High Rough Idle - Fixed by 91 ECU

[Grip]

So I did some searching and have literally read every idle thread there is. My car was idling ~2500 RPM's and was hard to start and ran rough. I did the normal troubleshooting. BISS, ISC, etc. and when it came down to me throwing parts at the car I decided to try a different ECU. This ECU is out of a 91 and for sure is a 91 ECU. Heres where it gets weird. I put the ECU in expecting the worst. No tach, worse idle. Come to find out, the car now idles at 1000 RPM, and is WAY smoother.

Mind you this is with no pin swapping done at all. I have read at one point that you had to swap pins to make the tach work correctly, and I was looking for that thread and didn't seem to find it.

My questions are:

1. Should the tach work at all? - Mine does fine on idle, and jumps around when revved.

2. What problems should I be experiencing with a 91 ECU in a 90 car without swapping the proper pins.

The problem that I am having now that I wasnt having before the ECU swap is that the car jerks and kicks and acts like it has no power for 5 seconds at a time. It almost feels like the car cuts off and comes back every few seconds.

 

[92AWDHX40]

Maf issues, never ran the car without switching the pins your supposed to. Check and change the ecu wiring pins 6 and 14 vfaq.com check it out.

 

[laserspeeddemon]

Putting a 90 ECU in a 91-94 involves swapping 2 wires. Putting a 91-94 involves a heck of a lot more.

Read the door jam in your car and tell me what month/year your car was made. Also a picture of the old ECU will help.

 

[Grip]

Could you give me an example of a "heck of a lot". That would be a factor in my decision to look for another 90 or keep the 91.

 

[Grip]

Putting a 90 ECU in a 91-94 involves swapping 2 wires. Putting a 91-94 involves a heck of a lot more.

Read the door jam in your car and tell me what month/year your car was made. Also a picture of the old ECU will help.

Was referring to what he said. He seems to think it invloves more. I read the vfaq.com and it said 6 and 14 going from 91 to 90 and 90 to 91. It didnt show a difference. I was just going to see if he had some verification to back up what he said.

 

[laserspeeddemon]

Ah here we go:
http://www.dsmtuners.com/forums/art...4-ecu-swap-into-1990-dsm-ignition-wiring.html

Took me some time to find this gem. But there you go. For us 90'ers we get to do the extra work for this job.

 

[steve]

Or just install a 90 tach signal converter into the 91 ECU and switch the two wires.

The 90 tach setup doesn't like feeding the 91+ ECUs and can cause the tach to behave as described.

 

[laserspeeddemon]

90 tach signal converter? Where is this device you speak of?

 

[steve]

Keydiver used to sell them. DSMChips.com | DSM ECU Chips Enchanced by Keydiver

 

[Grip]

Steve do you know anyone still selling those converters?

 

[steve]

I think I still have a couple. I'll check when I get back home to Chicago.

 

[Grip]

Ok, PM me if you do have some, Ill take one for sure.