2.5 ECM

[70barracuda]

I have a 86 cherokee 2.5 and just gathering some spare parts for road trips. Rockauto just got the ECM in stock but then I remembered how the later years for the 4.0 are an upgrade. Does this hold true for the 2.5? The 1990 ECM is a different part number than the 1986. 

[eaglescout526]

I think it does actually. Cause in 86 there was a wide open throttle switch that was used to where as the later years just use input from power steering pressure switch.  

[70barracuda]

55 minutes ago, eaglescout526 said:

I think it does actually. Cause in 86 there was a wide open throttle switch that was used to where as the later years just use input from power steering pressure switch.  

So will the 90 work in the 86? Its cheaper but not by much if its going to cause issues. Or is it even worth it?

[eaglescout526]

Yes it will work and yes it’s worth it. 87-90 refined upon the 86 ECU and I would run it. I hate how not much is known about the 2.5 ECU and what was refined over the years but I don’t think 87-90 changed. Course I’m curious and would like to try a 90 ECU in my MJ and see if I get any performance and or better mileage. 

[Ωhm]

2 hours ago, eaglescout526 said:

Cause in 86 there was a wide open throttle switch that was used to where as the later years just use input from power steering pressure switch

 

You need to determine if your vehicle has a WOT Switch or PSPS Switch?

[eaglescout526]

18 minutes ago, Ωhm said:

 

You need to determine if your vehicle has a WOT Switch or PSPS Switch?

Funny enough 86 has both switches. But the power steering switch had something to do with the the AC and idle in 86. If I recall. But they figured out they could just use the PS switch to also determine WOT conditions in 87. But the switch isn’t needed for the later years. Supposedly the YJ still uses such a switch but I could be wrong. 

[Ωhm]

87 vs 88 electrical manual wise, show ECU pin C200_8 as WOT(87) or PSPS(88). WOT needed to add fuel while PSPS needed to kick idle up (used when in parking lots to prevent stalling). IIRC

[eaglescout526]

1 hour ago, Ωhm said:

87 vs 88 electrical manual wise, show ECU pin C200_8 as WOT(87) or PSPS(88). WOT needed to add fuel while PSPS needed to kick idle up (used when in parking lots to prevent stalling). IIRC

Huh. Sounds about right. I know the WOT switch is basically gone in 88 so something adds more fuel for 88-90 years when at WOT. Which actually should be the ISA. Yeah I need to brush up on such. I remember reading a lot into it when I was doing the TBI swap on my XJ. 

[Ωhm]

53 minutes ago, eaglescout526 said:

I know the WOT switch is basically gone in 88 so something adds more fuel for 88-90 years when at WOT.

 

If 2.5L learned anything from the 4.0L, both being RENIX, I would hope it would be the TPS & MAP way of how to do fuel strategy. 2.5L still had ISA, with build-in Closed Throttle (CT) Switch. 4.0L learned CT.

[70barracuda]

Well i ordered the 1990 ECM. Guess we'll see how it runs with it and ill save mine as the backup.