N52 hesitation, stuttering, jerking, surging etc

[propaintballa]

Hi guys,

Seems I am drawn to this forum whenever I have car issues, which is relatively often! Since my Z4 saga I purchased a manual 325i, N52 powered like some of you will find in your Z4 2.5si. Naturally I have issues and I appreciate this isn't an E90 forum, but any help would be highly appreciated! For the record, the car has been to my trusted garage and one other during which they couldn't find the issue. One didn't think there was an issue simply because there were and still are no fault codes.

The Issue

When I first got the car this stuttering issues was far more pronounced and would appear when flooring the throttle. This action lead to the car almost feeling like a sluggish auto trying to downshift and causing a big jerk. I would then get a jerk at around 3.5krpm. It eventually got really bad to the point where the car stalled and wouldn't start. Turned out to be the exhaust VANOS solenoid, so I replaced both with genuine parts. Since then I have had a more subtle stuttering issue which is evident at around 1500rpm and 1800rpm, sometimes at different points in the rev range too, with the occasional jerk higher up the range and is further complemented with a bit of a rough idle.

Exactly what this feels like it hard to describe, but it feels akin to a misfire. Say I am going 30 in 3rd, the revs are about 1800 rpm, not labouring the car. With a constant throttle the car will surge, judder, stutter (so many words for it) which feels like a faint jerking back and forth. This can also be witnessed sometimes coming off the throttle around that particular rev range, where the car will judder as it slows. Generally in the low rev range there is a distinct lack of torque, at least consistently, with flat spots and hesitation under full throttle.

Attempted remedial actions

• 
  OEM MAF (Hella)
  2 Genuine VANOS Solenoids
  Checked and cleaned VANOS check/non return valves
  Oil and filter change with certified 5w30 fully synth and later 5w40 (Current)
  Checked Large DISA (had quite an amount of oil in the intake as I took it out)
  Replaced small DISA valve with genuine part
  Genuine Valve cover gasket
  OEM eccentric shaft sensor and seal
  Checked for vacuum leaks, albeit not with a smoke tester etc
  Listened for injector function, all sound the same with consistent 'ticking'
  Replaced all 6 coils with Bosch OEM part
  Replaced all 6 spark plugs
  Replaced CCV (twice) with Febi parts
  Replaced Valvetronic motor with a used unit
  Replaced Valvetronic motor gasket
  Replaced oil filter housing gasket
  Replaced 2 pre-cat o2 sensors with Bosch parts
  Cleaned MAP sensor
  Replaced oil fill lid and gasket
  DME update to latest version

Now, the symptoms fit almost exactly with others who have had issues with spark plugs and coils. Both the plugs and coils are relatively new (at least in my opinion). Off the top of my head, plugs and coils were changed last at a BMW dealer about 3-4 years and around 25,000 miles ago. I inspected the boots of the accessible coils and they look fine. Last time the garage had the valve cover off I was told the plugs looked fine too.

I am really at a loss with this and it's making the car such an effort to drive along with really poor fuel consumption (about 20-25mpg mixed). Please someone bestow upon me their wisdom! :violent1:

 

[ph001]

I think it's possibly your valvetronic motor but of course it's all really guesswork (esp if no codes stored) so you really just have to start changing things so it makes sense to start with the least expensive so first I would look at live o2 sensor voltages with INPA to make sure they are oscillating between the correct voltages and at the right frequency. The lambda value is critical at steady state throttle just like you describe above, and would tie in with poor mpg.

The next thing to eliminate would be the battery. If it's over 5yrs old I would replace it and make sure you have >13.8V from your alternator, you can get all sorts of weird and wonderful problems on the N52 with a high impedance battery.

Next would be coil packs and plugs. I know you 'suspect' they are OK but you need to be sure.

It's a little worrying that you have a lot of oil in your intake and of course this would point to a gunked up CCV valve (is it silver top or black top engine btw?). How much vacuum do you get when you remove the oil filler cap with the engine idling?

Then there is the second DISA valve which is a little awkward to get to as it's an inlet manifold off job.

Finally there is the VANOS unit itself but they very rarely go wrong on the N52 unless they have been severely neglected in terms of oil changes and they get all gunked up. Likewise things like timing chain tensioner - failure can mean the chain jumps a tooth and screws up the timing which results in poor performance but rare on the N52.


So I would do in this order:

1) Observe O2 sensor voltages in INPA
2) Fit new battery
3) Replace coil packs and plugs
4) Replace EGR valve and check pipes to sump for blockages
5) Replace / inspect second DISA valve
6) Replace valvetronic motor
7) Have VANOS unit stripped and inspected.

