Poorly Z4M, Idle bounce and poor throttle response/misfire

[Darren Slone]

I'm loving this thread!

As I have said before I'm not very hands on, read into that " at all" but this is fascinating, ps I still don't understand it all though

 

[goon]

Mine has the engine light on and tickover allover the shop must get it done soon.

 

[Adam D]

Latest update:

Have been using BP ultimate unleaded for a few hundred miles now and the idle dip/bounce has improved significantly as has the splutter from idle when blipping the throttle.

I plan on monitoring for the remainer of this tank of fuel and then try 1/2 tank of Vpower to see if there are differences in behaviour.

I did try to clear the idle valve via the top breather hose and some carb cleaner but this made no improvement when running the previously Tesco 99 fuel.

A new set of plugs probably wouldn't hurt, 34000 miles seems a lot in a performance engine. Inspection 2 is not going to happen for another year and a half which will probably be another 12000 miles away.

 

[exdos]

Since I discovered that my Z4MC appears to have a Absolute Throttle Position maximum opening of 76%, I thought I'd datalog this issue on my Z3MC (drive-by-wire), which I know records an ATP of 100%. So I took it for a run this morning and below is a graph from the ECU data.

It would appear that the "Calculated Load" is in fact the signal from of the accelerator pedal unit, and unlike a cable operated throttle, the drive by wire system progressively opens the throttles to match the increase in engine revs/ air consumption. From the graph, it would appear that the Absolute Throttle Position will only reach 100% at the "redline" (7600rpm for the Z3MC).

In the next few days I'll do a similar run with my Z4MC and it will be interesting to compare with this.

 

[Alastair]

Just to add more interest to this thread - I also have the rough-return-to-idle-from-blipping problem, though everything else about the car seems fine. No codes stored, etc. So very interested to see all the thinking that has been going on here, and hoping we can work out a possible solution soon!

 

[ga41]

Have your shop check your fuel injectors, mine had 2 or 3 of them that were out of spec. That helped i think. I can't be sure what exactly is the cause of this, probably a combination of things and i've had many things replaced already...

Car is still gone however as i'm getting the wheels refurbed. I haven't forgotten about this thread though and will update you all with any further findings.

 

[Adam D]

Update:

My original issue has significantly improved.

I have switched to BP ultimate unleaded fuel for the last two tanks, I also gave it a Italian tune up last weekend getting everything nice and warm

From reading it appears most fuels in the UK now have 5% ethanol added, web research suggests that BP ultimate does not contain ethanol (unless bought in the south west for some reason). Perhaps the introduction of ethanol into Vpower and it's use in Tesco 99 momentum affects the engine fueling at idle. Ethanol has a lower calorific value and leans out the fuel mixture leading to hotter running and higher consumption as the engine increases fuel injected to compensate, the normal oil temps seem a slightly lower on the gauge now compared to operating on Tesco 99.

The dip on idle if you tap the throttle is now quite minor and the engine response much improved with immediate thrust delivered at small throttle openings. The misfire coming off idle completely gone.

It would be interesting to see if other M's respond well to the BP fuel. I have just bought some Denso IXU24 Iridium Power spark plugs which will be replacing that stock NGK plugs at 34k miles. I hope to measure the resistivity of the coil packs as part I that job.

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[sammyz]

Had my 'M' for 5 years now, usually use tesco 99, no idling issues, no sensors failed 32,000 miles in and seems fine. Maybe uses a little more fuel than two/three years ago.

Always warm her up (oil up to temp) then give her a full thrash through the lower gears up to 7-8,000 rpm to get her blood circulating! Do this even through Winter when the car lives in the garage and only comes out every couple of weeks for a dry weather run.

 

[exdos]

I also gave it a Italian tune up last weekend getting everything nice and warm

Do this even through Winter when the car lives in the garage and only comes out every couple of weeks for a dry weather run.

IMO, these two things are essential for any car, but particularly for one which is virtually laid up for any length of time.

