UPDATED::: Z4M S54 Engine Hesitation - POLL

[Buzzard88]

What I have noticed though is that if I disconnect the MAF sensor then things are perfect but I guess doing this just means the DME is running in open loop mode. But it's interesting and probably points far away from there being a VANOS problem and more likely to be a sensor or leak problem.

[pcube]

Have you tried twisting the pins on the MAF sensor connector? This seemed to do the trick for me

Can I ask what pins you mean ?
Thanks

Somewhere in the middle of this thread it was mentioned. That forum member also used some kind of contact enhancer but I didn't.

[Spaniarduk]

Another update..

Thoroughly cleaned ICV, hoses, throttle bodies, butterflies. Replaced the throttle actuator sensor, inspected all lines. Problem persists. Bugger!

The ICV didn't really feel a concern when I initially removed it but once or twice I thought it was a little hesitant to move when shaking from side to side but that could have been where it was balance at the time and direction of the shake.

The procedure is not as bad as I thought. It probably took about 30 minutes to remove / disassemble, 60 minutes to clean, 60 minutes to reassemble, 10 minutes to feel disappointed about wasting my time.

Tomorrow my Lambda sensors arrive and will do the pre and post cats. If this fails to cure the problem then I don't know, maybe I will focus on the VANOS. FU&^^&%^%$%45.

Buzzard88, I'm following your progress with interest! As for the VANOS.... you may want to have a look at the following link and subsequent pages after that one. In particular the comments from Attilio .

Let us know how you get on after youve replaced the pre- and post-cat O2 sensors

[Buzzard88]

So I still haven't done the post cat sensors yet, but today I replaced all injectors with new units and still the same which is what I suspected would happen.

I can't help but keep going back to disconnecting the MAF sensor and everything is fine. From my understanding disconnecting the MAF sensor should run the DME in open loop mode??? Can anyone confirm this? Can anyone also confirm what sensors are ignored in open loop mode?

This week I will get around to doing the post cat sensors but I think they have no feedback on how the DME prepares the fuel & air.

[Spaniarduk]

I always thought the post cat sensors are there to feed back to the ecu and, if required, the ecu will make the engine run incrementally leaner for a given amount or air (there is the feedback from the air mass sensor) until such post-cat sensors are 'happy' with what they 'sniff' past the catalytic converters... i could be wrong, though.

[ph001]

It’s the pre-cat sensors that influence the mixture but even then only under light and steady state throttle. Under full throttle the lambda is ignored and mixture is calculated from the map (i.e injector duration is matched to airflow meter signal). So at full throttle you are essentially running open loop. Steady state throttle and idle is closed loop. If you disconnect the afm and run full throttle it must use some default value not part of the mapping.

[Lower]

So I still haven't done the post cat sensors yet, but today I replaced all injectors with new units and still the same which is what I suspected would happen.

I can't help but keep going back to disconnecting the MAF sensor and everything is fine. From my understanding disconnecting the MAF sensor should run the DME in open loop mode??? Can anyone confirm this? Can anyone also confirm what sensors are ignored in open loop mode?

This week I will get around to doing the post cat sensors but I think they have no feedback on how the DME prepares the fuel & air.

My understanding is that when the MAF is disconnected the ecu ignores all the adaptions/fuel trims. I think its a bad sensor that has pulled the adaptions to a point where the hesitation exists. Resetting the adaptions normally fixes the problem for a while until the adaptions have moved to the point that its a problem again. That in turn makes it difficult to identify the cause of the problem in the first place because everytime you change something you need to clear that adaptions which in turn make the problem go away for a while.

[Buzzard88]

Ok thanks to all who have responded. Your time is appreciated and valued to me.

Just confirming my only problem seems to be during idle. If the car is idling normal then if I stab the throttle quickly then it's so unresponsive and almost seems like or is a misfire.

If this happens when I am stationary and releasing the clutch then the car nearly stalls and definitely would sometimes if I were not managing it with my two feet. What it basically means is that I have to bring the revs on excessively early, so it has it's little hissy fit, prior to releasing the clutch. After this and at higher revs the car is super awesome as it should be!

This also makes it such a lucky dip when trying to match the revs when downshifting.