 

[propaintballa]

I think it's possibly your valvetronic motor but of course it's all really guesswork (esp if no codes stored) so you really just have to start changing things so it makes sense to start with the least expensive so first I would look at live o2 sensor voltages with INPA to make sure they are oscillating between the correct voltages and at the right frequency. The lambda value is critical at steady state throttle just like you describe above, and would tie in with poor mpg.

The next thing to eliminate would be the battery. If it's over 5yrs old I would replace it and make sure you have >13.8V from your alternator, you can get all sorts of weird and wonderful problems on the N52 with a high impedance battery.

Next would be coil packs and plugs. I know you 'suspect' they are OK but you need to be sure.

It's a little worrying that you have a lot of oil in your intake and of course this would point to a gunked up EGR valve (is it silver top or black top engine btw?). How much vacuum do you get when you remove the oil filler cap with the engine idling?

Then there is the second DISA valve which is a little awkward to get to as it's an inlet manifold off job.

Finally there is the VANOS unit itself but they very rarely go wrong on the N52 unless they have been severely neglected in terms of oil changes and they get all gunked up. Likewise things like timing chain tensioner - failure can mean the chain jumps a tooth and screws up the timing which results in poor performance but rare on the N52.


So I would do in this order:

1) Observe O2 sensor voltages in INPA
2) Fit new battery
3) Replace coil packs and plugs
4) Replace EGR valve and check pipes to sump for blockages
5) Replace / inspect second DISA valve
6) Replace valvetronic motor
7) Have VANOS unit stripped and inspected.

Thanks for your comprehensive response! Will try my best to address each part.

"Valvetronic motor" - Now, this has crossed my mind as I've seen a BMW bulletin which highlighted very similar symptoms and suggested the replacement of the motor if a DME update failed to resolve the issue. My thoughts on this were also supported by my mechanic telling me, when they replaced the valve cover after changing the gasket, the motor did a couple of cycles or behaved in an abnormal way during the first start up with the new gasket. This would also support my theory that the issue is more timing related, backed up by the fact that the symptoms can sometimes be apparent when off throttle during which time there is no spark or fuel, pushing me towards a timing related problem. What makes the think it isn't this is that there are no issues starting the car and I feel like there would certainly be a code for a mismatch with desired valvetronic position and eccentric shaft sensor actual position.

"02 Sensor" - This was also what I suggested to the garage as I had issues reading the data before I managed to get INPA. They suggested there were no problems here though were of the opinion this would also throw a code for mismatches, so not sure whether they actually checked. I will try to look into this myself. Do you have an idea of what I should expect to see?

"Battery" - Also crossed my mind as I read about poor connections causing similar issues. I did check this, however not the voltages. The battery has been replaced at some point, although not sure when.

"EGR" - To confirm, it is the silver top engine with the metal valve cover. Not sure about EGR on this particular engine? As for vacuum with oil cap, I'd say it's normal and in line with the 3.0si Coupe I had which had no issues of this sort.

"Coils/plugs" - To confirm, they were both replaced 20k miles ago in Jan 2015, is it likely there's an issue here, particularly with coils? Have read people running on original coils at 100k miles...

"DISA" - Small DISA you speak of I suppose was the next port of call, but as you say, a bugger to get to The oil in the manifold was a little worrying, was enough that it dripped out and over the throttle body.

"VANOS Unit" - I was wondering this too, though it has a good maintenance history, a majority of which has been at a main dealer, and as you say, I haven't really read about issues with this on the N52 and thought the problems were resolved from the (M54?) I forget.

I think I will check 02s again (My INPA version is confusing, with some bits in German) and report back. Do you think unplugging the valvetronic motor will tell anything at all?

 

[propaintballa]

Just tried to look at various things through INPA (confusing as hell) - The lambda sensors didn't seem to cycle like I'd expect to see in a sine wave type fashion, they seemed to stay at roughly the same voltage. Quite hard to tell without a graph though.

The VANOS positions were what stood out to me, though could be nothing. It appeared as if the reference position for cam angles and actual were quite different. I have attached some screenshots, unsure if they are any use without them moving in real time. The only other thing was that I noticed the throttle position sensor wasn't keeping a constant voltage or position. Seemed it was only deviating by .01 ish of a volt, but unsure whether this should be completely solid.

 

[ph001]

Sounds like you have a really good grasp on this and would agree with all of your points.

I don't think the engine will run with the valvetronic motor disconnected unfortunately so not sure there is any merit in trying.

The O2 sensor (pre-cat ones) should swing from about 0.1V to 0.8V over a period of around 1-2 seconds. Faulty ones have a reduced amplitude or miss cycles. This is what it should look like:



The EGR on the silver top engine is not integrated into the cover like it is on the black top so somewhat more serviceable. I think you defo need to investigate this if you have a lot of oil in the inlet, even if it's not related to your problem.

