Help! E34 Rev limiter hits @ 4700 rpm.

[foxese34]

Hello All,

First time BMW owner, long time amateur wrench turner.

I've searched and searched through here but couldn't find an answer.

I have a 95 525i automatic with the M50TU engine. It has 120k miles and is in good shape except...

The rev limiter kicks in at 4700 rpm. It does this under ALL conditions, cold, hot, shifting manually or parked in neutral. The engine runs great, no hesitation or weakness on 91 octane gas. It does get about 15 mpg around town and 21 hwy, which is not as good as it should be and it smells a little rich. No fault codes and it passed CA smog but was at the high end on some readings.

I've gone through just about every sensor I could per the Bentley and everything seems to be working. A local BMW repair shop thought the ECM might be bad so put in a different DME to no effect. What is left? I found two .25 inch metal shavings stuck to the camshaft position sensor magnet but could not identify a source. Will a non-functioning VANOS cause this? Is there a way that I can check the VANOS operation other than with the special BMW tools? I've already checked the solenoid function while removed from the car.

How about a shop in the Roseville/Sacramento, CA area that is REALLY good at weird stuff (already tried Bertinis).

Any help would be appreciated. I am sooooo frustrated!

Thanks,

CD

[witeshark]

Is it possible that someone installed a limiter from an ETA engine?

[foxese34]

Originally Posted by witeshark

Is it possible that someone installed a limiter from an ETA engine?

Thanks for the reply.

I don't think so. The car had the original intact DME module (as indicated by the matching VIN#). I bought a used DME from a junk yard and had the EWS reprogrammed. The new DME performs exactly same way that original does.

CD

[witeshark]

Any idea if a chip was changed out?

[foxese34]

Originally Posted by witeshark

Any idea if a chip was changed out?

I don't think so. Both of the ECM/DME's that I've had in it look like the tabs holding them closed have never been tampered with. Even if one had, the other shouldn't have the same behavior. Is there another module that inputs into the system other than the Bosche DME, located on the right side of the engine compartment?

CD

[witeshark]

It looks like you need to know more about all the criteria the engine control system uses to set the limiter. I don't know of any way to simply change it manually. Some sensor must be off, and I think your fuel economy is a big clue.

[darkhorse737]

it might that be the rev limiter thats causing u probs. it might be a fuel to air ratio prob thts causing ur car to sputter* sputter* sputter* at the rpm u say

take witeshark's tip and recheck fuel metering...

[foxese34]

Originally Posted by darkhorse737

it might that be the rev limiter thats causing u probs. it might be a fuel to air ratio prob thts causing ur car to sputter* sputter* sputter* at the rpm u say

take witeshark's tip and recheck fuel metering...

There's no sputter, stumble, or stutter. It's pulling strong and then it gives the rapid "dat, dat, dat..." of the fuel being electrically cutoff just as if it were at the redline. It happens at the same rpm wether at part throttle or full. It also does it in park or driving. First or second gear, haven't tried third, the car would be going too fast.

CD

[foxese34]

Originally Posted by witeshark

It looks like you need to know more about all the criteria the engine control system uses to set the limiter. I don't know of any way to simply change it manually. Some sensor must be off, and I think your fuel economy is a big clue.

That's what I had been thinking. So I went through the Mass Air, TPS, O2 sensors and checked the injectors for leaks. Replaced many old hoses to tidy up vacuum leaks. Also thought maybe it was stuck in "cold" mode due to bad engine temp sensor but that wasn't it either.

My main theory now is: what if the VANOS isn't cycling? The computer looks for the cam to reposition due to the solenoid energizing just above idle and then reposition back at a higher rpm (which I've read is somewhere in the neighborhood of 4500rpm). If the computer doesn't see the cam reposition, will it prevent further rpm rise? This would also affect fuel metering if the cam is not advancing and retarding as designed. How can I tell if VANOS is working? Mine makes no noise that I can hear as I rev it up and back. Should I be able to hear the solenoid as it picks up just above idle?

CD

[witeshark]

That's gotta be worth a look.

[Dirty_Tool]

interesting issue. Give Dave a call at Performance Motorworks in Rocklin. Im sure they can figure it out. 916 624-9656

[darkhorse737]

Originally Posted by foxese34

That's what I had been thinking. So I went through the Mass Air, TPS, O2 sensors and checked the injectors for leaks. Replaced many old hoses to tidy up vacuum leaks. Also thought maybe it was stuck in "cold" mode due to bad engine temp sensor but that wasn't it either.

My main theory now is: what if the VANOS isn't cycling? The computer looks for the cam to reposition due to the solenoid energizing just above idle and then reposition back at a higher rpm (which I've read is somewhere in the neighborhood of 4500rpm). If the computer doesn't see the cam reposition, will it prevent further rpm rise? This would also affect fuel metering if the cam is not advancing and retarding as designed. How can I tell if VANOS is working? Mine makes no noise that I can hear as I rev it up and back. Should I be able to hear the solenoid as it picks up just above idle?

CD

if any of the sensors or VANOS wasn't working, it would have thrown a CEL.

Have you done a scan yet? :-)

[foxese34]

Originally Posted by darkhorse737

if any of the sensors or VANOS wasn't working, it would have thrown a CEL.

Have you done a scan yet? :-)

Yes. I've done the stomp test and had no codes and I had it in a local bmw repair specialist shop for a diagnostic. They found nothing bad so recommended ECM/DME replacement. I changed that out but still have the problem.

I've been given the names now of a couple of other shops, I'll call and see what they think.

Thanks,

CD

[foxese34]

Originally Posted by Dirty_Tool

interesting issue. Give Dave a call at Performance Motorworks in Rocklin. Im sure they can figure it out. 916 624-9656

Thanks for the number. Dave seemed very interested and I'm taking it to him Friday. I'll post what he turns up.

CD

[paanta]

Sorry to revive a dead post, but did you ever figure this one out? My e34 535i is doing the same thing (except at 5600 RPM)