 

[RubyBlueZ4MC]

I recently used Tesco 99 for the first time and felt that my M was not right at all. Reverted back to a full tank of BP Ultimate and all is well again

 

[Shooter]

Do you know who produces the Tesco 99 ? BP, Shell, Exxon, Total ?

 

[exdos]

I've now datalogged my Z4MC for Throttle Position in the same way that I did for my Z3MC in the earlier post and the graph is below.

It would appear that the Z4MC is ECU mapped in a totally different way to Z3MC and that the Throttle Position Sensor shows that the throttle is definitely limited to 76% maximum opening. Over the few weeks that I've had my Z4MC I've fitted a pair of gutted exhausts and done some air-intake mods, all of which have increased the airflow for my Z3MC, but which have had no effect on airflow to the Z4MC. I cannot get the airflow of the Z4MC beyond 31lbs/min, even with the redline at 8000rpm, whereas with my Z3MC, I've been able to increase the airflow to over 34lbs/min with a redline at 7600rpm and with a noticeable and provable performance gain.

It therefore appears to me that the Z4MC is definitely deliberately restricted by the engine maps in its power output. Are there any engine tuners in our midst who can explain this more?

 

[ga41]

Might explain how some reputable tuners can get gains of up to 20hp with a remap on Z4Ms...

 

[daz05]

Exdos liking your work, we need a mapper on here ASAP!

 

[Gargybloke]

Interesting stuff....a question I always wanted to ask, the Bmw specs say the engine runs best on 98 so should we really be using Tesco 99?

 

[BMWZ4MC]

I've now datalogged my Z4MC for Throttle Position in the same way that I did for my Z3MC in the earlier post and the graph is below.

It would appear that the Z4MC is ECU mapped in a totally different way to Z3MC and that the Throttle Position Sensor shows that the throttle is definitely limited to 76% maximum opening. Over the few weeks that I've had my Z4MC I've fitted a pair of gutted exhausts and done some air-intake mods, all of which have increased the airflow for my Z3MC, but which have had no effect on airflow to the Z4MC. I cannot get the airflow of the Z4MC beyond 31lbs/min, even with the redline at 8000rpm, whereas with my Z3MC, I've been able to increase the airflow to over 34lbs/min with a redline at 7600rpm and with a noticeable and provable performance gain.

It therefore appears to me that the Z4MC is definitely deliberately restricted by the engine maps in its power output. Are there any engine tuners in our midst who can explain this more?

Very interesting findings Exdos

If the throttle openings and airflow differ as you describe, why is the quoted power figure for the S54 in the Z4M and E46 M3 338bhp whilst the same engine produces only 325bhp in the Z3M?

I could understand if BMW artificially restricted the Z4M so that it wouldn't out perform the E46 M3. Even more so if both the E46 M3 and Z4M were equally restricted. That way the S54 engine could be allowed derestricted throttle opening along with the other engine mods to give the CSL more power. But that doesn't explain why the late model S54 Z3Ms should be allowed to achieve full throttle opening when they wouldn't want for that car to be perceived as better than the then brand new E46 M3.

What we need to do is to data log a standard E46 M3 (M@rK) and a CSL (Toplad) exactly as you have for your cars. It would be very interesting if the CSL throttle performed as your Z3M, and the M3 the same as the Z4M...

Do you think that your intake and exhaust back box mods improved airflow in the Z3M but not the Z4M solely due to the throttle issue you describe? Or could it be that the Z3M has a more restrictive intake and exhaust as stock (which could be improved upon), whilst the Z4M system is less restrictive in these areas, and the restriction to airflow lies somewhere you have yet to modify?

Out of interest, where are you in the country? If you want another Z4M to datalog, I'm a willing volunteer. I have Remus back boxes, and I'll be making intake mods imminently...

 

[exdos]

Very interesting findings Exdos

If the throttle openings and airflow differ as you describe, why is the quoted power figure for the S54 in the Z4M and E46 M3 338bhp whilst the same engine produces only 325bhp in the Z3M?

Using my Dashdyno, I've already done baseline dyno runs and it confers with the published figures for the Z4MC. I've used the Dashdyno for other cars and it is very reliable and I trust it.

