Poorly Z4M, Idle bounce and poor throttle response/misfire

[Adam D]

I have almost exclusively been running on Vpower 99 but sometimes use Tesco Momentum 99 both performed similarly with less mpg with Tesco fuel. I understand Tesco 99 has a 5-10% ethanol added, Vpower now also uses some ethanol I believe.

Since I'm heading up to Silverstone tomorrow I topped my tank off with 25 litres of BP ultimate as that is nearest to me; I don't usually use it. The car seems happier on this and the idle dip seems to be improved - further use of this fuel will be tried to see if its a fluke.

Prior to posting I watched this video about the S54 coilpacks on youtube, I have used a glass of water to see if mine is producing any undue vibrations which might indicate a sparking problem (warm engine, 60/40 mix of Tesco 99/BP SUL, air con off). As far as I can see it looks pretty normal.

[youtube]z37jl4HXQjg[/youtube]

[youtube]oY_Nngik7aY?hd=1[/youtube]

As suggested above I thought I would revisit disconnecting the Throttle Position Sensor. The engine responded more keenly and crisply to the throttle pedal and revs freeier, it seems to protect itself more on idle with a little bounce. I did not drive the car and only undertook a static test.

[youtube]bKvXhol-C2Q?hd=1[/youtube]

With the TPS reconnected the throttle seems laggier and revs less freely - as if the throttle is on an elastic band. You wouldn't notice this unless you had experienced a similar car operating normally - you would perhaps put it down to the Drive By Wire throttle.

[youtube]r9D-9V-kKhM?hd=1[/youtube]

I will try to get some better videos in due course and will update the thread with any information I can gather.

 

[ga41]

It's difficult to see any difference in the two videos mate without actually feeling when and how much the throttle pedal is pressed.

 

[exdos]

ga41,

From what you've said, I think you might have come across part of the answer to a question which has puzzled me for some time, which is: What has BMW done in each vehicle model which has given different performances from the same S54 engine in the Z3MC, E46 M3, M3 CSL and Z4MC?

Since I got my Z4 MC I've done some baseline datalogging and I've been comparing this information with all the datalogs that I have for my Z3 MC, with the same S54 engine.

From this work, I've found that although the OEM air-intake of the Z4MC is very efficient (i.e. located in a zone of high pressure confirmed by pressure -v- speed recording with a Magnehelic Pressure Gauge) the actual air consumption recorded at the MAF is relatively less (per cylinder fill) than that recorded at the same RPM/speed from the MAF of my Z3MC (taking into account the different gearing). I have done a fair few different air intake mods to my Z3MC which, combined, have considerably increased the volumetric efficiency (VE) of the engine, which might explain this difference in airflow between the Z4MC and the Z3MC, and I'm about to do similar air intake mods to my Z4MC in an attempt to increase its VE.

I know for sure from ECU datalogging that the throttle position of my Z3MC opens from 7.4% to 100%, and I'll do some datalogging of my Z4MC in the next few days, and will specifically check the throttle position performance. I have a Citroen C2 VTS as a runabout/lugger, which has a throttle which will only open in the range from 17.6% to 76.9%. I had this thoroughly investigated by a Citroen dealer, who replaced all the parts of the entire air intake, and it was concluded that throttle opening is deliberately restricted by the ECU software (which is apparently very hard/impossible to remap on this Citroen), so I'm wondering if BMW has deliberately restricted the throttle in the Z4MC? If so, why?

In view of the fact that the E85/86 ///M was the only model which BMW installed the S54 engine in 2007/2008, then I think it would be right to assume that the S54 engine in the E85/86 ///M must have been manufactured from the strongest and most up-to-date revised parts. Would it be possible that the S54 engine, as fitted to the Z4MC/R, is actually identical to the S54 engine fitted to the M3 CSL and is deliberately restricted from matching M3 CSL performance by limiting throttle opening? Have we all got M3 CSL engines with higher-lift camshafts waiting to be unlocked? Lumpier idling with aggressive cams is a well known feature. I wonder?

 

[exdos]

0


In order to show what my datalogging involves, here's a video showing the kit I use. Click on the image if you'd like to play the video:



Both Magnehelic pressure gauge and DashDynoSPD are both mounted so that I can video record the pressures recorded by the pressure gauge at the same time as any other parameters recorded by the DashDyno. The DashDyno records information directly from the car's ECU directly onto a SD card. The data on the SD card can then be used by DashDyno software on a PC, and it can be read and examined directly within that software. The data can also be exported into other formats, (I use multipoint .csv) which can then be opened in Excel, where the information can be used in various formulas (I often calculate Volumetric Efficiency) and then various graphs can be prepared comparing several different logs in one graph etc.

