Misfire Cylinder 4, Bad startup, Lot of hesitation during acceleration.

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krasznai_bence

Member
UPDATE:
I have created 2 videos, an inside and outside POV to show you what happens at a cold start.
Inside: https://youtube.com/shorts/qDajUpuKdXA
Outside: https://youtube.com/shorts/LtWEuSgTmCk

Hey everyone,

To cut to the chase, I had a misfire on cylinder 6, when the car had around 30.000km, changed the spark plug and ignition coil and it resolved itself for a bit. Now, the car has almost 90.000 km, and for a while, under heavy load the car there would be a LOT of hesitation under acceleration, would go into limp mode, but I would just restart the car and it would resolve itself.

My dad and I changed all 6 spark plugs on the car(new NGK plugs) and now it seems like it didn't help, as it has gotten WORSE. Note, that we had a guy hooked up to the car during acceleration, and the fuel graph on how much fuel the car gets would go up and down and everywhere basically. So, we were told it could be a low / high fuel pressure pump / sensor, but honestly we have no idea, as we do not have any professionals near us.

Also, when I start the car, first the RPM goes screaming up over 2000, then dies down and goes below 1000, and up and down again until it balances out. However, after the engine had warmed up, and balanced out, this doesn't come back until the next cold start.

Anyone have any ideas? I'm not an expert regarding the mechanical parts of the engine, so excuse my basic way of explaining the events. Tomorrow if I can, I will try to video these things so it is easier to understand.

My car is a 2016 BMW Z4, sDrive35is, with almost 90.000 kilometers.

Any help is greatly appreciated!
 

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Could be many things but either HPFP or injectors are the most probable ..

Decent fault code reader would eliminate possibilities…
 
So since the stored code wrote cylinder 4, we swapped 3&4 around, but under acceleration the computer would start to show more cylinders misfiring, therefore we think it is something to do with a fueling issue.
 
Almost certainly one or more injectors..needs urgent resolution as bore damange and/or hydraulic lock casn ensue!
 
If your fuel pump is crashing and cannot supply proper fuel volumes and/or pressures it can cause misfiring and starting issues as well.
Really need some codes or you can be throwing expensive parts at it
Both HPFP and injectors are unfortunately known weak points and both pretty expensive.

Best of luck in the diagnosis and repair.
 
Typical injector failing open symptoms

Needs replacing ASAP if it is

Symptoms don’t accord with LPFP or HPFP normal failure

Could be HPFP seal failure in which case fuel in oil would be present
 
Okay, so an update!

I went in and gotten a code read, which was code 29F2 (DME: Fuel High-Pressure System, Fuel Pressure).

When we replaced the 6 spark plugs, it didn't get any better, however after replacing the 6 coils too, for a week or 2 it was working perfectly. Now suddenly, it has stopped working again, and at high rpm-s / speeds it jitters a lot.

Also, currently under cold start it does not do anything crazy. It starts up perfectly. However, under heavy (or now not even that heavy) acceleration it jitters a heck of a lot.

Anyone knows what this means? Why was it working perfectly all of a sudden? And why did it stop working all of a sudden?

So lost at this point.
 
Z4Dude said:
If your fuel pump is crashing and cannot supply proper fuel volumes and/or pressures it can cause misfiring and starting issues as well.
Really need some codes or you can be throwing expensive parts at it
Both HPFP and injectors are unfortunately known weak points and both pretty expensive.

Best of luck in the diagnosis and repair.
Click to expand...

thank you!
 
The.Analyst said:
Typical injector failing open symptoms

Needs replacing ASAP if it is

Symptoms don’t accord with LPFP or HPFP normal failure

Could be HPFP seal failure in which case fuel in oil would be present
Click to expand...

I don't think it is a seal failure, as there is no oil present.
 
Most probably now the HPFP is on its way out..if it’s misfiring at high rpm/load that’s a logical conclusion..sadly without major diagnostics tools /logging you’re just guessing ..a MHD / Protool data log is your friend..
 
B21 said:
Most probably now the HPFP is on its way out..if it’s misfiring at high rpm/load that’s a logical conclusion..sadly without major diagnostics tools /logging you’re just guessing ..a MHD / Protool data log is your friend..
Click to expand...

Thank you. I will try to get my hands on MHD or Protool but I have no idea where I can find that in my country lmao
 
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