Serving the Gainesville and Hawthorne Florida Area
Fuel Pumps: diagnosis and replacement
Pump Replacement: Mechanical: $80-$150
Parts and Labor
(Prices good for most domestic or import cars and light trucks)
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What a fuel pump does: gasoline engines
Fuel pumps supply gasoline to run a gasoline engine. The pump sucks gas from the gas tank and pumps it to the carburetor or fuel injection system.
There are two basic types of fuel pumps: mechanical and electric.
Mechanical pumps are mounted on the engine and are driven by the engine directly. (via an eccentric lobe on the camshaft)
Electric pumps are driven by the vehicle's battery and charging system (the alternator).
All modern fuel injected cars use electric fuel pumps, as well as some carbureted cars. Many carbureted cars use mechanical pumps.
ELECTRIC FUEL PUMPS
Most all cars today have electric fuel pumps. Often the fuel pump is in the gas tank.
ADVANTAGES OF ELECTRIC FUEL PUMPS They can't leak gas into your engine. They are less likely to develop external leaks. The electric pumps are capable of developing the high pressures needed for fuel injection at all engine speeds and conditions.
DISADVANTAGES They're usually more expensive than mechanical pumps and harder to replace. Many pumps are in the gas tank, making it a chore to get to them. Because they run off the battery/charging system, if the alternator stops charging you can't make it as far as if you had a mechanical pump. Vehicles with electric pumps often have larger alternators than non-electric pump vehicles.
CHECKING ELECTRIC FUEL PUMPS
Usually electric pumps work fine until they fail. Sometimes their normal "whirring" noise gets louder before they break. Sometimes they will stop when they heat up, and then start again when they cool off. If your car breaks down and you suspect the electric fuel pump, you can test it like this: Take the gas cap off. Have a helper turn the engine over while you listen at the gas filler. You should hear a "whirring" noise from the tank. (If the fuel pump is outside of tank, listen to it wherever it is. Most of them are in the tank, though.) Electric pumps also can fail anytime after 50,000 miles. Most cars run the fuel pump for a few seconds when the key is turned on. This pressurizes the fuel system so the car will have adequate fuel pressure immediately when the starter is engaged. Try turning your ignition on just before the "start" position: you should be able to hear your pump run for a few seconds.
WARNING: FUEL FILTER CHANGES
Many electric fuel pumps pump a lot more fuel than the engine could ever use. This excess fuel is returned to the tank via a fuel return line by a fuel pressure regulator. This is done to assure a constant fuel supply at a steady pressure. This is essential for electronic fuel injection to work properly.
Because of this you might pump 100 gallons of fuel through your fuel filter, but only consume 15 gallons of gas!
Fuel filters on fuel injected cars are bigger because of this, but they still should be replaced every 50,000 miles!
FUEL PUMPS RELY ON FUEL FLOW FOR COOLING AND LUBRICATION!!!
If the fuel filter becomes clogged the car will still run fine, but there won't be enough fuel flow to keep the fuel pump happy.
Alcohol in Gas
A lot of gas nowadays has up to 10% ethanol in it. Since they started this I've seen a LOT of fuel system problems. Ethanol, unlike Octane (the official name of gasoline) absorbs water. Ripoff gas stations have even been known to add a bit of water to their tanks to "stretch" their fuel supply. Even if you get a "good" tank of gas, if you run the tank less than completely full, the empty portion of the tank is filled with air. Especially here in Florida this air can contain a LOT of moisture. This moisture is then absorbed by the ethanol.
Because of this I've seen a LOT of fuel pumps fail, especially on a vehicle that has not been run for awhile, or been in storage. To prevent this, first, keep your tank full whenever possible. Avoid sleazy looking gas stations. They sell "fuel conditioners" that help a bit: it wouldn't hurt to add a can of one of those and fill your tank completely if you are going to store your car, or let it sit for several months. If you can find gas with NO ethanol, I'd say get that. UNDER NO CIRCUMSTANCES should you store a "flex fuel" vehicle with e-80 fuel (80% ethanol, 20% gasoline.)
MECHANICAL FUEL PUMPS
Mechanical pumps have been used for years and are less expensive than electric pumps. During a charging system failure, a car with a mechanical pump can drive for hundreds of miles, so long as the lights, A/C blower, wipers, etc. aren't used. The battery only has to fire the spark plugs.