The Magnehelic pressure gauge operates by using two tubes, where the pressure in one tube is compared with the pressure in the other. Since I wanted to see if there was positive pressure inside the Z4MC's air filter box relative to ambient pressure, I located a length of tube from the pressure gauge out through the passenger window, through the bonnet and into the air filter box; the other tube remained inside the car. When the needle moves to the right on the gauge, this shows that the pressure inside the air-filter box is above ambient pressure, and is benefitting from the "ram-effect" by the location of the opening of the OEM air-intake being in a zone of high dynamic pressure when the car is moving.

Below is a graph that I prepared from some data that I recorded to act as the baseline of my car in absolute OEM state, from which I can compare any mods that I might do.

 

[SweetRide]

I must be just lucky then but I have never noticed any stalling or ide rpm drops. Is it really a common thing?

There are loads of folks over here that have the 'dip' at idle. I don't think anyone's gone to as great of lengths to diagnose the issue however (as above)

 

[Gargybloke]

Interesting stuff exdos. When you look up the z4m camshaft part numbers on realoem, they only match to the non-csl M's though.
As it is a high performance engine, made for singing at high revs, perhaps we should all expect it to be a little lumpy at low revs? Its a great engine though, when I got the car I was initially surprised at how well it does cope at lower revs, in slow traffic and pulls smoothly from low down.

 

[ga41]

Interesting stuff exdos. When you look up the z4m camshaft part numbers on realoem, they only match to the non-csl M's though.
As it is a high performance engine, made for singing at high revs, perhaps we should all expect it to be a little lumpy at low revs? Its a great engine though, when I got the car I was initially surprised at how well it does cope at lower revs, in slow traffic and pulls smoothly from low down.

That's the problem, mine doesn't.

 

[Gargybloke]

I am sure it will sing sweetly again ga41, its got a great owner after all

How about something to do with the fuel pump itself? Has that been discounted?

 

[ga41]

I am sure it will sing sweetly again ga41, its got a great owner after all

How about something to do with the fuel pump itself? Has that been discounted?

If you'd see the state of my alloys you wouldn't say i'm such a great owner... It was wet, I tried to kick the tail out and a kerb just jumped in the middle of the road and hit me! At least that's my excuse. They're going for a refurbishment in a few days though.

Anyway back to the matter at hand! I mentioned checking the fuel pump and he said he already checked its flow rate and all was normal... :idunno:

 

[exdos]

ga41,

I've just been for a drive in my Z4MC with the ECU datalogger hooked up, and below is a screenshot of that entire run as appears in the datalogger's software on my PC. As can be seen from the red graph ((Absolute Throttle Position) the range of throttle opening on my Z4MC is from 7.1% to 76%. It would thus appear that ALL Z4MCs have restricted throttle opening (as I suggested might be a possibility) and therefore, you are not alone!

Please can you find out from your mechanic if the maximum throttle opening that he has found on your car is at 76%, not only from his diagnostic hook-up, but also as visually measured at the throttle bodies when the plenum has been removed and the accelerator is fully depressed?
Likewise, is the hardware physically capable of opening the throttle bodies to a full 100% or is the restriction entirely down to the software management of the "drive-by-wire" throttle system which prevents the hardware from opening the throttle 100%?

It seems to me that the Z4MC's engine is deliberately detuned and should be capable of enhancing either by relatively simple hardware changes or remapping in a way that permits 100% throttle opening.

 

[ga41]

exdos, please send me a larger version of that screen-shot to forward to my mechanic if you can. I'll PM you my email.

He pretty much ruled out any possibility that it's a mechanical or sensor fault that's causing the 76 degrees only opening. He was going to run the car on the road and read the throttle body openings while driving to see if it's something only happening when stationary or something. He said that on all M3's he's ever tested the throttle bodies they all opened at 90. He never had another Z4M though so he can't be sure that it's not simply normal for us... Sounds odd if it did though...

 

[ga41]

exdos, and also to confirm, you are NOT experiencing any issues like me and Adam D. Correct?

 

[exdos]

exdos, please send me a larger version of that screen-shot to forward to my mechanic if you can. I'll PM you my email.

He pretty much ruled out any possibility that it's a mechanical or sensor fault that's causing the 76 degrees only opening. He was going to run the car on the road and read the throttle body openings while driving to see if it's something only happening when stationary or something. He said that on all M3's he's ever tested the throttle bodies they all opened at 90. He never had another Z4M though so he can't be sure that it's not simply normal for us... Sounds odd if it did though...