I can have the car parked in the driveway with the engine running and in neutral, stab the throttle and burrrr (misfire or whatever it is). Then I can immediately disconnect the MAF sensor and it responds nicely and sharply to the throttle stab with no sign of burrr. While typing all this again my brain is saying ICV once again but I gave that a thorough clean and it wasn't too dirty at all. Perhaps I should try a new ICV. Soon I'll have enough parts to build a new car!

I am not totally convinced this is a misfire though. I actually think it is just a really bad fuel / air preparation cycle.

So my understanding is that the DME is operating in closed loop when my problem occurring.

[Buzzard88]

After looking for the post cat sensors I couldn't even find the cats. Now I feel pretty stupid as Australian cars are the Euro spec which apparently don't have cats at the headers, they are way back underneath the car.

[ga41]

After looking for the post cat sensors I couldn't even find the cats. Now I feel pretty stupid as Australian cars are the Euro spec which apparently don't have cats and therefore no sensors. So if anybody needs a new pair let me know.

Back to the drawing board on this one..

Euro cars just have the main set of catalytic converters. US cars have an extra set on the exhaust manifolds.

Euro: http://www.realoem.com/bmw/enUS/partgrp ... _M32&mg=18

US: http://www.realoem.com/bmw/enUS/partgrp ... _M32&mg=18

[Buzzard88]

After looking for the post cat sensors I couldn't even find the cats. Now I feel pretty stupid as Australian cars are the Euro spec which apparently don't have cats and therefore no sensors. So if anybody needs a new pair let me know.

Back to the drawing board on this one..

Euro cars just have the main set of catalytic converters. US cars have an extra set on the exhaust manifolds.

Euro: http://www.realoem.com/bmw/enUS/partgrp ... _M32&mg=18

US: http://www.realoem.com/bmw/enUS/partgrp ... _M32&mg=18

Thanks ga41. I was just editing my post to correct it but you beat me to it. Going out to do them now.

[BMWZ4MC]

After looking for the post cat sensors I couldn't even find the cats. Now I feel pretty stupid as Australian cars are the Euro spec which apparently don't have cats at the headers, they are way back underneath the car.

Where are you based in Aus?

[ph001]

I am not totally convinced this is a misfire though. I actually think it is just a really bad fuel / air preparation cycle.

So my understanding is that the DME is operating in closed loop when my problem occurring.

Yes, what you are essentially doing by stabbing the throttle from idle is transitioning from closed loop control (a/f ratio controlled by lambda sensors) to open loop control (a/f ratio controlled by ECU map against air flow meter signal). I'm just wondering that if by disconnecting the air flow meter the ECU never runs in the open loop state (because it's has no air flow information to allow it to do so), so you aren't going from one state to the other. I'm betting it stays in closed loop control all the time with the AFM disconnected.

[Muckinonthesofa]

I am not totally convinced this is a misfire though. I actually think it is just a really bad fuel / air preparation cycle.

So my understanding is that the DME is operating in closed loop when my problem occurring.

Yes, what you are essentially doing by stabbing the throttle from idle is transitioning from closed loop control (a/f ratio controlled by lambda sensors) to open loop control (a/f ratio controlled by ECU map against air flow meter signal). I'm just wondering that if by disconnecting the air flow meter the ECU never runs in the open loop state (because it's has no air flow information to allow it to do so), so you aren't going from one state to the other. I'm betting it stays in closed loop control all the time with the AFM disconnected.

Interesting. Excuse my ignorance but is it safe to run without the AFM connected?

[AndyBeech]

When you disconnect the MAF the car reverts to the Alpha-N map, which I believe estimates air volume instead using the engine speed and TPS. Do some Googling on it but IMO disconnecting the MAF doesn't prove anything conclusive as it doesn't really help you narrow down if a sensor is giving you an issue as the mapping has changed.

Have you tried INPA / DIS yet, see if you can run some tests and check for error codes. I fear your going to end up replacing a lot of expensive parts for no reason. For example, the ICV replacement is pointless, it really just works or doesn't it's a simple valve that opens and closes as you would have seen. Cleaning it is good but I wouldn't waste money replacing it.

It's safe to run without the MAF connected but absolutely no reason to do so long term unless you've specifically had Alpha N tuned for your modifications, such as running a CSL airbox where you have no MAF for example.

Oh, INPA would be useful for checking your long term trim's/adaptations, see if there's anything untoward there