N series and LPG

People, who want to drive BMW, but at the same time – don’t like to spend a lot of money on fuel, usually choose petrol engines and then install the LPG equipment.

For countless times, I have explained, that BMW N series engines cannot be normally used by gas (using stock management units with additionally installed gas management units), but, of course – if you want to save money – do as you wish.

Today’s patient: BMW 1-series, N46 engine. Gas equipment installed. Problems – uneven performance of the engine, time by time EML symbol lights up in the panel – the power of the engine is decreased. “Specialists,” said, that there are some problems with air mass meter.

Viewing the error messages shows only 2 errors (for me – some kind of a disappointment, because usually, engines with such “upgrade” have much more error messages recorded). But, taking in account, that the gas unit has been installed only recently, and in addition, the previous error messages have been deleted during a visit by “specialists” – no surprise at all.

 

The error messages – regarding proportion of the fuel mixture. Plausibility – so: mismatch of data (between Lambda probes and air mass meter), for both banks.

And in these images – “key” parameter marked:

Of course, % mark is a “make-up” of INPA, actually – the parameter marked is a multiplicative corridor of adaptation map. Obviously, this corridor is +/-30% (it means, allowed value: 0.70 .. 1.30). What does this “corridor” mean? While driving, DME compares data of air mass meter with predicted Lambda, which is reported by Lambda probes. If for some reason this result is different for more than -30% .. +30%, an appropriate error message is recorded, the engine switches for (one of many) emergency modes for some time.

 

Why the “specialists” decided, that the problem has something to do with air mass measurer? Because the air mass is mentioned in the description of the error message.

What other reasons can cause this error message? Actually, several – for example fuel pressure, incorrect amount of injected fuel. No.2 – becomes actual, when/if the car is equipped with a gas setup.

 

Viewing live data of fuel mixture (car runs on petrol):

1. incorrect offset type adaptation for the 1-st bank;

2. long time after pressing the accelerator pedal, the control probe indicates the oxygen in the exhaust: obviously, lean mixture and additionally – incorrect distribution of fuel mixture between cylinders (CO catalytic converters are not able to burn all fuel + air mixture, which comes in the exhaust);

3. pressing the accelerator pedal – lean mixture observed.

 

Symptoms, mentioned in point 2 and 3, disappeared, forcing the engine to work in problematic mode. The problem, mentioned in point 1, obviously, appeared due to an incorrect performance of the gas equipment (unsuccessful equalization of cylinders efficiency, while running on gas).

 

My verdict in the current situation – all components of the engine (as far as it concerns running on petrol) are performing correctly. All problems are caused (and will be caused) by the gas equipment.

 

And now a little about that, what kind of problems even PERFECTLY adjusted gas equipment can cause:

1. Even theoretically it’s not possible to maintain such high precision of the injected gas, that the DME of N series petrol engine would not regularly record error messages regarding fuel mixture (lean or rich), the error messages regarding air mass meter – data plausibility, Valvetronic plausibility, would not light on the EML symbol in KOMBI and would not decrease the power of the engine;

2. Even theoretically tests (evening of the engine performance) of the chemical and mechanical efficiency of cylinders in idle/driving are not working. DME is not able to even the performance of cylinders – the engine shivers, it’s power is decreased, DME records the error messages regarding trim of Lambda probes, loss of efficiency of catalytic converters, error messages regarding a voltage of narrow-band (control) Lambda probes;

3. Thanks to the incorrect temperature of the exhaust system (running on gas) + incorrect fuel mixture dispersion between cylinders (as a result of the problem, mentioned before):

  • life of CO catalytic converters is significantly shortened;
  • life of Lambda probes is significantly shortened – running on gas, probes are regularly overheated (heating algorithms are working incorrectly) and damaged when the unburned petrol/gas lights up.

4. Every time, when the engine is switched between gas and petrol, all possible (wide-band Lambda probes, air mass meter, throttle, Valvetronic, EGR, etc.) adaptations are destroyed – the possibility, that the engine will switch to emergency mode, is 99%. Yes, sometimes EML doesn’t light up, but the engine (especially it’s exhaust system) is subjected to significant stress;

5. Installing the “gas” spark plugs, the ignition coils (their resource shortens significantly) and DME (a possibility, that the transistors of ignition coil management are damaged, increases) have an additional load.

Short summary – if you are ready to cope (in the name of an economy) with vibrating engine, which sometimes suddenly stops, regularly looses power, EML (emergency) symbol regularly lights up in KOMBI, additionally, the most expensive parts of exhaust systems are damaged – welcome to the LPG club!

 

Yes, I have heard contrary arguments – for my car everything is in perfect order! I’m sorry, but I haven’t seen ANY engine, equipped with LPG, which would work in full functionality mode!

Most typical scenario – I remark, that the engine strongly vibrates in idle, but the owner of the vehicle says – in my opinion, everything is perfect! What else to add?

Or second typical scenario – on my remark, that the CO catalytic converters are getting damaged, the owner responds – I pass the TI, so everything is in perfect order! And then we find out, that during the last year the car drove below 10’000 km, additionally, CO/HC are close to allowed max values (accordingly – CO catalytic converters have lost at least 90 .. 95% of their performance). I think, everybody, who has some technical knowledge, sees the pitty picture, but for lovers of an economy – everything is perfect!