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Are valvetronis and vanos part of the cylinder head?

6K views 22 replies 6 participants last post by  autoque 
#1 ·
I'm curious if I can just replace the valvetronic and vanos units or if the whole cylinder head must be replaced to be able to change the valvetronic/vanos.

And what are the parts cost like without the labor? realoem does not list the parts separately. They only list the price of the cylinder head with the valvetronic and vanos.

My engine is a N52, 6 cylinder NA engine.
 
#2 ·
The VANOS is an actuator on the front of the head, which drives the camshaft. The actuator can be changed easily (relatively - look for the DIY in the E46 section), but the parts connected to the camshaft/chain is harder.

The Valvetronic is integral with the head and valves. The eccentric drive motor is easy, but nothing else is - you have to dissamble the valvetrain.

Neither requires the head to be removed, but it's not easy; unless you're going to DIY it's probably better to buy a head.

What is broken?
 
#4 ·
What is broken?
Not quite sure, even after more than three years of trips to various dealers and master techs, no one knows what's wrong.

I've got a warm start rough idle which lasts one to two minutes after the ignition. This started right after replacing the cylinder head under warranty for a tapping noise, a well known issue in the N52 engine. They changed the spark plugs, coils, MAF and cleaned various parts, tuned up the timing of the valves, disassembled and reassembled, the symptom got a little better, but never disappeared. So my final desperate move, throw expensive parts at it, especially suspicious is the cylinder head unit, which started this long painful journey. I'm out of warranty so I'm picking up the tab, but the dealer's willing to forgo the labor cost since they know I've been having this problem early on. However the dealer doesn't know whether the replacement will lead to fixing the problem as their diagnostic device tells nothing's wrong.

The whole head costs like over $5000 so I thought replacing the valvetronic and vanos is more sensible to a rough idle problem. By the way, absolutely no fault code stored except a code was found about a month ago indicating an error with the vanos solenoid valve, so the dealer replaced it rather than cleaning it and using it again, hoping it would solve the problem. But no go.
 
#3 ·
I'm curious if I can just replace the valvetronic and vanos units or if the whole cylinder head must be replaced to be able to change the valvetronic/vanos.

And what are the parts cost like without the labor? realoem does not list the parts separately. They only list the price of the cylinder head with the valvetronic and vanos.

My engine is a N52, 6 cylinder NA engine.
You cleaned solenoids but no-go?
 
#7 ·
BTW, before your post I was going to go with my gut feeling (thus replacing the valvetronic/vanos) but your guess, DSXMachina, has to be a better bet to go with than mine or anyone else who inspected the vehicle, because these so called technicians, including the master tech have absolutely no idea what's going on. Without the help of the dealer, I've got no one but myself to proceed with the repair. And you must know more than I do, so please tell me what you think is the problem and what I should do.
 
#9 ·
Upset? Heck no. I spent the weekend raking up leaves from too many oak trees, not much time for Bimmerfest. Surprised to find out that you're in South Korea, I don't know anyone in South Korea who I might be able to refer you to. (One of my techs is from S. Korea, but adopted to the US as an infant.)

So now you want to depend on the internet advice of a stranger 12000 miles away for possibly expensive car repairs that might not even work? Hmmm, OK, I'm in. It'syour dough, or wan in this case.

What year and model is your car? What is the mileage? Does the transmission seem to shift properly. Except for the idle roughness does it run normally at other times? When you starti it the first time of the day it idles good and is OK until you stop somewhere, restart the engine and then it runs rough for a while? How long is it rough? If you don't drive it, just sit there, does it stay rough for a long time? If it is rough, you drive it half a mile and then stop, is it still rough?
Are you certain this did not happen until after you had all the engine work done? Is it possible that the engine was running so bad before the repairs that you didn't notice a little idle roughness?
Answer my questions then I will answer yours.
 
#12 ·
It's a '08 X5 3.0si with 13,000 miles. Manufactured in May '08. N52K, a 3.0 liter naturally aspirated engine.

Yes, the transmission seems to shift smoothly and properly most of the time. The vehicle had the transmission replaced under warranty about a year ago because an error message appeared once and it entered into a limp-home mode. A restart cleared everything and it drove normal, but the dealer's diagnostic machine said to replace the transmission.

When I start the car in the morning (cold start), it doesn't do anything out of ordinary. And it drives fine, like there's no problem at all. But when it's all warmed up and I stop and park somewhere for five, ten minutes and up to four hours, and I restart the engine, it runs noticeably rough for about one to two minutes. At around three minute mark, it gets smoother, but sometimes a little roughness can still be felt via uneven power delivery when my foot is on the brakes and crawling forward ever so slightly. It's as if the engine is pulsating. Most of the time, when I'm stationary, after about two minutes, the engine smooths itself out and idles normally. By the way, the roughness seems to get worst after stopping for one to two hours and restarting.
Even right after a warm start, if I keep the engine rpm over 1000, like driving instantly or keeping the throttle pushed, there's no roughness or at least I can't feel it.
If I drive half a mile and stop, most of the time, the roughness disappears. But sometimes there's that last two percent of unsmoothness remaining.
The trick here seems to be to get the engine temperature back up to full operating temperature again ASAP by driving aggressively, then the engine gets smooth quicker.

