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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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Old 08-29-2006, 05:11 PM
lexmario21 lexmario21 is offline
Location: Dallas TX
Join Date: Dec 2005
Posts: 29
Mein Auto: 1999 328i
Vanos Problem E46

I found this article in http://bimmer.roadfly.com/bmw/forums/e39/7494631-2.html and I thought I would get you guys opinion on it?????

Letter sent to BMW/NA through local dealership:

May 9, 2005

Rajaie xxx
[address and contact info]

(Loach) xxx xxx
[address and contact info]

xxx xxx
Service Manager, xxx BMW, Inc.
[NC address and contact info]

Dear Mr. xxx (service manager):

BMW autos with the M52TU engine have been experiencing a cold weather related problem for the past few years. The problem has been dubbed the “vanos problem”. We both have (had) this problem and are out of warranty. We’ve taken the initiative to isolate the problem cause and seem to have identified the culprit. Below is an explanation of the problem and our findings.

The problem occurs on M52TU engine cars, 3 & 5 series 6-cylinder 1999-2000. It presents when the car is cold, ~ < 55° Fahrenheit, usually in the morning. The problem begins at the end of the warm-up period (elevated idle rpm). Thus the colder the car, the more delay after startup before the problem manifests. At the end of the warm-up period the engine begins a series of stall encounters. The engine rpm’s drop significantly, the engine shudders, and then the engine rpm’s recover. This engine jolt lasts ~1 second. It is followed by a steady idle for ~7 seconds. The cycle then repeats. This continues for ~4.25 minutes. The 7 second idle interval can also be shorter, even to a ~1 second interval. With some cars the engine will actually stall on one of the engine jolts. If the car is driven before/during the episode, the problem seems to be suppressed, unless the car shortly comes to an idle state where the problem reappears. If the hood is opened, a gear/chain like chatter can be heard during the stall encounters. The idle control valve can sometimes also be heard clunk open.
The M54 and M56 engines share the same vanos as the M52TU engine, but don’t exhibit the “vanos problem”.

At first we thought the problem was due to the idle control valve. But cleaning the ICV and then replacing it with a new unit did not resolve the problem. We then learned that the problem was vanos related. We realized that the problem takes place when the DME adjusts the variable timing at the end of the warm-up period. We received a tip from a BMW head mechanic that the problem was due to tight tolerances on the helical gears and that BMW was redesigning the splined shaft to solve the problem. Given that BMW has redesigned the splined shaft several times, we replaced the two splined shafts with the latest design splined shaft. There was no improvement. We received another tip that the problem was due to the vanos valves. We replaced the valve on the vanos exhaust side, and found no change. We tested the solenoids, and found them to work properly. We then decided to acquire a new vanos. We compared the new vanos with a vanos that had the vanos problem, and found them to be virtually identical. We did notice though that the piston seals on the new vanos protruded out further than in the used vanos. This we surmised was due to wear on the used vanos seals. We suspected the vanos problem was caused by a fault on the vanos exhaust side. There is a powerful spring at the vanos exhaust side which fully advances the vanos exhaust piston in the default/off state. We expect this design facilitates advanced exhaust valve timing when the engine is first started. To retract the exhaust piston (retard timing) would need significant oil pressure to counter the powerful opposing spring. Our conclusion was/is the worn leaking seals prevent the oil pressure build up needed to reposition the piston. We replaced both pistons on a used vanos with the pistons from the new vanos. The “vanos problem” resolved! We were also quite pleased to find that the car performance noticeably improved. The engine rpm’s were smoother/cleaner throughout the higher rpm range; this we know is the hallmark of the double vanos. Given the performance enhancements, we concluded that the vanos fault not only caused the cold morning symptoms, “vanos problem”, but also afflicted the function of the vanos during normal operating temperatures. This would not only affect driving performance, but would also afflict the function of the EGR (exhaust gas recirculation), which is highly reliant on the proper function of the vanos. EGR plays an important role in fuel consumption and emissions control.
It seems evident that the vanos malfunction is due to worn piston seals.

