I have a 91 318i with a 90 m20b25 swap and the revlimiter is hitting at like 5400 instead of 6600. Does anyone know what this could be? ECU maybe? It will run fine sometimes but other times it will hit revlimiter early and sometimes it will just die when i let off the throttle. I have no idea whats goin on.

 

It sounds like you have the revlimiter from an Eta series. They have a soft valve train and a limited revlimit to keep the valve float down in an attempt not to break anything. It might just be your ECM, look up the last 3 numbers on it. If thats the case i think you can swap it out for an I series ECM as long as you change the sensors as well. There was a very detailed write up on E30 tech or revlimited, i'll have to go find it....

 

When I first got the car it ran perfect. The revlimiter hit at the right time and nothing was wrong with it. The car and motor is still mint except this little problem. I think the fpr that i got off ebay was bad so i think i'm just gonna spend the money to get a new one. It can't hurt. Maybe the connection to the ecu is a little messed up. Or maybe some ground or something? I don't know i think i'm gonna do the fpr first cuz i know that will cause the rev limiter to hit early.

 

I didnt think about that. I am in the process of getting my first e30 and have been debating between I and E, 2 door and 4 door, and that was the first thing to pop into my head. It didnt even dawn on me that it had been running well....

 

sounds like ECU to me. get a nearby friend to come let you try his.