Z3 M52B28 - Rev Drop

[Jjim]

My Z3 is a prefacelift 2.8 - M52B28 engine. It has the 2.5 inlet manifold conversion and cold air filter.

I was having a rev drop issue under acceleration and high fuel usage. I ran the fault codes and found a permanent fault on the Cam sensor. So I ordered and fitted a new one from BMW. This fixed the fault code and improved the fuel consumption.

I am still having a problem with the revs dropping during acceleration.

An example of this is that I have changed up a gear and I am pressing the accelerator pedal (and holding it at the same point), and the revs will initially rise constantly and then dip 500 and then start to come back up.

My next thought is to search for a vaccuum hose / leak.

I want to get the car remapped anyway, but I need to get the revs working first.

Any thoughts or help would be greatly appreciated.

 

[Lee]

I think I understand what your saying, do the Rev's hang or slightly increase when you go to change gear ?

Me and @Dino D had been chasing something similar for a while and tracked it down to the ICV letting in too much air. We both fitted a restriction in the body of the ICV.

If this is the issue I can send you a link to the how to guide.

 

[Jjim]

I think I understand what your saying, do the Rev's hang or slightly increase when you go to change gear ?

Me and @Dino D had been chasing this for a while and tracked it down to the ICV letting in too much air. We both fitted a restriction in the body of the ICV.

If this is the issue I can send you a link to the how to guide.

Before I changed the Cam Sensor it would drop immediatly, since changing for a new sensor I change gear the revs then increase for a second and then drop.

 

[colb]

So no new codes after the replacement cam sensor, best check for air leaks as you suggest, best way will be to smoke test the system with a warmed up engine that way any cracks or splits will have expanded so if they are there smoke will appear and pinpoint the leak(s). Used my home made smoker on a 2.2 that had leaks, would not have found the cracks it had in the cam cover without the smoke machine. This one had bad overfueling because of the unmetered air getting in, knew this by looking at live data of the Short term and long term fuel trims, it was adding 20% more fuel as it thought it was running lean because of the extra unmetered air being seen by the exhaust sensors. In this case a replacement cam cover was fitted with new gaskets and that solved the air leak. Fuel trims returned to normal as soon as we started the car after the fix.
Story and pictures of smoke testing on this thread https://zroadster.org/threads/zed-shed-south-wales.30225/
You are a bit far away from me otherwise I would have smoked it for you.