push_eax

Hi there,

I've had a problem with my 535d for the last 2 months or so that's been causing me a headache. The problem is as follows:

When I'm at a higher cruising speed, with the engine in DS (6th) and the RPM @ about ~2050-2300 I every so often feel as if the engine has had the power cut off to. The rev counter drops about 300-400 rpm, the car feels as if it has slightly braked (most likely as a consequence of a loss of power), and then goes back to it's commanded speed, as if nothing ever happened.

This only happens during steady and stable driving at the given engine speed. It has never happened during acceleration at those engine speeds. The bad deal is that at the given engine speed, my road speed is usually in range of 140-170km/h, so it is very obvious. Of course, as stated it only lasts for a fragment of a second and then disappears.

On a 500km stretch of highway, this may happen anywhere between 0 and 5 times - so it is quite unpredictable. It is impossible to reproduce voluntarily.

Now, it is interesting that this behaviour started manifesting itself after I had my intake manifold replaced (volutarily) and a new iPod unit installed. This involved a reprogramming session by BMW.

I informed the BMW dealer, and we settled for an upgrade in the hopes that that would solve the problem. Of course it ain't free... However, the dealer also said that it might be some transmission problem (panic).

What do you guys think the problem might be?

Thanks,
Alex

Juffe

Hi Alex,

I had a similar issue with my previous 530xDA, and the local dealer managed to find the reason. It seems that the car "lost" the connection to the gearbox for a fraction of a second, causing a similar feeling as you describe. According to the dealer, there has been a known bug in the software causing this.

Anyway, the car was completely re-programmed with the latest software, and the problem was solved. Obviously, I don't know if your problem is of a similar nature, but well worth a try, as you mentioned yourself.

bertolli

Or it could be a faulty MAF (Mass Airflow Monitor) which normally manages the air intake into the engine. search for MAF in this forum. I'm currently having this issue (so at continious speeds sometimes the engine holds back and then picks up again). It then became worse by also having hick up issues when driving off (I have a manual gear) so I needed a more sensative clutch foot).
Now problem is that when hooking the car up on a computer it states nothing is wrong. However when we disconnected the MAF and took it for a test drive it was much more responsive. So I'll be ordering a new one which would hopefully resolve the power hick ups.
Then again in yourt case it could be someting else. I think step one is to go the dealer (or a specialist who has the same BMW software) and see what comes out of that. I hope it will be someting obvious and cheaply repairable.

Good Luck

push_eax

Though I do not think so, I cannot exclude this problem - or some other sensor or connection which leads to unpredictable "fraction second" power(?) interruptions. As the intake manifold was removed, then the mechanics may have forgotten to reconnect everything the way they should have.

In my case, as in yours, the a diagnostics session revealed no problems whatsoever...


Thanks for the input guys.

bigbadbull

Which Gear box? The SAT's in Sport mode lock out 6th... but the car will start in 1st, where normally it starts in 2nd...

If you have the SMG or Step, or manual please disregard.

higher

Had similar issue in a previous car.

When the car was idlling the rev counter needle would 'bounce' every so often. It would just drop down, the car would kind-of miss a combunstion cycle, then instandly pick-up back to normal, the whole event lasted maybe 0.2-0.5 second, but was always anoying. It was always worse in very cold weather and the car did this from new.

It only once in four-years had an event like yours where the it just lost power momentarilly, then neve happend again in four years of ownership, except a iddle speed. I used to sit in stationary traffic watching the reve counter needle bounce up and down.

Despite lots of trying BMW never did fix that problem, because as they correctly said, the drives normally, but it always pissed-me-off.

In your case the problem is whilist moving, so I would be very interested to hear how they cure this as I am sure my problem and yours are from the same familly of faults

push_eax

Actually, it is only while moving at a defined rev-range - the most critical being 2200-2300rpm. Below that, I get the behavior you state, especially with the cruise control activated with an uphill ahead. Of course, uphill, one would say that this is normal behaviour - that is, the computer attempting to maintain a particular speed by having to apply acceleration a bit more aggressively (that if it was down-hill or a 0% straight-away).

All this wild action has been apparent since my iPod-related reprogram session from BMW. I have another reprogram session in early January. They say that the software version they programmed my car with has already been upgraded, so they'll try that version in the hopes that it solves my problem. I'll get back to about my experience once I try their solution out. I hope that I have good news for you

higher

I didn't know the sotware upgrade for the Ipod installation / Idrive was 'tiotal' ie; also included the engine management software ? that is a surprise to me.

I thought it was just the sotware that manages the Idrive items, which are not engine management specific.

The enginer management software is usually hard programmed into a ROM chip, seperate from the idrive but I am not certrain about that on the 5 series. Would surprise me if they installed two seperate software management systems given the extra manufacturing cost etc, so maybe you are correct.

I heard that they really stuggle to install software upgrades, 80-90% failure rate, that's why it takes all-day to get the one good install out of 10. With a rate like that lot's of opportunity for glitches and problems like the one you experienced.

Maybe someone on here can confirm that and good luck would be really interested in your outcome.

push_eax

Though by trade I am myself a software engineer, I have no idea what the iPod software upgrade included (i.e.: engine management + iDrive software + etc). What you say, however, does sound logical as it fits within the modular software concept.

This said, I also had a new intake manifold installed during the same iPod installation + (related) software upgrade session, so this problem may also be related to the intake manifold + the software; but not only the manifold.

The BMW guy did a brain-storming session, subsequent to a check of software flaws caused by the particular software release (which they installed) - as released by BMW. He found no flaws of the particular software which I encountered, so surmised that a SW upgrade "might" solve the problem - not "will".

In all cases I'll get back to you about the upgrade experience. I will also ask what both the previous iPod upgrade included (engine mngmt SW, iDrive, etc) and the one that they will engage in in January.