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Corvette Fuel System Maintenance - Fuelish Behavior

A Corvette Fuel-Injection Cleaning And Maintenance How-To

Jul 1, 2009
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A preferred method for cleaning fuel injectors is with an ultrasonic fuel-injector cleaner/fuel injector flow bench, such as the ACE/ASNU unit shown.

The fuel-injection system that supplies the fuel to each cylinder of the engine in an '85-or-newer Corvette is so reliable that it seems to be almost maintenance free. The engine's fuel-injection system may be low maintenance, but it does have fuel-related components that need maintenance from time to time, such as the fuel pump, fuel filter(s), and the fuel injectors. The fuel injectors can-and most likely will-get "dirty" or contaminated by the deposits that gasoline forms in the fuel injectors as the gasoline flows through them.

How do you know when your fuel injectors need cleaning? The symptoms you will most often experience will be a gradual loss of engine power and/or a stumble/hesitation on acceleration as the fuel injectors in your Corvette get "dirty." These symptoms may appear so slowly with time and miles of driving that you may not even notice any problems. If you happen to get a bad tank of gasoline at some point, these problems can appear very quickly.

The port fuel injectors are located in a very hot area in the engine, and the injectors are subject to deposit build-up problems created by the high-temperatures effect on the fuel as it flows through the fuel injectors. The high underhood temperature that is common after you shut off your engine will also cause deposits to build up as the fuel boils in the injectors. These deposits will eventually distort the fuel-injector spray pattern and restrict the fuel injector's ability to supply the engine with the correct volume of fuel.

Diagnosing the Fuel-Injection System
The use of an automotive computer diagnostic scan tool is the best way to diagnose the fuel system in your Corvette. You can take your fuel-injected Corvette to a qualified shop that has all the latest diagnostic tools, or if you want, do the work yourself. There are many low-cost computer scan tools on the market that are user friendly.

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This "dirty" fuel filter was removed from a fuel injector. Once the "dirt" gets by the inline gas filter, it can plug the filter built into the fuel injector.

The long-term fuel trim data ('96-and-newer Corvette w/OBD-2 computer system) or the block learn data ('85 thru '95 Corvette w/ OBD-1 computer system) obtained from an automotive computer diagnostic scan tool can be used to read how much the computer is adjusting the fuel-injector pulse width so the engine has the correct air/fuel mixture. When the fuel-injector flow becomes restricted as the injectors get dirty, the computer will attempt to adjust the fuel flow by opening the injector longer through the use of its long-term fuel trim function. Fuel injectors that are dirty will need more pulse width (held open longer) than injectors that are flowing the correct volume of fuel for the engine's needs. If the injectors are leaking fuel, the computer will adjust the amount of fuel coming from the injectors by subtracting fuel through use of its long-term fuel trim function. The engine will perform its best when the computer does not continually have to correct for fuel injectors that are not supplying the proper volume of fuel.

Cleaning the Fuel Injectors
If the fuel injectors are "dirty" or leaking, there are several different options available to clean the fuel injectors. The options include:

1.A fuel-injector cleaning chemical that you pour into the fuel tank can be used to clean the injectors. We have had good results using an in-tank fuel injection cleaner such as Techron Concentrate Plus from Chevron. Several of our customers have told us they felt a noticeable increase in power with just one tank of gasoline treated with the cleaning solution in the tank. The disadvantage of the in-tank fuel-injector cleaning method is it does not allow you to check the fuel-injector spray pattern, plus the fuel "filter" built into the fuel injector may become plugged with any contaminants that may be washed into it. If the in-tank method does not supply the desired results, you may need to try another injector cleaning method.

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This shot shows what the fuel spray looks like as it comes out of the fuel injectors.

2. A second chemical method of cleaning the injectors is the use of a cleaner that is run through the fuelrails and injectors. This method allows a stronger mix of cleaning chemicals than you should put into the gas tank (the stronger mix of chemicals could possibly damage the fuel system). This cleaning method can do a good job, but again, it does not allow you to check the fuel-injector spray pattern, plus the fuel "filter" built into the fuel injector may become plugged with contaminants that may be washed into it.

3. Our preferred method for cleaning fuel injectors is with an ultrasonic fuel-injector cleaner/fuel injector flow bench, such as the ACE/ASNU unit we use. The ultrasonic cleaning method involves cycling the fuel injectors while the fuel-injector tips are immersed in an ultrasonic bath that uses an environmentally friendly cleaning fluid to clean the injectors. The flow-bench portion of this tool also allows a user to perform a flow test before and after cleaning, and it also allows the user to observe the fuel-injector spray pattern. This method is more labor intensive because it requires that the injectors be removed from the engine and installed on a test fixture to perform the testing procedure.

Checking the Fuel-Injector Flow
A fuel-injector flow bench, such as the ACE/ANSU unit, can be used to check the actual flow from the fuel injectors at any load condition or engine rpm (fuel injector on-time) you choose to simulate. The flow bench also allows the user to observe the injector spray patterns and actually measure the fuel flow from each fuel injector so the user can actually see if the injectors are truly flow matched.

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This photo shows the flow from a set of fuel injectors from FAST (fuel air spark tech /comp cams injectors). these are a replacement set for an LT-1 engine that are being flow matched.

Not all fuel injectors are created equal. Most new OEM fuel injectors are held to a +/- 2-percent production flow variance. Ideally, each fuel injector would flow exactly the same, but holding a production line to that standard would raise the cost of the fuel injectors substantially. The replacement aftermarket fuel injectors that you buy at your local auto parts store are in some cases not built to the same flow standards as the OEM fuel injectors are held to. Also due to part number consolidation, the aftermarket fuel-injector flow rate can vary as much as 25 percent when compared to the OEM fuel injectors that the computer in your Corvette was programmed for.

