One of the problems faced by the modern car owners is the engine RPM drop when using automatic gearbox. This failure consists in a sudden short-time engine drop when changing gears. For a second, you might think that you've run out of fuel. This kind of problem usually shows up in automatic gearboxes after 200,000+ kilometers. But there are some exceptions, when even 'younger' components may fail.
WHAT CAUSES ENGINE RPM DROP WHEN CHANGING GEARS
An automatic gearbox is a complex technical unit, each component of which performs its specific function. The whole transmission health depends on the functional accuracy of each and every assembly. The engine RPM drop when shifting automatic gearbox can be caused by many reasons, which may or may not be connected with the gearbox itself.
To find out the exact cause of the engine RPM drop when changing gears on a VAZ car or any other car, a professional diagnostic procedure is required. This procedure is performed in workshops that specialize in automatic gearbox repair. Even better if the workshop has a full-time expert that specializes in automatic gearboxes of your type (i.e. brand). Any efforts to repair the transmission yourself can only make things worse.
In some cases, the engine RPM drop when shifting to second or third gear have to do with electrical problems. The fault can be caused by poor contact or a broken wire. In this case, the electronic control unit (ECU) signal can't reach the gearbox. Also, one of the spark plug wires can be faulty.
If the problem is in the solenoid wires, then the engine RPM drop when shifting automatic gearbox is explained by the abnormalities of the liquid traffic mode. Clutches or other components of the gearbox can be damaged. To mitigate negative effects of the fault, it is advisable to change the transmission oil and add the AT tribotechnical compound by Atomium to it. The compound reverses the small surface damage of the clutches and planetary gears and improves performance of the friction pairs.
Let's take Russian cars as an example. Sometimes the engine RPM drop when shifting automatic gearbox has to do with ECU firmware. This failure often shows up on VAZ cars with the firmware I203EK34, A203EK34, (Lada 2111 with 1,500 cm3 8-valve engine), I205DO54 A205DO54, A205DO57 (Lada 2112 with 1,600 cm3 16-valve engine).
Adjusting the on-board computer settings eliminates the problem. Modification of the firmware calibration must only be performed by an experienced technician with a background in this area. Unprofessional intervention may cause more harm than benefit to the transmission.
The engine RPM drop when changing gears is often caused by a failed throttle position sensor (TPS). When in use, the cone of the TPS accumulates soot that prevents the correct rod movement. If a TPS works abnormally, the air-fuel mixture will not meet the requirements.
To eliminate the engine RPM drop when changing gears on VAZ cars or other cars, clean the throttle. If it did not have the intended effect, the throttle position sensor replacement is required.
IGNITION MODULE IS NOT OK
Sometimes the engine RPM drop when shifting automatic gearbox is caused by incorrect ignition timing. In case of the premature ignition, the air-fuel mixture is ignited when the piston is still moving upwards. Expanded gases impede movement of the piston and the whole crankshaft. In this situation, the fuel consumption is useless. In case of the delayed ignition, the air-fuel mixture is ignited when the piston has already passed the TDC and is moving downwards. The gases are being exhausted without any useful effect.
It's quite easy to set proper ignition timing. If you are experienced, you may try to do it yourself on a Russian car. Other modern cars are more sophisticated, so it would be better to adjust the settings at a car service.
FAILED FUEL PUMP
This is another reason of the engine RPM drop when shifting automatic gearbox. It's simple. The engine needs more fuel during the upshift but the fuel pump cannot provide required flow rate, for some reason. Underfilling and overfilling are equally bad for driving performance. In the former case, the fuel is not enough; in the latter case, the fuel is being poorly dispersed and incompletely combusted in the cylinder.
A common issue that leads to the engine RPM drop when upshifting is the clogging of the fuel pump filter. If cleaning the strainer didn't help to eliminate the RPM drop, replace the fuel pump.
FUEL MANAGEMENT UNIT (FMU) DEFECTS
If FMU is in a faulty condition, the engine RPM drop when changing gears is caused by mainly the same reasons as with a failed fuel pump. Increased load requires more fuel but failed FMU cannot provide the required pressure in nozzles.
In FMU, the membrane often gets out of order. You can detect it visually as there will be fuel leaks on the FMU. If the membrane's integrity is compromised, engine RPM drop when shifting automatic gearbox will definitely be a problem. In this case, replace the membrane or the FMU as an assembly.
HYDRAULIC UNIT CHANNEL CLOGGING
This failure leads to delayed gear shifting. For some time the gearbox is operating simultaneously in two gears, which causes the engine RPM drop when shifting automatic gearbox. In this case, clean the hydraulic unit and check the solenoids.
If the case is not too severe, you will fix it with small losses. Change the ATF liquid and add the AT tribotechnical compound by Atomium to it. Changing the oil will help remove dirt from the 'hydraulic brain' channels; and the nanoparticle-based compound will optimize the performance of the oil pump, as well as rubbing and friction pairs.
INSTEAD OF A CONCLUSION
The table lists most common causes and remedies of the engine RPM drop when shifting automatic gearbox. Some procedures can only be performed at workshops. They require skills and special equipment.
ENGINE RPM DROP CAUSES
Replace the wires, change oil and add AT compound by Atomium to compensate the gearbox damage.
Spark plug wires broken
Replace the wires, check the spark plugs, replace if needed.
Errors in ECU firmware
Calibrate the on-board computer settings at a workshop.
Clean the throttle; replace the throttle position sensor if needed.
Wrong ignition module adjustment
Failed fuel pump or FMU
Replace the fuel pump or FMU.
Hydraulic Unit channel clogging
Poor quality fuel