Z4 35is stutters on acceleration

[Hejnfelt]

Recently my 2013 LCI Z4 35is started stuttering on medium to hard acceleration. This happens in any gear whether in comfort or sport or sport+ mode.

It’s running MHD stage 1.

Since I have MHD, I thought I’d do a small log (attached) before taking it to the shop.

I did multiple logs and the behavior is the same.

In short what I see is boost is slightly off target but building and Short term Fuel trims are negative. Then suddenly Bank1 goes lean AFR15.9 while Bank2 remains normal and STFT1 adds fuel while STFT2 remains negative and car “stutters” between lean and rich on Bank1 for a split second until I go off the accelerator (as I am only trying to collect data).

Any suggestions what might be the culprit? I am not particularly technically inclined myself.

Additional info:

Mileage 97000km
Last oil change: 89000km (April 12th 2023)
Plugs changed at 67000km
Oil consumption negligible

Car had it’s intake valves cleaned just a month and a half ago where the valve cover gasket was replaced.

Car is generally meticulously cared for.

[B21]

Can you load the log into *********** makes it easy to analyse…

S P O O L S T R E E T

[Hejnfelt]

Absolutely, here you go

https://*********************/graphs...1-01-41.28782/

The page that must not be named from your post . com /graphs/log-07-29-2023-21-01-41.28782

[B21]

I can’t seem to see it…last log in general was 28th….can you post it to n54 section ..you can see my logs there?

[Hejnfelt]

I don’t know how to do that, but the app gave me this link which works for me without logging in.

Delete the spaces

https://www. s p o o l s t r e e t .com/graphs/log-07-29-2023-21-01-41.28782/

[Hejnfelt]

Decided to take a look under the hood, how hard can it be?

Removing air filter box revealed the charge pipe is sweaty.

Upon closer inspection it seems bank1 diverter valve is spraying oil all over the charge pipe. All the other connections seems dry. I know it’s common to have some oil in the charge pipe, but this much? Maybe a combo of problems?

See attached pictures.

This connection is obviously leaking a ton of air with the oil. Maybe the diverter valve is stuck?

Would using some teflon tape on this connection to help seal it temporarily be ok?

I am only looking for a short term fix as I have intercooler, chargepipe, hoses, TTE500 turbos on the schedule for winter.

Any thoughts are appreciated.

[KennyP]

Those diverter valve quickconnects have o rings that can leak... you can replace those O rings.... age does them in. Or maybe they were misaligned when put back together...
But the amount of oil is a bit concerning... im not saying it should be totally clean...but...
Also if you have remapped the car then you may consider upgrading to metal chargepipe... Haven heard them really fail on z4-s but in 335i-s with the same engine they sometimes crack under boost...

With a tune you should replace sparkplugs twice as often... if they were done 30k km ago then i would just replace them...
Also tune demands alot more from the coilpacks... Oem Bosch isnt that great... Bmw itself have updated their coilpacks twice now...from Bosch->Delphi-> Eldor. I replaced mine with Delphi coils though Eldor would have been better. Delphi was easily available so went with that.

If you want to know more about different bmw coilpacks then here is a good video for you:
https://www.youtube.com/watch?v=Tjsx-K1mjkQ

Did "Differ" do the intake valves cleaning? Did he also do that valvecover gasket?
I wouldnt mess with just the gasket... just replace the whole cover when it hasnt been replaced yet.. it has plastic pcv valve in it that can go bad, also with years of heat cycles plastic gets brittle and can crack... if you want piece of mind... just throw a new valve cover on it and be done with it. I did so a few years back. Car was also acting wierd on acceleration... PCV valve probably wasnt sealing... new valve cover solved it for me. I went with OEM BMW one... which was a bit expensive...about 500 eur i think, but you can get other brands aswell that cost as low as 150 eur. So if your paying for the work anyways... i wouldnt do just the gasket....

[Hejnfelt]

Yes Differ did the valve cleaning and everything looked good.

I am thinking the amount of oil could be due to the symptoms of the issue, not some other issue. But instead of trying to fix multiple issues at once, I want to fix one at a time and see how things progress.

I’ll install B58 coils and spark plugs in combo with the other upgrades this winter. Plugs were changed 30km ago but I only just put the MHD tune on it so car has been stock until 10km ago. Charge pipe gets changed too in the same process but I want to keep the diverter valves for a stealthy setup instead of going BOV.

[KennyP]

if yoou want to upgrade diverter valves... but not go with a big BOV.. then there is this option with plumbback:

https://www.turbosmart.com/product/k...-back-kit-bmw/

Though if you remove oem airbox and go with some aftermarket intake..Dual cone for example from Burger motorsport as i have fitted... then you will have more turbo noises regardless... spoolup and i can even hear those oem diverter valves sometimes...though its subtle...