I've also saved that information in .csv format, so I'll prepare a graph for you in Excel too.

As I said in an earlier posting, my Z3 MC has a throttle range of 7.4% to 100%, so the opening to a max of 76% seems unique to the Z4MC/R.

exdos, and also to confirm, you are NOT experiencing any issues like me and Adam D. Correct?

There's absolutely nothing wrong with my Z4MC. Whilst out on that recorded run, I specifically observed the idle on the datalogger's screen and it was held within very close limits.

 

[ga41]

Please note though that it's 76 degrees on mine, not 76%, roughly about 77-78 on a % scale.

 

[ga41]

Got your email.

 

[exdos]

I've delved a little more into this. In the Z4MC, there's a black plastic box on the floor beneath the accelerator pedal which seems to act as "stop", whereas on my Z3MC the pedal can touch the carpet and I get 100% throttle opening. However, I've found that this box is the accelerator control unit, and it is described here: http://www.bimmerfest.com/forums/showthread.php?t=316095

Is there an electronics wizzard on this forum who can tell me if this unit could be easily modified so that this unit can increase the range of throttle opening from OEM of 7% to 76% to one where the range is 7% to 100%. Would any other electronic modification be required to any other parts?

 

[Adam D]

It's difficult to see any difference in the two videos mate without actually feeling when and how much the throttle pedal is pressed.

Agreed, I thought that shortly after posting them. Its hardly scientific and repeatable sitting there jabbing the pedal like a looney (much to the neighbours annoyance I expect)

Really liking the technical investigations some of you gents are able to do; what software and cables would I need to probe the cars brain per se?

This seems interesting, maybe the TPS - a poster halfway down has a idle dipping problem on a Z3M S54.

http://www.zroadster.net/forum/viewtopic.php?f=6&t=9676

Lets just hope its not a misaligned throttle... looks painfully tricky to adjust and not something I would want anyone short of a master tech attempting.

http://tis.spaghetticoder.org/s/view.pl?1/06/55/26

Edit:

This website seems a goldmine of handy information, nothing on the Z4 S54 M but you can look at the TIS for the S54 under the E46 section.

http://tis.spaghetticoder.org/

 

[Gargybloke]

Exdos. Did you see if there is any difference to the final throttle open position with sports mode on? Just a thought which could be stupid as it should be the same.

 

[exdos]

Really liking the technical investigations some of you gents are able to do; what software and cables would I need to probe the cars brain per se?

I originally started out using a PC Laptop with an OBDII cable to a Serial ELMScan device and experimented with lots of different software, some of which was free and some of which was restricted-use Demo stuff. I found that the biggest problem I had was connectivity between ECU and laptop, and wasn't impressed with any of it, although I could see the usefulness of datalogging. I'm a Mac user and I found the messing about with setting up connectivity in Windows with HyperTerminal was a complete pain and totally unreliable.

I did a fair amount of research and decided to buy the DashDynoSPD device about 5 years ago, as found here: http://www.auterraweb.com/ It isn't the most intuitive thing to use, but it has great connectivity and being about the size of a TomTom device, it can easily be window mounted during driving/recording and has a suction fitting which is mega-strong! It can record many hours of data onto a SD card and can be hooked up to a GPS unit so that all your data can be played back in GoogleEarth so you can see precisely what your ECU says at any place/time. When driving at The Ring, I just switch it on and drive, and when I'm home I can then explore the data and see what was happening. I like to see what speeds I was doing around the corners from the data to see if I was trying hard enough. :driving:

The DashDynoSPD comes with bespoke software which also works on a PC and the DashDyno device can be used as a "pass-through" connector to a PC if the car is stationary, or laptop in a moving vehicle, where the larger screen and more detailed interface can be used. It also reads fault codes and clears them; it has a Dynamometer function which I find is very accurate and repeatable (calculates HP/Torque "at the wheels"), it times acceleration and also calculates fuel economy on the move. I've found it extremely useful and it has given me a great insight into the inner functions of my cars. It's not cheap but IMO it's not too expensive either, and it has already paid for itself one way or another, and being "techy", it's provided me with may hours of interest when not driving. I always take it with me when I go buying cars to see if they have any faults recorded; my new Z4MC was fault clear and passed its MOT today

 

[exdos]

Exdos. Did you see if there is any difference to the final throttle open position with sports mode on? Just a thought which could be stupid as it should be the same.

I did put the Sports Mode on at about 750seconds but no difference; it just makes the throttle responsive at the start of pedal travel and doesn't affect the limit of absolute throttle opening or idle. I did check.