Why Car Won’t Accelerate Past 40? And How To Fix - Perkins Automotive Service (2023)

Have you ever been driving along the highway and suddenly your car won’t accelerate past 40 mph? It can be a terrifying experience, especially if you don’t know what is causing it. If this has happened to you, there are several potential causes that could explain why your car won’t accelerate past 40 mph. From engine problems to transmission issues, understanding what might be behind this issue can help you get back on the road safely and quickly.

To solve this problem, it’s important to first determine what exactly is causing your vehicle not to accelerate beyond 40 mph. This could mean examining things like spark plugs, fuel filters or air intake systems. It may also involve taking a look at the catalytic converter or other engine components such as valves and pistons. Malfunctioning sensors in the transmission system can also cause acceleration problems so these should be checked too. In this article we’ll provide you some common problems, how to fix it and tips to keep your car accelerate good as new.

Table of Contents

Clogged or dirty air filter

The reason why a clogged or dirty air filter can cause a car not to accelerate past 40 is that it restricts the amount of air getting into the engine. A lack of oxygen will prevent your engine from correctly burning fuel and consequently, reduce performance. To diagnose this problem yourself, check your air filter for dirt or any blockages, replace if necessary and retest.

How to fix

How to fix Clogged or Dirty Air Filter Making Car Accelerate Won’t Past 40:

1. Check your air filter for dirt and blockages.

2. Replace the air filter if it is clogged or dirty.

3. Retest the car after you have replaced the air filter to ensure the problem has been fixed.

4. Additionally, inspect all of your hoses and belts to ensure they are in proper working order.

Fuel delivery issues

Fuel delivery issues can cause a car to not accelerate past 40 because there isn’t enough fuel being delivered for the engine to function properly. The most common symptom of this issue is hesitation when accelerating, as well as the inability to reach higher speeds. To diagnose this issue by yourself, look for any signs of fuel leaking from lines or tanks, check your spark plugs for wear and tear or evidence of fouling, and test your fuel pressure with a gauge. In addition, make sure all components related to fuel delivery system are functioning correctly (i.e., filters, injectors).

How to fix

How to fix Fuel delivery issues that make a car not accelerate past 40:

1. Check for any signs of fuel leaking from lines or tanks.

2. Inspect spark plugs for wear and tear or evidence of fouling.

3. Test fuel pressure with a gauge to ensure it is within the required range for your engine type.

4. Inspect all components related to the fuel delivery system, such as filters and injectors, to identify any malfunctioning parts which may be causing the issue with acceleration.

5. If necessary, replace faulty components or refuel to add more gasoline/petrol in order to attain optimal performance levels again while accelerating past 40 mph (64 km/h).

Malfunctioning throttle position sensor

A malfunctioning throttle position sensor (TPS) can cause a number of issues in your vehicle, including a lack of power or acceleration past 40 mph. The TPS is responsible for monitoring the position of the throttle and sending that information to the engine control unit (ECU). If the TPS isn’t working properly, it can lead to inaccurate readings and result in reduced engine performance. To diagnose this issue by yourself, you should first check all electrical connections related to the TPS and make sure they are securely connected. Then if possible test resistance levels at different throttle positions. If these levels are not within manufacturer specifications then it may be due to an internal fault in the sensor itself. Lastly, use an OBD-II scanner to further verify that any errors codes associated with a malfunctioning TPS have been correctly identified and addressed.

How to fix

To fix a Malfunctioning Throttle Position Sensor that is causing your car to not accelerate past 40 mph, you will need to:

1. Check all electrical connections related to the TPS and make sure they are securely connected.

2. Test resistance levels at different throttle positions and compare them with manufacturer specifications.

3. Use an OBD-II scanner to check for any error codes associated with a malfunctioning TPS and address them accordingly.

4. If necessary, replace or repair the sensor in order for it to function properly again, thus allowing your car to accelerate faster than 40 mph again.

Transmission issues

Transmission problems can make a car not accelerate past 40 because the transmission is not shifting correctly, which can cause a loss of power. To diagnose this issue, you need to check for any error codes in the vehicle’s onboard computer and then inspect all the transmission fluid lines and filters for signs of contamination. Additionally, you should check that all electrical connections are secure and gaps between components are properly sealed.

How to fix

How to Fix Transmission Issues Making a Car Not Accelerate Past 40:

1. Check for any error codes in the vehicle’s onboard computer.

2. Inspect all transmission fluid lines and filters for signs of contamination.

3. Check that all electrical connections are secure and gaps between components are properly sealed.

4. If necessary, replace faulty or damaged parts of the transmission system such as clutch, CV joint, bell housing, catalytic converter, etc..

Exhaust blockage

Exhaust blockage can make a car unable to accelerate past 40 mph due to restricted airflow in the exhaust system. This restriction can be caused by a build-up of carbon deposits, a broken or damaged air intake, or even an obstruction in catalytic converter. To diagnose problem on your own, start by inspecting all parts of your exhaust system for any signs of visible damage that could cause the blockage. Then check for any possible leaks or holes in the air intake tube and inspect the catalytic converter for any clogs due to dirt or debris buildup. Finally, examine your spark plugs and ignition coils for worn out components that may need replacing.

