Vehicle Losing Power: Reasons And Inspection (Case Analysis)



To check a car's performance, we can test its maneuverability and steering system, but the engine is the most important thing we should know well. As the core of the car, the engine is the key factor in the safety driving. However, in the daily running, the vehicle encounters a lack of power from time to time.


1. Common reasons

2. Inspection

    2.1 Ignition timing and ignition energy

    2.2 Ignition parts and ignition advance angle

    2.3 Cylinder pressure

    2.4 Camshafts, cylinder head, piston

    2.5 Air-fuel ratio

    2.6 Fuel pressure regulator

    2.7 Exhaust gas recirculation system

3. Case Analysis

    3.1 Diagnosis and troubleshooting

    3.2 Conclusion


1. Common reasons


●  Bad fuel pipe or electrical circuit


Bad fuel pipe and obstructed air intake make the air-fuel mixture too thin or rich. As a result, the ignition timing will be too late. The contact gap will be too small or too large. The exhaust pipe may leak. The ignition cable can't work properly. The distributor cam breaks, and there are excessive carbon deposits in spark plugs.


●  Insufficient cylinder pressure


The cylinder gasket does not seal. The valve seat ring is ablated and gets off, and it's not sealed. The valve spring is too soft. It doesn't work well. The gap between the piston and the cylinder is too large.


●  Abnormal gas distribution phase


●  Individual cylinder doesn't work


●  Too hot engine


The water pump and thermostat don't work well. The belt slips. There is too much scale in the cooling system.


●  Chassis failure


The clutch and brake aren't well-performed. The tire pressure is low.




2. Inspection


To inspect and repair the EFI engine, we should take care of the following aspects.


2.1 Ignition timing and ignition energy


The common reason for poor engine acceleration in ignition systems is incorrect ignition timing or insufficient ignition power.


The ignition timing can be tested by stepping on the accelerator and listening to the sound of the engine running. We can know how early or late the ignition is. It can also be tested by the ignition advance tester, which has a standard angle at idle.


The ignition advance angle increases when accelerating. If it is too large or too small, it causes poor engine acceleration.


The defective ignition parts lead to the problem of ignition energy. Check the resistance of the cylinder line and distributor, the gap and condition of the spark plug, and the distributor's conduction. Check whether the ignition coil and igniter are hot.


If necessary, the oscilloscope can be used to check the waveforms of primary and secondary coils. In this way, we can know where the problem is.


2.2 Ignition parts and ignition advance angle


The ignition energy of the spark plug and the ignition advance angle is particularly critical to the engine performance. If the ignition energy drops and the ignition timing is too late, the adequate pressure of the engine will be reduced. The output power will drop, and the response will be slow when accelerating.


Specifically, we should check whether the ignition timing is correct, whether the type of the spark plug is correct, whether the spark plug gap is suitable, whether the resistance of the ignition cable is in the specified range, whether the resistance of the ignition coil is correct, whether the battery voltage is suitable, etc.




If the ignition timing is too late, you should also check for problems with the crankshaft position sensor, mass air flow sensor, knock sensor, coolant temperature sensor and engine control module. If problems are found, then repair or replace the appropriate components.


2.3 Cylinder pressure


First of all, see if the engine can work. Check whether the air filter is blocked and determine whether an individual cylinder does not work. If so, find out the reason and location.


If the cylinder pressure is not in the range of 800-1300 Kpa or the differential pressure exceeds the standard, check whether the spark plug is tightened. Also, check the timing, cylinder gasket, timing belt position, piston ring sealing, valve sealing, etc.


At the end of the compression stroke, the cylinder pressure on the combustion of the mixture has a significant impact. If the pressure in the cylinder at the end of compression is small, the combustion rate of the mixture is low. 


The smaller the engine's effective power, the less conducive to the performance of engine power. These things lead to poor engine power and acceleration.


The cylinder compression pressure is caused by the too large gap between the cylinder and the piston. The cylinder gasket seal is terrible. The valve leaks. The gas phase is not correct. The resistance of the air intake is too large.