DISADVANTAGES When a mechanical pump fails, it can leak gas into your engine, thinning the oil and eventually destroying your engine. It can also leak externally and cause a fire. Mechnical fuel pumps would have a hard time providing the pressures and accuracy of flow and pressure needed for computerized fuel injection, thus all computerized fuel injected cars have electric pumps.
CHECKING MECHANICAL PUMPS Look at your pump every oil change (or have a
qualified mechanic check it once a year at least). Look for gas or oil coming from the pump. Check out any "gassy" smells. When checking you oil, watch for a smell of gas. I "feel" my oil when I check it: I wipe the dipstick off with my finger and rub it against my thumb. You can tell if it gets thin way before it does any damage. By all means suspect the fuel pump if your oil level starts to rise above the full mark! Cars can't make oil, they only lose it. That extra volume is probably gasoline! Mechanical pumps can fail anytime after 50,000 miles.
HOW MECHANICAL PUMPS FAIL
The best way to test a mechanical fuel pump is with a fuel pressure gage. Normal pressure is at least 4 pounds. The "backyard" way is to disconnect a fuel line, have an assistant spin the car engine over, and see if gas pumps out.
DANGER!!! Gas is flammable!!! It's also highly Inflammable!!!
That's why the gage is the preferred method.
Assuming tests determined a bad fuel pump, pumps fail in the following ways:
A mechanical pump has a rubber diaphragm which is moved back and forth, pumping the fuel. This diaphragm cam get a pinhole leak and fill your crankcase full of gasoline!
Most pumps have a relief hole which keeps SOME of the gas from getting in the crankcase if the rubber diaphragm breaks.
CHECK VALVE FAILURE
There are inlet and outlet check valves which can fail. On a pump like this a fuel pump pressure gage will "pulse" between a pressure and a vacuum, but will pump no gas.
CAM TO PUMP MECHANICAL FAILURE
On some motors the pump can be installed incorrectly, bending the pump arm or damaging the pump. GM V-8's have a plate and pushrod which drive the pump. Getting the pump arm under the pushrod can be tricky.
On some Ford engines the pump is driven by a roller cam bolted on the front of the timing gear. This cam can break and disable the pump.
A GM TRICK
There is a bolt on the front of the engine by the fuel pump. Remove that bolt and screw in a slightly longer bolt. This bolthole intersects the bore that the fuel pump pushrod rides in. This longer bolt will lock the pushrod in place, holding it up while you insert the fuel pump arm under the pushrod. Swap out the longer bolt for the original, bolt up the pump. This is a neat trick, because often the pushrod will keep sliding down quicker than you can get the fuel pump in place.
FUEL LINE LEAKS
If a fuel line gets a leak on the suction side the pump can "suck air" and stop pumping fuel. That's one good thing about checking the pump with a fuel pump pressure gage: it will show a pressure being made even if fuel is not being pumped. If you have a fuel pump that makes pressure on one side and creates a vacuum on the other then it's a good pump: there's a fuel line, filter, or tank problem.
Auto, Car, and Truck Article List
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
BAD CAR DESIGNS
Bad Drivers: How NOT to drive
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
Car Washing and Care
CARBURETORS:Car & Truck
CHECK ENGINE LIGHT
CLEANING: Engine Cleaning
CLUTCH REPAIRS: Car & Truck
COMPRESSION: Car Engine
COMPUTER CAR CONTROLS
CRUISE CONTROL / LANE GUARD
CV JOINT OR CV AXLES
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
FILTERS: OIL, AIR, ETC.
Flywheels, dual mass flywheels
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
HEADS & HEAD GASKET
HOSES AND BELTS
"IDIOT LIGHTS" AND GAGES
IGNITION TIMING: Car & Truck
AUTO JACKS: lifting cars safely
LEAN "Car runs lean"
LIGHTS: WARNING OR "IDIOT LIGHTS"
Limp Home Mode
NO START: Car Won't Start
OIL: What's right for your car?
OIL LIGHT ON OR GAGE LOW
RADIATORS: Car and Truck
RICH: Car runs rich
SEALS AND GASKETS
SELF DRIVING CARS / CRUISE
SERVICE ENGINE SOON LIGHT
STARTERS: Auto, Truck
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
WARNING LIGHTS OR "IDIOT LIGHTS"
Car Washing and Care
Washing and cleaning your car
WATER PUMP REPAIR
WINDOWS AND WINDSHIELDS
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