Coils / plugs. Failures seem to be somewhat random (esp on the non-bosch ones). I think they are around £20 ech so not a ton of money in terms of eliminating. I've even returned them to BMW when I was diagnosing with my M3 and they took them back no problem. Alternatively you can move them on Ebay with very little loss if not the culprit.

 

[ph001]

...just seen your images. Can you do a video of the lambda voltages on the adaption mixture screen (car must be fully warmed up first), post on Youtube and link to vid on here.

Other thing...on the raw values screen where you seeing any readings at all for HFM sensor air mass?

 

[propaintballa]

Coils currently are Bosch, I just feel like it would be a piss take for them to only last 20k miles! Not ignoring the other things you said but will focus on your last post.

Makes sense with the 02, though not sure that's what I'm seeing! Here's the video! https://www.youtube.com/watch?v=Iq5z9VJL46U

As for the HFM readings, did not notice that, but no, no reading at all...

The only other thing I noticed this time was this screenshot, top left corner. Now I'm not sure what this actually means, but I'm assuming it's battery charge rate or the voltage going to the DME. Seems high whatever it is, and also seemed to fluctuate with the odd dip in revs at idle. I have read about people who have not registered batteries having issues where they are constantly charging (which as we know is not supposed to happen on these cars).

 

[ph001]

Hmmm... those lambda voltages don't seem to be moving! But it could be related to the scanning freq of them as you say. The alternator o/p is about right for charging an AGM battery immediately after startup, it will probably drop after 15 mins or so.

I'm also not convinced that your airflow meter is working, I'm sure I remember seeing readings there on mine.

I think these readings now need comparing to a known good car before we can say much more. I have the 3.0 N52 but expect it should be very similar. I will see if I get chance to fire INPA up on it tonight to see how they compare.

Anybody else on here know if these somewhat strange readings are normal???

 

[propaintballa]

Hmmm... those lambda voltages don't seem to be moving! But it could be related to the scanning freq of them as you say. The alternator o/p is about right for charging an AGM battery immediately after startup, it will probably drop after 15 mins or so.

I'm also not convinced that your airflow meter is working, I'm sure I remember seeing readings there on mine.

I think these readings now need comparing to a known good car before we can say much more. I have the 3.0 N52 but expect it should be very similar. I will see if I get chance to fire INPA up on it tonight to see how they compare.

Anybody else on here know if these somewhat strange readings are normal???

Interesting! I'd really appreciate it if you could. I actually have the old one which is likely okay that I could also test in the mean time!

 

[ph001]

Incidentally, I do note the voltage on those lambdas on your vid is around 2V which would suggest they are wideband sensors which typically swing from 0-5V ish instead of 0.1 to 0.8V. They should still swing though.

I'll see if I can specifically look at those and the AFM for you....

 

[propaintballa]

That does indeed make sense. I have since put my old MAF back in and there is still no reading on HFM.

I have uploaded another video of the Lambda behaviour when revving the the car. They seem extremely sluggish to me and seem to go 'into the red' as it were. Hard to really tell with this type of readout I guess. See what you think...

https://www.youtube.com/watch?v=ijuR_0L8Lm4

 

[ph001]

OK, managed to get INPA on it this evening and to my surprise I also have no reading for AFM and my lambda voltages look similar to yours. However my Sensor signal vanos adaptations do look quite a bit different:









I wonder if it would be worth looking at your VALVETRONIC values (F5 menu, then shift + F1).....First I did idle then 2000rpm:

 

[AveZ4coop]

I have to say these symptoms are exactly what I had when a coil pack started to fail on my e86. I am not in anyway as knowledgeable as you appear to be, but for £120 it is probably worth doing.

 

[propaintballa]

Interesting... For some reason seems like my adapted VANOS values are quite a bit off the reference. Did you manage to look at my latest video and see how your lambda data respond to revving? I will have a look at the Valvetronic screen this morning and report back.

I have to say these symptoms are exactly what I had when a coil pack started to fail on my e86. I am not in anyway as knowledgeable as you appear to be, but for £120 it is probably worth doing.

Dammit, don't do that to me! I'm pretty reluctant just because they aren't very old and I've already thrown a load of money at the car to still have the same issue. Not sure if there's a way to individually test coils, which would make life a lot easier! I suppose I could always get a set from ECP and return them if it turns out not to be the issue...

EDIT: Actually might not be able to do that assuming the boxes are sealed -.-

 

[ph001]

Did you manage to look at my latest video and see how your lambda data respond to revving?

Yep - very similar. Not saying I understand why they don't swing around like they should, must be an INPA thing as I'm fairly certain they would with a scope on them.

Your batt volts look good so I think if the Valvetronic values check out OK you need to continue down the list:

1) Observe O2 sensor voltages in INPA
2) Fit new battery
3) Replace coil packs and plugs
4) Replace EGR valve and check pipes to sump for blockages
5) Replace / inspect second DISA valve
6) Replace valvetronic motor
7) Have VANOS unit stripped and inspected.

