Engine M13A - performance issues diagnostics

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Introduction

The purpose of this article is to mention all performance issues which a Suzuki M13A engine might develop, and then possible causes and diagnostic methods to determine the exact or at least the most probable cause.

Examples of performance issues are:

• stuttering,
• loss of power,
• uneven RPMs when idling or when throttle is applied,
• excessive fuel consumption,
• not able to start,
• overheating under normal load,
• etc.

Some issues and solutions

Exhaust Gas Recirculation (EGR) valve

An EGR valve helps reduce harmful emissions by introducing a small amount of exhaust gas, below the throttle plate, into the intake manifold. This has the effect of cooling the combustion chambers, as the incoming exhaust displaces part of the oxygen in the combustion chamber and takes up volume, even though it does not support combustion.

• A faulty EGR valve can cause rough idle and poor acceleration.
• If EGR is on during idle, stumble and even stalling will likely result.
• If EGR is on during hard acceleration, low power (from reduced air/fuel volume) is the result.
• If the engine stumbles or stalls at idle or lacks power under load, EGR may be staying on and not shutting off.
  • On the other hand, if the engine is pinking at cruise, EGR may not be turning on to cool down combustion chamber temperatures.

Idle Air Control Valve (IAC)

IAC is connected to the engine's primary air intake valve (the Throttle Body, or TB) and is responsible for making minor adjustments to engine airflow. While the IAC valve's effect is fairly minimal while the TB valve is open, many engines rely on the IAC for idle or low-speed operation. IAC valve mechanisms can become dirty and clogged.

Start-and-stall

The engine will catch and run for a second or two, stutter and die.

• If "blipping" the throttle prolongs engine failure, but doesn't prevent it = IAC
• If "blipping" the throttle results in immediate stalling = fuel-related failure

Deceleration failure

Lifting your foot off the accelerator, the engine's TB valve completely shuts. In the case of a malfunctioning IAC, it will starve the engine of air = stalling either while decelerating or after coming to a stop.

Weather factors

A very cold engine needs more fuel than a warm engine, which is important to know while diagnosing the problem. An obstructed or stuck-shut IAC will result in a rich air-fuel ratio at idle, so the engine will start very easily while cold and then die suddenly after a slight puff of black tail-pipe smoke. A stuck-open IAC might start fine while warm and may continue to run if the engine reaches high-enough RPM.

Intermittent Stalling

An intermittent stalling condition is one in which the vehicle might start fine, act as though it's going to die, idle smoothly and then die completely. Alternatively, the vehicle may run fine most of the time, but stall periodically and then restart with a bit of difficulty. Intermittent stalling almost always indicates a dirty or clogged IAC.

Dependency on temperature sensor

The temperature sensor tells the ECU it is at running temperature and the ECU adjusts the IAC. If the temperature sensor gives erroneous information, the IAC will fluctuate.

First case is disconnect the IAC plug, and if it settles at around 1400 RPM, you can more or less guarantee it's the temperature sensor.

Camshaft and crankshaft sensors

There are 2 sensors in the engine block which are related to the timing of engine's main moving parts - camshaft sensors and crankshaft sensor.

When either of these two sensors stops working, the ECU immediately shuts the engine down and it also does not allow the engine to start up (like when there is no fuel).

The camshaft sensor is located high up on the front of the engine. Therefore it is dead easy to change, but it very rarely fails, so there is rarely a need for replacing it.

The crankshaft sensor looks the same, but it is not an identical part. If is located low on the engine block and is much more fiddly to change. In accordance with Murhpy's law, that it the exact reason why it is much more prone to failure. After it becomes worn, it usually stops working when it gets hot.

If you have the above described issue and you are feeling lucky, just buy a replacement high quality crankshaft sensor and replace it.

If you prefer to have a confirmatory diagnosis before throwing money at an assumption, wait until the issue develops, then cool down the crankshaft sensor down (if you don't have a suitable aerosol, a fairy liquid bottle of cold water will do). If the engine operates normally after the crankshaft sensor has cooled down, it is confirmed that the crankshaft sensor is faulty.

The crankshaft sensor rarely gives a fault code on a computerized vehicle diagnostics, because the ECU usually thinks that the engine has just stalled and doesn't log anything.

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Page last edited on 25/03/2020 by user Bosanek