Flat, poor response-what to check?

[exdos]

In my opinion there is a sensor giving bad output that the ECU is adapting to.

Which sensors can be suspect that won't throw error codes? Have you checked for air leaks around the secondary air pump and other small pipe connections into the inlet pipe attached to the plenum etc.?

Lots of sensors can start to go bad and no put out an out put that is linear to the input. The throttle position sensors are my prime suspect as it would be quite possible for them to giving an output that is not linear to the input that the ecu is then trying to compensate feo.

There are no air leaks i can find.

This document might help. http://www.unofficialbmw.com/images/m3engineelectronic1.pdf I know the Z4M has a different DME but there's a comprehensive list of sensors in that document which I assume must be the same for the S54 engine.

Bearing in mind that you're not getting any error codes, could the idle actuator be a suspect besides the TPS? What about the ignition coils or even a damaged spark plug?

 

[beanie]

Just a quick update on this.

The car has been to BMW and they've run a diagnostic on it. No faults were found and in their opinion its fine. I disagree with this so i've ordered a TPS and a couple of spare intake clips to see if this makes any difference.

Ill also give everything a good clean whilst i'm there so as and when i get round to it i'll let you all know how it goes.

thanks for all your input so far chaps, with any luck this will work and i'll be able to get good crisp blips on the downshifts!

 

[Adam D]

Just a quick update on this.

The car has been to BMW and they've run a diagnostic on it. No faults were found and in their opinion its fine. I disagree with this so i've ordered a TPS and a couple of spare intake clips to see if this makes any difference.

Ill also give everything a good clean whilst i'm there so as and when i get round to it i'll let you all know how it goes.

thanks for all your input so far chaps, with any luck this will work and i'll be able to get good crisp blips on the downshifts!

Same response when BMW looked at mine twice... although they did replace the MAF on the second occassion.

 

[dalecan]

Just a quick update on this.

The car has been to BMW and they've run a diagnostic on it. No faults were found and in their opinion its fine. I disagree with this so i've ordered a TPS and a couple of spare intake clips to see if this makes any difference.

Ill also give everything a good clean whilst i'm there so as and when i get round to it i'll let you all know how it goes.

thanks for all your input so far chaps, with any luck this will work and i'll be able to get good crisp blips on the downshifts!

Why not ask them to do back-to-back runs with another car as the baseline?

 

[beanie]

Trouble is, they're not exactly common dealer fodder these days, least of all in italy where high taxes and petrol costs mean any M is a rare sight- i think I've seen just one z4m the entire time I've been out here so whilst its a good idea, I would have been waiting a while for that test!

Either way, Im convinced it's not quite right as even my old golf responds better to throttle blips. At virtually any point in the rev range all that's required is a quick jab and the revs flare nicely, it makes such a difference to my enjoyment of a car and makes every downshift, corner or roundabout approach so much more fun if I can get the same level and consistency of response from the Z then I'll be a happy man :wub:

 

[RobertRO]

A possible solution is to talk with Evolve guys and check if they can tweak the ECU to work with a traditional cable actuation of the throttle, instead of drive by wire.
Most likely, this change also implies cancelling the DSC, but for some Z4M owners that would be acceptable.

Since there are 2 throttle position switches (TPS), I suppose that one is used by the ECU to determine the actual opening of the throttle butterflies and thus calculate fuel and timing, and the other is probably used as a feedback for the drive by wire (= throttle by wire) system.
So it may not be extremely difficult.

If Evolve (or other tuner) may be able to tweak the ECU, then I'll gladly convert to cable throttle. I am positive that such a change would bring us a crisp throttle response.

 

[beanie]

Thought I'd give this a quick bump to update and see if anyone else has progressed with their hesitation issue.

I recently had a bit of paint done by the local BMW dealers (usual stone chip areas) and for some reason they must have disconnected the battery as mpg was reset and the windows lost their one touch function. Upon getting it back the car was better than ever, really responsive and all signs of hesitation had disappeared. It was a revelation and completely different to how it feels with a throttle reset.

Sadly, it's now returned to more or less how it was despite no longer being used for slow, menial driving and blips of the throttle at lower revs take more effort than they should. I don't find it such a big deal but knowing how crisp it can actually be has reignited my motivation to sort it!

I haven't had the tps fitted yet as I've been wanting to do it myself so I can get in and clean everything up but as I now have a garage to keep it in and the weather is crap I'll try and get it sorted when work subsides.

Edit: saying all that, I've been mighty tempted by the csl airbox like woots has. Perhaps this is the only solution....

 

[Putter Whore]

This is really interesting. I'm not at all technical. But I've noticed that my car seems to have slowed in its pick up in the two years I've owned it. At first I put it down to getting used to the power. But now I'm positive that it is slower at low revs but pretty much as fast as its always been when above c3500 revs. I've also noticed its increasingly hard to get a smooth change between 1-2 and less often 2-3 gears, so much so that it really spoils my enjoyment of the car. I reckon it's because the revs die off too quickly. However it drives at its smoothest when cold and the choke is kicking in.

I'm taking my car into a local independant who I've used since getting it. So will update you next week. He suggested plugging it in to see if anything crops up. As a side note and to support Exdos comments, I was also told to make good use of the power frequently, which I am more than happy to do. I do a lot of driving in traffic so feel its needed.

 

[Peter G]

I had same problem where car didn't seem responsive and would occasionally splutter. Then emission light was intermittent. Turned out to be a crankshaft sensor and a loose pipe on the manifold, under £200 to fix at main dealer. Drives great ever since.