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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 03-18-2015, 11:29 PM
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TheHockeytowner TheHockeytowner is offline
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How VANOS and its degraded seals can affect idle quality

The question of the week is, does the VANOS do anything at idle?

The answer is a resounding "Yes."

When you turn your car off, the VANOS pistons assume a "default" position. This position is consistent with the VANOS solenoids being totally de-energized (it's also a safety measure in case of solenoid failure). So, the only time the VANOS is "off" is when the car is off, or the solenoids have failed, or something controlling the solenoids, or a sensor that provides data for correct VANOS piston positioning, has failed.

When you start the car, the DME allows ~50 revolutions to pass, and then detects the position of the cams via the two camshaft position sensors. Using data from the crankshaft position sensor, the load signal (correct me if I'm wrong, load signal = accelerator pedal travel/signal?), intake air and engine coolant temperatures, the DME tells the VANOS to adjust timing on the camshafts.

The VANOS piston positions at idle following the 50 revolutions after start-up, will not be the same positions as after the engine warms up, the intake air temperature changes, etc. A lack of these changes, whether acute or chronic, might not even be perceptible to us. But...

If the VANOS cannot move its pistons out of the default position right after start-up, and the default position is not the ideal timing at idle for the given conditions, it's clear to see how idle quality can suffer. If the default position was ideal for idle in all conditions, the VANOS would not be active right after start-up.

Now for the million dollar question: can degraded VANOS seals affect idle quality?

Maybe. But so can a clogged VANOS oil supply line, faulty camshaft position sensors, faulty crankshaft position sensor, faulty VANOS solenoids, seized VANOS pistons, snapped or incorrectly-installed left-hand thread VANOS pistons bolts -- anything that would prevent the VANOS pistons from moving into their correct position, whether totally or partially.

This is the crux of the issue of VANOS' affect on engine performance, including at idle. VANOS seal degradation is certainly ubiquitous due to the use of Buna-N o-rings, but the performance-robbing/rough-idling symptoms run the full spectrum, from undetectable to unbearable.

Seal degradation that prevents the VANOS pistons from moving into their correct position based on input from the DME would affect every engine speed following start-up, including idle. So would seal degradation that causes the VANOS pistons to take too long to get into their correct positions, in response to input from the DME, and based on changing parameters (specifically the load signal -- increasing or decreasing engine RPM).

The name of the game for keeping these wonderful cars on the road is to aggressively diagnose the issue, starting with the most likely suspect. Given the well-documented Buna-N seal problems of all kinds, I conclude that the most likely suspect for decreased VANOS (and subsequently, engine) performance, without producing a fault code, is the Buna-N seals. All of the other failure modes listed (while far from comprehensive) would most likely produce a fault code stored in the DME.

Lastly, from the "VANOS bible":

"Smaller quantity of residual exhaust when idling due to smaller valve overlap resulting in improved idling"

Whatever that means

EDIT: the least amount of overlap does indeed occur at the "default" position, so it would make sense for this position to be used at idle. Basically don't believe anything I say on this forum. I'm going to bed, I'm VANOS'd out.
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Last edited by TheHockeytowner; 03-18-2015 at 11:46 PM.
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  #2  
Old 03-19-2015, 04:39 AM
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Fudman Fudman is offline
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Quote:
Originally Posted by TheHockeytowner View Post
When you start the car, the DME allows ~50 revolutions to pass, and then detects the position of the cams via the two camshaft position sensors. Using data from the crankshaft position sensor, the load signal (correct me if I'm wrong, load signal = accelerator pedal travel/signal?), intake air and engine coolant temperatures, the DME tells the VANOS to adjust timing on the camshafts.
I agree with everything except this article suggests that the DME uses only the camshaft position signal from the CPS and initially adjusts timing based on RPM and throttle position. Subsequent to the initial setting, intake air and coolant temperature are then used to make additional adjustments.

Quote:
Originally Posted by bluebee View Post
The reason valve overlap is reduced at idle (and startup) is to maximize compression within the cylinder and maintain proper combustion. Valve overlap allows both intake or exhaust gases to be expelled during the compression cycle, which creates a rougher idle at low rpms. Valve overlap is desirable at higher RPMs because as the fluid (air/fuel and exhaust) velocities increase, the fluid dynamic effects (e.g. scavenging) are used maximize engine power or efficiency.
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Old 03-19-2015, 06:43 AM
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bluebee bluebee is offline
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This is a great question:

There are two kinds of idle: cold and hot.

I don't know if the VANOS cares?

Do you?

Look at this diagram which shows the oil temperature is an input...

