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Fuel Injection diagnosis: Free to $100 ... Service and cleaning: $50-$100
(Prices good for most domestic or import cars and light trucks)
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Your car is probably fuel injected.

Instead of a carburetor, most modern cars use computerized fuel injection. This system supplies the proper fuel/air mixture for your engine.

A computer measures engine conditions and precisely sprays an exact amount of fuel into the intake manifold through fuel injectors.

FUEL INJECTION SYSTEMS: WHAT GOES WRONG

The FUEL INJECTION PUMP, FUEL FILTER, COMPUTER, AND ALL ITS SENSORS AND WIRING can make the fuel injection system fail. Individual injectors can become clogged with rust, varnish, etc. All systems have a pressure regulator, since fuel injection systems rely on very constant and accurate fuel pressure to operate properly. If the pressure is too high, the car will run rich.(Black smoke!) If pressure is too low, the engine will run lean or will not run at all! (Maybe the most common gasoline fuel injection problem is a bad fuel injeciton pump!)


ELECTRONIC COMPUTER CONTROLLED FUEL INJECTION

An electric solenoid is opened by the computer. The amount of fuel is controlled by how long the solenoid is kept open.

TYPES OF COMPUTERIZED FUEL INJECTION

THROTTLE BODY FUEL INJECTION

It's the simplest way to do fuel injection. A fuel injector sits on top of a throttle plate. Looks like a shower head. It opens 10 times per second regardless of engine conditions or rpm. The computer keeps it open longer or shorter times to vary the fuel to air mixture

MULTIPORT FUEL INJECTION

Here you have an injector for each cylinder. Often these injectors are also pulsed 10 times per second and kept open longer or shorter times to vary the fuel to air mixture

SEQUENTIAL FUEL INJECTION

Sequential injection doesn't fire all the injectors at once, although often they will only fire in a set of two (half the cylinders get a squirt of gas, then the other half, etc.) Even the most advanced sequential injection systems operate each cylinder's injector twice for each combustion cycle. (once on the intake stroke, once on the power stroke). The fuel sprayed each time is equal. The fuel sprayed during the power stroke is "stored". It cools the valves off, vaporizes, and gets sucked in along with the next injector spray, when the intake stroke comes around again.

CONSTANT FLOW FUEL INJECTION

The earliest gasoline fuel injection was constant flow. A mechanical linkage moved a calibrated rod in an orifice. This metered fuel to injectors at each cylinder. A throttle plate metered the air.

BOSCH CIS

A neat fuel injection system, Bosch CIS is found on all the Rabbits, some Volvos, and a bunch of other European rides. A hose connects the intake to the CIS fuel control assembly: often holding the air filter. A round plate blocks the airflow. As the engine sucks in air, this plate lifts up. It opens a valve, which sprays more and more fuel to the injectors at each cylinder as the plate lifts up. These injectors spray all the time the engine is running.

BOSCH AFC

Bosch AFC and licensed "copies" were very popular on Japanese, Swedish, and European vehicles in the 80's and 90's. It is an electronic fuel injection system which uses a vane airflow meter to measure the air taken in by the motor. The Vane Airflow Meter is just a flap on a pivot which is swung open as the engine sucks in air. The more air sucked in, the more the flap opens. The flap is connected to a variable resistor, which provides the computer input. The computer uses this as one of its primary inputs, then "tweaks" the mixture with the input of other sensors.

A NOTE ON ALL BOSCH FUEL INJECTION

The above Bosch fuel injection systems rely heavily on the coolant temperature sensor. A bad or disconnected coolant temperature sensor can really confuse the fuel injection control computer!!! It will run so rich that gas will practically drip out the exhaust pipe!

BOSCH CIS and AFC "TRICK"

The Bosch CIS and AFC systems both rely on a totally sealed rubber hose system from the intake manifold to the control assembly box (normally on top of the air cleaner) Often a hose will "fall off", making a vacuum leak. (there are several "branches" in the hose systems). The CIS control unit, or the AFC control unit will not be opened enough, the fuel mix will be wrong, and the car won't start. Find the hose that came off, plug it back in, it will start right back up.

From the factory these hose junctions often have no clamps. a hose clamp, zip strip, etc. can help keep the hose from falling off again.

Nevertheless, the real problem is probably old hard rubber in the hose assemblies. It would be nice to replace them, but they're pricey! ($100-$200 plus for the main hose).

And forget getting one at your local parts store: they're "dealer part only!"


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Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.


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A
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
AUTOMATIC TRANSMISSIONS
B
BAD CAR DESIGNS
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BELTS AND HOSES
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C
Car Washing and Care
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CHECK ENGINE LIGHT
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D
DISTRIBUTORS (IGNITION)
E
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
ENGINE CLEANING
EXPANSION PLUGS
F
FREEZE PLUGS
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
G
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
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HEADS & HEAD GASKET
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I
"IDIOT LIGHTS" AND GAGES
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AUTO JACKS: lifting cars safely
K
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LEAN "Car runs lean"
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Limp Home Mode
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MIL Light
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PCV Valve
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R
RADIATORS: Car and Truck
RICH: Car runs rich
S
SEALS AND GASKETS
SERVICE ENGINE SOON LIGHT
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T
THERMOSTATS
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
TIRE REPAIR
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V
VACUUM ADVANCE
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