How to fix

Here is a step-by-step guide to fixing exhaust blockage, making your car able to accelerate past 40 mph:

1. Inspect all parts of the exhaust system for visible signs of damage that may be causing a restriction on airflow.

2. Check for any possible leaks or holes in the air intake tube, and inspect the catalytic converter for any clogs due to dirt or debris buildup.

3. Examine the spark plugs and ignition coils for worn out components that may need replacing.

4. Clean out any carbon deposits from within the exhaust system using special cleaning solutions available at auto stores, as well as by physically scraping them off with an automotive tool such as a wire brush or vacuum cleaner with crevice tool attachment.

5. Repair any holes found in air intake tube using sealant designed specifically for automotive use and replace broken pieces if necessary; replace catalytic converter if it has gone bad due to excessive buildup of dirt/debris .

6 Change out spark plugs and ignition coils where applicable; reset error codes present in vehicle’s computer if needed after repairs have been made (this process will vary depending on make/model).

Ignition system problems

Ignition system problems can make a car won’t accelerate past 40 mph due to a lack of spark or fuel. Common causes include faulty spark plugs, ignition coils, bad wiring, or clogged fuel injectors. To diagnose these issues by yourself, first check all the spark plugs and replace them if necessary. Next, inspect the ignition coils. Finally, check the wiring and fuelling systems for any blockages or bad connections that could be inhibiting performance.

How to fix

Solution for Ignition System Problems that Make a Car Won’t Accelerate Past 40 mph:

1. Check all the spark plugs and replace them if necessary.

2. Inspect the ignition coil and test for any errors.

3. Check wiring connections for loose connections or damage to terminals like corrosion, which can inhibit electrical current flow from the battery to the starter motor and its components, like spark plugs and fuel injectors.

4. Examine fuel system for clogged injectors that would limit upper-RPM performance by reducing fuel delivery at higher RPMs such as over 40 mph; this could be caused by bad gas, deposits inside the injector port holes or problems with valves not staying open long enough when activated by engine control unit (ECU).

5. Finally, if all else fails consider replacing your ECU which should provide full power delivery at higher RPMs once again as it processes sensor data from various parts of engine accurately based on preprogrammed parameters set in memory chips inside ECU itself!

Limp mode

Limp mode is a safety feature of your car’s engine that kicks in when it detects some kind of problem. When this happens, the car will not be able to accelerate past 40 mph due to reduced power output. Diagnosing limp mode by yourself requires you to check certain parts in your engine for faults. You should begin by examining spark plugs, the fuel filter and pressure regulator, the mass airflow sensor and any vacuum hoses or connections. Additionally, check for O2 sensor malfunction or electrical errors that could be causing this issue as well.

How to fix

How to Fix Limp Mode and Make Your Car Accelerate Past 40 mph:

1. Check spark plugs for any faults or malfunctioning

2. Inspect Fuel filter and pressure regulator if any problems are detected

3. Check Mass airflow sensor and vacuum hoses or connections for possible issues

4. Look for O2 sensor malfunctions and electrical errors that could be causing the issue

5. Have a professional mechanic properly diagnose the problem to ensure it is fixed correctly

6. Replace any faulty components in the engine as needed to restore normal functioning of car

7. Once all repairs have been made, reset limp mode by disconnecting battery for 10 minutes then reconnecting it back again

Damaged or worn engine components

Damaged or worn engine components can make a car not accelerate past 40 mph because they reduce the amount of power that an engine can produce. Worn spark plugs, bad fuel injectors, faulty oxygen sensors, and clogged catalytic converters can all cause a car to lose power and may prevent it from accelerating beyond 40 mph. To diagnose these problems by yourself, you need to inspect the different parts of your engine using a scanner tool. You should also check the air intake and exhaust systems for any blockages that could be impairing performance.

How to fix

How to Fix Damaged or worn engine components and Make Your Car Accelerate Past 40 mph:

1. Check the spark plugs and replace them if they are worn or damaged.

2. Inspect the fuel injectors and clean or replace them if necessary.

3. Test the oxygen sensors for proper function and replace if needed.

4. Check for clogged catalytic converters, which can reduce engine power, and clean or replace as needed.

5 .Inspect the air intake system to make sure there is no blockage that could be impeding performance, such as from debris in the air filter or a cracked vacuum hose that is allowing unmetered air into the engine bay.

6 .Examine your exhaust system for any blockages, such as rust in your muffler that may prevent exhaust gases from escaping easily out of your car’s tailpipe, reducing engine power output further still.

7 .Finally, have your engine tuned to ensure that all of its systems are running optimally.

Faulty mass airflow sensor (MAF)

A faulty mass airflow sensor (MAF) can cause a car to not accelerate past 40 mph as the engine cannot get enough fuel. This is because the MAF measures the amount of air entering the engine, and if it is giving an inaccurate reading, it restricts or blocks fuel from entering. To diagnose this issue yourself, you should check for any damaged wiring or disconnected wires that could be causing interference with MAF readings. You should also check your air filter for blockage and debris which can limit air flow into the engine. Finally, testthe voltage output of your MAF sensor while driving to ensure it is within a reasonable range. If any of these steps show signs of failure or malfunctioning parts, they will need to be replaced in order to fix the issue with your car accelerating past 40 mph.

