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Engine Hesitates During Acceleration But Gives No Trouble Codes

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

To prevent engine hesitation and other performance issues, modern engines use a number of sensors to help locate faults within a number of systems, especially those impacting emissions.

Often, a component or system that is not working properly will trigger the check engine light (CEL) and a corresponding diagnostic trouble code (DTC). However, this doesn't always happen. It all depends on the configuration programmed into the computer to signal the fault.

When there is a problem but no trouble code, that makes it harder to locate the problem. And this includes those elusive problems that can lead to hesitation.

The next sections will help you concentrate on those components or systems that may be causing trouble but may not trigger a trouble code. Sometimes there is no trouble code because the particular fault is not severe yet, according to the computer algorithm in your particular model. Or the fault has occurred in a part of the system not monitored, like a vacuum hose for example.

It's recommended to have the vehicle repair manual for your particular model when diagnosing engine or other system problems. If you don't have this manual yet, you can buy a relatively inexpensive copy from Amazon. Haynes manuals include step-by-step procedures for many maintenance, troubleshooting, diagnostic, and parts replacement jobs, and electrical diagrams for many repair projects. So you can actually recoup your small investment soon.

Index

I. Faulty Manifold Absolute Pressure (MAP) Sensor

II. Spark Plugs and Spark Plug Wire Problems

III. Air Leaks

IV. Mass Air Flow Sensor (MAF) Issues

V. Fuel Injector Issues

VI. Fuel System Problems

VII. Exhaust Gas Recirculation (EGR) Valve Problems

VIII. Faulty Throttle Position (TP) Sensor

IX. Throttle Plate Buildup

VIDEO: Cleaning the Throttle Plate and Bore

X. More Hesitation Diagnostic Help

engine-hesitates-during-acceleration-no-trouble-codes

I. Faulty Manifold Absolute Pressure (MAP) Sensor

The engine control module (ECM, the engine's computer) uses the MAP sensor to detect engine load and add the proper amount of fuel as needed. The MAP sensor measures the load using a vacuum hose connected to the intake manifold.

However, a cracked hose that creates a small leak, and some other MAP sensor faults, may not be detected by the ECM. So these faults can lead to hesitation, rough idle, stalling and a decrease in fuel economy without triggering a check engine light (CEL).

If your engine is equipped with a MAP sensor, check along the vacuum hose for tears, damage or loose connections.

Also, make sure the hose travels in a downward slope to the connection at the intake manifold without sagging down. When the hose hangs, it may condense moisture or fuel, cutting airflow short and causing driveability problems. Reroute the hose or trim it as needed.

Replace the MAP sensor if any liquid comes out from inside the sensor itself when detaching the vacuum hose.

If necessary, troubleshoot the MAP sensor as well.

You can find more help on how to test the MAP sensor in your vehicle repair manual and the Resources section at the bottom of this post.

Read More from AxleAddict

engine-hesitates-during-acceleration-no-trouble-codes

II. Spark Plugs and Spark Plug Wire Problems

Problems in the ignition system, especially with spark plugs and spark plug wires, can lead to hesitation or stumble as you accelerate.

Car manufacturers recommend service intervals for the replacement of OEM spark plugs and wires. But you still should make a visual inspection of the spark plugs for signs of problems between service intervals. This is a good way to catch problems as they start before developing into performance issues.

Look for:

  • soot
  • carbon deposits
  • wet tips
  • signs of discoloration
  • worn electrodes
  • damage to electrodes
  • cracked porcelain

Also, check the spark plug wires' resistance using a digital multimeter (DMM). Consult your repair manual and the Resources section at the bottom of this post.

engine-hesitates-during-acceleration-no-trouble-codes

III. Air Leaks

When someone removes and replaces the inlet air duct between the mass air flow (MAF) sensor and the throttle plate, there's a chance that they don''t properly fit the duct ends together, causing unmetered air to leak. Unmetered air will not be taken into account when the ECM orders the fuel injectors to open.

