Whats the REAL Difference between a 90-91 ECU?

- All 90's are EPROM.
- 91's may or may not be EPROM

There are two wires swapped between the two ECUs.

Also, ECU has a wider range of fuel control on 91+ than on the 90's.

 

91's do have a larger fuel trim swing and the Idle switch and MAF reset pins are swapped.90 and 91 both may or may not have Eproms.

 

I agree now that all 1G model years may or may not be EPROM after more research. All of the 90's I've seen were EPROM and I saw that written somewhere, but I was misinformed, sorry.

Fuel trims on 90's auto-adjust from 100 +- 20% if I remember right.
Fuel trims on 91's auto-adjust from 100 +- 40% if I remember right.

Don't quote me on the exact numbers! I'll see if I can find documentation to back this up.

 

Some stuff:
http://www.hywell.org/plhelp/lo.html
http://www.vfaq.com/TMO/ (CTRL+F, search for "trim")

 

90 ECU's have two pins swapped, change these in the harness and you can run the other ECU.

They are the exact same size.

90 fuel trims have a range of 40%, and 91+ has a range of 80%.

90's have less agressive timing maps, and slightly richer fuel maps.

 

all 90's are e-prom

 

Wrong, I have a 90 Laser and it didnt have an EPROM in it. When it took a shit I went to a junk yard and pulled 4 ECU in all the 90 cars they had and none of them were ERPOM's. The 90 ERPOM's are the hardest to find and very expensive. The one I found after three months cost me 300 bucks and didnt even come with an aftermarket chip.

Michael

 

I own a 90 tsi and a 90 eclipse turbo FWD, neither have Eprom ECU's.

 

If you are doing a swap from a 90 to a 91-94 there is more then just swapping the wires on the ECU. You also need to swap the coil pack and ignition transistor from a 91-94 in. Also you don't need the noise filter any more, so you can just cut the plug off and connect the wires together. Here's a link to a more detailed description of the swap.

http://www.ecanfix.com/~mdhamilton/ecuconversion.html

 

TPS and CAS are also different ...if your doing the swap

 

Again, all 90's DO NOT HAVE E-PROMS! I have a 90 and man was an E-PROM ECU a real PITA to find. Also ran me a pretty penny.