Where would your car be without a fuel system? Stranded! And so would you. Before you find yourself in this situation, you might want to learn how repairs are done to an automotive fuel system. If not, at least read this article before you hire a mechanic to do the needed (or unneeded) repairs. You might decide to do it yourself. Or you might want to make sure the mechanic doesn’t treat you like a complete idiot. Your car’s fuel system is based on either a carburetor or a fuel-injection system. One or the other. Which one? If your car was built in the past 10 years, chances are it uses a fuel-injection system. If it was built more than 10 years ago, it probably uses a carburetor. The car’s owner’s manual and certainly its service manual can tell you which one you have. In this article, you also learn about repairs to fuel pumps, fuel tanks, and fuel lines (see the figure illustrating the fuel system components). All internal combustion engine cars have these parts.
Are You Starving Your Car?
This article offers solutions to many common fuel system problems. Here are some additional tips:
- Are you sure that your car has gas? If you don’t trust the fuel gauge, carefully lower one end of a cotton rope through the fuel filler pipe to test the depth of the fuel in the tank. A clean stick is better if it will negotiate all the turns in the filler pipe.
- If your car’s engine starts okay but dies when you put it in gear, the carburetor (if it has one) might need the fast idle speed adjusted.
- If your car seems starved for fuel, remove the air filter. If the engine then runs smoothly, replace the air filter with a new one. If the engine still does not run smoothly, use a vacuum tester to test the fuel pump and fuel lines as covered later in this article.
- A vacuum leak in a fuel-injection system, intake manifold, or vacuum line can cause all sorts of weird problems. Check vacuum hoses for leaks before repairing other parts.
- If your car runs erratically or even not at all, check the fuel filter; if it’s clogged, replace it.
- If your car sounds like a diesel engine when going uphill, buy a higher octane fuel or add an octane booster to your fuel tank (see your friendly auto parts retailer).
- If your car is difficult to start but finally does so, check the automatic choke as described in this page..
Painless Carburetor Surgery
The carburetor has been a vital part of a car’s power system since cars first drank, or guzzled, gas. The carburetor mixes fuel with air and sends it (through the intake manifold) to the engine cylinders for burning. A carburetor is a mechanical device; it’s not electronically controlled. That means it’s subject to wear. Small jets get clogged with junk from the fuel tank. The float inside the carburetor’s bowl or reservoir wears out or breaks. But, most often, poor fuel and too many gas additives take their toll on the carburetor, requiring that it be replaced. How can you tell? Troubleshooting tests can help determine the source of the problem. If it’s the carburetor, keep reading.
You have options. Sometimes, all your car needs is an adjustment or two. Because your carburetor is a mechanical device, you can rebuild it for less money than it costs to buy a rebuilt or new one. Or you can whip out your wallet and plunk your money down for a new one, but before you do, make sure you’ve considered the other options. Is rebuilding a carburetor difficult? Not particularly. In fact, the most difficult part may be selecting the right parts from the carburetor rebuild kit. These kits, available at auto parts stores for nearly all carburetors, are typically sold for more than one carburetor model. That means you’re going to have some parts left over when you’re done (leftovers are okay in this case). Instructions in these kits are generic, too. One solution to this problem is to stay away from the low-price leaders at automotive superstores. If you’re going to rebuild your car’s carburetor, get a kit from the dealer’s parts department or the original equipment manufacturer (OEM). It costs more, but it saves you time-and time is money.
A carburetor is replaced following these steps:
- Open your car’s hood and look for the carburetor. In most cars, it’s beneath a round metal part called the air-filter housing. Disconnect the large hose leading into the air-filter housing (if there is one) and remove the nut on top of the housing. Disconnect any other parts and hoses needed to remove the air-filter housing.
- You should now be able to see the carburetor. Disconnect the throttle linkage and the fuel line to the carburetor. You’ll probably need the car’s service manual as a reference so that you don’t remove the wrong parts. Remember, the carb cops are watching you!
- Remove the carburetor. For most cars, this means first removing the two or four nuts at the edges where the carburetor sits atop the intake manifold.
- Remove the gasket between the carburetor and intake manifold. If the gasket lifts off easily, you’re done. If it’s stuck, you must scrape it off. To do so, first plug the holes on the manifold with rags so that bits of gasket don’t fall in, making life more difficult. Then use a putty knife or other flat edge to remove all gasket material. (Don’t forget to remove the rag from the manifold holes when you’re done!)
- Buy or rebuild the carburetor. You can buy a new or rebuilt unit or you can rebuild it yourself with a carburetor kit. In general, rebuilding a carburetor means taking it apart, soaking parts in a carburetor cleaner, reassembling the parts, and adjusting them following the instructions in the kit.
- Install the new or rebuilt carburetor in the reverse order of how you took it out. Install the new gasket, the new carb, attach lines and linkage, a new air-filter housing gasket, and then the old housing.
- Finally, adjust the carburetor (if the manufacturer has provisions for adjustment) following instructions in the car’s service manual..
