Car jerks when accelerating
Causes & Solutions
If the car jerks when accelerating, the main cause is usually a defect in the fuel system. In this case, the diagnostic unit issues an error message "Rail pressure too low" or similar. The following defects in the fuel system can cause jerking when accelerating (or driving):
Other causes of a juddering car (but independent of the fuel system) can be the following:
1) Fuel filter clogged
Does the car jerk when accelerating? This may be due to a clogged or dirty fuel filter lie. This is usually under the Underbody protection on the driver's side attached. The filter costs about 20-35€ and should be changed occasionally.
For this reason, it also does no harm if, when the jerking occurs first replace the fuel filter. If the problem persists after the replacement, check the fuel pump.
Spare parts for your Fuel filter can be found here: *
2) Defective fuel pump
Depending on the car manufacturer, the fuel pump, also known as the feed pump, is located at the back near the tank or in the tank itself. Most of the time you get through the Removing the rear bench seat to the pump.
In principle Two faults on the fuel pump cause the vehicle to jerk:
Faulty power supply
The easiest way to check the power supply is to use a voltmeter or a multimeterwhich is based on DC voltage is set up. First of all, remove the covers and measures at the cable plugwhich is connected to the pump. The cable from the The ground pin is usually black in color. The Power supply usually has the color red and is a thicker cable. Between the two pins the voltage is not below 12 V when the ignition is switched on. Otherwise the cable path to the plug or the plug itself is defective.
Another cause of the voltage drop can also be a Defective fuel pump fuse be. Then check all plug connections, fuses and relays which release the current after the ignition is switched on.
Here you will find a multi-meter which we did not use in the photo above, but which we later switched to, as this can be used especially for low voltage ranges:
- Double protection & easy to use: Red soft protective cover, effectively improves the...
- The resistance is moderate: the gear position is accurate, the hole position is clear, and the color...
- Stable measurement: The back has an expandable holder and a pen holder that makes it easy to...
- Security protection: UT890D+ has a live function to differentiate between...
Pressure loss in fuel pump
Method 1: Pressure measurement with measuring device:
The test runs most smoothly if you have a Pressure gauge with the corresponding set to the fuel system. Install the pressure gauge in the fuel system and start the car. The The best position for installation is directly in front of the high-pressure pump in the engine compartment or on the Fuel lines between filter and fuel pump on the underbody. The pressure should correspond to the manufacturer's specifications, the usually between 3 -5 bar lie.
- 【FUNCTION】 The gasoline pressure gauge tests the pressure difference across the injector and displays...
- 【DOUBLE DIAL GAUGE】 The fuel pressure gauge has a 3.5 inch (9 cm) scale with a double...
- 【SEVERAL ADAPTERS】 The gasoline pressure gauge contains several fittings and hoses that can be...
- 【NORMAL PRESSURE】 Symptoms of low fuel pump pressure include...
Method 2: Checking the flow rate in a container:
As an alternative to the method with the pressure gauge, you can use the Check delivery rate.
The pump should pump approx. 0.375 l of fuel in 15 seconds. can deliver. To do this, you plug in the fuel filter, disconnect the supply line and feed it into a measuring container. Then switch on the ignition (in some cars also the starter motor) and let the Pump the pump for 15 seconds.
If the subsidized Amount of fuel much less than 0.375 l, you can use a Pressure loss go out. If the tank lines up to the fuel filter are intact, the fuel pump is defective and must be replaced.
Fuel pump costs
The costs for a New fuel pump (pump only) costs approx. 15 - 25€. Do you need the Replacing the entire conveyor unit costs between approx. 150 - 550€. We therefore recommend that you remove the delivery unit and only replace the fuel pump. However, it is more convenient to replace the entire delivery unit.
3) Defective rail sensor (fuel pressure sensor)
The fuel pressure sensor, also known as the rail sensor, is located in the Engine compartment directly at the start of the rail. The rail is a component of the common rail system which is used in most cars built from around 2000 onwards. The Sensor detects the high fuel pressure entering the rail for injection. If it delivers incorrect values, the engine begins to stutter or does not start at all.
Measurement of the rail pressure sensor
You can find out whether the rail pressure sensor is defective by checking the plug measures the pins. When starting the engine, you must switch between the individual pins and the ground (1st pin) each:
Costs rail pressure sensor
If this is not the case and the car continues to jerk when accelerating, the rail pressure sensor should be replaced. This usually costs around €35-75 and is quick and easy to install. In some cars, however, this is difficult to access, so the Effort strongly dependent on vehicle model from.
4) Defective high-pressure fuel pump
In addition to the fuel feed pump already discussed, which is located in the tank, there is also a high-pressure pump in the engine compartment. The high-pressure pump is used to High pressure is generated for injection into the common rail systemwhich up to 2500 bar can go. The car jerks when accelerating if the required high pressure (according to the manufacturer's specifications) cannot be achieved. It is not so easy to detect a defect in the high-pressure fuel pump. You are only on the safe side here with a Diagnostic device. The diagnosis can tell you whether a There is a pressure drop in the HP pump or is still communicating with it at all (power supply interrupted).
In contrast to the feed pump, you can Do not measure with the usual pressure gauge. From the high-pressure pump onwards, pressures in the 4-digit range prevail and the fuel is no longer transported in tubes. This only makes it more difficult to connect a measuring device. The fact is that you also need a High-pressure measuring device which in turn is in a different price range.
However, there is a way to find out whether the High-pressure fuel pump throws chips. This is done by pressing the Open the fuel filter and run a magnet over it. If metal shavings collect on the magnet, you can assume that they come from the HP pump.
High-pressure fuel pump costs
If the pump is actually throwing chips, you should replace it immediately and replace the Have the fuel system cleaned.
