Rapid rise in revs?

Paul Rice

Paul Rice

Zorg Guru (V)
Supporter
British Zeds
The M44 Massive
Joined
Sep 7, 2013
Points
198
Location
Doncaster
Model of Z
Z4 2.5 E89 23
Having a possible issue with the 2.5 Z4.

Symptom: Sudden rise in revs when accelerating between 3 - 3500 rpm? car does accelerate but not in relation to the revs.

Initial thoughts Clutch, after doing the following test, Handbrake on 2nd gear move off car stalls (As it should) so no clutch slip!

Never having a straight six BMW engine before, Is this a character of the engine or a clutch fault not shown by the above test or something more sinister.

Any thoughts?
 
Must be a clutch issue in my mind. Everything else should be locked so would raise in speed with revs
 
Mnbrennan said:
Must be a clutch issue in my mind. Everything else should be locked so would raise in speed with revs
Click to expand...
Yep my first thought but doesn't slip under other loads, which made me question my initial thoughts.
Only other oddity under harsh acceleration goes through a split second of what feels like engine vibration similar to mount wear or in front wheel drive drive shaft wear.
Looks like a clutch in the new year, that will put the wheel re furb on hold.
 
Might be a daft question but do you hear the engine note change as well as see it on the rev-counter?
 
G4FUJ said:
Might be a daft question but do you hear the engine note change as well as see it on the rev-counter?
Click to expand...
Not significantly although it is quiet at both 3000 and 3500 RPM.
Forgot to mention does rise to 3.5 then drop straight back to 3
 
Possible vacuum leak maybe? Disa valve related possibly.
 
That's OK, so long as you can hear a difference.
We had a similar case with a Morgan owner a year or two ago. Turned out to be a duff tacho... :)
 
The clutch doesn't explain the rise in revs, but if the clutch was fully engage the car would speed up. Could something be disengaging the clutch temporarily?
 
Possibly a DMF issue. Do you get any judder on take off Paul?

Tony.
 
Hope it's nothing expensive Paul, don't need that at Xmas. Still, plenty of time to sort it out over the winter ready for trips out in better weather.
 
Z Victor 1 said:
Hope it's nothing expensive Paul, don't need that at Xmas. Still, plenty of time to sort it out over the winter ready for trips out in better weather.
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Thanks Ken, Car runs very well other than this glip, hopefully not the clutch but as it looks like its a keeper at least it will be one less thing to go in the future
 
Paul Rice said:
Having a possible issue with the 2.5 Z4.

Symptom: Sudden rise in revs when accelerating between 3 - 3500 rpm? car does accelerate but not in relation to the revs.

Initial thoughts Clutch, after doing the following test, Handbrake on 2nd gear move off car stalls (As it should) so no clutch slip!

Never having a straight six BMW engine before, Is this a character of the engine or a clutch fault not shown by the above test or something more sinister.

Any thoughts?
Click to expand...
I can't say for sure what could be the problem. Over 50 years of driving a clutch, however, this has happened to me on 4 or 5 occasions. The clutch would start to slip in the highest gear. Just a little at first. Then the slip would start to be more pronounced. As it worsened, it would start to slip in the next highest gear. If it was a 5 speed, by the time it started to slip in 3 gear, it was only a few miles away of totally going bad. With those cars, there was a clutch cable that could be adjusted. While this helped, it was a signpost telling of what was up ahead. I hope its something causing the problem that's easy to fix that I'm not aware of on newer cars...............Frankie
 
Paul Rice said:
Rapid rise from 3 t

Rapid rise to 3500 then straight back down to 3000 so not the pedal, nice idea though, cheap fix
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Is it not fly by wire on those? Might be worth getting codes read.
I once drove a 330i that had a weird fly by wire throttle issue that made it impossible at low speeds.
 
I think I read somewhere that theres an inspection plate on the bell housing for checking the clutch assembly although the pressure plate would obscure it
 
Hi Paul, I think I would keep driving it to either fix itself as it's possibly a glitch due to lack of regular use or it will get worse gradually to the point of being obvious what is wrong. Either way fingers crossed for a cheap fix.
 
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