Vanos Rebuild Start Hesitation

[sapote]

The front side is the smaller chamber .

The smaller end with the hex is threaded to the splined shaft, and this is the rear side. No?

[sapote]

1. I don’t really know how it works without VANOS influence as it appears the small chamber always has high pressure applied regardless, and oil in the large chamber should be sealed by the solenoids, so disabling VANOS or unplugging the solenoid pack should mean the pistons are just locked at whatever their last position was.

2. Also not sure what happens to piston position when pressure eventually bleeds off on the small chamber side as the engine is shut down.

1. What does it mean "without vanos influence"? No oil pressure, or solenoids are not energized?
For no oil pressure, then the rotation of the sprockets apply a force on the helical splined shafts, cause them to move forward to their max retarded.
For no power applied to any solenoids then they all closed, so the constant oil pressure on the smaller side will push both pistons forward to their max retarded.
So either cases would cause cams to be retarded at 130 for IN and 83 for EX, and this is another proof that the Manual is wrong saying ADVANCED 83*
Edited: I was wrong on this. If no power applied to solenoids then they are closed to seal the front chambers, and so the pistons should not move instead of moving to the max retarded as I wrote above.

2. If the engineers wanted to have the cams at max advanced during cranking as I think, then during engine shut off, the DME detects the key turned off, then it energizes both intake solenoids to pressurize the larger end of the pistons to advance the cam as the rpm slowing down. Why not? Then during cranking, the DME also energize the same two intake solenoids to keep the pistons at the same advanced position.

[sapote]

1. The front side is the smaller chamber which has a constant pressure applied. The back side which is the larger chamber is where pressure is fed or bled by the solenoids. The larger surface area on the back side allows the same amount of pressure to overcome the pressure in the smaller chamber, moving the piston forward toward the engine. When pressure is bled from the large chamber the pressure in the small chamber pushes the piston backward away from the engine. Large chamber would be the side with the cap on the front of the VANOS body.

2. I don’t really know how it works without VANOS influence as it appears the small chamber always has high pressure applied regardless, and oil in the large chamber should be sealed by the solenoids, so disabling VANOS or unplugging the solenoid pack should mean the pistons are just locked at whatever their last position was.

3. Also not sure what happens to piston position when pressure eventually bleeds off on the small chamber side as the engine is shut down.

1. See how concficting the 2 highlighted statements? And you said the larger end of the piston is the front side covered by the cap
2. You're right that without power applied to the solenoids, this keeps the pistons at the last positions.
3. it should stay the same place as the sealed oil in the front cannot push it to move.

[jamesfoley]

2. If the engineers wanted to have the cams at max advanced during cranking as I think, then during engine shut off, the DME detects the key turned off, then it energizes both intake solenoids to pressurize the larger end of the pistons to advance the cam as the rpm slowing down. Why not? Then during cranking, the DME also energize the same two intake solenoids to keep the pistons at the same advanced position.

Yes, at idle the cams should be in their default positions so when shut off they are at the ideal positions for next start. It pulses all solenoids fast using the high oil pressure until it achieves the cam angle it needs. I don’t think that the oil pressure exists during cranking to do this.

1. See how concficting the 2 highlighted statements? And you said the larger end of the piston is the front side covered by the cap

I see what you mean but I think that’s just where the front of the VANOS body is not the same as the front of the piston. Back side of the piston is generally the side with the larger surface area that pushes the piston outward, regardless of orientation.

[sapote]

I see what you mean but I think that’s just where the front of the VANOS body is not the same as the front of the piston. Back side of the piston is generally the side with the larger surface area that pushes the piston outward, regardless of orientation.

On the car, the best way for everyone to agree is to use the car body when referring to left right front and rear sides.

Part orientation should be referenced the same way.

[jamesfoley]

Got TestO working graphing both bank 1 intake and exhaust camshaft actual positions and DME expected positions.

