[DaanBMW]

Have some crazy stuff going on, all related to the VVT system, more specifically the VVT motor and ESS sensor. All after a simple work on it.

Problem
-> The car doesn't start w/ ESS plugged in. Unless the car is warm. What this means is that if I started it some other way, it starts no problems. If I leave it overnight in the garage (~50F, so not too cold) it cranks but fails to start. If I keep trying and trying, then it eventually does start.
-> If I unplug the ESS (which then uses the fail-safe throttle control instead of the VVT), it starts immediately, incl. when cold.

Work that triggered it
I changed my valve cover (new, OEM). As part of this job, as a preventative thing I also changed the ESS (eccentric shaft sensor, new, Siemens VDO). Battery was disconnected, DME box was opened to move the harnesses out of the way. It all went well maybe with one small exception: During the job, when we took the VVT motor off, we did everything by the book, incl. the full rotation CW (bolted), then turning CCW and letting the motor push itself out (unbolted). The only somewhat odd thing was than we re-assembled it when turning CW to let the VVT motor pull itself in, the overall travel was quite short, and eventually the motor had to be kind of pushed up such that the bottom bolt hole was aligned with the bracket on the vlv cover. We let the VVT motor read the stops after such a job, I swapped the motor 2 times before.

Questions
The way I see it - The problem is for sure part of the VVT, but it could be the VVT motor (due to the re-assembly issue above), the ESS (which could be faulty), or even the VVT relay inside the DME/e-box (from what I read in the meantime).

• anyone have any sure-fire ideas what the culprit is here ?
• how does the VVT motor really figure out the stops ? are they mechanical ? meaning if we put the motor in but maybe not in the same relative engagement position to the eccentric shaft gear as it was when we pulled out, does it really matter ? After the job we also tried using an Allen key to mechanically rotate the VVT clockwise to see if we find a stop/resistance, and we did.
• how can the temperature of the engine influence the engine start when the VVT is involved, yet not influence it when using throttle control ?

I actually realized that while this could all be engine temperature related, it could also be fuel related, and the multiple crankings help finally bring fuel in (haven't tested anything on that front yet).

Any ideas would be v. helpful.

[DaanBMW]

Hmm, I was at least thinking someone know how the VVT stops are figured out.. Anyone ?

[hassmaschine]

Have you read any codes? and I mean with an actual BMW-specific code reader. If you're going to post generic P-codes, you may as well give up now..

As far as the learn procedure - it's done automatically by the DME. Normally, you don't need to intervene manually for this process.

The first question in my mind is, when you did your VGC, you had to remove the VVT motor as part of the process. Did you manually set the VVT motor to the "service" position? That is, did you release the tension on the eccentric shaft by using a hex key to turn the motor clockwise until it was fully released? Otherwise, you risk damaging the VVT motor, or even worse, breaking the shaft off the motor.

As much as I know about the N52 electronics, funnily enough - I have never had to bother with manually forcing the VVT learn procedure, but I know there is a way, and I have seen it posted here before. I guess that's the double side of having an engine that's basically trouble free? Anyway, when I did my MILVS, I didn't have to do anything after to "relearn". As far as I know, the DME took care of that on it's own (you can sometimes hear the VVT motor "clicking" during the start sequence if you turn on the ignition, but don't start right away).

Meanwhile, I would leave the car with the ESS unplugged until you figure this out. It won't hurt the engine at all - the biggest side effect is your rev limit will be 6500rpm, and you will lose some efficiency. The DME is smart enough it will default to using the throttle plate to control load (the VVT will automatically go to full lift).

FWIW, I didn't replace the ESS when I did my MILVS - because overwhelmingly, I stick by the hard-learned rule, "if it ain't broke, don't fix it".

[DaanBMW]

Yes, I did the VVT per the book, I described in the OP. And re-done the full turn a couple of times since...

Codes ? I have plenty. Most are read using INPA, yesterday's was using BT tool.

They are all VVT related. Depending on what happened last:
- initially when it didn't start - 2a38 2a45 2a77 2a3f 2a37 2a47
- yesterday, when it wouldn't start even w/ ESS unplugged (go figure) - 2a31 32 47
- right now after another VVT relearn and driving it - 2a37, 39, 47
- and [drumroll] this morning when it wouldn't start again, only cranked - no errors whatsoever !! explain that, a full failure to start after 4 tries, no codes. How is that even possible ??

