My Car Loses Power Going Uphill

Updated on December 23, 2019
Dan Ferrell profile image

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

When your car loses power uphill, check common sources of trouble first.
When your car loses power uphill, check common sources of trouble first. | Source

When your car loses power going uphill, there’s no specific system or component you can blame. For example, you may be dealing with a:

  • weak or worn fuel pump
  • clogged catalytic converter
  • faulty automatic or manual transmission
  • bad engine control sensor

Certain problems in any of these components or systems can make the engine feel sluggish when accelerating uphill.

The following sections give you a brief description about common problems in some specific systems or components that can cause your vehicle to lose power when going uphill.

Index
1. Worn Fuel Pump and Fuel System Problems
Testing Fuel System Pressure
Checking Fuel Pump Valves
2. Clogging Catalytic Converter
Testing a Catalytic Converter
3. Transmission Problems
4. Maintenance and Worn Parts
A worn fuel pump can make your car struggle going uphill.
A worn fuel pump can make your car struggle going uphill. | Source

1. Worn Fuel Pump and Fuel System Problems

If you drive a modern vehicle, the fuel system in your car is fitted with an electric fuel pump, usually inside the fuel tank.

The fuel pump is designed to push fuel from the fuel tank to the fuel injection system under a specific pressure range. After miles of service, though, fuel pump internal components wear out and efficiency decreases. Often, this symptom manifests itself gradually. You may notice the engine struggling under high loads as you drive uphill or tow a trailer.

In fact, other parts in the system may fail as well. But there are a few tests you can do at home.

Fuel Pump Test Warning

When testing the fuel pump and system, follow the safety precautions described in your vehicle repair manual to prevent an accident.

Testing Fuel System Pressure

If you suspect a problem with the fuel system, make first a visual inspection for signs of leaks. Pay special attention to the following components:

  • fuel rail
  • fuel pressure regulator (FPR)
  • fuel hoses
  • fuel lines
  • fuel injectors

A leak in the system might be the cause of the problem.

A common way to test the fuel pump is by checking system fuel pressure. You’ll need a fuel pressure gauge if you want to do this procedure yourself. For this test, you also need to relieve fuel system pressure to connect the gauge.

Some systems have a Schrader valve (fuel rail test fitting) you can use to connect the pressure gauge; otherwise, you’ll need to use a tee for this purpose. If the fuel rail has a fuel pulsation damper, you can use this connection for the gauge.

Probably you’ll need to relieve system pressure first to connect your gauge. Consult your vehicle repair manual for the test steps for you particular fuel injection system, if necessary.

If you don’t have this manual yet, you can buy a relatively inexpensive manual through Amazon. Haynes manuals come with step-by-step procedures and photos for many troubleshooting, parts replacement and maintenance projects you can do at home.

Also, this post on testing system fuel pressure can guide you through the process.

When conducting the test, keep these points in mind:

  • Follow the specifications for the test (for example: engine off or idling).
  • Usually, fuel pressure is slightly lower when the engine is running.
  • When the engine is running, you may see the pressure gauge fluctuating slightly because of the injectors opening and closing.
  • Unusual gauge needle fluctuations may indicate air in the system.
  • Pressure above system specifications will cause a rich air-fuel mixture.
  • Pressure below system specifications will cause a lean air-fuel mixture.

High fuel pressure may come from a:

  • bad fuel pressure regulator
  • clogged return line
  • faulty fuel pressure regulator vacuum line

Low fuel pressure may come from a:

  • clogged fuel filter
  • leaking fuel pump check valve
  • worn fuel pump
  • dirty or clogged in-tank fuel filter sock
  • clogged fuel line
  • faulty fuel pressure regulator

Checking Fuel Pump Valves

A common electric fuel pump has a check valve at the outlet connection of the pump to keep the fuel line pressurized when the engine is shut off. Also, a pressure relief valve may be located close to the check valve to open when too much pressure builds up. Either valve may fail and cause fuel pressure to drop.

