Mitsubishi 4A9 engine

Engines of the 4A9 family were created by engineers of Mitsubishi Motors in 2004, and were produced at the DaimlerChrysler plant in Germany. Accordingly, these engines were installed on Mitsubishi Colt, as well as on the co-platform Smart ForFour. Later they were sold to several Chinese automakers. For example, the 1.5-liter engine is installed in Zotye Z300, produced in Belarus.

For Mitsubishi company it was the first 4-cylinder engine with an aluminum block. The cylinder head has 16 valves, two camshafts, the inlet one has a phase shifter of MIVEC system. There are no hydrocompensators. The timing is driven by a roller chain.

The family 4A9 includes “fours” with a volume of 1.3, 1.5 and 1.6 liters. Also were created and 3-cylinder engines 3A9 with displacement from 1.0 to 1.2 liters. All versions have the same cylinder diameter – 75 mm, the piston stroke differs.

We will dismantle the younger “four” 4A90 with a capacity of 1.3 liters, rated at 95 hp. The engine was removed from the Mitsubishi Colt 6 of 2005 year of manufacture. The same engine in Smart (or Mercedes) catalogs is designated as M135.930.

Technical specifications

What can be said about the reliability of the 4A90 engine?

The engine turned out to be rather compromise, it has unpleasant features that lead to overhaul. Although quite a few of these engines have passed 300 000 km.

Extraneous sounds and their sources

Many owners of cars with a 4A90 engine in operation are concerned about various suspicious sounds and knocking. Their source may be loose thermal insulation screen of the exhaust manifold, burned exhaust manifold gasket, gasket between the exhaust manifold and the intake pipe. MIVEC clutch and even detonation can also often be the source of extraneous sounds. More about it – further on in the text.

Aconditioner pump and compressor

Extraneous noises and vibrations can come from the pump and air conditioner compressor. Bearings in them are broken. The vibrations and sounds they cause usually change or disappear depending on the load on the drive belt.

The Right Oil

Since the 4A90 engine was developed also for the needs of Mercedes, the corresponding tolerances apply to it. Specifically, the oil must comply with tolerances not lower than 229.1. The best is pure synthetic Mobil1 0w-40 or 5w-40, and it is poured from the factory. You can use good analogs with high tolerances 229.3 or 229.5, oil should be changed every 7000 – 8000 km.

However, there is information that in Japan in this engine they pour low-viscosity oil 0W-20.

If the engine does not like the oil, you will know about it almost immediately by detonation and oil burning. More about it below.

ECU

The engine control unit of the 4A90 engine may start to malfunction. This will be manifested by several jerks when driving or accelerating, similar to a malfunction with the gas pump. Or the traction drops strongly, the rpm decreases, the engine almost stalls. At the same time Check Engine and engine overheating indicator lights up on the dashboard. And after a few seconds all these symptoms disappear and the engine starts to work normally. Of course, the malfunction will manifest itself in the future. Practice shows that the problem is in the engine control unit. It has to be changed by flashing the immobilizer of your car.

Throttle valve

With the throttle valve of the 4A90 engine, classic malfunctions occur: the car can stop responding to the accelerator pedal, the rpm can live its life (that is, float, strongly decrease at idle), and the engine will not start well or sometimes stall. In some cases, malfunctions in the throttle assembly are indicated by corresponding errors.

Cleaning the throttle plate almost always helps. After putting it in place, it must be adapted, otherwise during the next few days of operation, the idle speed will be elevated, at the level of 2000 rpm.

But if the engine has lost power, and the rpm does not rise above 3000, then you need to go to the dealer and re-flash the software. The described fault and the method of its solution have been described by the manufacturer.

Crankshaft pulley

The crankshaft pulley on the 1.3-liter engine (4A90) is cast, and on the 1.5-liter engine it is damped. But their dimensions are the same.

Thermostat and engine temperature 4A90

For the sake of increasing efficiency, Mitsubishi engineers made the 4A90 engine hot. The thermostat is fully opened when the antifreeze is heated to 95 °. But in hot weather and with active fast driving the antifreeze heats up more, even up to 110°. Under such conditions, oil degrades quickly, oil caps get stale and conditions for detonation arise.