The M54 and M56 engine autos utilize the same vanos as the M52TU but do not encounter the “vanos problem” (cold morning stall cycles). These engines have equivalent oil pressure characteristics to the M52TU, and thus are not more able to overcome the seal leak and build the needed pressure. We thus expect that the M54 and M56 engine autos are also encountering vanos malfunctions due to worn piston seals.

We suspect the M52TU cold engine “vanos problem” is related to the M52TU DME. The DME is likely not receiving the anticipated indication from the camshaft position sensor, and reacting in a way that causes the engine to almost stall. The DME could be over opening the ICV causing the engine to almost stall. This can also explain the ICV clunk that is sometimes heard during the engine attempted stall. We expect that the M54 and M56 DMEs function differently and thus do not instigate the cold engine stalls.

Upon further inspection of the vanos piston seals, we’ve found that each seal is not one component but a set of two rings. There is an outer Teflon seal ring, and an inner (supporting) elastomer o-ring. We believe it is the inner elastomer o-ring that wears and shrinks, causing the outer Teflon seal ring to retract, and thus creating the leak condition.

BMW does not provide the vanos pistons or piston seals as a separate part. A new (remanufactured) vanos needs to be purchased to acquire the piston seals. A new vanos costs ~$500. A BMW dealership vanos replacement repair is ~$1,000.
Some owners have had their vanos replaced one winter only to have the “vanos problem” recur the next winter.

The “vanos problem” is practically an epidemic. There are numerous M52TU owners with this ailment. It’s also evident that a routine replacement of the 6-cylinder double vanos piston seals is necessary for the proper function of the vanos.

We would like to see BMW be more forthcoming with information on this issue. We also would like to see BMW provide the piston seals as a separate part. This would significantly reduce the part costs of the repair. Redesigning the seals so they may have a longer functional lifespan would be a greatly welcomed solution.

As can be expected, we feel compelled to share our findings publicly. We are open to the possibility of doing this in coordination with BMW.

Your response will be greatly appreciated. Rajaie xxx will act as the primary contact. Thank you for your assistance.

Rajaie xxx & (Loach) xxx xxx

Letter received from BMW/NA:

July 6, 2005

Mr. Rajaie xxx
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Old 08-29-2006, 06:14 PM
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KrisL KrisL is offline
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what kind of opinion are you looking to get?

That's been posted here before.
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Old 08-29-2006, 08:13 PM
ATLBMW ATLBMW is offline
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Old 08-29-2006, 08:17 PM
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adrian's bmw adrian's bmw is offline
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Originally Posted by ATLBMW View Post
great answer.
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Old 12-20-2006, 11:16 AM
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Nov99328i Nov99328i is offline
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I was going to hunt for a sensor or something along those lines!! Wow, I am having the trouble on cold mornings as well, but I resolved my problem(temporarily) by driving it HARD for a few miles when hot after I reset the engine light (VANOS exhaust valve stuck code). This seems to last a few days or weeks. Is there a DIY for this, or are too many special tools involved?
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Old 12-21-2006, 03:26 AM
Passenger Passenger is offline
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And what's been done about ? Bugger all.
It's an issue that folks should actually kick off about loudly. It's clearly a design and manufacturing fault which should be addressed far more sympathetically by BMW. They should either make those parts available or subsidise the cost of the current repair approach.

The only thing that puzzles me about this issue and it's symptoms is that it may often be intermittant and not grow worse over time..as would be expected with any common wear issue.

Last edited by Passenger; 12-21-2006 at 03:37 AM.
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Old 01-21-2007, 06:23 AM
Rowag Rowag is offline
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Well now that I've got the "death clatter" around 2k RPM and the occasional idle dip I'm hoping for a sensor problem, but if it's my VANOS I'll be miffed. O-rings are the root of all evil.

Does the M54 engine have the same VANOS setup and o-ring concern, or is this specific to M52TU?

Edit - appears that it's the same. We'll see what the problem is at the dealer (this car only has 22k on it). If it's the VANOS I'd love to get the old unit back and find a supplier for these o-rings if that's the problem.

Last edited by Rowag; 01-21-2007 at 07:01 AM.
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