N52 hesitation, stuttering, jerking, surging etc

It's actually the pre-cat sensors I can't see, weirdly, but can see them in INPA and they look okay. Was having issues with INPA recently but managed to sort it and check some stuff again. Did another VVT relearn and that kind of thing. Couldn't really see anything indicative of a problem when the hesitation happens apart from some pretty all over the place short term fuel trims on occasion, nothing concrete.

Some better news though. I managed to construct a ghetto vacuum tester which has lead me to a small vacuum leak at the valvetronic motor. I had a feeling this needed to be replaced anyway, as although there is no oil coming out of it, per se, it has some residue around it. I have no idea whether this size leak is large enough to cause the issues I am having, but I suppose the only way to find out is to replace it. Other good news is that I couldn't seem to see any other leaks.

IMG_20190603_134146.jpg
 
That is the most enjoyably hood smoke tester I've seen in a while. This is definitely something I need to do.
 
Capa said:
That is the most enjoyably hood smoke tester I've seen in a while. This is definitely something I need to do.
Click to expand...

I'm glad you approve :D I've ordered a new VVT motor gasket for the grand total of about 9 quid from the local dealer, should get it and install it wednesday if all else goes to plan. Is this going to put an end to my chapter in this thread? I'm not going to hold my breath, put it that way!
 
I feel like there's some kinda smoke, breath related pun there. Particularly given the fat assed doob you appear to have rolled. (:

Lazy as I am, don't suppose you have any links for the pump you've got there?
 
Capa said:
I feel like there's some kinda smoke, breath related pun there. Particularly given the fat assed doob you appear to have rolled. (:

Lazy as I am, don't suppose you have any links for the pump you've got there?
Click to expand...

At this point, I don't want to ruin the whole thing for you, but I also don't want to lie to you. Whilst I would love to take credit for said fat doob, it was a merely a dank edit because I forgot to take a picture the poorboy-special with the actual smoke source installed. Instead, I used the cheapest cigars I could find 8)

As for the pump, it can be found here: https://www.amazon.co.uk/Am-Tech-S1495-Hand-Tools-Transparent/dp/B003WOQRNK/ref=sr_1_1?keywords=am-tech+s1495&qid=1559648601&s=gateway&sr=8-1

It doesn't get great reviews, but for my street masterpiece, it was fine! Weirdly, it was actually a hissing/bubbling noise from the VVT motor that put me on to the leak before I saw the smoke.
 
A man after my own heart, haha. Thanks for the link. I've ordered up one of them bad boys, and some gloves.

Come saturday it'll be a trip to the cornershop to find some of the dirtiest smokes I can lay my hands on.
 
So what's the procedure for doing the smoke test - doesn't all the gas just pass straight out through the exhaust on the N52 or are they all closed with ignition off?
 
Capa said:
A man after my own heart, haha. Thanks for the link. I've ordered up one of them bad boys, and some gloves.

Come saturday it'll be a trip to the cornershop to find some of the dirtiest smokes I can lay my hands on.
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Can't wait for your whip to blaze it too. Post back with results!

ph001 said:
So what's the procedure for doing the smoke test - doesn't all the gas just pass straight out through the exhaust on the N52 or are they all closed with ignition off?
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This was something I wondered before doing it. Basically I just put a glove over the intake pipe, cut a little hole in the finger, inserted my pipe then taped it up as best I could. Initially I pumped it without any smoke to see if it would hold pressure for the same reason you have suggested. It held pressure, so I tried it with the ignition on to make sure the throttle plate was open and it still held pressure. From this I can assume that the inlet/exhaust valves are closed when the engine isn't being cranked. I appreciate that isn't a very eloquent explanation, but it seemed to achieve what I set out to. Smoke and pressure was lost when opening the oil filler cap during the process. I did check the exhaust when I started the car after I had been smoking it, and I couldn't smell or see any of the cigar smoke. It's possible that the general fumes made this impossible or I just wasn't quick enough to the back of the car though.
 
The smoke would just fill the intake manifold, then the crankcase via the oil separator system (I believe), via the rocker cover. Some will enter the cylinder/s but it would be negligible.

I may have a conclusion to my woes and it was fixed with the almighty INPA. The function is not available in ISTA/D.
In the Adaptions menu of INPA, one of them is "gelernte Varienten" (option F7). This deletes the learnt variants coding in the DME (loosely translated from German). Let the car go to sleep (lock vehicle for 5 mins), then all should be good.

However, you must ensure everything is ship shape as in all existing issues, leaks, faulty solenoids, faulty coils, aged plugs etc are all rectified first.