This type of problem will lead to hesitation, especially at low speeds.

Check for an improperly connected inlet air duct, and possible damage to the duct itself. You may need to remove the duct for better inspection.

engine-hesitates-during-acceleration-no-trouble-codes

IV. Mass Air Flow Sensor (MAF) Issues

A faulty MAF sensor can cause all kinds of driveability issues:

  • hesitation during acceleration
  • lack of power
  • misfires
  • surges

The most common problem withthe MAF sensor is dirt trapped inside the sensor, usually around the hot wire. Often, using a MAF sensor cleaner will help restore proper operation.

Consult your vehicle repair manual and the Resources section at the bottom of this post for help.

engine-hesitates-during-acceleration-no-trouble-codes

V. Fuel Injector Issues

Although not as common as in the past, problems still assault fuel injectors after miles of service and cause a number of issues, including hesitation or stumbling during acceleration.

A fuel injector may:

  • clog
  • leak
  • short out

Inspect and test fuel injectors as necessary. Consult your vehicle repair manual and the Resources section at the bottom of this post for more help with fuel injectors.

engine-hesitates-during-acceleration-no-trouble-codes

VI. Fuel System Problems

A fuel system may have other problems besides fuel injector problems. Other common issues that may lead to hesitation include:

  • Bad fuel pressure regulator (low fuel pressure)
  • Worn fuel pump (insufficient fuel volume reaching the intake)
  • Fuel flow interference inside the intake (buildup around intake valves)

If necessary, check the fuel system for proper pressure and volume. Consult your vehicle repair manual and the Resources section at the bottom.

engine-hesitates-during-acceleration-no-trouble-codes

VII. Exhaust Gas Recirculation (EGR) Valve Problems

The EGR system allows a metered amount of exhaust gases back into the cylinders to lower engine temperature and reduce harmful emissions of oxides of nitrogen (NOx).

Common problems in the EGR system include the accumulation of carbon deposits inside passages between the exhaust manifold, EGR valve, and intake manifold.

Buildup can prevent the EGR valve from opening or closing properly. If it prevents the valve from closing, it can cause the engine to hesitate during acceleration.

The EGR valve and passages should be checked from time to time to make sure buildup is not interfering with system operation.

On vehicle models equipped with an EGR valve-control solenoid, troubleshoot the solenoid for proper operation. A leaking solenoid will lead to hesitation as well.

engine-hesitates-during-acceleration-no-trouble-codes

VIII. Faulty Throttle Position (TP) Sensor

The TP sensor signals the computer the amount of throttle opening so the computer can enrich the air-fuel mixture accordingly.

As the throttle opens, the computer adds extra fuel to the cylinders to prevent a lean condition.

It's not uncommon for the internal resistance of the TP sensor to fail after thousands of miles of service, causing engine hesitation or a no-start condition.

You can troubleshoot the TP sensor using a digital multimeter. See the Resources section at the bottom of this post for more help.

engine-hesitates-during-acceleration-no-trouble-codes

IX. Throttle Plate Buildup

The throttle plate, and the inside of the throttle body, can accumulate carbon deposits over time.

This will interfere with the proper operation of the throttle plate, and disturb proper airflow.

Uneven amounts of air and airflow patterns can lead to idle issues, and hesitation during acceleration.

Use carburetor cleaner and a shop rag to remove buildup from the throttle bore and plate.

Also, check the throttle linkage for binding. The throttle cable connects the accelerator pedal to the throttle plate. Depending on your particular model, check the cruise speed control cable as well.

The following video shows how to clean the throttle plate and bore without removing the throttle body, which works in most cases.

Consult your vehicle repair manual as well.

Cleaning the Throttle Plate and Bore

X. More Hesitation Diagnostic Help

The previous sections should help you in your diagnostic when dealing with a hesitation issue and you find no DTCs in the computer memory.

Furthermore, this other post on engine hesitation during acceleration, listed in the Resources section below, expands on this problem and will help you as well, if necessary.

Resources

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2021 Dan Ferrell

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