Don’t Choke Your Car to Death
A choke has a strangle-hold on the carburetor. Pretty graphic, huh? The choke limits the amount of air going into the carburetor. Why? Because as a car starts, it needs a richer (more fuel, less air) mixture than when it’s tooling along the highway. The automatic choke system knows that the car’s engine isn’t warm enough yet (because it’s measuring the temperature of the exhaust gas), so it uses a butterfly valve to keep some of the air from flowing into the carburetor. A butterfly valve is a shaft with a “wing” on each side that chokes or blocks air flow through the carburetor’s throat when the shaft is turned. This butterfly doesn’t fly, however, and it isn’t very pretty. How do you know whether your car’s carburetor choke isn’t working? Common sense. Is your car “cold-blooded” and difficult to keep running the first time it’s started? Among other things, the automatic choke might not be working automatically. Some cars get help from a vacuum or electric assistant that reduces excessive choking. Sounds gruesome, doesn’t it? If your car sends out black exhaust smoke when it starts, the automatic choke’s assistant is probably not working.
An automatic choke is replaced following these steps:
- Find the automatic choke. On some cars, it’s located on the side of the carburetor; on others, it’s mounted nearby on the manifold. Unfortunately, some systems have choke parts under the carburetor. Follow the instructions for digging your way down to the carburetor by removing the air-filter housing.
- Using your car’s service manual, figure out what type of automatic choking system it has and where the components are located. Without starting the car and while the engine is cold, put your ear near the carburetor while your lovely assistant presses the gas pedal. You should see and hear the choke butterfly valve move. If it doesn’t, try moving the butterfly by hand and checking the attached parts for smooth movement. If something seems stuck, try to free it. The cause is often a loose connection or something in the way.
- Depending on the type of choke system, you can use a carburetor choke cleaner spray to clean and free up mechanical parts. Don’t spray any electronic parts with this stuff. How can you tell the difference? If in doubt, wires leading to a part identify it as electrical.
- If your automatic choke system’s thermostat needs an adjustment, follow the service manual’s instructions for adjusting it. In most cases, you loosen the choke cover and turn it to the next index mark on the cover’s body, and then retighten the screws. If the thermostat doesn’t respond to adjustment, it’s probably broken and needs replacement.
- To replace an automatic choke system component, identify and remove the defective component, and then take it to a full parts house for an exact replacement. Some choke systems are an integral part of the carburetor and cannot be replaced easily. In this case, you’re stuck with buying a new or rebuilt carburetor.
- To adequately test your car’s rebuilt carburetor, start the car and drive it by your favorite mechanic’s garage, honking.
Fuel-injection systems are more efficient and more trouble-free than carburetion systems. Even so, they may need periodic repair or replacement. Most cars built since 1986 use fuel injection rather than carburetion. Some cars used it even before that. The two most common types of fuel-injection systems today are throttle-body and multiport. There will be a quiz later, so pay attention-and drop that spitball! A throttle-body fuel-injection system is similar to a carburetor, except that the amount of fuel is controlled electronically rather than mechanically. The fuel/air mixture is then distributed by the intake manifold to the cylinders. A multipart fuel-injection system electronically controls the distribution of fuel through one or more fuel rails (like pipes) to each cylinder’s fuel injector. Multiport fuel injection (MPFI) is also called multipart injection, port fuel injection, and other creative names. Same thing. Still awake?
So what can go wrong with a fuel-injection system? The system is controlled by the electronic control module (ECM) or the computer, which makes all the major decisions. So if the ECM is damaged, problems begin showing up in components it controls, including the fuel-injection system. Fortunately, these things don’t fail very often, especially on newer systems in which the design bugs have been worked out. Unfortunately, when they do go awry, they go extremely awry-and Einstein can’t fix them. The solution then is to have a qualified and honest mechanic (I knew one once, but he died-broke!) test and replace as needed. How can you tell if your car’s fuel-injection system is sick? That’s a toughie. Much depends on the type of fuel-injection system your car has, and whether other causes have been ruled out. Your car’s service manual is the best source for specific ailments and cures, but to understand them, let’s look at typical fuel-injection system repairs.
Fuel-injection systems are complex. Tackle repair at your own risk. They can be repaired successfully by mechanically inclined car owners with a good service manual and the right tools. Really they can. Plan on spending some time scratching your head, however. A well-written service manual with lots of illustrations specific to your car’s engine really makes the job easier. Fuel injectors should last about 50,000 miles, and other parts in the system should last about twice as long.
Fuel-injection systems are repaired following these steps:
- Relieve pressure in (depressurize) the fuel system. Fuel-injection systems are pressurized, so working on the fuel system requires that you first relieve system pressure. Your car’s service manual or an aftermarket manual shows you how. Typically, you remove the filler cap on the fuel tank and then loosen the specified pressure reliever (a bolt or fitting).