One thing I also noticed is my coolant temp no longer swings wildly, where it used to simulate an intermittent stuck open thermostat (it would randomly cycle down to <80*c). There is a chap on the American E90 forum that describes this peculiar behaviour in detail and a lot of 330i E90 owners described the same symptoms which led to misleading diagnosis resulting in unnecessary replacement of the thermostat and coolant pump (although these are known to fail). From this experience I can say that this is simply a symptom of the illness if you know your thermostat and coolant pump are healthy/recently replaced. I am not sure if an engine overheat scenario triggers a permanent mode in the DME because my engine did overheat once due to a failed coolant pump (red symbol on the cluster, coolant boiled out of the expansion tank). Others will have to chime in with their vehicle history to see if there is any truth to this theory. There is official documentation describing several operating modes of the N52 DME including a high output mode which triggers the map thermostat to open up under command earlier than the traditional function of the thermostat. I was always assuming I somehow kept triggering this mode in normal driving. So far, I have been unable to reproduce the fluctuating coolant temps despite colder weather requiring the heater to be on max. I did replace the clutch and flywheel so I haven't done any redline blasts yet, but i have accelerated hard up to 5000rpm several times without issue. Hope this helps :)
 
So I've just been out to replace the VVT motor gasket and I don't really have anything to report back, other than that the gasket needed to be done and that the test drive seemed smoother, but it was only a short blast. Idle seemed slightly smoother but tbh, I'd call the difference insignificant, if there even is one. So I guess this Rules out the cause of my issue being a vacuum leak. I've reset adaptions again to test tomorrow so I'll keep y'all updated.

The only other thing I have noticed which I am glad I got the chance to record, was a sound that I could describe as a marble bouncing off a granite worktop or something similarly hard, at a random and erratic rate. This rattle is different to the one I posted on here before which sounded more clunky, this sounds more 'tappy'. I videoed from the bottom of the car to rule out the noise being from the gearbox and then videoed from the top. I am convinced my problem is a collapsed valve spring or a lifter/intermediate lever issue. The sound is easily distinguished in the video when I capture it from underneath as the injectors aren't interfering. It sounds like it is coming from the top/rear of the engine. I have also heard a similar sound from the car if I am in a higher gear at lower RPM and I floor the throttle, it gives a similar if not the same sound rattle for a second.

I've also noticed from the video a pretty audible hissing noise when the camera is under the car. I wonder if there is an exhaust leak somewhere... Hmmmm.

https://youtu.be/hopDFho0jFY

[youtube]hopDFho0jFY[/youtube]
 
Hmmmm. Interesting.

At least the vacuum leak is ruled out, although that doesn't do much for actually finding a fix. Maybe use the ghetto smoke tester up the exhaust too? Not that I really suspect an exhaust leak to be the cause of your issues...

I'm going to do the smoke testing thing over this weekend, I'll see if I can keep an ear out for a similar noise...
 
Capa said:
Hmmmm. Interesting.

At least the vacuum leak is ruled out, although that doesn't do much for actually finding a fix. Maybe use the ghetto smoke tester up the exhaust too? Not that I really suspect an exhaust leak to be the cause of your issues...

I'm going to do the smoke testing thing over this weekend, I'll see if I can keep an ear out for a similar noise...
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I could do, and I have certainly read about people with exhaust leaks causing running issues if the leak is near/in between o2 sensors. But then again, I don't think my STFTs go lean enough for that to be the case. None the less, that hissing noise I suppose is worth investigating. Oh good, let me know how you get on!
 
Admittedly I’m only listening on my phone but I can’t hear any noises on that video that would concern me particularly. Sounds pretty normal to me.

This thread is getting pretty long now, perhaps you could recap the problem you are experiencing and what you have tried so far.
 
ph001 said:
Admittedly I’m only listening on my phone but I can’t hear any noises on that video that would concern me particularly. Sounds pretty normal to me.

This thread is getting pretty long now, perhaps you could recap the problem you are experiencing and what you have tried so far.
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Sure thing - RECAP:

Symptoms

  • Hesitation/jerking when accelerating from low RPM, most prevalent when in a high gear
  • Juddering/surging when going constant speed or applying light throttle, particularly around 1500-2000 rpm
  • Strange behaviour when decelerating in gear, similar to jerking when accelerating but more random and like someone is poking the throttle as the car slows
  • Various noises, high pitch marble-like rattle towards the rear of engine
  • Rough/shivering idle
  • Blowing-like sound from exhaust on hard acceleration, very subtle but either sounds like a leak or gasses not escaping properly

Parts replaced

DME update to latest versions
Both VANOS solenoids
Valve Cover gasket
Eccentric shaft sensor and seal
MAF sensor
VVT Motor Gasket (found vacuum leak around it)
Intake manifold gaskets
6 Bosch Coils
6 NGK Spark Plugs
CCV and 3 main CCV hoses
5w30 LL04 Oil and filter
Inner DISA valve
Cleaned VANOS check/non-return valves

Troubleshooting

Listened to all injectors, all function with the same pitch when solenoids are activated. Primed the fuel rail with injectors installed but out of the cylinder head to check for leaks, no leaks. I haven't tested the spray pattern but have run several doses of injector cleaner.