BTW, this is a funny related joke that we can get a kick out of in our quest for the facts amidst a sea of butt-dyno results.
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Last edited by bluebee; 06-30-2015 at 01:40 PM.
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  #4  
Old 03-19-2015, 09:27 AM
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TheHockeytowner TheHockeytowner is offline
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Quote:
Originally Posted by Fudman View Post
I agree with everything except this article suggests that the DME uses only the camshaft position signal from the CPS and initially adjusts timing based on RPM and throttle position. Subsequent to the initial setting, intake air and coolant temperature are then used to make additional adjustments.

The reason valve overlap is reduced at idle (and startup) is to maximize compression within the cylinder and maintain proper combustion. Valve overlap allows both intake or exhaust gases to be expelled during the compression cycle, which creates a rougher idle at low rpms. Valve overlap is desirable at higher RPMs because as the fluid (air/fuel and exhaust) velocities increase, the fluid dynamic effects (e.g. scavenging) are used maximize engine power or efficiency.
Nice, thanks Fudman
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Old 03-21-2015, 11:24 AM
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TheHockeytowner TheHockeytowner is offline
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'Bee, I think there is a difference, since engine coolant temp is one of the parameters used to adjust the timing. But that comes after the "initial" setting based only on the positions of crankshaft/camshafts, which occurs 2-5 seconds after start-up.

As for that 2-5 seconds, whether the engine is cold or warm at that point is moot, until the DME gets the coolant/intake air temps.

It's very possible that the "default"/emergency positions, that is the positions the camshafts take immediately upon start-up, might be the ideal positions for idle at some intake and engine coolant temperatures. But I'd be very surprised if they were the ideal positions for the full range of those temperatures. Why have an infinitely-variable cam timing system that uses all sorts of different parameters to determine the best timing for the conditions, if it just defaults to a small set of positions?

Re: cold start, the product lit says that VANOS helps warm the cats up faster. This is in conjunction with the SAS.
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Old 03-31-2015, 04:36 PM
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This thread says that "idle quality" issues are specific to certain engines (actually certain DME program versions) and NOT to the VANOS used!
- VANOS Diagnostics - are my seals OK?

In summary, the E39 M54 seems to use the SAME VANOS as does the E39 M52TU, but only the M52TU has the idle problems (which, the thread says, will be solved with a DME update and/or new seals).

Rajaie says...
Quote:
Maybe I can help clarify some things.

The 99-00 M52TU engine cars are known for cold weather cold start idle jolts and possible stall. When the engine is first started the vanos is set in a default position which fully advances the exhaust timing and fully retards the intake timing. This prevents any intake/exhaust valve opening overlap and allows for pure air/fuel mix needed to start a cold engine. At startup the air/fuel mix in significantly enriched and the idle is raised. This is needed to start a cold engine. The secondary air system is turned on to pump air (oxygen) into the exhaust manifold. This combusts the excess unburned fuel and heats up the cold cats.

The cat catalysts need high temperatures to function. When the cats are cold they are non-functional and exhaust escapes untreated. Bringing the cats up to operating temperature asap is an important emissions control criterion.

Once the engine warms up and the idle is lowered the next focus for the DME is warming up the cats. The vanos is used to do this. Usually the spark is delayed and the exhaust valve timing is retarded. This apparently creates an after burn effect. This is used to warm up the cats. It's at this time that M52TU engines encounter the idle jolts caused by the failed vanos seals. The vanos works on engine oil pressure. At low idle the oil pressure is at its lowest level. The exhaust side of the vanos has a spring which advances the exhaust timing by default. This causes the exhaust timing to be fully advanced when the engine is being turned off. This assures no intake/exhaust valve overlap needed to start a cold engine. Retarding the exhaust timing requires great oil pressure to overcome the spring force and retard the vanos piston and timing. Due to the seals failure and oil leakage and the low oil pressure due to the low idle, the exhaust timing can't be retarded correctly. This somehow causes the engine to have the idle jolt encounters. This might also be related to the DME reaction to the vanos failure.

Replacing the vanos seals repairs the vanos and resolves the M52TU cold weather cold start idle jolts and possible stall.
01+ M54 and M56 engine cars have the same vanos and same failing seals but don't experience the cold weather cold start idle jolts and possible stall. It seems evident this was resolved with a software change. I'm not sure what was done. This software patch is now also available for M52TU cars. If the latest software is updated at the dealership the problem is resolved. Owners who have done this also note some performance improvements. BMW (Siemens) likely also changed the PWM (pulse width modulation) signals that drive the vanos solenoids and the vanos function. The pulse duty cycle might be further increased on the exhaust side to better overcome the oil leak and overtake the spring to retard the timing.
It is evident though that the software updates do not bring the vanos to proper function. Many owners with 01+ cars with the latest software updates have installed the vanos seals and reported significant performance improvements.