[hassmaschine]

It seems plausible that the new ESS is no-good. You didn't happen to keep the original, working sensor did you? The common denominator here is 2A37, which is the ESS sensor.

It's late and I don't know all the codes off the top of my head, but I'll try to check tomorrow.

[DaanBMW]

yes, I still have the old one. but removing & putting the vlv cover back with a new set of gaskets each time is kind of a no-no

[UncleShrek]

Interesting, i had some codes come up after this job as well, we cleared them twice and codes haven't come back. Codes were for the ESS, it starts, runs fine too with one exception
The idle is a bit bouncy but only at idle, no CEL or anything yet. My mechanic wants to swap out the ESS for the original (i want to buy a new oem one) but am hesistant since everything is working fine, and the fact that its another charge for doing the work. I would hate to pay again and have something else be the issue.

[nsjames]

there is a relearn procedure you can do in ISTA.

or you can press the gas pedal down ten times immediately after you turn on the ignition.

your symptoms are very similar to my failing ESS. It just doesn't like the cold. I sometimes have to do the relearn just to get it to read properly so the car will start. After it starts it's fine as long as it stays warm.
I'd say the ESS you put in sucks.

I'd not have an issue pulling the VC and reusing the gaskets. They're all rubber. They haven't had a chance to heat cycle and take a set just yet.

[DaanBMW]

Originally Posted by nsjames

there is a relearn procedure you can do in ISTA.

or you can press the gas pedal down ten times immediately after you turn on the ignition.

your symptoms are very similar to my failing ESS. It just doesn't like the cold. I sometimes have to do the relearn just to get it to read properly so the car will start. After it starts it's fine as long as it stays warm.
I'd say the ESS you put in sucks.

I'd not have an issue pulling the VC and reusing the gaskets. They're all rubber. They haven't had a chance to heat cycle and take a set just yet.

...this thing with the 10x is a bit odd, only read it in 1 other thread and I actually - in desperation - did that too. No cigar...

As for relearning VVT stop, INPA has them too - either only the lower stop of both of them. Finding a "procedure" is not the point...


*************

I still am surprised that NO ONE has chimed in as to WHAT the VVT motor stops are ? How are they determined ? Is there a mechanical feature that is actually used as a hard stop ? Is it just some angular (read fictitious) position ?

Judging by the un-install/install procedure for the VT motor I'd say it is something mechanical, but the actual definition of the un-install is "until you feel a slight resistance, then stop" ... so not a hard stop but still some sort of mechanical stop (per pelicanparts.com)

Maybe it is when the cam follower hits the cam ramp-up ? Just my guess... Someone has to know... :-)

[hassmaschine]

They are definitely mechanical limits of travel. There is a casting on the head and a casting on the eccentric shaft. A stud that threads into the head sets the stop distance for full lift. The 'find stops' procedure just runs the VVT motor t until it finds them, which is why it 'clicks' when you run it.

The maximum open position is something like 95% of the way to the full lift stop (I bumped mine up to 97% or something like that). That translates to 172 degrees or 9.7mm of lift (stock).

[nsjames]

Originally Posted by hassmaschine

They are definitely mechanical limits of travel. There is a casting on the head and a casting on the eccentric shaft. A stud that threads into the head sets the stop distance for full lift. The 'find stops' procedure just runs the VVT motor t until it finds them, which is why it 'clicks' when you run it.

The maximum open position is something like 95% of the way to the full lift stop (I bumped mine up to 97% or something like that). That translates to 172 degrees or 9.7mm of lift (stock).

this.

doing the relearn procedure forces the VT motor to move whether the DME knows the ESS position or not.

so if you have a dead spot in your ESS, as I suspect I do, it forces the shaft to move and then it may or may not settle on the dead spot. Thus resolving my no start temporarily.

[DaanBMW]

OK, I was afraid we might have somehow screwed up some "preset" stops (via driving the VVT with the Allen key). Sounded like that was not the case.

Indeed, after replacing what turned out to be a bad ESS now everything is back to it's regular routing (if only I could solve my rpms dropping when taken out of gear :-) )

Thanks all !