The cost of a new high-pressure fuel pump is depending on car model and manufacturer approx. 450€ - 950€.
5) Fuel lines leaking
If the fuel system components mentioned were not the cause of the stuttering, you should next check the fuel lines. Typical places where "leaks" can occur are:
If pressure or diesel or gasoline escapes at the points mentioned in the supply line, first check the seals. These may be outdated and therefore not seal completely.
6) Defective spark plugs or ignition coils
This problem mainly concerns Gasoline engine. In the combustion process of a petrol engine, the spark plugs work continuously (ignition of the petrol-air mixture). The engine can therefore start to stall if a spark plug fails.
The check is carried out with a Multimeter which is set to [kOhm]. should be. Remove the engine cover and disconnect the ignition coils. Then unscrew the spark plugs (make sure the engine is not hot → risk of breakage!) and measure the Resistance at the spark plug.
Spark plug measurement
Hold one measuring tip of the multimeter to the thread and the other to the center electrode of the spark plug. If the resistance is above approx. 6 kOhm the spark plug is defective and must be replaced. Repeat this process for all spark plugs (the number of plugs depends on the number of cylinders in the engine). The costs for new spark plugs usually amount to 5-10€ per piece.
Measurement ignition coils
Check the unplugged ignition coil in the same way as for the spark plug, measures the resistance. You should connect a resistor directly to the plug (primary winding). measure between 0.3 - 1 Ohm. Higher resistance values indicate a fault in the ignition coil.
7) Mass air flow sensor defective (LMM)
A mass air flow sensor that delivers incorrect values can severely impair the combustion process and cause the car to jerk when accelerating. The mass air flow sensor measures the intake air and is located directly after the air filter on the intake manifold.
The air mass meter can be checked for 2 species The first method requires less effort and is a better solution.
Method 1: Check mass air flow meter with multimeter
In this method measure the power supply and the signal voltage at the connector pins.
To do this, create a Measuring tip on the ground pin (black cable) and with the Then you go through the individual pins. You can find out which pins are which by trial and error or you can get a circuit diagram of your model on the Internet.
For example: Many BMW vehicles have this pin assignment on the mass air flow sensor:
- The display and MCU are mounted on the same board (mainboard) to enable the use of...
- The rotary encoder has been added, making parameter setting quicker and easier
- Quimat Q15001 Oscilloscope is an assembled ready machine with shell.NOT DIY part, it can be used for...
- Detailed operating instructions, troubleshooting guide and wiring diagram are also included....
Method 2: Test drive with LMM disconnected
This method is a Function test of the air mass meter. Unplug the LMM and start the engine. If the car stops jerking during the test drive with the mass air flow sensor disconnected, the cause of the fault has been found. This method is also the The only thing that can say about 100% is that the sensor is defective.
Cost of mass air flow meter (LMM)
A New mass air flow sensor costs between 70-110€ depending on car model and manufacturer and is very easy to replace. However, it should be noted that the measurement cannot tell you 100% whether the LMM is intact. For example, the sensor may be contaminated and therefore provide incorrect values. If the problem no longer occurs with the LMM unplugged, this is a 100% buy signal.
*Favorable offers for Mass air flow meter can be found here:
8) Compression pressure of the cylinders too low
If the compression of one cylinder is too low, this means that the Cylinder leaking is. This results in a Loss of power and the car jerks when accelerating or driving.
To check the compression pressure per cylinder, you need a measuring device: a so-called Pressure gaugewhich can display the pressure in [bar]. You can carry out the measurement with the same measuring device as for the fuel pressure, but you will need special adapters for this.
To measure the compression pressure, you must first unscrew the spark plugs (glow plugs on diesel). Then select the psuitable adapter for your vehicle from. In total there are approx. 5 adapter types that could be used for your vehicle.
Measuring compression pressure
Once you have found the right adapter, screw it (very) tightly onto the pressure gauge. Now mount the pressure gauge in the spark plug well and let the engine turn for approx. 4 seconds.
Then read the values from the measuring device. Here it is advisable to compare the measurement results with to compare manufacturer values. You can find these in your workshop book or on the Internet. The rule of thumb is that a deviation of approx. 15% from the manufacturer's specifications indicates a leaking cylinder and is therefore considered a defect.
Typical and healthy pressure values are:
- Can be used universally thanks to numerous adapters (glow plugs and injection nozzle attachments)
- Can be used for almost all vehicle types, e.g. BMW, Mercedes-Benz, Ford, VW, Toyota, Renault, Volvo, Mazda, PSA, Opel, Nissan, Vauxhall
- 1 pressure gauge 0 - 70 bar, tolerance +/- 5 %
- 1 contra-angle handpiece
Cost of cylinder head gasket
If the measured pressure values deviate significantly, this can have various causes. One of the most common causes is a Defective cylinder head gasket. This is not too expensive with approx. 70-100€, however, the Enormous amount of work. A comprehensive understanding of engine assembly is required to replace the CCD. Changing the cylinder head gasket in the workshop usually costs around €1000, depending on the vehicle model. Defective cylinder head gaskets or outdated cylinders that leak are not uncommon. You should therefore look out for signs when buying a used car. Our Checklist for buying a used car can help you save a lot of money in advance!
9) Car jerks-AGR valve coked up
To know whether the clogged EGR valve is the actual main cause, you must first check the Function of the EGR valve know. If the EGR valve in stuck in an open stateexhaust gases continuously enter the intake tract. As a result, the car starts to jerk and causes a loss of power.
Is your car still jerking when accelerating? Then we recommend the Remove and clean the EGR valve. Once the EGR valve has been cleaned, you can also Check the function of the EGR valve.
A defective EGR valve (with cooler) can cost up to approx. 750€as the EGR cooler is made from a special metal material.
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