[Hejnfelt]

Thanks, I really appreciate all the knowledge you’re sharing with me. I’ll check it out.

Currently my goal is to go in the direction of the Mr5 solution for airbox modification but that’s a winter topic.

[B21]

Originally Posted by KennyP

if yoou want to upgrade diverter valves... but not go with a big BOV.. then there is this option with plumbback:

https://www.turbosmart.com/product/k...-back-kit-bmw/

Though if you remove oem airbox and go with some aftermarket intake..Dual cone for example from Burger motorsport as i have fitted... then you will have more turbo noises regardless... spoolup and i can even hear those oem diverter valves sometimes...though its subtle...

I tried briefly DCIs but didn’t like to sound..so went with Forge diverter valves into some VSRF turbo inlet pipes..each to their own..

[B21]

Originally Posted by Hejnfelt

Yes Differ did the valve cleaning and everything looked good.

I am thinking the amount of oil could be due to the symptoms of the issue, not some other issue. But instead of trying to fix multiple issues at once, I want to fix one at a time and see how things progress.

I’ll install B58 coils and spark plugs in combo with the other upgrades this winter. Plugs were changed 30km ago but I only just put the MHD tune on it so car has been stock until 10km ago. Charge pipe gets changed too in the same process but I want to keep the diverter valves for a stealthy setup instead of going BOV.

Maybe you have PCV issues as well as a charge pipe issue…with the engine at idle do you get positive pressure from the oil filler cap?

[B21]

Originally Posted by Hejnfelt

Thanks, I really appreciate all the knowledge you’re sharing with me. I’ll check it out.

Currently my goal is to go in the direction of the Mr5 solution for airbox modification but that’s a winter topic.

I assume you saw my positive experiences with my Mr.5 version?

https://e89.zpost.com/forums/showthread.php?t=2034639

[Hejnfelt]

Originally Posted by B21

I tried briefly DCIs but didn’t like to sound..so went with Forge diverter valves into some VSRF turbo inlet pipes..each to their own..

The stock ones wouldn't work at your power level B21?

Originally Posted by B21

Maybe you have PCV issues as well as a charge pipe issue…with the engine at idle do you get positive pressure from the oil filler cap?

I was thinking that as well, but did this check and there is no pressure at idle.

Originally Posted by B21

I assume you saw my positive experiences with my Mr.5 version?

Yes I did and I like the setup. Might hit you up for a guide regarding materials used.

[Hejnfelt]

I think I am dealing with a couple of problems at once.

I decided to change the 4 O-rings at each end of the 2 diverter valve hoses, 4 in total and see if this changes anything.

I know one should not make conclusions from used O-rings but the 2 O-rings that came from the front side diverter valve hose connections looked visibly thinner than the correct 24x3.5mm NBR70 rings.

The 2 O-rings that came from the rear side diverter valve hose conections looked like stock O-rings. I am guessing that maybe someone at some point changed the O-rings in the front diverter valve hose and eye-balled the sizing. Not inconceivable on a 10yo vehicle. It might have even happend when the vales were cleaned as I have a picture of the engine bay during cleaning with those specific hoses disconnected. Already shot the shop a message.

I cleaned things up and took the car for a test drive. The car feels noticeably better in the low and I think the O-rings fixed the boost leak but time will tell if there is oil on the charge pipe again. But there is still a problem.

Like before, the car revs until now having a misfire on cylinder 1 and Check Engine Light code 29CD. Happens around 4000rpm. Previously the stutter would happen at 3300-3400 rpm.

I did the test 3 times, misfire on cylinder at same RPM, load, etc and CEL every time. Stop, shut off and start, no more CEL but code is stored. Car still drives fine under any kind of normal load.

Since I don't have the tools to pull the spark plugs, I booked diagnostics appointment Wednesday and will have them focus on Spark plugs and coils first.

[B21]

Originally Posted by Hejnfelt

I think I am dealing with a couple of problems at once.

I decided to change the 4 O-rings at each end of the 2 diverter valve hoses, 4 in total and see if this changes anything.

I know one should not make conclusions from used O-rings but the 2 O-rings that came from the front side diverter valve hose connections looked visibly thinner than the correct 24x3.5mm NBR70 rings.

The 2 O-rings that came from the rear side diverter valve hose conections looked like stock O-rings. I am guessing that maybe someone at some point changed the O-rings in the front diverter valve hose and eye-balled the sizing. Not inconceivable on a 10yo vehicle. It might have even happend when the vales were cleaned as I have a picture of the engine bay during cleaning with those specific hoses disconnected. Already shot the shop a message.

I cleaned things up and took the car for a test drive. The car feels noticeably better in the low and I think the O-rings fixed the boost leak but time will tell if there is oil on the charge pipe again. But there is still a problem.

