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Old 07-31-2019, 04:54 PM
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Join Date: Jul 2019
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Cool Unequal cylinder bank duty cycle - why so different?

Hi all, I need a little help. Thanks in advance.
Background information: The initial problem was the thing idled like crap and threw CEL, also didn't run well when coming to a stop or accelerating until about 1500 RPM. The thing is a 2008, 4.8i, X5.

I use Autoenginuity for diagnostic purposes which works well enough as I'm not interested in becoming a programmer, hat off to those of you who do. Checked timing on bank 1 and vanos control units because the duty cycle was around 2 percent compared to bank 2 around 60 percent at idle. Timing was off for bank one, corrected. New vanos solenoids (back story isn't good) and camshaft position sensors for bank 1.
Also checked locking of vanos and for excessive wear of camshaft bearing cap ledges ( look just like TIS picture of good enough). All the non-return check valves seat with back pressure and open just fine. All intermediate levers are installed correctly and the camshafts look almost new. Compression check has all the cylinders around 180 and leak down test were all in the acceptable range. Put the thing back together, hook up the battery give it a minute to find the stops for VVT then push the go button and it runs perfect during warm up. Drive it around for about 30 minutes and notice that it is missing a little but getting better with time (I assume it is mapping because the battery was disconnected for about a week) and CEL is not lit.

Now the fun part. Give it back to wifey and say to her "your all set, no need for new car, happy motoring". She has it for about a day and gives it back saying "thing runs like crap" at this point something has to go.....
Anyway, also a fun fact - If I disconnect any vanos solenoid thing starts and runs as it should although CEL is back as expected. Nice and smooth with no funny business while stopping or starting out from stop. I think this is true because the VVT gets set to max, spark is controlled from the crank, camshafts lock at the initial position and the throttle plate behaves like a throttle plate should.

At this point I think that the duty cycle on bank 2 is the problem as I can get it up to around 98 percent while bank 1 hangs out in single digits. I interpret this to mean that the solenoid valve / vanos actuator can't maintain the camshaft in the DME commanded position. Or the DME is in need of repair but doesn't have a condition that causes CEL or faults in the stack. If the thing ran like crap and had misfires with vanos disconnect I'd suspect a bad crankshaft bearing for cylinders 1 and 5, but because it runs so well in that condition I don't believe that is the case.

If you'd care to look I have several data files and reports that I can send if it would help out.

Again any help would be greatly appreciated.

Last edited by TCRIX5; 08-03-2019 at 08:12 AM. Reason: Editorial
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