I have no idea what the exhaust cam is doing when it fires up, but thats where the hesitation I feel is. This is a smaller hesitation than usual, but logging every engine start with my laptop is a ball ache. Video is of the same start, doesn't really come across well but it can be felt and heard in the car, this one being one of its better starts so hesitation is short.

Car hasn't been used for around 2 days before this start, so cold engine.

I'm assuming TestO reporting values for bank 2 is normal? With only 1 intake and 1 exhaust sensor, not sure where the exhaust bank 2 actual value is coming from in that left hand side table.

[jamesfoley]

Here is a good one, roughly 3 hours after the video in my above post. Hesitation at start and ran rough until RPM settled just under 1k:

[jamesfoley]

First start after the car sat for a week while I was on holiday, hesitatesas the engine was trying to catch while cranking and then runs fine.

[sapote]

In 3 videos I see engine ran normal. The M3 doesn’t start up smoothly as non-M cars.

[jamesfoley]

In 3 videos I see engine ran normal. The M3 doesn’t start up smoothly as non-M cars.

My previous M3 never did this, and this never happened before I had the VANOS done, so to me it doesn’t feel like it’s a normal thing…

[jamesfoley]

Just a small update with some data I have.

Results of VANOS test, and adaptations taken with DIS:


Cold start with hesitation, graph of VANOS intake and exhaust actual and DME expected positions:


Warm car running, key off and then engine start again, car did not hesitate this time but still has weird 10 degree jump on the exhaust positions:


I also have a VANOS cam position log which was started just after the cold start graph. It seems that both cams do stick to the DME requested position with a degree or two of difference, so I think its working as expected.

There are a couple of rows I've highlighted in orange though where there is a 10 degree difference in the exhaust cam actual and expected, seems to be at engine stop and start.

https://docs.google.com/spreadsheets/d/1u9PBg3NKFgR7Bph15trebvIxyyKTSn6TYibcxIgrvok/edit?usp=sharing

The car did run super rough while it was testing the exhaust side of the VANOS which I'm assuming is expected as its fully advancing and retarding the cam?

[sapote]

Cold start ex vanos issue:
The ex expected is 3 degrees retard but the actual shows 50 retard. So the ex couldn’t advance from max retarded to 3 degrees retarded.

[jamesfoley]

Cold start ex vanos issue:
The ex expected is 3 degrees retard but the actual shows 50 retard. So the ex couldn’t advance from max retarded to 3 degrees retarded.

Scales for the graphs are different, exhaust cam actual is -1 degree when expected is 12 degrees for some reason. They then align to 3 degrees, +/- a degree.

However the same discrepancy is there when the car starts normally, so I don’t know if it’s actually a problem, or if the car just starts easier when warm even with this cam position difference on the exhaust.

VANOS test proves there is nothing wrong with the timing as it reaches the expected positions without an issue.

Don’t know if perhaps my exhaust cam position sensor is just doing a shit job at reading the cam on engine start, though if it was the sensor I’d expect drivability issues somewhere.

Also don’t know if that’s just how the DME works for the version I have.

[sapote]

Scales for the graphs are different, exhaust cam actual is -1 degree when expected is 12 degrees for some reason. They then align to 3 degrees, +/- a degree.

However the same discrepancy is there when the car starts normally, so I don’t know if it’s actually a problem, or if the car just starts easier when warm even with this cam position difference on the exhaust.

VANOS test proves there is nothing wrong with the timing as it reaches the expected positions without an issue.

Don’t know if perhaps my exhaust cam position sensor is just doing a shit job at reading the cam on engine start, though if it was the sensor I’d expect drivability issues somewhere.

Also don’t know if that’s just how the DME works for the version I have.

Cold start graph shows totally different than warm start.
Vanos test was done with warm engine and so it’s fine.
if the cam sensor is glitchy then you would have error codes

[jamesfoley]

Cold start graph shows totally different than warm start

Only because of the Y axis scale, the actual values are the same.