The failed vanos seals in the majority of cases don't cause fault codes. Albeit we have seen many cases of fault codes due to failed vanos seals. It might also be that over the life of the car the failed vanos seals might well cause a fault code.
The vanos is not fully failed due to the failed vanos seals. This is why vanos failure codes aren't prevalent. The vanos is able to adjust the timing, but it is slow and sloppy when doing it. It has been noted to me that when running the GT1 (BMW tester) vanos test this can be seen on the screen. The Autologic (aftermarket tester) vanos test fails the vanos.

So to the OP, it's not just if the target and actual positions match. Its how quickly is the vanos achieving the target position.

The vanos is a hydraulic actuator. It uses oil chambers at the fore and aft of a piston to position the piston. The piston is mounted to a splined shaft. Positioning the vanos piston positions the splined shaft. Positioning the splined shaft modifies the relative rotational position of the camshaft to the crankshaft. This is BMW's variable valve timing system. When the vanos seals are failed, oil from the oil chambers leaks across the piston and doesn't allow the oil pressure to build up in a timely manner to effectively position the piston, splined shaft, and camshaft timing.

Variable valve timing has many benefits. Overall improved power and torque, particularly lower torque. Smooth power delivery. Flatter torque curve. Improved fuel consumption. With the failed vanos seals the engine performs worse than an engine without variable vanos timing. With functioning vanos seals the engine performs better than an engine without variable valve timing.
A possibly useful test is to disconnect the vanos intake solenoid electrical connector. This will cause the DME to not use the vanos and for the vanos to go into the default timing position of exhaust fully advance intake fully retarded. I expect if the vanos seals are failed the engine will perform better in this position, and if the seals are functioning the engine will perform worst in this position.

The vanos seals are failed on all the cars. The seal O-rings are made from Buna. This is the same material the valve cover gaskets are made of. Most of you are well aware what happens to the valve cover gaskets over time and use. Now imagine a small sliver of this installed in the bowels of the engine under oil pressure. It fails in a much quicker time than the valve cover gaskets. Numerous owners have now replaced the vanos seals and they have ALL reported failed seal O-rings.

Hope all this helps.
TX says...
Quote:
...M54 DME does [things] to hide the problems that the M52TU DME just doesn't do.
bmwbum says...
Quote:
The M54 motor came with the same VANOS unit as was used on the M52TU.

The same VANOS.

The M54TU motor doesn't exhibit the cold start up stalling condition that the M52TU motor does.

BMW apparently fixed the software bugs in the M52TU DME that was screwing up the cold idle process and successfully applied them to the M54.

They used the same VANOS on the M54 without any issues.
bmwbum repeats...
Quote:
Ever wonder why the 2001 cars that use the same VANOS (and seals) as your car never suffer from the cold idling problem?

BMW fixed the idle problem in 2001 without changing anything inside the VANOS.

I wonder what they did? If I knew, I'd do it to my 2000 car and fix the idle problem.

Most likely a software change.

See also:
- Pinpoint questions: Do we know what the double VANOS camshaft advance curve looks like (1) & how does the VANOS work (1) & what are our options if our BMW E39 VANOS seals have started to deteriorate (1) & what parts to replace while replacing your VANOS seals (1) & what is a reliable objective test of the before and after effect of VANOS seals (1) & what are the meanings of the two key metrics for the DIS/INPA VANOS postition and leak tests (1) & why do only some engine models experience VANOS-related cold idle problems (1) & what do old VANOS o-rings look like before and after replacement (1) & what exactly moves, holds, and returns the VANOS pistons to their proper positions (1) & why would a VANOS seal need to be "broken in" for "performance" (1) & do we know what E39 VANOS oil pressure should read (1) does the VANOS piston spin with the camshaft (1) & how on earth can VANOS increase the intake valve lift by 0.9 mm (1) & what can go wrong when replacing VANOS seals and o-rings (1) & does anyone really understand how the VANOS works (1) & a list of canonical posts referred to by Rajaie detailing a summary of the VANOS issues solved with new o-rings (1) (2) (3) (4) (5) (6) (pdf)
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Last edited by bluebee; 03-31-2015 at 11:11 PM.
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  #7  
Old 06-28-2015, 10:32 AM
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bluebee bluebee is offline
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Your ears may be ringing ...
> E39 (1997 - 2003) > Changed my Vanos Seals
Quote:
Originally Posted by sixpot_simon View Post
600-1200 rpm is what I meant. FWIW one of the graphs you posted shows vanos active at 1000rpm, so effects just off idle are plausible.
This is a technical discussion, which means it needs real world detail.
As far as I can figure out, VANOS does absolutely NOTHING below or at idle, nor above 3,000 RPM.

TheHockeyTowner has a good thread where he tries to make an argument (somewhat convincingly but not totally so), that VANOS operates below 1,000 RPM, but, this is one of the cases where just knowing how the VANOS works would be a blessing.
- Does the M54 engine experience VANOS-related cold idle problems or not (1)

The fact is, nobody really knows the range at which it affects engine operation.

