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Old 12-03-2012, 09:53 AM
stuartjohn24 stuartjohn24 is offline
Officially Welcomed to the 'Fest
Location: Chippenham, Wiltshire, UK
 
Join Date: Jun 2011
Posts: 664
Mein Auto: BMW E65 745i
Hi Guys,

This makes real interesting reading!!!!

I've been trying to diagnose a performance issue on my 745i for months!!!!

I'm experiencing hesitation or lagging when trying to accelerate, it's most pronounced when cruising and then going to accelerate and there is nothing there, the engine note changes but very little acceleration happens!!!!

It does happen from a standing start, where you feel reduced torque/power and a lot of the time a blowing exhaust sound, but the exhaust is leak free!

It's possible to feel what appears to be a slight misfire at idle or when revving as described in the first post.

However I will get the odd day where the car drives beautifully, plenty of torque and much more responsive throttle.

What annoys me is the throttle response was instant when I first bought the car, a little stab on the throttle and you could feel the power and acceleration instantly! There are no error codes whatsoever.

This fault has run me round the houses, it causes the gearbox to act up, it's slow to change gears, jerks sometimes as the engine isn't delivering the power smoothly. I've had trans issues around the same time tho ha happened which initially made me think the box was causing it. I've had the car and trans checked over by a ZF workshop and all is good.

It appears what I thought was transmission noise is actually exhaust noise, if the theory is correct and the VANOS adjusters are crap then could the added noise in the exhaust be caused by the exhaust valves being opened too early?

I mean other times when I drive the car it's quiet and at idle you wouldn't know the engine was running!

There are some things that's throwing doubt on this, it's not a very well known failure. I'm struggling to find information anywhere else on the net that confirms these go bad.

Secondly they do not operate in the same way that the M54 VANOS units do, these don't have o-rings but spring loaded vanes that separate 5 or so chambers where oil pressure is controlled either side to adjust the timing.

To be honest the design does not look particularly robust, it will wear out at some point and leakage between the vanes is expected which is why the VANOS control is closed loop.

Which brings me onto the next point, if these adjusters are playing up wouldn't the DME recognise that? I can see your values in INPA and they look ok (correct me if I'm wrong!) the desired angle and the actual angle are almost identical.

Could it be that as they wear out and oil leakage across the vanes increases the response time lengthens and they become slower to adjust the timing?

I mean don't get me wrong I'm just trying to understand why this has not been picked up before an is a known issue for such drivability issues, has anyone else changed these adjusters and has it fixed any issues?

I don't fancy spending 700-800 on new adjusters to find its no better!

Stuart
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