Dacia Logan cars with 8-valve K7J and K7M gasoline engines (1.4 and 1.6 liters) have a signature disease – jerking, misfiring at low speeds, especially when shifting from 1st to 2nd gear. Many drivers change sensors, corrugations, and clean the throttle assembly to no avail, but the jerking problem persists. However, the solution to the issue of jerking during acceleration on K7J and K7M engines is quite simple.
Symptoms of failures of Dacia K7J, K7M 1.4, 1.6 liters, diagnostics
We need to be clear—we are talking about the misfires and jerks of the K7J and K7M engines at low revs. Most often, jerks are felt in first and second gears, very rarely in third, but at low throttle. In most cases, you can exclude them from the list of suspects: It is worth checking the spark plugs and wires, as well as the ignition coil. On 8-valve K7J, K7M engines, the coil has its own disease. In short, it is the destruction of the coil body due to the different coefficient of thermal expansion of the valve cover where it is attached and the coil body. Because of this, moisture gets inside the coil through microcracks, and the voltage breaks through to the body. Checking these parts will not take much time. Instead, you can safely discard these parts and begin to eliminate the main issue that causes misfires and jerks at low speeds in the K7J and K7M engines on Logan, Sandero and some other Renault or Dacia vehicles. The global reason that Logan accelerates with failures is the lean of the working mixture. But within the range of 2000-2500 rpm. The reason for this is most often the intake manifold gasket of the 1.4 and 1.6 liter K7J and K7M engines. Here are the catalog numbers:
The most common reason for the failure of K7J and K7M Renault, Dacia
It is worth checking the spark plugs and wires, as well as the ignition coil. On 8-valve K7J, K7M engines, the coil has its own disease.
In short, it is the destruction of the coil body due to the different coefficient of thermal expansion of the valve cover where it is attached and the coil body. Because of this, moisture gets inside the coil through microcracks, and the voltage breaks through to the body.
Checking these parts will not take much time. Instead, you can safely discard these parts and begin to eliminate the main issue that causes misfires and jerks at low speeds in the K7J and K7M engines on Logan, Sandero and some other Renault or Dacia vehicles.
The global reason that Logan accelerates with failures is the lean of the working mixture. But within the range of 2000-2500 rpm. The reason for this is most often the intake manifold gasket of the 1.4 and 1.6 liter K7J and K7M engines.
Here are the catalog numbers:
However, there is no need to rush to buy a new manifold gasket until we check that its fault is 100% proven.
How to check the gasket of the intake manifold Dacia Logan
To do this, you need to drive your Logan onto a lift or into an inspection pit. Carefully inspect the rear of the engine from below, where the intake manifold is located. Namely, the junction of the lower part of the manifold and the cylinder head.
If the gasket has dried out and lost its elasticity, we will see pronounced oily stains, which is not at all typical for the intake manifold.
Question. Where does the engine oil come from at the intake? The reason is that the oil is forced into the intake anyway by the breather at high revs.
In addition, the very fact that oil gets into the intake tract can indicate serious engine problems, such as a clogged catalytic converter, clogged valve cover breather, etc. But this is a separate topic for discussion.
How to remove the K7J and K7M engine intake manifold
In the meantime, remove the battery terminal, since all the work will be done near the starter.
The next step is to dismantle the air filter housing. To do this, remove the air duct corrugation and unscrew the four bolts of the filter housing – two in the front and two in the back.
An important point is to immediately remove the breather tube of the valve cover and check the presence and condition of the rubber seal. If for some reason it is not present, you will have to buy it. For some reason, many garage technicians ignore the presence of the seal.
When the housing is removed, it is highly desirable to blow compressed air into the area where we will be working. There is a lot of dust and dirt accumulated here.
Remove the four injector power connectors and the throttle position sensor connector, as well as the intake air temperature sensor. And the absolute pressure sensor on the right side of the throttle.
Remove the connector from the idle speed sensor from the rear end of the throttle body.
Remove the throttle cable from the rocker arm and the tie rod on the other side of the rocker arm.
Unscrew the throttle assembly mounting bracket, bit T30.
Remove the throttle assembly. Do not forget to check the condition of the bottom seal.
After dismantling the throttle, be sure to cover the hole with a cloth.
Disconnect the pipe connecting the manifold to the brake booster. There are two clips on the sides. Move the pipe to the side so that it does not get in the way.
Disconnect the tube that goes to the absorber. Simply pull it to the side.
Remove the fuel hose. Theoretically, you should first relieve the pressure in the system by removing the fuel pump fuse and running the engine until it stops.
But it is highly undesirable to do so, because the pressure will drop to zero, which will lead to the fact that after assembly, the injectors will begin to overflow gasoline.
After removing the fuel hose connection, fuel may leak, so be sure to have a rag handy. Then be sure to seal the hose connection with it. Also be sure to seal the hole on the fuel ramp.
Get down under the car and free the manifold from the harnesses, there are two of them - one smaller and one larger.
Now you need to remove the metal bar that supports the manifold. To do this, clean and lubricate the threads, unscrew the nut with a 13 mm socket head and the 16 mm bolt at the bottom of the bar with a box-end wrench.
From the bottom, you can unscrew the two manifold mounting nuts with a 10 mm socket head. This can also be done from the top.
From above, unscrew the two bottommost nuts, one of which is behind the starter. From under the hood, unscrew the four upper manifold mounting bolts, also with a 10-mm socket head.
You can remove the manifold and inspect the condition of the gaskets.
Replacement of manifold gaskets Renault/Dacia Logan 1.4, 1.6 l
Now clean the manifold thoroughly, both inside and out. Before doing so, remove the fuel ramp and the throttle cable arm.
Use any aerosol detergent (brake cleaner, carburetor cleaner, etc.) to thoroughly clean the manifold and throttle body.
Lubricate the rocker arm axis, throttle ball mount, and throttle actuator linkage. It is advisable to lubricate with dry grease, but a more affordable grease that does not corrode plastic will do. Silicone spray, for example.
Install the new manifold gaskets in place, making sure that the gaskets are pressed tightly and evenly into the grooves.
Be sure to apply thread sealant to the pre-greased upper four manifold bolts. The thread sealant is needed because the bolts are in contact with the oil lines in the cylinder head. This will ensure a tight seal and prevent engine oil from leaking through the threads.
Now clean the cylinder head bore and reinstall the manifold. Reassembly is in reverse order, but care must be taken to ensure that all harnesses and hoses connected to the manifold are routed correctly.