Hesitation / Missfire under mid to hard acceleration only

S

SkoomaD

Member
Hi Guys,

Not sure if anyone will be able to help me who's come across this before but i've trawled posts for suggestions and can't find anything exactly the same as I am experiencing.

So as I say car hesitates a little and feels like a missfire and or loss of power under mid to hard acceleration and it's audible the whole engine note changes as it happens like you are letting off the gas. It's almost like traction control kicking in but no traction control light and not in situations where wheels would be breaking loose anyway. There are no fault codes logged no EML light nothing to indicate an issue. Car idles well and tootling around you wouldn't know there was a problem at all.

Only recently got the car its an early 3 litre model and i'm going over it and just sorting any issues I find to get it back ship shape again as it needed a little TLC. The car ran fine when i initially got it this seems to have developed after i've done some bits of work on it although I can't see what I could have done to cause the problem if it is indeed me. I have replaced the valve cover gasket as it was leaking oil badly when i got it. I have also replaced the oil filter housing with a new one as that was also leaking badly so alternator and belts and so on will have been off. Other than that new discs, pads, front struts, track rods, air filter, lower arm bushes that's about it before the issues started. Also replaced the CCV system but this was the first job I did and the problem didn't develop until more recently.

I've tried new plugs which seemed to help a little at first but is now back to being as bad as it was before. I've also purchased two new coils and tried them in cylinders 1/2 then 3/4 then 5/6 to see if it helped.. no joy. Plugs 1/2 did look a little sooty (not wet) when i removed them, rest i'd consider normal

It has even been to BMW today for an airbag module replacing (airbag light was only warning light i did have) so I had them update the DME to the latest version in case it was some sort of software bug and if anything it seems to have made the problem worse rather than better (which i'm guessing is more down to the ecu re-learning)

Anyway sort of at my wits end with it i've no idea what to look at next as with no codes I don't really have a whole heap to go on! Any suggestions greatly appreciated. Cheers.
 
I know you mentioned swapping coils out with no joy but to me it really does sound like a coil/spark issue.

My experience (may or may not be of value).

I had the exact same symptoms - intermittent random misfire when trying to power with no codes.

What happens if you try to drive through the sputtering? Ie: keep throttling.

Mine was consistently happening once a day usually at the same turn to work.

Finally one day I got fed up and next time it misfired, I just kept throttling - and it kept sputtering worse - before the car eventually went into limp mode and threw an CEL.

THAT gave me a code for cylinder 4 and I checked that coil again. I had checked it previously and thought it fine but I saw a tiny crack on the rubber of it which I guess was actually enough of a sign.

Failing that, i had a similar occurance in my previous car (not a Z4) and it turned out to be the fuel pump. Consistent cutouts on high throttle input.
 
You say it feels like you're closing the throttle or traction control is cutting in when the problem arises. You don't mention misfires, so I suspect an air:fuel ratio issue rather than spark (unless it is misfiring and you haven't said so).

The air:fuel ratio (AFR) can be affected by air or fuel, so perhaps you can investigate those two things?

Air:

1. You say you replaced your air filter. Did it all go back together correctly? Can you remove the new filter (or swap your old one back in) and go for a drive to eliminate that?

2. Did you split/tear any hoses when working around the air filter? You could have an air leak that's messing up the AFRs.

3. Is the induction side of the engine standard or are there any long aftermarket hoses that could be collapsing at wider throttle openings?


Fuel:

1. Fuel pressure can become an issue if the fuel filter becomes clogged or if the pump output pressure drops. Something to bear in mind, but not a common issue I don't think.

2. Dirty injectors can restrict fuel flow. Again, not massively common, but something to bear in mind.

3. You would probably be aware of any fuel leaks that could be reducing your fuel pressures, but it might be worth a sniff.



A good rolling road operator could help you here if you have no joy with your own efforts. Monitoring the AFRs and fuel pressure during a simple dyno test would help with the diagnosis. A rolling road also allows you to prod and poke around the engine (with care) while the car is running. I found it to be an amazing tool for such issues.