- Follow manufacturer’s directions for testing and repairing or replacing components. Typical components include the air intake system, throttle body, fuel rail (MPFI), fuel pressure regulator, fuel injectors, and electronic control module. Sometimes you can fix a system simply by tracing down all the wires and hoses, attaching those that have worked themselves free or are damaged. Sometimes not.
- If you are able to repair your car’s fuel-injection system within a reasonable time and cost, try not to act smug.
Fuel Tank and Fuel Line Repairs
A fuel tank is simply a reservoir for your car’s fuel. Fuel tanks typically hold from 10 to 20 gallons of fuel, depending on the car’s fuel efficiency. (My 40-year-old Continental has a 25-gallon fuel tank, accurately suggesting a low number of miles to the gallon. My Honda acts very smug about its small tank and efficient mileage.) Cars are designed to travel 300 to 400 miles before running out of gas. Unfortunately, human bladders are smaller and need more frequent pit stops. What can go wrong with fuel tanks and fuel lines? They can spring a leak. A small point of rust can become a hole in a few years. If the hole is in a tank or line housing fuel, the fuel can leak out and cause more problems than just low fuel efficiency. If you find puddles of fuel under your car, you know that the tank or line needs repair. Do it before the leak becomes a fire hazard. The best insurance against such leaks is a full undercoating of the underside of your car to minimize rust. Depending on the size of your car, undercoating can cost about $25 in materials plus your labor, or about $100 to $150 if a shop does it for you. Make sure a rust inhibitor is applied first.
Fuel tanks and fuel lines can be repaired following these steps:
- Visually inspect your car’s fuel tank and fuel lines, looking for small wet spots. Touch the spot with a finger and then sniff it to see whether the liquid is gasoline. If so, look for other leaks and repair or replace the part as needed.
- To repair a fuel tank, purchase and apply an internal or external fuel tank sealer. Internal sealers are poured into the fuel; external sealers are applied to the holes on the outside of the tank. Internal sealers find and seal all holes, seen and unseen, but might not be recommended by the car’s manufacturer because they can clog a system. External sealers are easy to apply, but can’t ensure that unseen holes are sealed.
- To replace a fuel tank on a fuel-injected car, first depressurize it, as described previously. This isn’t necessary on a carbureted car. Then drain or siphon the fuel from the tank into one or more large gas cans. Detach the fuel tank from the inlet pipe and the output fuel line. Find and remove the straps or hangers that attach the fuel tank to the car. Carefully lower the tank to the ground and remove it from underneath the car. Replace it with a new or rebuilt replacement tank. Don’t try to make one fit that doesn’t.
- To repair a fuel line, first determine whether the entire line or only one spot needs replacement. A damaged line can be repaired, but a rusted fuel line will soon spring another hole and should be replaced. A rubber fuel line that has developed a leak is probably old and needs to be replaced entirely. If your car is fuel-injected, depressurize the fuel system before working on it. Larger auto parts stores have fuel lines cut to length and bent for many newer cars. Otherwise, you might need to buy a straight fuel line along with some bending and flaring tools to make it fit your car.
- Realize that, once done with this job, you’re a better person for the experience…
Fuel Pump Repair
Fuel pumps use suction to pull fuel from the tank and deliver it to the carburetor or fuel-injection system. Older cars used mechanical fuel pumps that were operated by
the engine’s camshaft. Newer cars use electromechanical or solid state fuel pumps. An electromechanical pump uses electricity to power the mechanical suction diaphragm. Solid state fuel pumps rely on electronics to do the job and have no mechanical parts. One more time: If your car has a fuel-injection system, make sure you depressurize the fuel system before working on it. See the instructions provided earlier in this article.
To replace a fuel pump, follow these steps:
- First, find the dam thing. Your car’s fuel pump could be mounted on the side of the engine, somewhere in the engine compartment, near the fuel tank, or even inside the fuel tank. Your car’s service manual helps you pinpoint it.
- Test the fuel pump. Some fuel pumps can be tested without taking them off the car, but others must be removed (see step 3). To test the pump, you first need to remove the fuel lines from the pump. Before disconnecting the input line, find a way of blocking it so that fuel from the tank doesn’t spurt out. For a rubber input line, use Vise-Grip pliers to clamp the line. For a metal line, use a cap or a wad of putty to block flow after the input line is disconnected. Check input vacuum pressure with your finger or a vacuum gauge over the input. The car’s service manual tells you what the input vacuum should be, but your finger over the input can give you a good idea as to whether the fuel pump is working. Check the fuel pump output pressure and volume in the same way.
- To remove the fuel pump, remove the mounting bolts that attach it to the engine block, frame, or tank. Fuel pumps inside a fuel tank typically can be accessed through a cover underneath a back seat or a trunk mat. Disconnect any electrical wiring. Drain any gas in the fuel pump or bowl into a gas can. Remember: Smoking while you’re working on the fuel system can really be hazardous to your health and to those within a wide range of your location!
- Replace the fuel pump with one of the same output. Your car’s specifications tell you what pressure and volume the fuel pump should be able to produce.