ecu question !! 2.8 or 3.1 ?????

[BigZ24]

hi have rebuilt an 2.8 motor from my 1988 Z24... in the rebuilt i put piston and crankshaft from 3.1 ..so now i have a 3.1 motor.... i put some agresive camshaft from crane cam...but the question i askind myself is .... whit this news motor what is the best...stay whit my 2.8 computer or put and 3.1 computer or .... any better solution. the reason i askind this is cause somebody told me that my car will run lean whit my 2.8 computer....oh yes and the car was 5 speed manual(y dont know if it can affect the computer )

[bszopi]

The ECMs should be the same, all you'd need to do is swap out the MEMCAL for a 3.1L manual one.

[91z24audio]

Your ecm should be the same as a 3.1 car but you will need a programmed chip to really make it run right.If you still have the car apart you could send it to someone to get programmed.You probly will run a bit lean with a cam and upgraded engine size.

[SCREECH]

Reprogramming the chip would most likely be the route you would need to take. With the 3.1L engines, GM started using the digital EGR valves. The 2.8s did not have this setup. Therefore, if you try to run a 3.1 computer on your 2.8 engine (assuming you did NOT make any changes to the harness or EGR valve when you enlarged the displacement of the engine) it will not run properly as it will not be able to correctly control the engine.

Now, someone is welcome to correct me if I'm wrong...but back a while ago when the computer died in my '90 Eurosport (3.1), I grabbed the computer out of my '87 Eurosport (2. and it would barely run. The computers were the same, just the PROM chip was different. Once I swapped the 3.1's PROM chip into the computer from the 2.8, the car ran normally again. Running a newer computer (from a 3.1, digital EGR) on an older engine (older style EGR), I suppose could possibly work, but I would be surprised if it did.

The other option, other than programming your 2.8 chip, would be to update your vehicle with the components that were changed when the 3.1s were intro'd. Like I said, I know they went to a digital EGR, but I am not certain what other changes, if any, were made. Perhaps someone else can fill us in on that aspect of it.

[TurboGTU]

your best bet is to get a memcal from a 89, 90 5spd 3.1 for a baseline. Those don't have the Digital EGR, and have the idle and fueling tables for the 5spd. Check the GMPCM site for one. Mechanic list the cars and their respective bins. Also what cam did you get...also did you do any port work, exhaust work...stuff like that.