It's not stated clearly in the references, although it is alluded to scores of times, so, we've been able to piece together the fact (the M54) VANOS turns on at about 1000 and shuts off at about 3000 and we think it's a table in between (square, sine, or parabolic, we don't know).

For now, until someone (who actually understands the VANOS) can prove otherwise, I'm sticking with the fact its effect on the engine starts at 1000 and ends at 3000.
- Do we really (truly) know what the ENGINE camshaft advance curve looks like with VANOS (1)
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  #8  
Old 06-28-2015, 11:03 AM
Henka Henka is offline
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Just changed my vanos seals on my bmw 728i. I had rough idle in cold starts. New seals solved the problem. But no changes in power or fuel consumption...
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  #9  
Old 06-28-2015, 11:34 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by Henka View Post
Just changed my vanos seals on my bmw 728i. I had rough idle in cold starts. New seals solved the problem. But no changes in power or fuel consumption...
Did you apply the DME update first?

What else did you change?

What did you measure, before, during, and after?
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  #10  
Old 06-30-2015, 01:22 PM
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bluebee bluebee is offline
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Just FYI, I have been referencing this excellent thread, time and time again, e.g., in this thread today (although I fear almost nobody is reading it)...
> E39 (1997 - 2003) > Changed my Vanos Seals
Quote:
Originally Posted by .:Moe:. View Post
I just finished replacing my vanos seals from beisan systems and all I can say is wow. My 528i is running smoother at idle and at 2 to 3k rpm it has a grunt I have never heard it make before (in a good way). Love the torque and power gain as well.

I was wondering if there will be any other noticeable change that would be made later on, I've heard it takes 300+km for the seals to break-in and by then will anything change?

Ps. Bought the car with bad seals

See also:
- Do we really (truly) know what the ENGINE camshaft advance curve looks like with VANOS (1) & what are the ENGINE inputs to VANOS and how does the VANOS actually affect ENGINE OPERATION (1) & what are all our options if our VANOS unit has actually started to fail (1) & what additional parts should we replace while replacing your VANOS seals (1) & what is a reliable scientifically objective test of the before and after effect of VANOS seals (1) & what are the meanings of the two key metrics for the DIS/INPA VANOS postition and leak tests (1) & does the M54 engine experience VANOS-related cold idle problems or not (1) & why you want to update your DME before replacing VANOS o-rings on the M52TU engine to solve cold-idle "jolts and stalls" (1) & what do old VANOS o-rings actually look like before and after replacement (1) & what exactly moves, holds, and returns the VANOS pistons to their proper positions (1) & why would a VANOS seal possibly need to be "broken in" for "performance" (1) & do we know what our VANOS oil pressure should read (1) & a DIY to replace the VANOS vanos oil line (1) & the answer to the question of whether the VANOS piston spins with the camshaft (1) & an explanation of what it means when BMW Marketing says the VANOS increases the intake valve lift by 0.9 mm (1) & what can go wrong when replacing VANOS seals and o-rings (1) & a list of canonical posts referred to by Rajaie detailing a summary of the VANOS issues solved with new o-rings (1) (2) (3) (4) (5) (6) (pdf)
  • M52 - single VANOS I6 engine [1997-98 528i]
  • M52TU - double VANOS I6 engine [1999-00 528i/iT]
  • M54 - double VANOS 2.5 liter I6 engine [2001-03 525i/iT]
  • M54 - double VANOS 3.0 liter I6 engine [2001-03 530i]
  • M62 - (no VANOS) "straight up" V8 Engine [1997-98 540i]
  • M62TU - single VANOS V8 engine [1999-03 540i/iT]
  • S62 - double VANOS V8 engine [2000-03 M5]
*******>********>
bmw_e39_m52tu_m54_engine_training_material_includi ng_vanos.pdf (978.0 KB, 83 views)
BMW_Vehicle_Communication_Software_Manual.pdf (1.12 MB, 39 views)
introduction_to_all_bmw_model_engine_transmission_ identification.pdf (1.27 MB, 76 views)
bmw_e39_e46model_MS42 MS43_ECM_M52TU_M54_engine_fuel_system_training_mat erial.pdf (8.04 MB, 62 views)
rajaie_and_loach_letter_to_bmw_on_the_6-cyl double vanos problem assessment.pdf (344.4 KB, 39 views)
rajaie_letter_to_bmw_on_the_6-cyl-double-vanos-problem-assessment.pdf (304.7 KB, 12 views)
rajaie_canonical_summary_of_bmw_vanos_seals_issues .pdf (1.17 MB, 18 views)
BMW_E46_Central_Body_Electronics_ZKE_V.pdf (2.27 MB, 28 views)
bmw_E53_X5_m54_engine_training_manual_siemens_ms43 _M54B30.pdf (2.52 MB, 9 views)
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Last edited by bluebee; 06-30-2015 at 01:26 PM.
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