This time, the owner of G31 Alpina B5 approached me for help.
First, here is a little about this BMW, upgraded by Alpina. The basic information can be found in the Alpina web resources; in this entry, I will mention only specific nuances.
Alpina indicates that the B5 model is equipped with an 8-cylinder petrol power aggregate. If we look at BMW databases, we can see that the G31 was never equipped with an 8-cylinder N63 (or S63) series engine. The most powerful are 540i and 540iX, which have B58 6-cylinder power aggregate installed.
This car is rebuilt exactly from the 540iX model – here, the confirmation (for the cause of confidentiality, only the first part of VIN is visible).
Here, ISTA identification: N63 series engine, two DME management modules.
Instead, if we check the online tool RealOEM, this vehicle still figures as 540iX with B58 series power aggregate:
What is worth mentioning regarding N63/S63 engines of this generation?
These engines are equipped with:
a. VANOS both for inlet and outlet camshafts;
b. Valvetronic for inlet valves;
c. HPFP – one-plunger “small ones” HPFP, separate for each bank. Rail pressure in idle: 50 bar, max – 350 bar;
d. injectors – solenoid management. To ensure a swift reaction from the injector, they are opened at an increased (around 70V) voltage.
What changes has Alpina made for these N63/S63 series engines? Of course, the exhaust is changed. The DME software has been changed. But – both turbines too are changed. Alpina has installed larger TwinScroll turbines instead of “stock” turbo aggregates.
As a result, the impressive 800Nm torque from 2000 RPM has already been reached.
Without any illusion, enough time is needed to reach this torque by 2000 RPM. But, from (around) 2700 to 3000 RPM, this torque is available almost immediately.
Now, it’s time to come back to today’s patient.
The exact car has been purchased with a symbolic (around 15.000 km) mileage. Now, the mileage is around 58.000 km. A small thing for BMW! But already, for a while (around 20.000 km), the engine runs unevenly. Misfires can be felt in idle. One time, even group misfires started; the Check engine lit up.
The error messages regarding this case you can see in this print screen:
Here is the complete crash of the 2nd bank! 3 out of 4 cylinders are switched off; they feel as if they had group misfires. Then, the turbo aggregate and the last “living” cylinder. The car was left running on a 4-cylinder atmosphere.
If this were the Siemens DME error message list, I would assume that the injector of the 5th cylinder had started to leak. But, taking into account that this engine is managed by Bosch DME (and these DME have serious problems with identifying the culprit cylinder in idle), I don’t believe in this list. Only it is clear that some of the cylinders of the 2nd bank have had misfires. Which cylinder (or, maybe, Lambda probe or some other hub) is the culprit? Who knows.
After restarting the engine, it restored normal performance (if not counting the previously mentioned uneven performance). Such excesses have not been repeated. We can only assume that the misfires are the ones to blame.
The car has visited the dealer center. Based on the complaints regarding uneven idle, the dealer has performed a service procedure – cleaning of the spark plugs. No positive effect was reached. The dealer says that he can’t help with this. The owner of the car has installed new ignition coils and spark plugs, hoping for some improvement – zero effect.
Feeling a certain dose of hopelessness, the car owner turned to me.
Initially – a first view of the basic parameters of the fuel mixture of both banks.
As we see, the multiplicative LTFT of both banks is close to 1.00. Integrators: close to 1.00 too. The Lambda for both banks is correct (1.00); it’s confirmed by the control probers of both banks. Everything is fine with the basic things.
Let’s move to the Rough run data. Let’s start with the most suspicious – the second bank. Exactly here, the large crash happened.
The idle is not perfect (regarding possible causes – a bit later). It looks like the newest – “vector” method – is not used. But – all cylinders performed correctly, and no misfires were observed.
Exactly as in the previous 20 seconds, the next 20 seconds are without misfires; the mechanical efficiency of all cylinders is correct, too.
Let’s see what is happening in the 1st bank!
First 20 seconds – without surprises. Everything is fine.
The next 20 seconds look much more interesting:
Around the 30th – 31st second, the green curve indicates the reduced mechanical efficiency of the cylinder.
Around the 40th .. 42nd second, the “picture” becomes even more suspicious! What is this green culprit?
And here is the answer – it’s cylinder No.2!
Let’s zoom in on the data:
We can clearly see that there are quite regular at least part misfires in the 2nd cylinder. The culprit for the uneven idleness has been found!
The owner of the car tried the option of 1500 RPM and reported that the misfires could now be felt even more pronounced.
With the 2nd bank, everything is fine as previously, but… the 1st bank in the 1500 RPM mode:
And zooming in:
and like this, too:
and like this:
Yes, without a doubt – the culprit can be clearly seen! The same 2nd cylinder!
What could be the reason for the cylinder’s behavior?
Ignition system problems can be dismissed – the spar plugs have been cleaned and replaced, and the ignition coil has been replaced, too. All spare parts – BMW.
Obviously, there are problems with the injector. Possible options:”
a. the injector is leaking. Does the spark plug get flooded? The option is dismissed because the average fuel mixture is correct, and the performance of other cylinders is also correct. The sparkplug is not flooded, and no group misfires were observed;
b. the injector is not opening. I haven’t met such a defect;
c. beam of the injector is too wide (dismissed because the spark plug is not flooded) or too narrow (in theory, it is possible, but I haven’t met such detection for these injectors), or – sporadically poor atomization;
d. incorrect fly-time (BMW calls them “minimal injection” too) adaptations, which could be caused by previous misfires, incorrect maintenance, etc.
I asked the client two, in my opinion, important basic things:
a. is the AC of the car always on;
b. was the re-adaptation of the car performed after the repairs.
I got two “nos,” which means that before blaming the injector, the basic jobs should be performed.
Jobs to be done:
a. turn on the AC;
b. re-adapt the engine.
The engine re-adaptation consists of several basic stages:
a. deleting the old adaptations;
b. adaptation of the flywheel;
c. creating the fuel mixture and injector adaptations for warm engine;
d. creating the fuel mixture and injector adaptations for cold engine;
e. evaluation of the results of the new adaptations.
P.S. Of course, if the repair of some specific hub (for example, Valvetronic) has been performed, additional service procedures for this hub should be performed.
Continuation in the part 2.
