Z4 missfire

[tomkinson36]

Hi,
Having a missfire problem with my E89 z4 from 2012. I have recently bought it, it had been sat for about a year so I gathered it would have some teething issues. Was running fine when I bought it, put new tires on it and took it for a full service with new spark plugs. As I drove out the service I filled it up with 95 octane fuel as the station didn’t have working premium tanks. On the drive back I had a flashing engine light and a misfire. One I restated it it cleared and I hobbled back to the garage where they cleared the code. They had it for a few days, put new coil packs on it and a new o2 sensor it was pulling up an open circuit for which cost me all in £500. Hasn’t fixed anything though. Anytime I go over 70% throttle in 2nd or 3rd it judders with no power and I have to lift off (misfiring) and it will do the same in 5th and 6th with even less effort on the throttle.
Any advice is greatly appreciated.
Thank you.

 

[B21]

I see you're getting increasingly desperate posting it in several places..

here's my reply for others reading this....



Two things before anything else. The flashing light means the misfire is damaging the catalyst, so every time you provoke it to check whether it's still there, you're spending money. And stop buying parts — £500 has gone on coils and an O2 sensor without anyone yet checking the one thing that actually changed.

Because that's the bit that stands out. The car ran fine, went in for a service, and came out misfiring. New plugs went in that day. Nobody has taken them back out since, because they're new — and new isn't the same as correct. A plug with the wrong part number, the wrong heat range, or a gap knocked out of shape in fitting will fire perfectly at idle and give up entirely under load, because the voltage needed to jump that gap climbs with cylinder pressure. Which is precisely your symptom: fine gently, falls over at 70% throttle, worse in the tall gears where the load is higher still.

So pull all four and look at them. Check the number on them against what BMW specifies for the N20 — they're pre-gapped and not meant to be adjusted, so a plug someone has "checked" with a feeler gauge is already suspect. Look at the condition too: one oil-wet or sooty plug among three clean ones names a cylinder for free. And ask what brand of coils went on, because cheap aftermarket coils on a direct-injection turbo are their own well-known misery.

If the plugs check out, then it's live data rather than another part. Someone needs to watch commanded against actual fuel rail pressure while the fault happens — if actual pressure sags away from commanded as the throttle opens, it's fuel delivery, and your car has an obvious reason for that after sitting for a year: stale fuel, a tank that's been breathing moisture, a strainer and pump sitting in it, gummed injectors. Ask for the exact codes as well, not "a misfire" — a single-cylinder code and a random one point in completely different directions, and if they've been clearing them without writing them down you've paid for information and binned it.

The 95 octane is a red herring, incidentally — it's the minimum BMW specifies and a healthy N20 runs on it happily. And one for the list rather than the panic pile: 2012 is in the window where N20 timing chains gave trouble, with a cold-start rattle and a whine that builds with revs as the tells. Worth listening for, but I'd exhaust the free checks first.

 

[tomkinson36]

I see you're getting increasingly desperate posting it in several places..

here's my reply for others reading this....



Two things before anything else. The flashing light means the misfire is damaging the catalyst, so every time you provoke it to check whether it's still there, you're spending money. And stop buying parts — £500 has gone on coils and an O2 sensor without anyone yet checking the one thing that actually changed.

Because that's the bit that stands out. The car ran fine, went in for a service, and came out misfiring. New plugs went in that day. Nobody has taken them back out since, because they're new — and new isn't the same as correct. A plug with the wrong part number, the wrong heat range, or a gap knocked out of shape in fitting will fire perfectly at idle and give up entirely under load, because the voltage needed to jump that gap climbs with cylinder pressure. Which is precisely your symptom: fine gently, falls over at 70% throttle, worse in the tall gears where the load is higher still.

So pull all four and look at them. Check the number on them against what BMW specifies for the N20 — they're pre-gapped and not meant to be adjusted, so a plug someone has "checked" with a feeler gauge is already suspect. Look at the condition too: one oil-wet or sooty plug among three clean ones names a cylinder for free. And ask what brand of coils went on, because cheap aftermarket coils on a direct-injection turbo are their own well-known misery.

If the plugs check out, then it's live data rather than another part. Someone needs to watch commanded against actual fuel rail pressure while the fault happens — if actual pressure sags away from commanded as the throttle opens, it's fuel delivery, and your car has an obvious reason for that after sitting for a year: stale fuel, a tank that's been breathing moisture, a strainer and pump sitting in it, gummed injectors. Ask for the exact codes as well, not "a misfire" — a single-cylinder code and a random one point in completely different directions, and if they've been clearing them without writing them down you've paid for information and binned it.

The 95 octane is a red herring, incidentally — it's the minimum BMW specifies and a healthy N20 runs on it happily. And one for the list rather than the panic pile: 2012 is in the window where N20 timing chains gave trouble, with a cold-start rattle and a whine that builds with revs as the tells. Worth listening for, but I'd exhaust the free checks first.

Thank you, but ai isn’t going to help a huge amount. I’m just trying to see if anyone else has had similar problems and could help

 

[bigwinn]

Thank you, but ai isn’t going to help a huge amount. I’m just trying to see if anyone else has had similar problems and could help

Totally disagree with you there

The root cause in my experience of working on cars is that if something goes wrong, go back to what you just did

 

[B21]

Thank you, but ai isn’t going to help a huge amount. I’m just trying to see if anyone else has had similar problems and could help

Er that's not AI that's 10 years on E89s and 350k words I've written on a 5 volume book on E89s.. and a number of misfires I've had..including as bigwinn says unintentional (in my case self inflicted.. given rarer things like VANOS / Bore score misfires are either too little or two much fuel or not enough sparks.. either its garage related or say your HPFP has just decided to call it a day which does happen on earlier N20..as sated data logging is your best friend in this circumstances ..I leave you to find your own way..