2.4 Camshafts, cylinder head, piston


The engine's camshaft mainly controls the air distribution phase and drives the signal disc of the camshaft position sensor. It can correctly respond to the rotation angle of the camshaft.


If the camshaft is misaligned during installation, or if the camshaft drive wheel is loose from the camshaft, it leads to misalignment and affects the engine performance.


2.5 Air-fuel ratio


If the fuel pressure is low, use the oil pressure gauge to test the oil pressure of the fuel system. Disconnect the fuel circuit between the filter and the fuel distribution tube. Connect the oil pressure gauge, and tighten the pipe joint.


Use the starter to measure the high and low oil pressure. If the oil pressure is not normal, it is a problem with the fuel circuit. The fuel pump, filter, accumulator, fuel pressure regulator and injector must be checked.




2.6 Fuel pressure regulator


We can increase the throttle or unplug the vacuum line of the fuel pressure regulator to see if the oil pressure increases by 50Kpa.


2.7 Exhaust gas recirculation system


If the exhaust gas recirculation control system is still in circulation during engine acceleration or heavy load operation, it makes the content of exhaust gas in the cylinder too large and the content of the air-fuel mixture to be reduced.


The combustion speed of the mixture will be reduced. The engine power will be reduced. The acceleration will be sluggish.


3. Case Analysis


Here is a Buick with 4 cylinders and EFI engine. The power and the acceleration is weak.


3.1 Diagnosis and troubleshooting


When the car was sent to repair, the idle speed was normal. When it was in the P position, the acceleration was weak. When it was in the D position, the acceleration was weak. It could not reach the high speed. 


During the previous maintenance, the owner cleaned all the injectors. He replaced the fuel filter, fuel pump and fuel pressure regulator. However, the problem was still not solved. Then, he replaced all spark plugs, ignition cables and ignition coils. The issues still existed.


The car has no trouble codes. Use SCANNER-MT2500 to detect the data flow. The sensor data is normal. Open the air conditioning at idling, the idle speed rises, indicating that the idle speed control system is normal.


Use SUN500 to test each cylinder. They are normal. The dynamic waveform of ignition is also good. The exhaust emissions data and CO content are low. The air-fuel ratio is 19.5:1 or more. The mixture is obviously lean. It may be caused by insufficient fuel injection.


Remove and re-clean each cylinder injector, idle channel and throttle body. Restart the car. The power is still insufficient. Check if the three-way catalytic converter is normal.


In further inspection, the fuel pressure is slightly low. The fuel filter, fuel pump and fuel pressure regulator have been replaced. 


Check if impurities in the fuel tank have blocked the pump inlet or tank cover, resulting in the formation of a vacuum in the studio oil tank so that the fuel pump can't work properly.


First, replace a fuel tank cover of the same model. Drive the car on the road. The power is still insufficient, so remove the fuel tank and find a lot of impurities in the tank. However, the fuel pump screen is not all plugged. Clean the tank and retry the fault.


Re-test the data flow of the sensors. The water temperature sensor and intake manifold pressure sensor work well. The fuel pressure is insufficient. The culprit is the fuel pipe.




Check whether the fuel filter is blocked again. Remove and replace the filter. The filter was installed backward. Re-install the fuel filter in the correct direction. Drive the car on the road. The power has no problem. The acceleration is good.


After the road test, the exhaust emission data is normal when re-checked with SUN500. The air-fuel ratio becomes normal. The exhaust emission data is good. Everything is all right.


3.2 Conclusion


The fuel filter on this car has essentially the same port at both ends. It was initially installed incorrectly and not carefully observed during the repair.

Updated Products

Delcoribo Motor Products Co., Ltd.

Economic Development Zone, Jinhua, Zhejiang, China

Tel: +86-579-8275-8180

[email protected]

Subscribe to Our Newsletter

Home|Terms of Use|Privacy Policy|© 2022 delcoribo.com, Inc. or its affiliates.
  • Follow Us

We use cookies to improve your browsing experience. By using this website, you consent to the use of cookies. More
Yes
No

Top