A Cold-stalling Engine – Causes and Cures Part 2

Preamble
Ever since the World saw the first single-cylinder petrol engine driven Car, a ‘Carburetor’ became synonymous with it. Later on with the advent of multi-cylinder Engines, so did the ‘Distributor’ or ‘Delco’s.

During the last Century, both evolved considerably – till the ‘Euro-II’ like Pollution Norms got the better of them. For, the Carbs worked on a principle of ‘reaction’, which could easily get ‘stifled’ for so many reasons.

Thus, a System of ‘controlled-feeding’ of Fuel + Air + Ignition Spark to an automotive engine evolved in the early ‘80s. A ‘system’ like that had to be based on its ‘needs of the moment’, such as the load on it, engine rpm/road speed etc. Let’s see basically how such a system works…

It all started with ‘Single-point’ Fuel Injection Systems – virtually an electronic replica of the Carbs of yore but soon led to ‘multi-point’ Fuel Injection Systems – some what akin to the’ Multi-Carb’ high performance Cars of the past.
‘Mpfi’ stands for ‘multi point fuel injection’. This system injects fuel into individual cylinders, based on commands from the ‘on board engine management computer’ – popularly known as the Engine Control Unit/ECU.

The ‘Fuel Injectors’ are precision built fast-acting ‘Solenoid Valves’, like Washing Machine Water inlet Valves. These have either single or multiple ‘Orifices’ which ‘spray’ fuel into the inlet manifold of a Cylinder upon actuation, from a common Rail/Header pressurised to around 3 bar, fed by a high pressure electrically drive fuel pump inside the Petrol tank of the Car.

The ‘on-board’ ECU primarily controls the Ignition Timing, idling speed and quantity of fuel to be injected. The latter is achieved by means of controlling the ‘duration’ for which the Injector solenoid valve coil is kept energized – popularly known as the ‘pulse-width’.

The ECU in turn is controlled by the ‘data input’ from a set of ‘SENSORS’ located all over the Engine and its Auxiliaries. These detect the various ‘operating states’ of the Engine and the performance desired out of it. Such Sensors constantly monitor: 1. Ambient Temperature, 2. Engine Coolant Temp., 3. Exhaust/manifold temp., 4. Exhaust ‘O2’ content, 5. Inlet manifold vacuum, 6. Throttle position, 7. Engine rpm, 8. Vehicle road speed, 9. Crankshaft position, 10. Camshaft position, etc.

Based on a ‘programmed’ interpretation of all this input data, the ECU gives the various ‘commands’ to the Engine’s fuel intake, idling speed and spark ignition timing systems, to deliver an overall satisfactory performance of the Engine from start to shut down, including ‘emission control’.

To get the best out of an MPFi System, one should use – a) The OE recommended Petrol Additive or the new generation ‘Premium’ Petrol’s REGULARLY and b) NEVER Tamper with the OE Wiring Harness of the Car – EVEN to install the ubiquitous Music System OR any other Electrical Accessory - other than those ‘approved’ OE/Dealer and designed to suit the Car’s Wiring Harness ‘Couplers’. ‘BUTCHERING’ OF THE ORIGINAL CENTRAL WIRING HARNESS OF A VEHICLE IS AN ABSOLUTE TABOO FOR MPFi CARS.

Despite such a foolproof system and programming of the ECU, situations do arise in cold climates that lead to either starting problems first thing in the morning or the engine stalling under some or the other driving conditions.

Following are the possibilities that can lead to such situations - assuming that the Car has been serviced in line with the OEM recommendations:

i) That one is not allowing enough time for the fuel-pump to ‘prime’ the System, as evidenced by an audible ‘click’ sound in the Cabin of the FP going off after a few secs of turning on the ignition.

ii) That one is giving too short a Crank. The first one in the mornings has to be relatively a little longer than the ones during rest of the day.

iii) That one is unknowingly stepping on the Accelerator Pedal - even partially - which one is not supposed to for Mpfi’s.

iv) Faulty Coolant Temp and Air Intake Sensors/their Couplers - usually the latter for Cars less than 2-yrs old.

v) Worn-out or larger than recommended Spark-plug Gaps.

vi) Clogged Fuel-Injectors – one should be using a good Petrol Additive regularly like a daily Vitamin Pill with our regular/unleaded Petrol – or instead, the now more freely available detergent pre-mixed fuels.

vii) The main reasons for a petrol engine to stall are - a) either under or over supply of fuel, b) loss of ignition c) mechanical locking while shifting gears or braking etc., or d) un-sustainable/low idling rpm. If these happen rather regularly, other than ‘c’, then the engine needs to be ‘scanned’ at an authorised service centre to determine the cause and remedied accordingly.