If the fuel flow and spray pattern are not the same from each fuel injector used on an engine, the air/fuel mixture delivered to each cylinder of the engine will vary. When the air/fuel mixture varies by more that 6-8 percent from cylinder to cylinder, the engine will have cylinders that are running too rich and cylinders that are too lean. When each cylinder of an engine does not have the correct air/fuel mixture, the engine's power output, drivability, and fuel-mileage potential will suffer. The fuel injectors should always be replaced as a set, unless you are confirming the replacement injectors flow volume and spray pattern are the same as the original injectors by flowing them on a fuel-injector flow bench.

The General Motors Multec fuel injectors that were used in the Corvette Tuned Port fuel-injected engines produced in 1985 through the early '90s had problems where the insulation on the fuel injector coil windings would deteriorate and then allow the injector coil to short circuit. The problems you may experience can vary from an occasional one-cylinder miss (caused by an intermittent short in the injector coil) to a totally dead cylinder (a shorted coil in the injector coil that no longer supplies any fuel to the cylinder). To test the Multec fuel-injector coil for an intermittent short circuit, we use the OTC/SPX No. 3397 fuel-injection tester (this tool checks the fuel-injector coil while it flows current through it) and/or by flowing the fuel injectors on the ASNU fuel-injector flow bench. If one or more fuel injectors have failed due to shorted coils, we would suggest replacing all the injectors because the coils in other fuel injectors will most likely short/fail in the near future.

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Clean injector flow as seen on the ACE/ANSU fuel-injector flow bench. The fuel injectors are clean and now flow within 2-percent of each other.

Performance Tuning
The race teams that are building and tuning Corvettes for professional competition are using tools such as Innovate Motorsports' wide-band oxygen-sensor system to tune the air/fuel mixture each cylinder gets from the fuel-injection system. The use of a wide-band oxygen sensor in the header tube of each cylinder will allow the tuner to read the air/fuel mixture of each cylinder at any engine operating condition on the dyno or at the track. The data obtained by reading the air/fuel mixture of each cylinder, plus the fuel-injector flow bench data of each fuel injector are used to fine-tune the air/fuel mixture of each cylinder. The engine will give you the maximum performance from each gallon of gasoline when all the cylinders of the engine have the correct air/fuel mixture.

Preventing Dirty Fuel Injectors
The best preventive medicine to help prevent dirty or fuel flow-restricted fuel injectors is the use of a gasoline that has detergents in it to help keep the injectors clean and prevent deposit formation before it becomes a problem. Many of the car manufacturers recommend the use of a gasoline that conforms to the new Top Tier gasoline standards to help keep the fuel injectors clean. Top Tier gasoline has detergents in it that will help keep the fuel injectors clean as you use it, and many of the major brands of gasoline are now being blended to the Top Tier gasoline standards. The level of detergents in Top Tier gasoline is not always strong enough to keep your injectors clean, so from time to time you may need to add some extra cleaning power to your gasoline.

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The data from a diagnostic scan tool can indicate if the fuel injectors are in need of service.

The use of an in-tank fuel-injector cleaner such as Chevron's Techron Concentrate Plus at the same mileage schedule as you change your engine oil is a good way to ensure your fuel injectors stay clean. A dose of Techron Plus will raise the level of detergents in a tank of gasoline to about ten times what it is in a typical Top Tier gasoline. Techron Concentrate Plus is one of the best in-tank fuel-injector cleaners we have used; the "plus" is it helps protect the cars fuel system against the corrosive effects of the sulfur commonly found in today's gasoline. These harmful sulfurs can corrode the fuel-level sending unit in the gas tank and cause the fuel-level gauge in the car to malfunction. The most common symptom of a corroded fuel-level sending unit is a fuel-level gauge that may stick or not read the correct level of gasoline in the fuel tank. The sulfurs' corrosive effects may also create excessive wear to the electric fuel pump(s) that are in the gas tank and thus shorten the fuel pump service life.

When you park your Corvette for the winter or any time the fuel will remain in the tank for more than a couple of months, we highly recommend you use a gasoline storage stabilizer such as STA-BIL from Gold Eagle in the gas tank. As gasoline ages it turns into a gummy varnish-like substance that will create problems in almost every part of the fuel system. This old gasoline can cause the fuel injectors to stick open, closed, or restrict the fuel flow through the fuel injectors, and it is also hard to clean out of the fuel tank, lines, and fuel pump. The only practical way to clean a fuel injector that is stuck open or closed by exposure to bad gas is to remove them from the engine, and then have them cleaned with an ultrasonic fuel-injector cleaning system or replace them with new fuel injectors.

The Clean Advantage
When all the fuel injectors are flowing the correct amount of fuel to each cylinder, the engine performance will be at its best, supplying your fuel-injected Corvette with maximum power and fuel economy. Each of the fuel-injected Corvettes (as well as many other brands of cars) we worked with during the research for this article had a noticeable increase in power and drivability after cleaning the fuel injectors. Fuel-injector maintenance and service is an important part of proper vehicle maintenance. Choose the fuel-injector cleaning method that works best for you, and don't forget to change the fuel filter.


Innovate Motorsports
Irvine, CA
San Ramon, CA 94583
John Bishop's Corvette Service
Burlingame, CA
OLE's Carburetor and Electric
San Bruno, CA
Top Tier Detergent Gasoline



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