This entry is dedicated to everyone, who thinks, that his car’s diagnostics case is complicated and repair – expensive. I believe you will change your mind after this entry. In this entry will be a minimum amount of images – with them the length of the entry would become inadequate.


Patient: E90, N43 series engine. Some time ago the maintenance of the engine was performed: new spark plugs and ignition coils, CCV repaired and rebuilt, NOXEM installed. The engine worked in Stratified charge, no claims regarding fuel system.


One day I got information, that cold engine tends to shiver. When starting a cold engine, I concluded, that it rhythmically (after every 10 seconds) shivers – DME restarts. Taking into account, that in my experience there were similar cases, the cause of the problem was quickly indicated: incorrect IBS data. Replacing and encoding of battery solved the problem. More about this problem read here.


It looked, that all problems are as if solved, but… On the next morning, I received information, that the engine continues to shiver. Yes, now it didn’t shiver for one second, but – a moment after starting shivered very strongly, as if it had lack of fuel. In addition, the shivering was very strong, the engine shut down, it was not possible to control the fuel mixture (probes were disconnected). Then, suddenly, the engine again performed perfectly, LTFT, integrators – correct. Fuel pressure (both LP and HP) – correct even during shivering.

Taking into account, that pressure sensors indicate fuel pressure, but not that, if the air has gotten in the system, I decided to explore the fuel topic more closely. I had some suspicions because LPFP pressure was not so stable as it’s supposed to be (its jittering overreached +/-150 .. 200 hPa, although for the good system it is only +/-30 .. 40 hPa).

Next problem was found quickly. LPFP system didn’t pump fuel for “wrong” side to side of the pump. On the “wrong” side regularly 10 .. 15 liters of fuel was left! More about this read here and here.

To be 100 % confident, LP fuel system was observed for a long drive, and there was no doubt – fuel pumping was incorrect! Taking in account, that in 9 of 10 videos (which client has sent as a proof of engine shivering) the fuel amount in the tank was 1 .. 2 units (several liters), there was completely no doubt – there are serious problems! Additionally, several times the error message was recorded: misfires of several cylinders due to low fuel level (level in the fuel tank: 7 liters; EKP has detected the dry mode of the pump).

Taking in account, that fuel filter was already 10 years old; repair of over-pressure and backflow valves is not intended, it was decided to replace the fuel filter together with fuel pumping hub (it’s not possible to separately buy fuel filter and valves).

After replacing this hub, fuel was correctly pumped to the pump’s side. Problem solved? No! Problem continued! Directly after starting the engine everything was perfect, but after a moment the car as if suffered fuel lack – again!

Control equipment of LP and HP was connected:

Manometers indicated following situation: HP drops slowly (dropping to 120.000 hPa during 20 .. 30 minutes), but LP drops quite swiftly (to 0.0 bar during 20 minutes). Obviously, the leak is also in backflow valve of the fuel pump! For this car (common rail system), the air can quite simply get in the fuel system due to leaking pump. A moment after starting the air gets in HPFP and – the car starts to “consume” air instead of fuel!

After replacing the fuel pump, the pressure of the LP system dropped much slower: after a period of 6 hours it still was around 1.5 bar. Will the problem be finally solved?


No! Although the appearances of the problem have slightly changed, the car continued to lose the power, shiver. Yes, it didn’t completely shut down. In the moments, when the car worked, everything was perfect, but power loss, restarting of DME, was an everyday issue.


Next cold start indicated group misfires in cylinder No.3, DME has disconnected it. HPFP was switched off, rail pressure – around 5000 hPa. Yes, indeed, cylinder No.3 was not able to perform normally with correct rail pressure (Lambda of 2-and bank: strongly decreased: around 0.85; after restoring the performance – incorrect mechanical efficiency of cylinder and misfires continued). Taking out the injector and checking, as mentioned here, the injector was leaking fuel. No doubt – injector of cylinder No.3 was leaking! After replacing the injector – Lambda of both banks – ideal ( 0.99 .. 1.01), integrators – ideal (-5 .. +5 %), mechanical efficiency – correct (+/-10 %).

When the engine warmed up, misfires in cylinder No.2 appeared. Stratified/idle (../F5/Shift+F6/F5) data indicated, that the injector of cylinder No.2 has started to leak (its trim data in Stratified charge were dropping swiftly, in Homogeneous mode Lambda was below 0.9, not taking in account the integrator value – 20 .. -25 %)! One more problematic injector? Unfortunately, yes. Replacing the injector solved the problem in the 2-nd bank. Problems solved? No!


After 15 minutes drive suddenly the EML symbol in KOMBI lighted up, error messages regarding misfires of cylinder No.4, fuel trim in the 1-st bank (rich mixture, not taking in account integrator of -30 %). Stratified/charge data, Lambda in 1-st bank confirmed – there is a problem with the injector of cylinder No.4 (../F5/Shift+F6/F5 data of cylinder reached -3.01 mg/stk). And as a bonus – completely incorrect mechanical efficiency of cylinder No.1 (around 50 % of necessary). Replacement of injector of cylinder No.4 solved trim and misfire problems of cylinder No4, but incorrect mechanical efficiency and reduced Lambda of 1-st bank (in a set with integrator -25 .. -30 % – obviously, the injector was leaking) solved the replacement of injector of cylinder No.1.


After replacing all 4 injectors, all problems disappeared – the power loss, DME restarting. Yes, it’a not possible to identify the cause of the problem – if by mistake E85 (bioethanol) was filled instead of petrol, or some fuel additions (maybe even some additives, which gas station haven’t flushed out of their system). Harsh, but a fact – swiftly progressing problems were with all possible elements of fuel system: pump, valves, injectors. Repair, in this case, cost around EUR 1500!


My suggestion to all owners of cars with common rail – use only fuel form large, checked out operators, keep in the fuel tank at least 10 .. 15 liters of petrol. Even if it happens to fill low quality fuel, the will be less possibility to pull in the dirt in the system and this “bad” fuel will be diluted with quality fuel. Additionally – the fuel pump will be cooled down, less possibility to pull in the dirt from the bottom of the tank (on the pump side).