E30 m52 obd2 5500 rpm problem.

[robbyg739]

I have a 1991 318is with an M52B28 obd2, I had the swap done a while back and have had quite a few problems. It doesn't want to rev all the way to 6500, it hits a rev limiter like wall at 5500 and cuts out. The ecu shows no faults or codes of any kind. No vacuum or air leaks, and its getting plenty of fuel. It has a brand new MAF, and spark plugs. My mechanic just changed the crank sensor hoping that would work, nope. He tried using a different gauge cluster to see if it was sending a bad speed signal or something to the ecu, that didn't work either.


Here is a picture of the top of the ECU, someone told me it was actually an OBD1 ecu, and as far as I'm aware my engine has no OBD1 parts. http://imgur.com/IwIgCci When I had the engine swap done I was made aware that it was obd2. Clarification on that would be nice.

Some quick info about my car:

-Exhaust doesn't have o2 sensors.

-The ecu only has EWS deleted.

-Engine was an automatic but had the wiring harness spiced over.


Help me so I can turbo this beast!

[DesertBMW]

That is OBD2 for sure. it is in limp mode. Could be few things, missing speed signal, missing EGS CAN communications, bad crank sensor wiring(there was a recall for this).

[Axxe]

We had this issue, our solution was to wire the speed signal input to the rpm so it receives a non-zero value. I believe the issue relates to the top speed limiter, to keep people from exceeding the electronically limited top speed by limiting rpm in all gears when speed isn't detected.

[robbyg739]

We had this issue, our solution was to wire the speed signal input to the rpm so it receives a non-zero value. I believe the issue relates to the top speed limiter, to keep people from exceeding the electronically limited top speed by limiting rpm in all gears when speed isn't detected.

Interesting that you bring that up, the car has always had a top speed issue, i could never get it to go above 115mph, and gearing and ratios should allow it to like 130+. Getrag 260 and a 3.73 lsd.

I'll have to bring this to the attention of my mechanic, he thinks it is coolant related. Due to him taking it out one morning after changing the crank sensor. It was on a cold start and it would Rev to 6500, then it warmed up and went back into limp mode.


I appreciate the advice so far thanks guys!

[328ijunkie]

Needs a flash or VSS

[robbyg739]

You all pretty much nailed it, it was the lack of a speed sensor signal that was causing the limp mode issue. My mechanic rewired the speed signal input from the ecu to something else and problem solved.

Car is coming home in a few days, although I still need to clean up the wiring harness.