It stopped ..downhill ?

UK forum for general and technical discussion about the Z3 roadster

Moderator: Gazza

Post Reply
warhammer23
Joined: Sun 16 Feb, 2014 22:28
Posts: 50

  BMW other

It stopped ..downhill ?

Post by warhammer23 » Sat 29 Jul, 2017 19:09

"Interesting" one:

After i get out of work, i have to drive on a downhill part which is very steep at around 100 meters long with 2 bends.
Engine cold of course, in gear, and every time i start to break to stop at the intersection, i noticed that the idle hesitates a little and drops below normal. Then it comes back as usual once the car is leveled. Didn't take much notice until today. I think it did this with all my cars at that particular spot.

And today it stopped the car altogether. You should have seen me in the middle of the intersection ..hm why no steering and power :lol:
Luckily i was alone and then the car started back with no hiccups after the first try.

So what else? Don't think it was a driving error ... It was raining heavily, had somewhat of low petrol level but still not for the light to come out which is around 8 L. I know they are not that accurate but still .. will try to recreate the scenario tomorrow.

Any ideas ? The car since i had it for a year now, rock solid knock on wood, today the first weird one. Fresh MOT, fresh oil change, it did a 2000 mile trip in one week etc

1997 M52b28 Manual

Thank you.

John Wilson
Joined: Fri 12 Jun, 2009 13:11
Posts: 239

  Z3 roadster 2.0
Location: Diss

Re: It stopped ..downhill ?

Post by John Wilson » Sat 29 Jul, 2017 22:25

Could it be the idle control valve just needs a clean out?

warhammer23
Joined: Sun 16 Feb, 2014 22:28
Posts: 50

  BMW other

Re: It stopped ..downhill ?

Post by warhammer23 » Sat 29 Jul, 2017 22:31

Will have a look at that as well still waiting for the rain to stop. Thank you.

Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2108

  Z3 roadster 1.9

Re: It stopped ..downhill ?

Post by Del » Sun 30 Jul, 2017 09:04

Not sure how steep this hill is but really there are only two things that I can think of that would be affected by the car being positioned on a very steep incline. Firstly, the petrol (as you have already outlined) and secondly, the engine oil. The latter is affected by extreme car "positioning" as evidenced by the fact that tracks cars have to fit baffles in their sumps to stop momentary oil starvation with sharp cornering etc. The "valve lifters" are hydraulically operated by engine oil. In my 1.9 engine these are susceptible to "sticking" when the oil is cold and the lower engine oil viscosity number is too high - resulting in a splutter and rough idle for a few seconds when starting. Is it possible that the combination of a steep incline, causing a momentary hesitation in oil circulation and a cold engine oil, could affect you valve operation in the same way for a few seconds?

warhammer23
Joined: Sun 16 Feb, 2014 22:28
Posts: 50

  BMW other

Re: It stopped ..downhill ?

Post by warhammer23 » Sun 30 Jul, 2017 09:09

Yes, sounds viable as well. :-?

I know the m44 has roller tappets.
Mine has 5w30 and always check my levels and it has plenty aka on the second line when cold.

After i finish work today will go for another try and see what happens.

warhammer23
Joined: Sun 16 Feb, 2014 22:28
Posts: 50

  BMW other

Re: It stopped ..downhill ?

Post by warhammer23 » Mon 31 Jul, 2017 18:36

Ok. Went back the next day, with even less fuel.
Saw how the rpm started to drop like under 500 rpm for a brief second and then came back to normal.
Didn't accelerate in that second and i think that's what i did then, i hit a blind spot and the ecu went to sleep per say.
This time i was a little gentle with the breaking i mean not that suddenly (the hill is very steep, then boom, flat surface as you arrive at the intersection) and the rpm drop was smoother.
So yeah myth busted.. for now.

Will try to record it one time ...

Post Reply

Who is online

Users browsing this forum: Bing [Bot] and 3 guests