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

Generic solutions

Try pulling apart every connector in the engine bay that you can find and spray it with contact cleaner, fill with petroleum jelly and re-connect. This fixes a remarkable number of problems.

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.

Mass air flow rate issues

The engine needs a constant feed of air in order to burn fuel and to make explosions in its cylinders which make it run.

The feed of air is determined as a mass air flow (MAF) rate, usually expressed in grams/second or lb/min etc.

However, a MAF sensor does not exist "per se". Instead, the MAF is calculated based on individual readings from several different sensors. Those sensors are usually:

• IAT (Intake Air Temperature);
• MAP (Mass Air Pressure);
• TP (Throttle Position);

If either of these sensors are bad, the ECU will not mix the fuel and air properly, which usually leads to one of the following problems:

• Engine stalling;
• Uneven engine RPMs when idling (RPMs go up then down and so on);
• Too rich fuel mix (raw fuel smells from the exhaust);

However, the ECU will have a default / "failsafe" parameter "mapping", which it will use if it detects a failed sensor. Therefore, if you are having one fot he above mentioned issues, you can try diagnosing the cause by unplugging one of the above mentioned sensors in turn.

For example, if the engine RPMs are uneven when the engine is idling, when you unplug the sensor that's sending bad signals, the idle RPMs should stabilize. It might still behave improperly (for example idle "fast" - on high RPMs), but idle RPMs should be stable. If this kind of change happens, you have found the bad sensor.

O2 ("Lambda") sensors

Jimnys with M13A engine have two such sensors, which are quite expensive.

These are feedback sensors which inform the ECU about the composition of the exhaust fumes, so that the engine can adjust the fuel/air mixture accordingly.

A typical issue which a bad O2 sensor causes is significantly to drastically increased fuel consumption, usually accompanied by reduced power. However, they can cause other issues as well (someone should contribute to this chapter).

Engine heating / cooling issues

There can be several reasons why the engine tends to overheat easily (under normal load) or for its temperature gauge in the instrument panel to become erratic (unprovoked significant changes in engine temperature during driving).

If some of the mentioned issues happen on a regular basis, the following notes can serve as a diagnostic guidance.

Clogged engine coolant heat exchanger

• Going through water (especially muddy water) can muck up the engine coolant heat exchanger (wrongly called "radiator") and cause it not to cool effectively, making the engine more likely to overheat.
  • If the heat exchanger is visibly full of debris and muck, then it should be carefully cleaned. This is best done by draining the engine coolant from the system and removing the heat exchanger from the vehicle.

Worn viscous locking hub of the cooling fan

• The engagement mechanism (viscous hub) of the viscous fan (the big fan in front of the engine coolant heat exchanger) can become worn, causing the fan not to lock up and spin as fast as it should. This then severely hampers heat exchanger's performance.
  • If the fan is your prime suspect, you can temporarily mechanically lock it (so that it always spins) with zip ties or something and see if your issue(s) disappears or not.
  • If you remove the fan from the vehicle, make sure that you do not place it in a horizontal position.
    • Reason: With used viscous fans, that position might ruin the viscous set up in its hub, decreasing its mechanical resistance.
  • A replacement viscous hub for this fan is available in the BigJimny store.

Additional notes on how to check if the viscous coupling unit / hub of the fan is working properly:

• With a cold engine, grab the fan blades and see if there is side to side play or a rattle.
  • If there is, the viscous hub is worn.
• With a cold engine, try to turn the fan by hand.
  • If it feels stiff, but will turn, the viscous hub is OK.
  • If it feels loose and spin easily, the viscous hub is worn.
• Go for a drive with the window open.
  • When you first drive off, the fan should roar like a vacuum cleaner when you rev the engine from cold. Then the noise should disappear when hot.
    • No idea why this happens, as it is the exact opposite of what you would expect. Possibly the fluid has to warm up before it can start working properly.

Faulty thermostat

• The engine coolant thermostat can become faulty, not opening up when the engine reaches operating temperature, and thus not allowing the engine coolant to flow from the engine through the heat exchanger and back around.
  • When the engine gets hot, turn on the cabin ventilation to the maximum flow and the highest temperature settings. If the airflow remains relatively cold rather than heating up, that usually indicates a faulty engine coolant intake thermostat.
  • A thermostat can be tested by removing it from the car and putting it into a pan and then pouring boiling water from a kettle onto it.
    • If the thermostat does not do anything, it is faulty.
    • If you see it pop or move, then it is working properly.
    • A non-faulty Jimny thermostat activates at the temperature of around 83 degrees C, so boiling water will trigger it.
    • Note: If a thermostat is removed from the engine, you will need a new gasket to put it back in. At this point you may as well replace it with a new thermostat, since they are quite cheap and come with a new gasket.

Faulty engine coolant temperature sensor

• The engine coolant temperature sensor can become faulty.
  • To check that sensor, it would have to be removed, placed in a pot of water and then the pot heated up, having a thermometer in the pot as well to watch the temperature. Then, using a multimeter, check the resistance of the sensor at different temperatures of water in the pot (outlined in the factory service manual).

Worn engine coolant pump

• Engine coolant pump ("water pump") can become worn, which decreased the flow rate of the coolant through the system.

Blown engine head gasket

• The seals between the coolant passageways in the engine and the oil passageways in the engine can become worn (usually called "blown head gasket"), allowing coolant and oil to mix.
  • Are there any strange fluid dots or bubbles on the engine oil level dipstick?
  • Are there specs of oil on the top of the coolant when looking in the heat exchanger with the cap off (with a cold engine)?
  • Note: If engine's head gasket has gone, it could be as a result of the engine getting too hot and the head warping. You could fix it and it will happen again as the cause has not been eliminated. Therefore, first eliminate the cause, and then fix the head gasket.

An air pocket in the cooling system

• An air pocket can exist somewhere in the engine coolant distribution system, in the engine block itself or in the heater core (the part of the engine which emits heat into the cabin's ventilation system). ** An air pocket can severely hamper or even block the flow of the engine coolant through the system, thus rendering the heat exchanger useless.
  • • Even worse, if the air pocket is in the engine block, that part of the engine can locally super-overheat and become damaged.
  • The highest risk of developing an air pocket is when replacing the engine coolant or servicing parts of the engine coolant distribution system.
  • Even if the heat exchanger and the engine coolant expansion reservoir show there is sufficient amount of coolant in the system, an air pocket somewhere could be blocking its distribution, thus effectively blocking the system from being filled with coolant to its nominal level.
    • Sometimes, because of vapour-lock or small holes in tubing between the engine coolant expansion reservoir and the heat exchanger, the coolant doesn't flow back into the heat exchanger. This means that you can have little or no coolant in the heat exchanger but still have plenty of coolant in the expansion reservoir. Therefore check the level of coolant in both of them.

I would start with draining and flushing the cooling system, and at the same time taking the rad off and pressure washing from the engine side to the bumper side to try and remove any debris. At the same time check the thermostat is still operating correctly.

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Page last edited on 30/03/2020 by user Bosanek