 

[propaintballa]

Did you manage to look at my latest video and see how your lambda data respond to revving?

Yep - very similar. Not saying I understand why they don't swing around like they should, must be an INPA thing as I'm fairly certain they would with a scope on them.

Your batt volts look good so I think if the Valvetronic values check out OK you need to continue down the list:

1) Observe O2 sensor voltages in INPA
2) Fit new battery
3) Replace coil packs and plugs
4) Replace EGR valve and check pipes to sump for blockages
5) Replace / inspect second DISA valve
6) Replace valvetronic motor
7) Have VANOS unit stripped and inspected.

I think you might be right. So I checked the Valvetronic screen which looks pretty similar to yours, the only thing I noticed which looked odd was that my expected airmass (top right) was bouncing up and down by about 6 when at idle, but not when at 2000rpm. Have attached the screenshots

 

[ph001]

Hmmm, yeh your calculated air mass is about 28% different to mine at idle. I'm really not too sure what that calculation represents though as the value is higher at idle than at 2000rpm so I think we can conclude a lower value is more air. We must remember that we are comparing a 3.0l car to a 2.5l one so I guess that makes sense then.

As you say, can't see anything else particularly unusual there, although mine wasn't bouncing around.

 

[propaintballa]

Hmmm, yeh your calculated air mass is about 28% different to mine at idle. I'm really not too sure what that calculation represents though as the value is higher at idle than at 2000rpm so I think we can conclude a lower value is more air. We must remember that we are comparing a 3.0l car to a 2.5l one so I guess that makes sense then.

As you say, can't see anything else particularly unusual there, although mine wasn't bouncing around.

This makes sense. Would be extremely handy for the car to throw a relevant code! I might just have to bit the bullet and try new coils, which I think are most likely at this point. If not, then spark plugs and go from there. I don't want to do both at the same time as I would like to know what's actually causing the problem!

Do you know if it is possible to have a faulty coil that doesn't appear faulty when doing the "unplugging test"? As in, unplugging each coil one by one as the engine is running to see if the action of unplugging it changes the engine behaviour. As I have done this and the revs are affected for all of them.

 

[ph001]

This makes sense. Would be extremely handy for the car to throw a relevant code! I might just have to bit the bullet and try new coils, which I think are most likely at this point. If not, then spark plugs and go from there. I don't want to do both at the same time as I would like to know what's actually causing the problem!

Do you know if it is possible to have a faulty coil that doesn't appear faulty when doing the "unplugging test"? As in, unplugging each coil one by one as the engine is running to see if the action of unplugging it changes the engine behaviour. As I have done this and the revs are affected for all of them.

Totally agree on doing the coils first. Aged / worn plug gaps manifest as a misfire at >50% load, typically at around the rpm where peak torque is made. It's very characteristic. You can also get them breaking down electrically around the ceramic of course which is a similar symptom to a dodgy coil pack. That's pretty rare though.

In terms of the coil unplugging test - that is really only effective if the coil pack is permanently faulty. More often than not they go intermittent at specific loads which gives the misfire / poor running.

BMW had no problem at all taking all 6 back from me when I was playing around with the M3. It's not like they get particularly dirty or marked when trying them and they just came in individual boxes which had a folded flap so the packaging was completely undamaged.

 

[propaintballa]

This makes sense. Would be extremely handy for the car to throw a relevant code! I might just have to bit the bullet and try new coils, which I think are most likely at this point. If not, then spark plugs and go from there. I don't want to do both at the same time as I would like to know what's actually causing the problem!

Do you know if it is possible to have a faulty coil that doesn't appear faulty when doing the "unplugging test"? As in, unplugging each coil one by one as the engine is running to see if the action of unplugging it changes the engine behaviour. As I have done this and the revs are affected for all of them.

Totally agree on doing the coils first. Aged / worn plug gaps manifest as a misfire at >50% load, typically at around the rpm where peak torque is made. It's very characteristic. You can also get them breaking down electrically around the ceramic of course which is a similar symptom to a dodgy coil pack. That's pretty rare though.

In terms of the coil unplugging test - that is really only effective if the coil pack is permanently faulty. More often than not they go intermittent at specific loads which gives the misfire / poor running.

BMW had no problem at all taking all 6 back from me when I was playing around with the M3. It's not like they get particularly dirty or marked when trying them and they just came in individual boxes which had a folded flap so the packaging was completely undamaged.

Great info, thank you so much for your help so far! I have ordered a new set of coils from OPIE. They only stocked Bosch, not the Delphi coils which I believe are supplied now, but for just under £100 for a full set, I can't complain too much. Will still check the price of them from BMW just in case they're similar, I doubt it though.