Make sure you report back as you progress/fix the issue! :thumbsup:
 
Cheers for responses guys, so:

tomrdy said:
What happens if you try to drive through the sputtering? Ie: keep throttling.
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Basically it will keep accelerating and just sputtering as the revs build, at higher RPM it seems to be less noticeable 3 - 5k seems to be the worst, above that its harder to tell there's a problem. I have driven through numerous times to try get some light to show as you say. Like you suggest my first instinct was spark plugs / coils, I think i'd have to have a double failure of them at this point though and be extremely unlucky not to have swapped the bad one out (unless of course there were two faulty at the same time).

You don't mention misfires, so I suspect an air:fuel ratio issue rather than spark (unless it is misfiring and you haven't said so).
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I'm leaning towards misfires, I might perhaps take a short video so I can show the symptoms I'm experiencing.

1. You say you replaced your air filter. Did it all go back together correctly? Can you remove the new filter (or swap your old one back in) and go for a drive to eliminate that?
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It seemed to, I'd done this a couple of times already with the various jobs and it went fine. However I'll go back over the pipes as you say maybe even swap the filter back out as I did replace the stock one with a panel filter on the off chance it doesn't like that also.

2. Did you split/tear any hoses when working around the air filter? You could have an air leak that's messing up the AFRs.
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I don't think so but will check over. I've been working on it steady away in the garage trying to be meticulous as possible, but it's possible for sure.

3. Is the induction side of the engine standard or are there any long aftermarket hoses that could be collapsing at wider throttle openings?
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All standard that I can tell.

Fuel:

1. Fuel pressure can become an issue if the fuel filter becomes clogged or if the pump output pressure drops. Something to bear in mind, but not a common issue I don't think.

2. Dirty injectors can restrict fuel flow. Again, not massively common, but something to bear in mind.

3. You would probably be aware of any fuel leaks that could be reducing your fuel pressures, but it might be worth a sniff.
Click to expand...


I am wondering about injectors or clogged cats or something next and wondering if it's worth trying some sort of fuel additive, although I don't really believe in magic potions haha its usually something that needs swapping out. Again I'm not ruling out the fuel filter and pump just looks like a massive pain of a job so I'd want to know it was that before i embarked on it. I can't smell any fuel although perhaps fuel starvation is an issue, as you say a rolling road would be useful to diagnose any problems if I really get stuck.

I do also have a couple of bits of software installed on my laptop that i used to diagnose the airbag fault so not sure if those could be used to monitor anything as I drive and give an indication as to the problem. Not done a lot with the BMW stuff I have a little more experience with the VAG software as it seems a little more user friendly.

Will spend a bit of time today see if I can see any hose issues and perhaps take it for a run and make a short video of the issue.
 
It does sound like a classic coil / spark plug issue to me. What plugs did you fit when you replaced them? I think you probably need to remove them all again and inspect the electrodes. Coil packs - again which ones did you buy (cheap chinese or genuine OEM)? Again I would just buy 6 new ones for what they cost from a reputable source as there are plenty of fake chinese ones doing the rounds on Ebay.

Other than that, the early 3.0 cars do suffer from the concertina part of the hose splitting on the elbow on the intake, so you really need to check this area carefully....

Finally there is the possibility of the DISA valve not working correctly as that does change over at about 3-4k rpm. I wouldn't expect a misfire from it as such though, more a hesitation / lack of power.

split elbow.jpg

M54 Disa valve.jpg
 
It does sound like a classic coil / spark plug issue to me. What plugs did you fit when you replaced them? I think you probably need to remove them all again and inspect the electrodes. Coil packs - again which ones did you buy (cheap chinese or genuine OEM)? Again I would just buy 6 new ones for what they cost from a reputable source as there are plenty of fake chinese ones doing the rounds on Ebay.
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Used the OEM NGK plugs as I didn't know what was fitted already which as I say did actually seem to help a little at first. The coils I tried with are just bosch ones from car parts for less (basically ECP) they were cheap but I would have thought genuine bosch parts would at least work. I may just buy 4 more for peace of mind as you suggest as I managed to get them for like 16 quid each with discount. That was a nice change to the ones for my golf I had to buy last year at £600 for the set!