Ignition coils

Ignition coils can shoot out on the cylinder-head through dried-out insulating rubbers. There are ignition skips, which are indicated by errors, as well as dips when gaining speed.

Oil in the plug wells

Oil can get into the spark plug wells: it seeps here through blistered oil seals in the valve cover. At the factory, the oil seals come only together with the original valve cover (it costs from 150$ to 270$), which costs a lot of money.

The most economical take out the old oil seals and put in their place non-original suitable size.

Carter gas vent valve

Usually at a mileage of about 100 000, the VKG valve loses its tightness due to accumulated carbon deposits and ceases to perform its functions normally. This affects the engine operation: the rpm may float, there may be a small amount of air suction.

A serviceable valve should be blown in one direction – from the valve cover to the intake manifold. There should also be a normal stroke of the valve stem. This is checked on a running engine with the valve unscrewed, but put on it with a hose to the intake manifold. When the inlet port is closed, there should be a clicking sound indicating that the stem has moved.

Injectors

Contaminated injectors cause vibrations at idle, sluggish idle speed reduction and sluggish idle leveling.

The 4A90 engine has Siemens Deka injectors, which are similar to those on some VAZ engines.

Detonation (“finger ringing”)

Detonation is another very common problem of the 4A90 (and 4A91) engine. Detonation manifests itself on a warmed engine, especially in hot weather and on low-grade gasoline, under load. When detonation occurs, the engine rings and vibrates slightly between 2000 and 3000 rpm. Such ringing may weaken or disappear after turning on the “heater” of the passenger compartment to maximum.

This detonation is manifested due to a short-term laying of piston rings, when the combustion chamber gets engine oil, combustion of which leads to an increase in temperature in it.

It is noticed that when checking the compression on a warm and hot engine can be different readings, that is, the piston rings can still “sour” and normally perform their function. And then in some modes again lay down.

Valve clearances

Engines of the 4A9 family do not have hydrocompensators in the valve train. Thermal clearances should be checked every 40 000 km and adjusted if necessary. Adjustment is made by selecting cups. The manufacturer has provided 30 sizes of tappets, one costs about $10.

The timing chain

The 4A91 engine is practically not noticed with such a problem as stretching of the timing chain. If it does have to be replaced, it is at mileage over 200,000 kilometers.

MIVEC clutch and its valve

Another likely source of extraneous noise is the phase shifter clutch of the MIVEC system. It rattles on a cold engine for some time after starting the engine.

The valve that controls the clutch may also be malfunctioning. With its malfunction, there are short-term and haphazard failures of traction, twitching, floating revolutions. These symptoms may disappear when disconnecting the electrical connector on the valve. Even with a faulty valve, the engine loses power, Check Engine lights up due to an error indicating a malfunction in the MIVEC clutch valve.

In most cases, the valve can be cleaned in a suitable cleaner. But sometimes the valve stem and valve seat wear out – there is wear and tear between them. To check this, you can shake the washed valve – if it rattles the stem, you need to buy a new one.

Piston ring seizure

The problem of piston rings sticking is inherent in the engine 4A90 and 4A91 (1.3 and 1.5 liters, respectively). It should be said that the rings stick not so much because of engineering miscalculations, but because of the engine’s unsuitability to low-quality gasoline and incorrect oil. If the miniature pistons of these engines overheat, the oil starts to burn and clog the grooves of compression rings and clog the oil rings. The same story with wrong (unsuitable) oil: it clogs grooves on pistons, breaking mobility of rings.

As a result, Mitsubishi engine starts to consume oil up to 1 liter per 1000 km. With oil appetite this motor can pass a couple of tens of thousands of kilometers, but usually it all ends with burning out of one of the valves or even destruction of pistons with damage to the block. It was possible to avoid the breakdown of the 4A90 and 4A91 motor by replacing the piston rings.

Interchangeability of engines 4A9

Engines of the 4A9 family are similar in size and are interchangeable. They are the same on the supports, on the mounting of the gearbox. But there is a difference between the European and Japanese versions: the starter on the Japanese sets on the left, on the European on the right. There are also differences in the exhaust manifold due to the presence of the EGR system on the Japanese versions. If desired, the early 4A90 or 4A91 can be replaced by a late (since 2010) 1.6-liter version 4A92, which has an improved piston group.