jones]

I am also wanting to switch to a eprom ecu, is the 91+ ignition system any better than the 90, why was it changed in 91, and is it only the coilpacks/connector that would need to be changed if not using the tach adapter?

 

[donniekak]

I am also wanting to switch to a eprom ecu, is the 91+ ignition system any better than the 90, why was it changed in 91, and is it only the coilpacks/connector that would need to be changed if not using the tach adapter?

If you do not use the adapter, you need to run some different wiring to convert your 90 harness to use a 91-94 coil and ptu. It is way easier to run the adapter and switch the pins at the ecu. I have a 90 and use a 91-94 eprom ecu.

 

[Michael Jones]

Will the car run differently with the newer style ptu/coilpacks, are there any advantages to the newer style ignition, why was it changed?

 

[steve]

Unless you know the engineers it will be difficult to answer the why question.

The big advantage is being able to easily replace bad parts rather than having to go digging for unique parts now 18+ years old.

There might have been performance advantages but I know that there were cost advantages to the new (91+) setup at the time of the change. It's simpler with less parts.

 

[Michael Jones]

Okay, thanks. The reason I ask is because my 94 1.8 engine/ecu seemed to idle smoother than the 90turbo engine/ecu does and I would like that back now that I have no good ecu. If the caps were on the verge of going bad would that cause a slightly rough idle condition or is that just the way the 2.0 DSM's are?

 

[steve]

The reason I ask is because my 94 1.8 engine/ecu seemed to idle smoother than the 90turbo engine/ecu does and I would like that back now that I have no good ecu. If the caps were on the verge of going bad would that cause a slightly rough idle condition or is that just the way the 2.0 DSM's are?

There is really no reply to this because I can't tell from here what a "slightly rough idle condition" is and if it's related to anything your asking about or if it's due to something else. For all I know you might have the balance shafts out or worse just the belt to the front one cut/broken.

I can say that I've seen 90 cars in good shape that idle as smoothly as anything out there and I've seen lots of later cars that ran like the junk there were.

I tell people to replace the 90 specific stuff so that they can maintain their cars in the future. Everyday that goes by it's harder and harder to source good parts for the unique first year DSM's. Unless your keeping a museum quality car just upgrade it.