I've had that hose off in the picture and had a look over it when I did the CCV it looked good. Not looked at the DISA tho, if I remove it is there and easy way to test it when removed?
 
I had the same problem, it was caused by a failing coil pack.

I changed all six and the problem was still there, found that with later Bosch coil packs the caps do not 'click' into place like the originals. Another inspection and I found one of the caps sitting 2mm higher on one of the packs, seated this correctly and problem solved. I would always change all of the coil packs together (same as spark plugs) as they have all done the same amount of work and if one is failing, the rest are sure to follow?

Have had many miles of trouble free motoring since.

Hope this helps.
 
My bad - clearly you mention misfires in your initial post, and even the thread title. Forgive me, I hadn't been awake long! :oops:
 
SkoomaD said:
Not looked at the DISA tho, if I remove it is there and easy way to test it when removed?
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They usually suffer from the pin coming loose or the flap falling apart so should be quite obvious.
 
ph001 said:
SkoomaD said:
Not looked at the DISA tho, if I remove it is there and easy way to test it when removed?
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They usually suffer from the pin coming loose or the flap falling apart so should be quite obvious.
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Additionally - they can be tested using INPA. You symptoms don't sound like DISA issues though - as with the above. Sounds ignition-y.
 
[youtube]6Po7Jw7yiag[/youtube]

It's not hugely obvious on the vid but the car isn't pulling right and you can hear it struggling if you listen.
 
[youtube]gMoA7DKkkeQ[/youtube]

What you think? Hate the sound of my own voice but it's easier than typing paragraphs trying to explain it's condition.
 
SkoomaD said:
[youtube]gMoA7DKkkeQ[/youtube]

What you think? Hate the sound of my own voice but it's easier than typing paragraphs trying to explain it's condition.
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get a rebuild kit....very easy job

https://x8r.co.uk/products/bmw/bmw-disa-repair-kits
 
get a rebuild kit....very easy job

https://x8r.co.uk/products/bmw/bmw-disa-repair-kits
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Ordered that, cheers, hopefully this one isn't too far gone to be repaired. Hopefully it's the issue i'm experiencing, lets see.
 
Once I've rebuilt and tested i'll report back if it's cleared up my issue, you would think it can't be helping anyway!
 
My DISA was like that too. Free spinning pretty much so non operational.

That caused idle lumpiness for me occasionally - so perhaps you're getting the lumpiness on throttle.

Fingers crossed the rebuild kit solves this!

You'll be able to test the operation after rebuild by plugging it in (leave out if motor) and turning to ignition (don't start the motor).

The probe should create a vacuum and you'll see the flap close (or open I can't remember which). Either way it will move and when you turn off, it should revert and there may be an audible "thaaack" sound from the rubber vaccuum/plunger bit retreating.
 
Ok so i've rebuilt the DISA with the kit suggested and the car is much much happier. Took it for a short blast tonight and It pulls a lot stronger than it did and my issue seems to have almost entirely gone :)

I say almost entirely as It did seems to stutter a little at one stage on part throttle for a few seconds but other than that it was much much better so thank you for all the advice.

I'm wondering if perhaps the slight hint of the issue I had before is simply it either it learning as it's had the DME reflashed on a bad DISA valve and now its fixed its wondering what the hell is going on. Or perhaps things are a little sooted up still from it running poorly. Do you think there is any value in running some sort of fuel additive through it or is it more likely to do more harm than good?

I'm fairly certain it can't be coil related so I think I'll return the new coils I bought and just keep the two original ones I bought as spares.

Again thanks for all the input.
 
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