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-   -   Vanos bank duty cycle?? (https://xoutpost.com/bmw-sav-forums/x5-e70-forum/110635-vanos-bank-duty-cycle.html)

TCRIX5 08-03-2019 08:20 AM

Vanos bank duty cycle??
Does anyone have an idea of acceptable duty cycle for the vanos system on a 08 4.8i? I understand it should change but there must be a tolerance for an engine at idle.

ard 08-03-2019 12:27 PM

What are you trying to do, fix, or understand?

There are tools we have for testing and measuring the operation and function of the vanos. As I recall, 'duty cycle' isn't one of the metrics....

TCRIX5 08-04-2019 10:21 AM

Understand to fix. I have an ongoing problem with engine performance when hot and coming to or leaving a standstill. Currently using Autoenginuity software to collect data but I need some help evaluating the data. PM me and I'll send you a couple of files, after an hour here trying to post a file I can't get it done. Thanks

ard 08-04-2019 01:35 PM

if you cannot attach it to a post, you cannot attach it to a PM.

You can either: Place the file somehwer on the internet, so that it is publicly accessible, and put a link here...


upload the file to bimmerfest, then place a link to it here.

VANOS is usually evaluated by a functional test, that measures the ability of the system to obtain advance and retard goals (min specs).

pshovest 08-04-2019 05:01 PM

Move the vanos solenoid in question to the other bank. If duty cycle problem moves to the other bank, clean/replace solenoid. If problem remains on original bank I would think there is a mechanical problem with vanos adjustment mechanism.

ard 08-05-2019 12:30 AM

On other cars (ie S62) the vanos solenoid actuators will get clogged with oil/crud. The screens clog and congeal, the decompose...this all leads to solenoids that are sluggish. They will not achieve the target positions.

Remve them, and clean AGGRESSIVELY with carb cleaner. I will actuate them with a 5V source, paying attention to the sound it makes. You want a nice, loud click/snap. Flush them with copious blasts from a aerosol carb cleaner, not just passively soak...check the sound as you go.

As long as you are taking it out, might as well.

TCRIX5 08-05-2019 01:46 PM


The link above should get you to plot of duty cycle bank 1(2) vs RPM. Green and blue graph lines look almost the same color so Bank 2 duty cycle is the line with the large down spike.

Things I've done to date:
40k miles ago valve stem seals - no smoke and still works like it should.
Within last 1K -
[Bank 1] check timing - intake cam was off by about .5 cm. Set timing replaced vanos solenoids and camshaft sensors. No oil in eccentric shaft sensor connector so I didn't replace. I chose to replace solenoids due to finding non OEM parts installed (discussion for another time). Cleared faults, test drive for about 100 miles result being no faults stored but it doesn't idle as it should. I performed vanos duty cycle test again and it hasn't changed, essentially the same as the graph I provided the link to. At this point I determined that my assessment of bank 1 performance was wrong and that in fact bank 2 is the problem.
[Bank 2] following above I pulled the vanos for both inlet and exhaust and find more junk from china (search the part number and I could buy them for 14$ each, again different discussion). Swap in two used but clean and functioning solenoids with new software and perform road rest, same result as before and the graphs look the same. Into the bank I go, in the process of removing the cover I f'd the eccentric shaft (my fault, sometimes I suck). But i did find the timing to be spot on and the camshafts look perfect, intermediate levers installed correctly, no blocked oil passages or leaking check valves.

I suspect one of the following but don't know for certain:
(1) Bank 2 vanos adjustment unit is stuck, they were locked when I checked the timing. That doesn't mean one or the other will move when required.
(2) DME has a fault that does not set the CEL or record a fault. Unlikely, but if sending the thing out for R/R is the right answer, then off it goes. I don't have data to support, but again I don't know.
(3) Bad crank bearings. I'm pretty religious with oil and filter changes. The damn thing runs great and is smooth like new without vanos.

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