Before the cylinder head replacement three years ago, I never had any issue with the engine except for the lifter noise when the ambient temperature was cold. This all started right after the cylinder head replacement.
The funny thing is, when I drove about 300 feet out of the dealer lot after the cylinder head replacement, the car suddenly rocked sideways uncontrollably for a few seconds like it was in a tornado. So I went right back to the dealer but no code found. Although it never again exhibited the roughness in the same magnitude, it was the start of this whole thing.

Hope I answered all your questions. If you have any more questions, please let me know and I will do my best to explain them to you. Thank you so much for reading and your help!
 
#13 ·
When a cold engine is started the computer operates it using what is called idle control strategy. Starting and ensuring a smooth idle on a cold engine is the hardest thing the computer ever has to do. Your engine starts and idles properly on cold start. It also idles properly when it is fully warmed up and stopping for lights and stop signs, and also any time you are moving along at any speed. My conclusion then is that the mechanical components (including your Vanos/Valvetronic/valve train components!) are all properly installed and in good operating condition. If they weren't, your idle problem would occur under all operating temperatures. Which brings me to my guess, it's temperature related (I can just hear all the techs going "Well d'oh! Of course it's temperature related, but what is it?)

Interestingly, the problem is not occurring cold, but hot, or at least warmed up. It's got what we refer to as a hot start problem, also called a heat soak problem. When you start your engine the first time of the day the temperature is whatever the air temperature is. When you're driving the average engine temperature is whatever it says on your dashboard gauge; around 195F for coolant and 235F for oil.

Notice the use of the word "average". There are areas in the cylinder head which get far hotter than that. Operating temperatures can be well over 500 degrees at times. Coolant or engine oil flowing over these areas help to carry away the localized very high heat. Until you shut your engine off! Then the heat from these areas radiates and conducts out to surrounding components and brings them to a temperature much higher than they'd ever see on a hot Summer day on the highway. This 'heat soak' can raise all kinds of issues which disappear once the component(s) is "cooled" back down to 195F. It's my guess that one of your engine sensors -and you have a lot of them- misbehaves when it's too hot. Which one?

I'm going to eliminate the throttle position sensor, and the mass air flow sensor, and the intake air temperature sensor, and all the cam activators and sensors. and the crank position sensor and knock sensor. All these devices commonly cause major headaches, but they don't dovetail with your symptoms. That leaves me with the coolant temperature sensor. It's buried on the cylinder head, is difficult to get at on your engine, and is a primary culprit whenever idle is messed up. I believe something happened to the sensor or the wiring harness when your cylinder head work was done.

The computer is smart, but dumb to the extent that it does what it's programmed to do based on input from many sensors. The one it leans on the heaviest is the coolant temperature sensor. It needs this info to 'choke' (richen) the mix when cold, or to adjust it when warm. If the computer gets a bad but plausible (in other words, possible) signal, it assumes the signal is correct, doesn't set a code or turn on a light, and uses that signal to operate the engine. If your CTS (coolant temp. sensor) is messed up it can send a bad signal under certain conditions. I'm guessing that's your problem.

If I had your car in the shop I would duplicate your problem conditions and graph RPM against MAF, TPS and CTS. I'd then run a Mode 6 scan which would show me all kinds of anomalies which might not meet the "throw a code" threshold, but still be causing the problem.* The critical thing to watch would be engine temperature following the heat soak.

So, my guess is a faulty engine temperature sensor circuit. Or carboned up intake valves. Nah, not going for that on this one, unless Orient thinks so, then I'm totally in line for it. :D

*(I'd also pay close attention to what the intake cams are doing on a hot start. It they aren't indexing properly due to binding or slight misadjustment you can get a rough idle, but this is somewhere near the bottom of my guesses of the Top Ten possible reasons for your rough/surging idle. Also, bad cam indexing usually sets a code.)
 
#14 ·
THANK YOU SO MUCH, GOOD DOCTOR!:bow:

One question. You said it could be the coolant temperature sensor and later you mentioned the faulty engine temperature sensor circuit. Do they mean the same thing? Would replacing the coolant temperature sensor fix the engine temperature sensor circuit?

Thank you very much again. You are a godsend!
 
#15 ·
Don't set me on any pedestals, I haven't fixed a thing, and the odds are against it being so simple.
What I mean by the circuit is the wiring harness, the connector and the sensor itself. A chafed wire, bent connector pin or shorted sensor or who knows what.

I want to mention one more time that someone with decent equipment should be able to do a proper diagnosis before you change anything. You've got a very complicated machine and all I did was take an educated guess based on the history and symptoms.
 
#16 · (Edited)
Not a VANOS expert, but I did have a colleague with an E36 that forgot to install the drive helix on the VANOS and when the engine was started it would bend the exhaust valves in #1, #2, & #3 cylinders only. That took a bit of study to find the culprit!!! I am sorry to say it took two sets of exhaust valves for him to find the problem....:-(

I know that VANOS seals can cause cold idle roughness.....
 
#22 ·
Just replaced the coolant temperature sensor. But it makes no difference to the symptom.

Thank you for your help though. It was still worth the try. I'm looking to replace the valvetronic parts and vanos. Or maybe the whole cylinder head just to be safe.
 
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