How to fix

How to Fix Faulty Mass Airflow Sensor (MAF) That Makes a Car Not Accelerate Past 40 MPH:

1. Check for any damaged wiring or disconnected wires that could be causing interference with MAF readings.

2. Check your air filter for blockage and debris which can limit air flow into the engine.

3. Test the voltage output of your MAF sensor while driving to ensure it is within a reasonable range.

4. Replace any failing or malfunctioning parts in order to fix the issue with your car not accelerating past 40 mph.

5. Check the air intake system for any signs of leakage which can throw off MAF readings.

6. Inspect the throttle body and its linkage to ensure they are clean and in working order.

7. Clean or replace the mass airflow sensor (MAF) if necessary, as this could be causing inaccurate measurement of air intake.

8. Check the fuel pressure and make sure it is within the manufacturer’s specifications.

9. Repair any broken vacuum hoses, as these can cause air to enter the engine incorrectly and lead to incorrect MAF readings.

10. Finally, reset your car’s computer system by disconnecting the battery for 10 minutes and then reconnecting it. This will reset the computer to its original settings and help fix any issues related to a faulty MAF sensor.

Vacuum leaks

A vacuum leak can cause a car to not accelerate past 40 mph because it allows unmetered air into the engine. This can affect the performance of the engine and cause misfires, loss of power, or hesitation – all of which will prevent acceleration past 40 mph. To diagnose a vacuum leak by yourself, you need to visually inspect all hoses and fittings for cracks or holes and check them with a vacuum gauge. You also want to make sure that there are no loose intake manifold bolts that may be allowing air leaks. If all appears okay then you should try spraying carburetor cleaner around any suspicious areas while listening for changes in engine idle speed as this could indicate an area where air is leaking in. Finally, you should replace any worn or damaged hoses or fittings with new ones before running the car again.

How to fix

How to Fix Vacuum Leaks That Make a Car Not Accelerate Past 40 mph:

1. Visually inspect all hoses and fittings for cracks or holes and use a vacuum gauge to check if air is leaking.

2. Check for loose intake manifold bolts that may be allowing air leaks.

3. Spray carburetor cleaner around any suspicious areas and listen for changes in engine idle speed as this could indicate an area where air is leaking in.

4. Replace any worn or damaged hoses or fittings with new ones before running the car again.

5. If the issue still persists, it may be a larger issue such as an electronic/sensor problem or clogged fuel injectors and will require further investigation.

Conclusion

In conclusion, if your car is not accelerating past 40 mph it could be caused by a faulty MAF sensor or vacuum leaks. To fix the issue with the MAF sensor you should check for any damaged wiring and debris that can limit air flow into the engine, test its voltage output while driving to ensure it’s within range and replace any malfunctioning parts. A vacuum leak can be diagnosed by inspecting all hoses and fittings for cracks or holes, checking loose intake manifold bolts, spraying carburetor cleaner around suspicious areas and replacing worn/damaged parts. If these steps don’t resolve the problem then further investigation such as an electronic/sensor problem may need to be looked at.

Read more: Why Car Engine Loud When Accelerating? And How To Fix It

FAQs

What could cause a car not to accelerate past 40 mph?

A number of things can cause a car not to accelerate past 40 mph, including an issue with the mass airflow sensor (MAF), vacuum leaks, clogged fuel injectors, or another electronic/sensor problem.

How do I diagnose an issue with the MAF sensor?

To diagnose an issue with the MAF sensor you should check for any damaged wiring and debris that can limit air flow into the engine, test its voltage output while driving to ensure it’s within range, and replace any malfunctioning parts.

How do I check for a vacuum leak in my car?

To check for a vacuum leak in your car you need to visually inspect all hoses and fittings for cracks and holes; use a vacuum gauge to see if air is escaping from them; spray carburetor cleaner around suspicious areas listening for changes in engine idle speed; and replace worn/damaged hoses or fittings before running the car again.

What should I do if these steps still don’t fix my acceleration issues?

If these steps do not resolve your acceleration issues, then you may have a larger issue such as an electronic/sensor problem or clogged fuel injectors and will need to take it to a professional mechanic for further investigation.

What should I do to prevent further acceleration issues?

To prevent further acceleration issues, you should regularly check your car for any damaged hoses or fittings and replace them if necessary. Additionally, it is important to keep an eye on the MAF sensor and ensure that its voltage output is within range. Finally, you should also regularly check your fuel injectors for any blockage that may be preventing your car from running smoothly.

Why Car Won’t Accelerate Past 40? And How To Fix - Perkins Automotive Service (1)

Freddy S. Simmons

I am an experienced author and expert in the automotive industry. With over 20 years of experience in the field, I have a wealth of knowledge and expertise to share with his readers. I am passionate about helping car owners stay informed and empowered when it comes to taking care of their vehicles. Through my website, I aim to provide practical advice and solutions for common car-related problems, as well as insightful reviews of new car products and technologies.

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