Why does my Harley- Davidson engine lope?

Do-it-yourself car maintenance and repair is written by Dan Ferrell.He is certified in automation and control technology.

When RPMs cycle unsteadily, an engine "lopes" or "surges".A car may surge between 600 and 1000rpm.

Since one or more systems may be behind the fault, you need a practical way to approach your diagnostic.In this guide, systems or components as potential sources of problems are laid out in the following sections starting with the most common and frequently presented to check the system.They can point you to the problem.Scan the computer memory for diagnostic trouble codes if it is on, and check the flagged systems first.

When it's cold, your engine lopes.Engine performance is affected by temperature.A number of sensors are used to increase the temperature on a cold engine.A few components found in some models can cause an engine to lope when cold, either because they become faulty or wear out after miles of service.

See if your model has any of these components.It's a good idea to read the vehicle repair manual for your make and model.If you want to locate and repair almost any component in your vehicle, you can use an aftermarket Haynes manual.

An engine that lopes when warmed up is associated with problems in specific components.

Fuel pressure can decrease when components in the fuel system wear out.You can check the fuel system using a fuel pressure gauge.Decrease fuel system pressure.If your system has a test valve, you can cover it with a shop rag and use a small screwdriver to depress it.With the engine off, do this.The fuel pressure gauge should be connected to the test port.Start the engine and check the pressure on the fuel gauge.Take a note of the gauge reading.3.Make a note of the pressure by removing the vacuum hose from the fuel pressure regulator.Take your readings and compare them to the specifications in the repair manual.Pressure shouldn't go up a lot.To shut the fuel return line if the pressure is low, place a rag over the line and use a pair of pliers.The return line can be damaged by using the rag.

6.Your fault may be with one or more fuel injectors if the pressure in steps 2 and 3 matches the specification listed in your manual.If you want to check fuel flow and amount of fuel through the injectors, you can have a shop do an injector balance test.If that injector is working, you should notice a change in idling RPMs.If you want to go to the next injector, you need to plug back the electrical connection.Any injector that does not produce a noticeable change in engine idling when unplugged is a suspect of failure.This is a dirty and quick balance test.If you suspect more than one injectors, you can either have a shop confirm your findings or use the help of a vehicle repair manual.Leave the fuel pressure gauge connected after hooking up a hand-held vacuum pump.While watching the fuel pressure gauge, gradually apply 4 in-Hg of vacuum to the regulator.When vacuum is removed, pressure should decrease as you apply it.Attach a vacuum gauge to the vacuum hose.The vacuum should be checked at idling.If there is no vacuum, look for a blocked vacuum hose or port.The regulator should be replaced if there is adequate vacuum.The vacuum gauge should be disconnected and the vacuum line reconnected to the fuel pressure regulator.5.Wait for about 5 minutes and check the fuel pressure gauge.The pressure should hold.You may have a:

A bad sensor may cause an engine to lope.The sensors give information to the computer.

ignition timing problems on high-mileage engines may be caused by a worn or skipped timing belt, or worn-out timing gears.In most modern vehicles, the car computer is the only one that can change the timing.Timing can be adjusted on older models with a distributor, but you can still check it using a timing light.

Check the systems and components that have been flagged first.

It's not uncommon for sludge to fill and cause problems in the PCV system.Sometimes a hose leak can cause the engine to lope.

The exhaust gas recirculation valve on many vehicle models operates through vacuum and is controlled by a vacuum regulator, which can cause leaks in the vacuum hose, or the valve itself to get stuck open.The problem may cause the engine to lope at cruising speeds, depending on the type of valve.

Engine performance issues are created when carbon accumulates around the throttle bore and the plate.You can remove the build up with a cleaner.

After a few years of operation, the idle valve is a common failure on modern vehicles.There are deposits of carbon inside the valve or along the ports.Sometimes the valve stops working at the end of its service life.

Engine performance issues can be caused by the ignition system.Engine performance issues can be caused by bad spark plugs, wires, distributor and distributor components.

The service interval is suggested by your car manufacturer.The service schedule can be found in the car owner's manual.As necessary, replace components.

Sometimes a compression leak from a cylinder head gasket can cause the engine to lope.This usually happens because the engine has high mileage, or a particular failure, like overheating, caused the gasket to blow. To check for a leaking head gasket, do a cylinder compression test using a vacuum gauge.If you don't have a vehicle repair manual, consult it.

A piece of fuel or a vacuum hose can be used to check for vacuum leaks around the intake manifolds.

Sometimes, just opening the hood and paying close attention to engine sounds can help.Vacuum leaks are a frequent source of engine performance trouble.You can use a trick if the sound is not obvious.

Air filters can accumulate dirt and foreign matter as air flows into the engine, which can cause performance problems if not replaced at regular intervals.

If your engine has a high mileage, it is possible that the camshafts are worn and cause the engine tolope.This is a general check.

It is possible to remove carbon build up around valves and cylinders with a decarbonizer like Seafom.It can be difficult to properly diagnose valve closing problems.You can use a vacuum or compression gauge to diagnose this type of mechanical problem.It's a good idea to read your vehicle repair manual.

When your car lopes, it's a good idea to start your diagnostic with the systems or components that may have given you trouble recently.You can use the strategy presented here to find the source of the problem faster and to make the repair yourself.

The article is correct to the best of the author's knowledge.Content is for entertainment purposes only and does not substitute for professional advice in business, financial, legal, or technical matters.

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