I have investigated a number of parameters and conducted adaption resets/VVT relearn cycles. Parameters include o2 sensor function, all look normal, rough running which all look within spec, VANOS positions look to be good from reference/actual positions with some lag but unsure what is considered normal.

Without making this post long in itself, my current train of thought regarding the cause of this problem relates to the cylinder head, here's why. The behaviour is very mechanical in nature, it happens at the exact same points in the rev range without any significant perceptible deviation. The behaviour manifests during deceleration, not in the exact same way, but similarly, during which time injectors, spark, air for combustion and related hardware are not a factor. Which leads me to the projected cause. I think there is a problem with (likely one) lifter, intermediate arm, valve spring or valve on the exhaust cam side. This would fit with the noise, lack of power low down, hesitation, jerking at constant throttle and even when decelerating. If a valve is sticking or only opening partially then I believe these symptoms would fit. I suppose this could also happen with slight damage to a valve. The reasons I am hesitant to try and diagnose the problem along that path is I feel the problem would likely be present during the entire rev range, there would be rough running data in diagnostics to support this.

Next steps

Compression test (I guess if a valve issue is present, compression will be low, though only if it is sticking open)
Just leave it because I'm tired thinking about it -.-
 
I'll admit I'm not a million miles off leaving it. I do want to replace my small DISA and sort the noise out that I have, but the car will probably be departing in the next 12 months, so I'm not going to go and rebuild the engine or anything to that effect.

That said, I quite like pottering around trying to fix it on a sunny weekend.

For reference, I have had a compression test and it found surprisingly strong compression, rather than weak. I'm not convinced our issues are exactly the same, but there are some similarities...
 
Capa said:
I'll admit I'm not a million miles off leaving it. I do want to replace my small DISA and sort the noise out that I have, but the car will probably be departing in the next 12 months, so I'm not going to go and rebuild the engine or anything to that effect.

That said, I quite like pottering around trying to fix it on a sunny weekend.

For reference, I have had a compression test and it found surprisingly strong compression, rather than weak. I'm not convinced our issues are exactly the same, but there are some similarities...
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That's the problem. My car is barely worth the amount I've already put into it, but the 'fixer' side of me takes over and wants to know what the hell could be causing such an illusive problem. I feel I am going to have to leave and put up with it unless it worsens. I can't actually remember what your problems are exactly anymore because quite a few people have posted in here now. Gonna PM you.
 
I’d have a modest bet on it being your Valvetronic motor. I think it’s about the only thing that can cause problems on deceleration.

I have heard of one instance of the VANOS compression rings failing on a 2.5 N52, but seems relatively rare compared to Valvetronic motor failures.... https://z4-forum.com/forum/viewtopic.php?f=3&t=114584&p=1651180&hilit=Vanos#p1651180
 
ph001 said:
I’d have a modest bet on it being your Valvetronic motor. I think it about the only thing that can cause problems on deceleration.
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Darn, that was the other thing I was supposed to mention and I think that's a very good suggestion as it's obviously valvetrain related. Thinking about it, though it does the relearning process without error, when I was watching the reference vs. actual position, I did notice it hunt a tiny bit. Say the specified value was "94", the motor would reduce to 95 then creep down. I'm going to have to watch this page whilst I am driving and revisit the VVT motor as the potential culprit. Might have time to test it this evening, at which point I'll report back.

This would also fit with post #16 in this thread: https://www.e90post.com/forums/showthread.php?t=886211
 
I just want to throw it out there, couple of people saying the CCV is serviceable on the plastic topped n52K.

Seems to be counter to what realOEM & this thread are telling me - any ideas which is the truth?
https://www.e90post.com/forums/showthread.php?t=1312867
 
Capa said:
I just want to throw it out there, couple of people saying the CCV is serviceable on the plastic topped n52K.

Seems to be counter to what realOEM & this thread are telling me - any ideas which is the truth?
https://www.e90post.com/forums/showthread.php?t=1312867
Click to expand...

I and someone else definitely suggested it was in fact, serviceable. I guess it depends whether the parts that are not replaceable, such as the channels in the valve cover are blocked and what not. I seem to remember seeing a post about someone pushing sludge out of their CCV channels with the plastic top.

Here's a link to a rebuild kit: https://vanos-bmw.com/product/11127552281-bmw-valve-cover-repair-kit-n52-n51-n52n-n52k

I'm sure there are other similar kits out there
 
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