I could understand if BMW artificially restricted the Z4M so that it wouldn't out perform the E46 M3. Even more so if both the E46 M3 and Z4M were equally restricted. That way the S54 engine could be allowed derestricted throttle opening along with the other engine mods to give the CSL more power.

That's my thinking. I originally got into air-intake modding of my Z3 MC in an attempt to discover why my S54 engine made less torque/power than the E46 M3 and it transpires that the air-intake/exhaust are both restrictive essentially because of the "reverse flow" design for silencing reasons. Remove the reverse flows and Hey Presto you're in the same torque/HP band! From data-logging and my own scientific curiosity I've also discovered a few other little tricks to increase the air pressure in front of the air-intake system which additionally induces more air through the MAF, and the ECU maps seem sufficiently wide in operation to accommodate this and increase the fuelling to match. I've had no reason to ever think of remapping my Z3MC it just gets better with the more air I can feed it. I was expecting/hoping the Z4MC would be the same, but this doesn't appear to be the case.

But that doesn't explain why the late model S54 Z3Ms should be allowed to achieve full throttle opening when they wouldn't want for that car to be perceived as better than the then brand new E46 M3.

BMW probably didn't expect someone like me to spend as much time and effort on analysing the air-intake of the Z3MC

What we need to do is to data log a standard E46 M3 (M@rK) and a CSL (Toplad) exactly as you have for your cars. It would be very interesting if the CSL throttle performed as your Z3M, and the M3 the same as the Z4M...

I'm meeting a friend this week who has an E46 M3, so I'll see if I can datalog his car.

Do you think that your intake and exhaust back box mods improved airflow in the Z3M but not the Z4M solely due to the throttle issue you describe? Or could it be that the Z3M has a more restrictive intake and exhaust as stock (which could be improved upon), whilst the Z4M system is less restrictive in these areas, and the restriction to airflow lies somewhere you have yet to modify?

I think that the problem is solely down to the throttle issue in the Z4MC. Take a look at the graph below, which I've compiled from the data that appears in the previous two graphs of my Z3MC and Z4MC I've posted in this thread. What I have done is divide the airflow, as recorded by the MAF, by the RPM for each line of datalogging at approx. 0.5sec intervals and then multiplied the figure by a constant (1000) so that it would appear above "0.0" on a graph to give a "cylinder fill quotient". If you then compare the plots for the Z3MC against those for the Z4MC, you'll see that my Z3MC fills the cylinders more than the Z4MC does because I've been able to harness the "ram effect" and the Z3MC will accommodate this.

In comparison, the Z4MC ECU seems to "refuse" to increase the throttle opening beyond 76% and so won't allow the potential air flow (because of increase in pressure from my mods) to produce a greater Volumetric Efficiency, whereas the VE of my Z3MC just increases with each beneficial air-intake/exhaust mod.

Out of interest, where are you in the country? If you want another Z4M to datalog, I'm a willing volunteer. I have Remus back boxes, and I'll be making intake mods imminently...

West Midlands. I'll send you a PM.

 

[SweetRide]

Might explain how some reputable tuners can get gains of up to 20hp with a remap on Z4Ms...

Exactly. It's also why running a tune (like ESS, Evolve, AA etc) is the PROPER way to take advantage an aftermarket CAI (AFE, GruppM) and to free up the extra power via a more aggressive map. You can throw headers into that mix too. Those items may work on the car, but until you have a tune that can take advantage of them... You're leaving power on the table.

 

[SweetRide]

It would appear that the Z4MC is ECU mapped in a totally different way to Z3MC

It's leagues different than the Z3MC AND the E46 M3. That's why there's a comparatively small # of tuners for our cars. Small production numbers and complicated tune-ability = make sure the right shop touches your car.

 

[exdos]

It's leagues different than the Z3MC AND the E46 M3. That's why there's a comparatively small # of tuners for our cars. Small production numbers and complicated tune-ability = make sure the right shop touches your car.

Please can you expand on what you know about the Z4MC's ECU and mapping so that I can ask the "right" questions of certain tuners?