If the fuel pressure regulator tests OK, you can also check for a leaking valve by monitoring fuel pressure after the engine is shut off. If pressure drops, you may be dealing with a leaking check valve.

Similarly, you can rule out a clogged fuel filter and fuel line by testing fuel pressure at the fuel pump outlet connection. This might not be an easy task on some models, since you need access to the pump output port. On some models, though, you can hook up the pressure gauge to the fuel filter input line; however keep in mind that a low pressure at this point might be due to a clogged fuel line, weak or worn fuel pump or restricted filter sock in the tank, depending on your particular model.

If your catalytic converter is clogged, replace it.
If your catalytic converter is clogged, replace it. | Source

2. Clogging Catalytic Converter

The catalytic converter is part of the exhaust system. Exhaust gases flow out the cylinders through exhaust ports, into the exhaust manifold, and through the catalytic converter and tailpipe.

As a key component of the emission control system, the catalytic converter turns hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) into harmless gases.

Although it has no moving parts and can work trouble-free for thousands of miles, performance issues can reduce the efficiency or seriously damage a catalytic converter. A common cat converter problem is clogging, usually from overheating. Raw fuel from engine misfires can quickly increase the cat’s temperature and destroy the catalyst element, causing a blockage that prevents the flow of gases.

Another problem is physical damage. For example, the internal structure may become fouled, collapse or break.

Symptoms of a clogged catalytic converter may include:

  • carburetor backfiring
  • backfiring at the intake manifold
  • loss of engine power at high speeds or while driving uphill
  • stalling soon after engine has started

Testing a Catalytic Converter

There are three simple methods you can use to test for a restricted catalytic converter or exhaust system.

  • Use a vacuum gauge to monitor engine vacuum.
  • Use a pressure gauge to monitor back pressure.
  • Use a mallet to check the cat’s physical condition.

When diagnosing your cat:

  • make a visual inspection and check for cracks and dents.
  • Use a rubber mallet to tap the converter; rattling sounds indicate internal damage.

Keep in mind that any type of restriction in the exhaust system can have the same effect as a clogged catalytic converter.

Issues with an automatic or manual transmission can also cause a vehicle to struggle under load.
Issues with an automatic or manual transmission can also cause a vehicle to struggle under load. | Source

3. Transmission Problems

Particular transmission problems, whether automatic or manual, can also cause the engine to lose power under load or going uphill.

In a manual transmission, for example, a clutch disc may slip when worn out. You’ll notice the engine racing while accelerating slowly after a stop, when shifting, or going uphill.

In an automatic transmission, worn bands or torque converter can also cause similar problems. If the transmission slips in gear, there may be a problem with a stuck valve, internal leaks, low fluid level or a clogged filter. If necessary, take in your vehicle for a diagnostic.

Check ignition system components that may be causing trouble like distributor cap and rotor.
Check ignition system components that may be causing trouble like distributor cap and rotor. | Source

4. Maintenance and Worn Parts

Lack of proper maintenance and faulty components are other common source of poor engine performance. So you may want to check the service schedule for your particular model and scan the car’s computer for potential diagnostic trouble codes, even if the check engine light is not on.

You can find the service schedule in your car owner’s manual or your vehicle repair manual. And, if you don’t have a code reader or scanner, your local auto parts store may download the trouble codes for you.

Some components you may want to check or replace, depending on your particular model, include:

  • spark plugs
  • spark plug wires
  • distributor cap
  • fuel filter
  • air filter
  • vacuum hoses
  • EGR valve and system
  • cylinder compression

Worn spark plugs can cause a misfire when driving uphill. You may feel the car jerking or losing power. In fact, as any of these components begins to wear out or become restricted, you may not notice it until your car is under load, like going uphill. The effect can be a reduction in fuel economy, weakened spark and poor combustion.

Consult your car owner’s manual or vehicle repair manual for other components particular to your model that you may need to check or replace.

Also, bad connections, like loose or corroded grounds, can rob power to your engine. Even a corroded fuse connection can affect your engine under load, like in the following video.

How a Bad Electrical Connection Can Rob Engine Power

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

    © 2019 Dan Ferrell

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