Like before, the car revs until now having a misfire on cylinder 1 and Check Engine Light code 29CD. Happens around 4000rpm. Previously the stutter would happen at 3300-3400 rpm.

I did the test 3 times, misfire on cylinder at same RPM, load, etc and CEL every time. Stop, shut off and start, no more CEL but code is stored. Car still drives fine under any kind of normal load.

Since I don't have the tools to pull the spark plugs, I booked diagnostics appointment Wednesday and will have them focus on Spark plugs and coils first.

The misfire code is typical of a bad coil or plu..of if you are really unlucky a faulty injector..

Have you read the Index number on each injector?

[B21]

Originally Posted by Hejnfelt

The stock ones wouldn't work at your power level B21?



I was thinking that as well, but did this check and there is no pressure at idle.



Yes I did and I like the setup. Might hit you up for a guide regarding materials used.

DCIs are used by many folks with very heavily tuned N54s..just don't like the visual look, the noise and the very poor filtration..plus heat soak can be a problem..

My design is simple..I uuse 50mm domestic waste pipe fittings from any plumbing supplier together with a Pipercross c/f foam filter which costs around £150..simples..

[Hejnfelt]

So it was a simple issue after all.

Ignition coil on cylinder 1 was almost toast. Installed new and car pulls strong to redline WOT in all gears.

Fixing the air leak on the intake pipe diverter valve hose was just an added benefit.

B58 coil upgrade is now on the top of the list of modifications. The Nexsys system looks great but they’re USA based, if anyone has any other Europe local service providers who sell a similar solution, I’m ready to buy it

As for the acceleration issue it seems fixed for now.

[B21]

Originally Posted by Hejnfelt

So it was a simple issue after all.

Ignition coil on cylinder 1 was almost toast. Installed new and car pulls strong to redline WOT in all gears.

Fixing the air leak on the intake pipe diverter valve hose was just an added benefit.

B58 coil upgrade is now on the top of the list of modifications. The Nexsys system looks great but they’re USA based, if anyone has any other Europe local service providers who sell a similar solution, I’m ready to buy it

As for the acceleration issue it seems fixed for now.

I bought the Nexsys kit from the US..sourced my coils from Autodoc..

Not sure like so many things I do whether it’s over kill for just a 550bhp Z4..

First time I did MHD it showed a bad coil

Glad it’s working out

[Hejnfelt]

I guess being in the UK, it's a bit easier to buy from the US? Inside EU it's annoying having to pay import toll 10% of the combines cost of the product and shipping and additional VAT of the whole sum on top, so the price becomes prohibitively expensive.

The way I see it, the data shows stock coils on the N54 will fail when pushing past stock power which I already am. I might as well swap all the coils to B58s and be done with it. B58 coils seem to be totally overbuilt for their purpose, which is a good thing. From my experience in racing, when you buy quality you only cry once.

[B21]

UK has same issues buying from US as you do…now thanks to the muppets that voted for Brexit we have the same issues getting stuff from Europe..madness..

FWIW I fitted new NGK coils n plugs and had no issues at 400 BHP with MHD V10 stage 2+

My tuner who has done 100s of N54 tunes thinks the Nexsys is over kill..my defence is I bought it before I met him…

[KennyP]

im sure noone had replaced coilpacks on your car before... and car had coils that came from the factory... so they were 10 years old already and had many miles on them... coil dont last forever you know...
Mine worked fine for 3 years on cobb stage 1 then when car got about 10-11 years old they started acting up... ordered all 6 new coils from Autodoc ( Delphi brand) and its been ok for the last 3 years...they didnt cost much either... i think it cost 150 eur for all 6 coils...
Im sure you dont have to go crazy with ignition when running stage 1 or even 2... Uprated turbos is probably a different story...

Brexit does affect us in Estonia aswell... I used to buy alot of carparts fom UK shops... even my KW suspension came from Demon Tweaks in UK.. for Honda i used Tegiwa a lot... Now i cant do that... import duty and VAT that adds more than 20% to the cost. So i search for parts now on polish, german or even french webshops...
For example i ordered a used left sportseat from uk ebay last month... My drivers seat had some wear on it... so i took leather and bolsters from uk manual passenger seat that hadnt got much use and swapped them over to my electric sport seat frame... basically had to strip both seats down to the frame... took me a day... now seat is like new... and i have an extra seat in the garage . New ivory nappa leather covers are expensive to buy new... 500-600 for seat base and 800+ for the back portion on Hubauer webshop in Germany...
So found one and only Ivory Nappa leather seat for sale in UK...
Point is i had to pay 115 eur of import fees to get it in the country. Still all in.. it was a bargain...